Report: 1999-05-01 Measurement of the Ozone Concentration ...

CONTRACT NO. 95-337 FINAL REPORT

MAY 1999

Measurement of the · Ozone Concentration Aloft by Lidar

During the Episode Monitoring Periods of the 1997 Southern California Ozone Study

Disclaimer

The statements and conclusions in this report are those of the NOAA/ERL/ETL and not

necessarily those of the California Air Resources Board. The mention of commercial products,

their source, and their use in connection with material reported herein is not to be construed as

actual or implied endorsement of such products.

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Mr. George, and Ms. Lisa Olivier, meteorologist. Ms. Gloria Schurman, secretary, processed an

unusually large amount of paper work for the numerous person-trips to the field study site in a

timely and accurate manner. Dr. Bob Weber, physicist, and Mr. David Welsh, computer

specialist, in the ETL's System Demonstration and Integration Division (ET4) helped us in

downloading meteorological data and other information in SCOS97 from the ET4's web site.

This report was submitted in fulfillment of Contract #95-337 entitled "Measurement of

the Ozone Concentration Aloft by Lidar during the Episodic Monitoring Periods of the 1997

Southern California Ozone Study" by the National Oceanic and Atmospheric Administration's

Environmental Technology Laboratory under the sponsorship of the California Air Resources

Board. Special thanks are due to Mr. Leon Dolislager for his valuable help in providing

important information for the background of this experiment and managing field operations; and

for his critical review of the manuscript and many helpful suggestions. Work was completed as

of May 1999.

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Acknowledgments

Mr. Richard Marchbanks, optical engineer, re-designed the mechanical part of the two

dimensional scanner, re-coated the mirrors, and carried out miscellaneous hardware preparations.

The new design significantly improved the stability of the scanner. During the 1997 Southern

California Ozone Study (SCOS97) Experiment, Mr. Marchbanks was responsible for deploying

the ozone lidar at the site, and took a major role in setting up, realignment, troubleshooting, and

operation of the lidar. He was the only person in the crew that went to every episode in SCOS97.

Mr. Keith Koenig, computer engineer, upgraded the lidar's data acquisition system. He installed

new digitizer boards and a QNX operating system, re-wrote lidar operation programs for scanner

control and raw data acquisition. He wrote programs for real time display of lidar raw data and

real time display of preliminary ozone concentration and aerosol backscatter profiles, as well as

various programs for on-site noise removing and system calibration to support the real time data

analysis. The major improvement of the data acquisition system was the capability ofreal-time

display that enabled the crew to view the current ozone and aerosol vertical structure, and thus

helped them to make decisions about lidar operation (e.g., changing scanning parameters,

lengthen working hours if the structure was interesting). Dr. Christoph Senff, research scientist,

was one of the lead persons of the second-shift crew with an emphasis on science issues. His

parallel post-processing of the data in the intercomparisons and the first two-days of the first

episode in August 1997 provided a double check to the quality of data analysis. Dr. Wynn

Eberhard, physicist, gave advice to the planning of the operation and managed the budget of the

project. Ms. Kathleen Healy, computer analyst, set up a workstation in the lidar site to provide

on-site data analysis. She re-wrote the tape reading and raw data averaging program, and wrote

and modified all the data displaying programs in IDL language. Ms. Joanne George improved

the plotting subroutine in the data analysis programs. She also modified a color table in the data

display programs which covered a large dynamic range and thus allowed detailed structures and

time variations of aerosol profiles to be well distinguished in color graphics. Mr. David

Greenstone, student assistant, and Mr. Hutch Johnson, associate research scientist, were the

major field support personnel. The field supporting crew also included Mr. Koenig, Ms. Healy,

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TABLE OF CONTENTS

DISCLAIMER

ACKNOWLEDGMENTS

TABLE OF CONTENTS

LIST OF FIGURES

LIST OF APPENDICES

ABSTRACT ·

EXECUTIVE SUMMARY

BODY OF REPORT

I. INTRODUCTION

II. THE ETL OZONE LIDAR

2.1 The lidar system OPAL

2.2 Improvements of the scanning system

2.3 Upgrades of the data acquisition system ·

2.4 Improvements of data analysis

III. LIDAR OPERATION IN SCOS97

IV. OZONE AND AEROSOL CONCENTRATIONS ALOFT AS MEASURED BY LIDAR DURING HIGH OZONE EPISODES

V. SUMMARY AND DISCUSSIONS

REFERENCES

GLOSSARY OF TERMS, ABBREVIATIONS, AND SYMBOLS ·

APPENDIX A

APPENDIX B

APPENDIXC

APPENDIXD

APPENDIXE

FIGURES

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V

Vil

ix

xi

Xlll

1

3

3

8

8

9

11

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19

23

25

26

27

29

30

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Figure 1

LIST OF FIGURES

Time-height charts of ozone concentrations and aerosol extinction coefficients at

355 nm during the episode of August 4-6, 1997

Figure 2 Time-height charts of ozone concentrations and aerosol extinction coefficients at

355 nm during the episode of September 3-7, 1997


355 nm during the episode of September 27-29, 1997


355 nm during the episode of August 22-23, 1997


355 nm during the episode of October 3-4, 1997


355 nm in the evening of August 4, 1997

Figure 7 Time-height chart of ozone concentrations and aerosol extinction coefficients at

355 nm during one scanning at about 2120 PST on August 4, 1997


355 nm from late afternoon to evening on September 5, 1997


355 nm during one scanning at about 1800 PST on September 5, 1997


355 nm in the evening on September 28, 1997


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LIST OF APPENDICES

APPENDIX A

APPENDIXB

APPENDIXC

APPENDIXD

APPENDIXE

SCOS97's modeling domain of southern California and adjoining environs

Quotes from Reference 5: R. Lu and R.P. Turco, "Ozone distributions over

the Los Angeles basin: 3-dimensional simulations with the SMOG

model," Atmospheric Environment 30, No. 24, pp. 4155-4176 (1996).

(a) The model computation domain and topography

(b) The simulation results on line A-A'

Lidar operation days in SCOS97

(a) Schematic figure of the lidar system OPAL

(b) Optical layout of the transmitter and receiver of OP AL

Analysis on the statistical error in ozone concentrations

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355 run during one scanning at about 1720 PST on September 28, 1997


355 run during one scanning at about 1820 PST on September 28, 1997


355 run September 29, 1997

Figure 14 Time-height charts of ozone concentrations and aerosol extinction coefficients at 355 run in three scanning operations at about 0620, 0720, and 0820 PST on September 29, 1997

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ABSTRACT

In the SCOS97-NARSTO1 field study the NOAA Environmental Technology Laboratory

(NOAA/ETL)'s ozone profiling atmospheric lidar2·3 (OPAL) was deployed in the Los Angeles

urban area (El Monte Airport). During intensive operation periods (IOPs), OPAL operated

continuously for more than 20 hours per day, providing vertical profiles of ozone and aerosol in

an area important for understanding ozone evolution and transport, as well as for air quality

model performance validation. In this 4-month long field campaign, OP AL detected persistent

ozone and aerosol layers aloft on most days during the IOPs. Very frequently, a lower layer of

ozone and aerosol at 1000-1500 m (msl) and a higher layer of ozone and aerosol at 2000-2500 m

(ms!) were observed by the lidar. These layers existed simultaneously during a time period from

the late afternoon till midnight, when they started to dissipate. Sometimes, they persisted

through the night and could be seen in the early morning.

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EXECUTIVE SUMMARY

This final report describes the profiling of ozone and aerosol during the SCOS97-

NARSTO field measurement campaign by the NOAA Environmental Technology Laboratory

(NOAA/ETL)'s ozone profiling atmospheric lidar,3 (OPAL) in El Monte, CA.

OPAL transmits three ultraviolet (UV) wavelengths (266,289, and 355 nm) in an eye

safe manner. The first two are for ozone profiling and the third is for aerosol profiling. The lidar

has the unique capability of measuring profiles of ozone concentrations from near the surface to

2-3 km above the ground level and aerosol profiles up to 10 km. Prior to the SCOS97-NARSTO

field study, a redesigned 2-dimensional scanner was installed on the lidar. The vertical scanning

capability provides a valuable internal system check, enables frequent calibration, and permits

analyses of horizontal variability in pollutant concentrations and of pollutant flux.

During intensive operational periods (IOPs) in the SCOS97-NARSTO field study, OPAL

operated continuously for more than 20 hours per day, providing vertical profiles of ozone and

aerosol in an area important for understanding ozone evolution and transport, as well as for air

quality model performance validation.

The lidar was located at the El Monte Airport, about 15 km south of the foothills of the

San Gabriel Mountains, which have a ridge line north of El Monte at altitudes about 2-2.5 km

above mean sea level (ms!). The intent of choosing this site was that the polluted air mass in the

return flows from the San Gabriel Mountains could be detected by the lidar. The site elevation is

90 m (ms!).

During the SCOS97-NARSTO field campaign, OPAL detected persistent ozone and

aerosol layers aloft in the SoCAB. One layer was just above the top of the marine boundary

layer, the other was at the same altitudes of the mountain ridge line north of the site. These

layers existed simultaneously during a time period from the late afternoon till midnight, when

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I. INTRODUCTION

Although ambient ozone concentrations have declined significantly as a result of major

reductions in the emission of volatile organic compounds and nitrogen oxides, southern

California continues to have the worst ozone problem in the United States. The complex

meteorological and chemical processes taking place in the region are not fully understood. The

1997 Southern California Ozone Study (SCOS97) was planned to provide a new milestone in the

understanding of relationships between emissions, transport, and ozone standard exceedances in

southern California, as well as to facilitate modeling to refine estimates of the additional

emission reductions required to attain the National Ambient Air Quality Standards. The study

was conducted in coordination with the North American Research Strategy for Tropospheric

Ozone (NARSTO). Thus, the field campaign is known as SCOS97-NARSTO.

The study's modeling domain of southern California and adjoining environs (see

Appendix A) includes the rectangular area between approximately 32 °N and 36 °N latitude and

between 115°W and 121 °W longitude, an area of205,000 square kilometers. The data collected

are being extensively analyzed to determine how reductions in emissions might impact air

quality, and also to quantify transport of pollutants between neighboring air basins.

The field activity started June 16 and ran through October 15, 1997. The existing

monitoring network was supplemented with additional sites for the collection of continuous air

quality and meteorological data. Moreover, during selected periods (generally, 2-3 days) when

high ozone concentrations were forecast, additional monitoring and sampling occurred. During

these intensive operational periods (IOPs), four to five aircraft, instrumented with ozone

monitors and other monitoring equipment, made two to three flights per day; up to 75 balloon

soundings were made per day; and additional samples of volatile organic compounds and

carbonyls were taken.

As a high technology remote sensing instrument, the NOAA Environmental Technology

Laboratory (NOAA/ETL)'s ozone profiling atmospheric lidru2·3 (OPAL) was deployed in the Los

1

they started to dissipate. Sometimes, they persisted through the night and could be seen in the

early morning. The continuous lidar observations during the intensive operational periods of

SC0S97-NARSTO provided detailed temporal variations of ozone and aerosol vertical profiles

that have never been available before. Further analysis of the lidar data, combined with wind and

other observational data, will contribute significantly to the understanding of the formation and

transport of the ozone layers, and bring new insight into important issues in air quality research

in southern California.

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II. THE ETL OZONE LIDAR (OPAL)

2.1 The lidar system and the principle of ozone remote sensing

OPAL is a differential absorption lidar (DIAL) system, which transmits three UV

wavelengths (266,289, and 355 nm) in an eye-safe manner. The first two are for ozone profiling

and the third is for aerosol profiling. The innovative hardware design of this lidar makes it

efficient, compact, and easily transportable.

A DIAL system transmits laser pulses at two wavelengths in an absorption band ( or

around a narrow absorption line) of the gas species under measurement. The wavelength with a

higher absorption coefficient is called the "on-line" wavelength and the wavelength characterized

by a lower absorption coefficient is called the "off-line" wavelength. Range resolution of a

DIAL system depends mainly on the differential absorption coefficient of the wavelength-pair.

Thus, proper selection of a wavelength pair is important to the range resolution ( and the

maximum detection range) of a DIAL system. The corresponding lidar equations at the two

wavelengths take the form:

rilz) 2 = CA.-P.(z)T; (z),z z2 (1)z .

where the subscript i for various parameters in the equation stands for off-line (i = 1) and on-line

(i = 2) wavelength, respectively; P(z) is the detector-received power of the atmosphere

backscattered radiation (in Watts) from range z (in m), CA is the instrument constant (in W m3 sr),

11(z) is the overlap function, and P(z) is the atmospheric volume backscattering coefficient (in m·1

sr·1). T2(z) is the two-way atmospheric transmission, taking into account attenuation by

molecular scattering, aerosol scattering, and ozone absorption,

T2 (z) = exp{-2 z

f[a-m(z')+ 0- + a ,p ,(z')]dz'}, (2)0 0 0

0

3

Angeles urban area. The lidar was located at the El Monte Airport, about 15 km south of the

foothills of the San Gabriel Mountains, which have a ridge line north of El Monte at altitudes

about 2-2.5 km (ms!). The intent of choosing this site was that the polluted air mass in the return

flows from the San Gabriel mountains could be detected by the lidar. The site elevation is 90 m

(ms!).

The objective of the OPAL measurements was focused on ozone layers aloft. Layers of

high ozone concentrations aloft in the South Coast Air Basin (SoCAB) in California have been

reported by many measurement projects. These layers may result from complex mesoscale flows

in the basin, including sea breezes and thermally forced daytime up-slope flow in the mountains

(so-called "chimney effect"). It is hypothesized that these high-concentration ozone layers aloft

may contribute significantly to ozone standard exceedances in the basin by recycling pollutants

from previous days, and/or increase ozone concentrations in downwind basins by transport.

During IOPs, OPAL operated continuously for more than 20 hours per day, providing vertical

profiles of ozone and aerosol in an area important for understanding ozone evolution and

transport, as well as for air quality model performance validation. The lidar results showed very

interesting ozone and aerosol layers aloft. One layer was always on top of the marine boundary

layer, and the other at about the same altitude of mountain ridge line in the San Gabriel

Mountains north of the site.

2

even higher. Using a larger & can reduce the relative error, assuming that on is statistically

constant. [A least-squared fit (either parabolic or linear) for the section of the curve, !ilnF, can

further improve the accuracy.] Thus, there is a trade-off between the accuracy of ozone

concentration retrieval and the range-resolution. At far ranges, or after a layer of very high ozone

concentrations and considerable thickness, the signal-to-noise ratio (SNR) decreases sharply.

The signal decreases because of the decreasing two-way transmission T2(z), defined in Equation

(2), and the reversed range-square effect in Equation (1). The relative increase in noise mainly

originates from the inherent shot noise, which is a random fluctuation in photoelectrons and

proportional to the square root of the signal, thus the SNR caused by this factor is proportional to

1Jp = Jp . Due to the decreasing SNR, we need to take a longer & to achieve a

reasonable accuracy. But even so, the random error in retrieving ozone concentrations are still

greater at far ranges. A detailed error analysis in ozone concentrations is described in Appendix

E. Examples of error in ozone concentrations as a function of altitude are also plotted in

Appendix E.

OPAL is an Nd:YAG-laser-based lower troposphere ozone lidar, specifically designed

for measuring ozone in the boundary layer and the lower free troposphere. (See Appendix D for

the schematic figure of the lidar and the optical layout of the transmitter and receiver.) This

ozone lidar has unique features due to its innovative designs:

• Range coverage

The lidar has the capability of measuring ozone from near the surface ( about 15 to 60 m)

to about 3 km, allowing a complete ozone profiling in the boundary layer and in the lower

free troposphere, whereas in other DIAL systems, the minimum detection range is

typically 500 to 1000 m. This range-coverage is due to a multibeam transmitter2·3 design

that reduces the enormous dynamic range of the lidar signals (which is a typical feature of

incoherent lidar systems), providing good signal-to-noise-ratio (SNR) in both near and far

5

where om and oa are the extinction coefficients of molecules and aerosols, respectively; a,,3 is the

absorption coefficient ofozone, and p03 is the ozone density.

Let F(z) = Pi(z)/Pi(z), the off-line-to-on-line ratio of the lidar signals. Taking the

logarithm and differentiating ln[F(z)], we have

(3)

where .6.a,,3 is the differential absorption coefficient of ozone, and

A(z) = .!!.._{1n[P 1(z)])+2da (z)+2da (z), (4) dz Pz(z) m a

where .6.o"' and .6.oa are respectively the differential extinction coefficients of molecules and

aerosols. If the three terms in A(z) are properly estimated through aerosol data analysis, we can

derive the ozone concentration p,,3

dlnF(z) -A(z) dz (5)

Po3 =

In data processing, the differentiation dlnF(z)!dz is calculated numerically. The interval

of dlnF(z) and z, i.e, MnF and&, are finite, and the range interval & consists of more than one

range gates. Thus the range-resolution of ozone concentrations retrieved from lidar signals is

not the range gate of the signal digitizer, but related to the range interval & for carrying out the

differentiation. Due to the presence of noise and signal fluctuation, the real data .6.lnF' = .6.lnF +

on, where on is the noise difference at z and z + &. When & is small, .6.lnF is also small, thus

the absolute value of error in ozone concentrations, i.e., on/&, can be comparable to MnFI&, or

4

An off-axis paraboloid Newtonian telescope has been designed as the receiver. Special

baffles in the telescope and an optical filter system in the detector package are employed for

rejecting the daytime background radiation while keeping a high optical transmission for the

receiving system. The receiver is assembled side by side with the transmitter on an invar optical

board.

A data acquisition and processing system based on a PC is employed. Lidar output

signals are digitized and pulse-to-pulse raw data are written on DAT tapes. The data files are

first processed by a raw data averaging and display program. The output ASCII files are then

processed with a sophisticated signal retrieval program to obtain ozone and aerosol profiles. The

upgraded data acquisition system consists of a four-channel, 12-bit, 30 MHz digitizer, and a

computer with both QNX and DOS operating systems, which enables a real-time display of the

ozone lidar raw signals and the first-cut ozone profiles. Details are described in Section 2.3.

The lidar is installed in a well-insulated, temperature-controlled laboratory, modified

from a 20-foot sea-container (seatainer). Because the laboratory has an air-bag cushioned floor

and is mounted on an air-ride trailer, the lidar is transportable. The mobile laboratory has two

compartments. The lidar is in the aft compartment; the computer and other instruments, cabinets

and counters are in the forward compartment. There is an opening on top of the seatainer to

allow lidar observations. A turning mirror set installed on the lidar optical board directs the

horizontal laser beams up through the opening in the vertical direction, and also turns the

atmosphere-backscattered radiation into the receiving telescope. A two-mirror scanning system

is installed on top of the opening. The operation modes of the scanning system are: (1) steering

the beams in the horizontal direction for system calibrations and horizontal measurements, (2)

steering the beam in the vertical direction, and (3) scanning through elevation angles between 30-

150 ° to make scanning measurements in one vertical plane.

Prior to the SCOS97-NARSTO field study, a redesigned 2-dimensional scanner was

installed on the lidar. The vertical scanning capability provides a valuable internal system check,

7

ranges. The multibeam transmitter configuration requires a very high alignment accuracy

and system stability. Very precise lateral transfer retroreflectors and a laser beam

analyzer have been employed to assure the alignment accuracy. An invar optical table

and a well-designed supporting system provide the needed system stability.

• High optical efficiency and compact size

The unique design of the detector package makes the optical efficiency very high (about 3

to 10 times higher than similar ozone lidar systems). In addition, the multibeam

transmitter provides flat range response that allows a greater gain of the detectors to be

employed. With these features the system has a modest laser pulse energy requirement

and can use a small-sized telescope. Thus, the lidar is compact in size ( ~ 1 m3) compared

with similar systems.

With the multibeam configuration, four beams are output from the transmitter, three two

color beams at 266 and 289 nm (with energy allocation of 8%, 18%, and 74% among beam #1, 2,

and 3), and one beam at 355 nm. The wavelength pair 266/289 nm has been chosen to obtain a

high differential absorption coefficient, which provides the basis for high spatial and temporal

resolution of the measurement. The online wavelength at 266 nm is obtained by frequency

quadrupling the fundamental wavelength of the YAG laser. The offline wavelength is produced

by Raman shifting the frequency-doubled YAG output (at 532 nm) through a deuterium Raman

cell to 632.5 nm, and then frequency-summing 532 and 632.5 nm to 289 nm through a nonlinear

crystal. 532 nm was used in the 1993 Los Angeles Atmospheric Free Radical Study (LARFS)

experiments for aerosol profiling. For eye-safety reasons, however, the channel was changed to

355 nm. The 355 nm is a product of frequency-tripling, by using the residual energy at 532 and

1064 nm. Thus, the transmitter is basically all solid state with wavelengths that are fixed, saving

the lidar from problems usually associated with dye lasers. These three ultraviolet (UV)

wavelengths are eye-safe for airplane pilots and passengers (the cutoff wavelength for airplane

windows is at 375 nm).

6

higher than the old 12-bit digitizer.

• A QNX operating system was installed that allowed real-time display of the signal

as well as the preliminary processed time-height ozone concentration and aerosol

distributions.

• Preliminary calibration data could be processed on-site to support the real-time

display of ozone concentrations and aerosol profiles.

• Upgraded lidar operational programs allowed more frequent system calibrations.

2.4 Improvements of data analysis

• System calibrations were frequently carried out through horizontal observations.

The calculated system calibration functions were then checked with the surface

ozone value and corrected if needed. The corrected calibration functions were

smoothed to minimize the fluctuations caused by statistical noise. Moreover, a

linear interpolation was used to calculate the calibration function for each lidar

vertical or scanning file. These measures reduced the ozone concentration

systematic error caused by any residual change in the scanner system to less than 2

ppb.

• Improved the algorithm and related program of removing the signal-induced

fluorescence in the tail of the signals.

• A parallel processing of part of the data through two different programs provided

internal comparisons, and the differences between ozone concentrations were

mostly within 10 ppb.

• For scanning data at elevation angles other than 90 °, ozone concentration p ( or

aerosol extinction coefficient o) versus range, r, were transferred to ozone

concentration or aerosol extinction coefficient) versus altitude, h, through the

9

enables frequent calibration, and was desired to address both monitoring and modeling issues.

The lidar has the unique capability ofmeasuring profiles of ozone concentrations from

the surface to 2-3 km above the ground level and aerosol profiles from 30-45 m up to 10 km.

The raw data were recorded with a signal sampling interval of 5 m. With an averaging of 600-

1200 pulses (5-10 min), the retrieval of ozone concentrations has a range resolution from a few

tens of meters in the lower boundary layer to 150-200 m at about 3 km. Range resolution

decreases with height because the signal-to-noise ratio is lower at farther ranges. The aerosol

profiling at 355 nm has a maximum range of about 10 km with a range resolution of 15 m.

2.2 Improvements of the scanning system

The original 2-D scanning system developed in 1995 was re-designed. Major

improvements included:

Redesign of the mirror mount, to minimize the mirror-warping effect during

ambient temperature changes.

A sealed closure of the whole scanning system that keeps a better environment for

the mirrors during the non-operation hours.

A better baffle system that blocks the light scattered by the mirrors from entering

the receiver and the UV detection system ( although in later episodes of the field

study, because the mirrors became highly contaminated during the study,

scattering from the mirrors was too strong to be fully blocked).

2.3 Upgrades of the data acquisition and operation system

The data acquisition system was upgraded. The major improvements were:

• The old one 8-bit, one 12- bit cards were replaced by two 12-bit, two-channel

Gage digitizing cards. The sampling rates of the new digitizers were three times

8

III. LIDAR OPERATION IN SCOS97

OP AL was set up at El Monte Airport during June 2-11, 1997. It operated during five

ozone intensive operational periods in SCOS97, i.e., (1) August 4-6, (2) August 22-23, (3)

September 3-7, (4) September 27-29, and (5) October 3-4. The major episodes were the early

August and late September IOP's, during which the surface ozone concentrations were well

above the national 1-hour standard. Intercomparison experiments were carried out on June 11,

and July 8. The total number of operational hours was about 350. A listing of the operational

dates during SCOS97 is provided in Appendix C.

During the IOPs, OP AL operated continuously for 20 hours in a normal day (2 shifts of

crew), beginning at 0300 PST, and ending at 2300 PST. When the vertical structure was

interesting the operation continued through midnight. During a normal hour of operation,

measurements consisted of 5 minutes for system calibration (horizontal orientation), 5 minutes

for characterization of system noise, 12 minutes for scanning in a vertical plane, and 30-40

minutes for vertical profiling. When there were hardware problems or power blackouts, or some

operator was testing, modifying, or adjusting software or hardware, lidar operation stopped,

leaving small gaps in data taking. There were only one and half days (September 3-4, 1997) that

the lidar was down due to a laser hardware failure. New parts were ordered, the lidar system was

re-aligned, and the observation resumed in the morning of September 5.

Lidar operation was significantly improved through real-time display. The crew was able

to view the current vertical distributions of ozone and aerosol. When higher ozone and/or

aerosol layers aloft were observed (usually during the period of late afternoon to midnight),

additional scanning operations were carried out to confirm the existence of the layers aloft. Real

time results inspired the scientists to have more ideas about future research in ozone formation

and transport in the Los Angeles Air Basin.

As mentioned in Section II, system calibrations were frequently carried out through

11

equation h(i) = r(i)sin¢,, where his the altitude, r is the slant range, i is the bin

nwnber of the slant range, and ¢, is the elevation angle. After this transfer, the

altitude interval b.h is less than the slant range interval b.r , i.e., 15 m, by a factor

of sin¢,. Thus the p(h) and a(h) were interpolated between adjacent points to

allow the altitude interval b.h to be 15 m, same as that in vertical data files. The

resultant ozone profiles can then be plotted in time-height charts in a Cartesian

coordinate, and thus avoid some artificial interpolation effect as found in the polar

coordinate.

• Different color tables are used for ozone concentration and aerosol display to

cover different dynamic ranges. Gaps were inserted in the graphics when data

gaps existed, to avoid artificial interpolation in the contouring routine.

The improvements in scanner hardware, the frequent calibrations during operation, and

improvements in data processing significantly reduced the systematic error caused by the system

overlap function and the interference from the signal-induced fluorescence. The quality of the

data retrieval are shown in scanning data displays, where the artificial curves caused by the

system are removed, and horizontal layers of atmospheric ozone concentrations and aerosol

extinctions are shown (see examples in Figures 7, 9, 11, 12, and 14).

IV. OZONE AND AEROSOL CONCENTRATIONS ALOFT AS l\.1EASURED BY LIDAR DURING HIGH OZONE EPISODES

To display temporal and vertical variations in ozone and aerosol measurements, data for

each day of the intensive monitoring periods during SCOS97-NARSTO were plotted in

contoured time-height charts, and one chart a day in Figures 1-5. Time-height charts of ozone

concentrations and aerosol extinction coefficients at 355 nm are plotted on Figures 1-3 for the

three episodes of greatest interest, i.e., the first episode of August, and the first and second

episodes of September, respectively. Figs 4-5 are the charts for the second episode of August

and the episode in early October, respectively. For easy comparison, all data in one episode are

plotted on one page, with the same time scale (0-24 PST) and altitude scale (0-2500 m msl),

using the same color scale for ozone concentrations and aerosol extinction coefficients at 355

nm. The unit for ozone concentration is ppb, and the unit for aerosol extinction coefficient is

0.01 km- 1• Occasionally the highest values of ozone concentrations are beyond the scale, and

thus small areas in the charts are plotted in white. In each figure page there are 4-6 charts. Time

height charts of ozone concentrations are in the upper row, and time-height charts of aerosol

extinction coefficients at 355 nm are in the lower row. In this way the diurnal variation of ozone

and aerosol profiles as well as the day-to-day change can be easily seen.

The time-height charts are created through programs written in IDL (Interactive Data

Language). These programs read the time series (mostly 5 min interval) of one-dimensional

ozone or aerosol data files into a two-dimensional array, each column of the array represents one

vertical profile at a specific time. Then the programs call a standard routine, CONTOUR, in the

IDL software package to draw contour lines at a constant interval. A color table is assigned to

show ozone concentrations or aerosol extinction coefficients at different levels. In principle,

contouring processing includes interpolation. To avoid interpolation through data gaps (which

may cause artificial temporal variations), data sets containing such gaps were plotted in separate

contoured sections before and after the gap. It can be seen in the figures, i. g., in Figure 3, time

height chart on September 28, 1997 contains two gaps.

13

horizontal observations, because the atmosphere is homogeneous or nearly so in the horizontal

direction. However, the lidar site was near the fence of the airport and the ground level was 2 m

lower than the nearby street, the scanner on top of the lidar trailer was only 2.4 m (8 feet) above

the street level, exact horizontal measurement was impossible. The elevation angle was 1.6-1.8 °,

to keep the beams slightly higher than any ground objects (which was checked through a

telescope). However, the horizontal observations were toward NNW direction where the terrain

had a slope of about I. I O Thus the lidar beams were fairly parallel to the ground - only about •

few meters above the ground in the calibration range. In terms of AGL (altitude above ground),

these observations were nearly "horizontal".

12

concentrations lay just above the top of the marine boundary layer. According to the temperature

soundings, the top of the marine boundary layer decreased from about 800 ms! at 1700 PST to

about 500 mat midnight. The altitudes of this ozone layer aloft decreased simultaneously with

the underlying boundary layer. This layer could still be seen in the early morning of August 6.

The lower ozone layer during the evenings of September 5 and 6 was also very

interesting. Notice in Figure 2, the layer between 1000-1500 m had almost identical temporal

and spatial variations in these two days. The layer started at about 16 PST, and ended at about

18-19 PST, with ozone concentrations higher than 100 ppb, and height increasing with time from

1000 m to 1500 m. There was another layer observed after the ending of the previous layer on

September 5. It started from 18 PST and lasted till midnight. Ozone concentrations in this layer

were lower, in the range of70-80 ppb. The height of this layer increased from about 800 m to

about 1400 m at midnight. It still could be seen in the early morning of September 6. Details of

the evening of September 5 are plotted in Figure 8.

When high ozone concentrations were present in the lower layer, an aerosol layer was

always observed at the same altitude, with very similar patterns of structures, as shown in the

evening of August 4 (Figure 6), August 22 and 23 (Figure 4), September 5 and 6 (Figure 2 and

8) , and the second episode of September (Figure 3).

Layers at Higher Altitudes

Ozone and aerosol layers often appeared at altitudes above 2000 m, mostly between

2000-2500 m. The strongest ozone layer at these altitudes that OP AL observed in SCOS97 was

during the evening of August 4 (see Figure 6). Ozone concentrations in this layer were about 170

ppb when first observed. This layer lasted from 16 PST till midnight. The altitude of the layer

started from about 3000 m, lowered to about 2200 m 19-20 PST, and increased again with time

to about 2500 mat midnight. Ozone concentrations began to decrease after 21 PST, but still

were higher than 100 ppb. Aerosol extinction coefficients at 355 nm in this layer were also very

15

In the SCOS97-NARSTO field study, the nearly continuous lidar observations revealed

diurnal variations in urban Los Angeles area which were not observable in the past. The diurnal

pattern in high ozone episodes seems fairly consistent in each episode. In this field study, OPAL

detected persistent ozone and aerosol layers aloft during the IOP's. Usually there are two layers

of ozone and aerosol layers aloft: one below 1500 m, the other above 2000 m.

Layers at Lower Altitudes

In early mornings, ozone concentrations were nearly zero in the surface layers, while

aerosol extinction coefficients at 355 nm were high. Above this nightly boundary layer, around

500-1000 m there was always a layer with relatively high ozone concentrations. According to

continuous measurements through the night, the morning layer was the leftover from the previous

night. The altitude of this layer was often lower in the early episodes in August and early

September, and higher in the episodes in late September and early October. Ozone

concentrations in this layer increased after sunrise, and mixed down to the ground at noon time

(12-14 PST). During noon time, the high ozone layer extended from the surface to 600-1000 m.

After 14 PST ozone concentrations began to decrease in the lower part of the layer. But often

ozone concentrations kept increasing in the upper part of the layer until near sunset ( see charts of

August 5 and 6 in Figure 1, charts of August 22 and 23 in Figure 4, and charts of October 3 and 4

in Figure 5). Ozone scavenging by nitric oxide emissions in the late afternoon and night was

clearly indicated in the lower part of the boundary layer. The strengthening of ozone in the upper

part might be caused by the return flow from the San Gabriel Mountains that injected polluted air

into the top of the inversion layer.5

From late afternoon or early evening, a layer of higher ozone concentrations was always

observed between 1000-1500 m. In the early evening on August 4, ozone concentrations in this

layer were higher than 100 ppb. The layer lasted until midnight, when ozone concentrations

decreased to the low 70s in ppb. In the mean time, the altitude of the polluted layer also

decreased from 1500 to 1000 m. The details were plotted in Figure 6. This layer of high ozone

14

The most complicated multi-layer structures were observed on September 29 (Figures 13

and 14). It can be seen in Figure 13 that there were several layers below 1500 min the morning,

the uppermost two layers merged at 8 PST, and the lower layer merged with the boundary layer

at about 10 PST. Then the upper layer curved down and to some extent mixed with the lower

layer in the early afternoon, but the two-sublayer structure still remained. In the afternoon, the

two layers separated again. But only in the upper part were the ozone concentrations high. In

Figure 14, scanning data at about 0620, 0720, and 0820 PST were plotted to show the morning

structures in detail.

These multiple structures in the lower layer may be caused by complicated structure in

temperature profiles, as we saw in a previous experiment in the Los Angeles urban area (the

LARFS experiment in 1993, in Claremont, CA).8 They may also indicate complicated mountain

return flows. Apparently the middle layer at 1500 m in Figure 9 is not just above the boundary

layer, as modeled in Reference 5. The formation of polluted air in different layers in late

afternoon might be caused by return flows off mountains with different heights. These returns

flows may have different directions, because the mountains have slopes facing the sea-breeze and

sun at different angles. Thus, the complex layering structure of the atmosphere could also be a

result of the complex local and mesoscale meteorological processes.

17

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18

V. SUMMARY AND DISCUSSIONS

Layers of high ozone concentrations aloft in the South Coast Air Basin (SoCAB) in

California have been reported by many measurement projects. These layers may result from

complex mesoscale flows in the basin, including sea breezes and thermally forced daytime up

slope flow in the mountains.

It is hypothesized that these high-concentration ozone layers aloft may contribute

significantly to ozone standard exceedances in the basin by recycling pollutants from previous

days, and/or increase ozone concentrations in downwind basins by transport.4•5 During the 1987

Southern California Air Quality Study experiment, trajectory studies in two cases showed an

upper level recirculation in the middle of the SoCAB.6

During the SCOS97-NARSTO field study, NOAAIETL's OPAL detected persistent

ozone and aerosol layers aloft in the SoCAB. In most cases one layer was just above the top of

the marine boundary layer, the other was approximately at the altitudes of the mountain ridge line

north of the site. More complicated multi-layer structures were often observed in early morning

or in the evenings below 1500 m ms!. The co-location of the ozone and aerosol layers implies

that they probably originated from the same sources and processes. The modeling of Lu and

Turco in Ref. 5 has a transect line that passes near El Monte, i.e., A-A' [See APPENDIX B (a)].

The simulated ozone concentrations at three different times of the day are plotted in three figures

in APPENDIX B(b). These figures indicate the interactions between the sea-breeze and the San

Gabriel Mountains. Two layers of ozone are formed aloft from the return flows off the San

Gabriel Mountains: one layer was injected into the top of the inversion layer at about 1000 m, the

other comes from the mountain top and has its center located at about 2500-3000 m. At 1600

PST, the two layers can both be seen at a distance about 30 km from the coast. This is very

similar to what we observed at El Monte. However, lidar observations often detected a layer a

few hundred meters above the marine boundary layer, and sometimes with more complicated

structures. There might be multiple inversion layers ( or thermally stable layers) in temperature

19

profiles that cause this complexity. Return flows offmountain tops at different altitudes with

different azimuths might be another possible cause. Further analysis of the lidar data in

conjunction with meteorological data from the collocated RWPIRASS profiling system and air

quality data obtained from occasional aircraft spirals at El Monte should improve our

understanding of the atmospheric processes. Moreover, we strongly recommend, in the future, a

joint observation study of the powerful ETL Doppler lidar (i.e., the ETL's TEACO, which can

measure the 3-D wind field in a large area) and the ozone lidar. Working together, these remote

sensing technologies provide much more insight into the formation and evolution of polluted air

layers. These improved insights into the mechanisms and processes contributing to the

exceedance of the ozone standards in the SoCAB and surrounding areas will improve the

technical basis of attainment plans.

Ozone scavenging is indicated by the decrease of ozone concentrations mainly near

ground level. In the layers aloft, the trends of ozone concentrations and aerosol extinction

coefficients at 355 nm in the evenings were often opposite to each other: ozone concentration

decreased with time, while aerosol extinction coefficients at 355 nm increased. After sunset,

when the photochemical production of ozone stopped, the scavenging and dispersion processes

continued. N02 was created when ozone was scavenged by nitric oxide emissions. Various

nitrogen compounds (e.g., N02, N20 5) and radicals act as reservoirs of potential oxygen atoms

which are necessary for the formation of ozone. Any such compounds available in the following

morning would enhance ozone formation after sunrise. The increase of the 355-nm extinction

coefficient with time at night from the surface to 3 km may imply an increase in the aerosol size

due to the increase in relative humidity at night. Because 355 nm is close to the peak of an N02

absorption band, a portion of the increase in the extinction coefficient may also be attributed to

additional absorption by N02• However, the N02 absorption would only be about 10-20% of the

355-nm aerosol extinction coefficients, even ifwe assume N02 concentrations were as high as

100 ppb.

During daytime, ozone concentrations increased after sunrise in the boundary layer and

20

the layers aloft due to the photochemical processes that produce ozone. In the late afternoon

ozone concentrations decreased in the lower part of the boundary layer due to the scavenging by

NO and advection of cleaner air with the sea-breeze. Aerosol extinction coefficients at 355 nm

had similar temporal variations in daytime as that of ozone concentrations. The similar temporal

variations might be attributed to the production of smog aerosols in high ozone layers.

The continuous lidar observations during high ozone episodes in this field study provided

time variations of ozone and aerosol vertical profiles that have never been available previously.

Further analysis of the lidar data, combined with wind and other observational data, would

contribute significantly to the understanding of the formation and transport of the ozone layers,

and bring new insight into important issues in air quality research in Southern California.

21

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22

REFERENCES

1. E. M. Fujita, J. Bowen, M. C. Green, and H. Moosmuller (1997 draft), 1997 Southern

California Ozone Study (SCOS97) Field Study Plan. Report prepared by Desert Research

Institute for California Air Resources Board, Sacramento, CA. Contract No. 93-326.

2. Yanzeng Zhao, J. N. Howell, and R. M. Hardesty, "Transportable Lidar for the

Measurement of Ozone Concentration and Aerosol Profiles in the Lower Troposphere,"

A&WMA/SPIE International Symposium on Optical Sensing for Environmental

Monitoring, October 11-14, 1993, Atlanta, Georgia, pp.310-320.

3. Yanzeng Zhao, Richard D. Marchbanks, and R. M. Hardesty, "ETL's Transportable

Lower Troposphere Ozone Lidar and Its Applications in Air Quality Studies, " 42nd SPIE

Annual meeting, 31 July 1 - 1 August, 1997, San Diego, California, Application ofLidar

to Current Atmospheric Topics IL Proceedings ofSPIE #3127, pp.53-62.

4. J. L. McElroy and T.B. Smith, "Creation and fate of ozone layers aloft in southern

California," Atmospheric Environment 27A, No. 12, pp. 1917-1929 (1993).

5. R. Lu and R.P. Turco, "Ozone distributions over the Los Angeles basin: 3-dimensional

simulations with the SMOG model," Atmospheric Environment 30, No. 24, pp. 4155-

4176 (1996).

6. S. G. Douglas, R. C. Kessler, C. A. Emery, and J. I. Burtt, "Diagnostic Analysis of Wind

Observations Collected During the Southern California Air Quality Study," final report,

prepared under Contract No. A832- l 33 for California Air Resources Board, Sacramento,

CA, by Systems Applications International, San Rafael, CA ( 1991 ).

7. Y. Zhao, R. D. Marchbanks, C. J. Senff, H. D. Johnson, and Leon Dolislager, "Lidar

23

Profiling of Ozone and Aerosol in the SCOS97-NARSTO Experiment," 19th

International Laser Radar Conference, July 6-10, 1998, Anapolis, Maryland.

8. Yanzeng Zhao, John A. Gaynor, and R. Mike Hardesty, "Demonstration of a New and

Innovative Ozone Lidar's Capability to Measure Vertical Profiles of Ozone Concentration

and Aerosol in the Lower Troposphere," Final Report to California Air Resources Board,

Contract No. 92-328, December 1994.

24

GLOSSARY OF TERMS, ABBREVIATIONS, AND SYMBOLS

LIDAR

DIAL

RASS

RWP

NOAA

ETL

PST

AGL

MSL

Light Detection and Ranging (Lidar is a system that transmits laser beam(s) and

collects backscattered radiation through telescope(s). The received radiation is

then transferred to electronic signals by optical detectors. Since the backscattered

radiation from different distances has different time delays, the signal is range

resolved.)

Differential Absorption Lidar

Radio Acoustic Sounding System

Radar Wind Profiler

National Oceanic and Atmospheric Administration

Environmental Technology Laboratory (former Wave Propagation Laboratory)

Pacific Standard Time

Above Ground Level

Mean Sea Level

25

APPENDIX A

SCOS97's modeling domain of southern California and adjoining environs: an area of205,000 square kilometers (downloaded from the NOAA/ETL/ET4 web site). The lidar site was collocated with a RWP system at El Monte (No. 12 on the map).

26

APPENDIXB

Quotes from Reference 5: R. Lu and R.P. Turco, "Ozone distributions over the Los Angeles

basin: 3-dimensional simulations with the SMOG model," Atmospheric Environment 30, No. 24,

pp. 4155-4176 (1996).

(a) The model computation domain and topography

SI ~

g81~ :i SI

~

........

~

Pacific Ocean

120.00 119.50 119.00 118.50 118.00 117.50 117.00

LONGrruDE (W)

Fig. I. The model computational domain and lopography arc illustrated. The larger map defines the area over which mesoscale dynamical calculations are carried out. The inner perimeter indicates the domain used for the air quality (chemistry and microphysics) simulalions. Heavy solid lines indicate the coastline. Contour lines correspond to terrain elevations; the contour intervals are 200 m. The lines AA'. es·. CC.

DD' and EE' give the locations of the vertical cross-sections discuS5:Cd in the 1exr.

27

,., ,., -----------------s----, ,., ..,

,.. .., .., ,.,

g ).0

uI ,., ,., .. ,.,

APPENDIX B (Continued)

(b) The simulation result of ozone concentration along line A-A'

__... _(ba) ,.,

Fig. 4. Calculated ozone concentrations (contours. m intervals of 2 pphmv) for .a vcnicaJ cross•scction thal extends from Santa Monica Bay 10 the San Gabnel Mountains (AA' in Fig. I) on 27 August !987. The

topography is highlighted by scnping. (al 10:00 PST; (bl 14:00 PST.

..•

OJ

o.o L.L...-'-.::E::l...l.i...lr,,lm,:i!IJWIJ.UJ. ow»»~»~~~~~mmm~~~rnow»»e~~~~~~mm~~~~rn

Diaaooe doo,: lbe croa«dioa (tm) ,.,

s.s

s.o

4.S

g 4.0

3.S

3.0

! -8

2.S

2.0

l.S

1.0

o.s

0.0 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 ISO 160 170

Distance along the cross-section (km)

Fig. 6. Simulated ozone concentrations (contours. in intervals of 2 pphmvJ for vertical cross-section AA' (Fig. l)exlending [rom San1a Monica Bay to the San Gabriel Moun lams at 16;00 PST on 28 August 1987.

28

APPENDIXC

List ofLidar Operational Dates in SCOS97-NARSTO:

June 2-10, Set up and testing

June 11, 1997 - Intercomparison I

July 8, 1997 - Intercomparison II

August 4-6, 1997

August 22-23, 1997

August 24 (4 hours)

September 3 (4 hours) and September 5-7, 1997

September 27-29, 1997

October 3-4, 1997

29

APPENDIX D

(a) Schematic figure of the Iidar

Trunn.itter/ niccivcr

NOAA's Ozone Lidar

Torain.al

[!!] Com.p■ tcr •d Bloctronic1

30

APPENDIX D (continued)

(b) Optical layout in the transmitter and receiver

Optical Layout of the Modified Transmitter

Nd:YAGLucr

Dov.tDria.m lt.1111.u Cell With HD 111.d XD Lou

Optical Layout of the Detector Package

14J&¥J¥&L11 I

ksa it' · ··went t1r~· rto ttYtt I

31

APPENDIXE Analysis on the statistical error.in ozone concentrations

Ozone concentrations are calculated using Eq. (5) in Section II (The ETL Ozone Lidar) of

the final report. A differentiation of the logarithm ratio lnF(z) needs to be carried out

numerically. Ozone concentration is proportional to the slope of lnF(z), i.e., d lnF(z)ldz, which is

statistically estimated using least square methods. The following is a detailed derivation of the

variance and the standard deviation of the slope, and the resulting statistical errors in ozone

concentrations.

1. Linear least square fit

Using linear least square method to fit yin a range interval from z = z1 to z 2 , where

=z - k!iz, z 2 = z + kAz, z = + z 2 ) I 2 = Z;, the range at the jlh sample point, Az isz1 (z1

the range gate of the digitizer, and 2k+ I is the total number of sample points used in the least

square fit. The linear estimate of ln[F(z)], y, is a linear function ofrange z:

y = a+ b(z- z). (1)

The variance of the slope bis

s2(y) s2(y) s2(y)(j2 = k = k = k (2)2L(z;+J - z;)2 (Az)2 Lj2 2(Az)2I j

J=-k J=-k J=I

I k

where s2(y) is the variance ofy, defined as: s2(y) =-- '°'(Y . - y . . )2, where Y is the 2k - I ~ I+1 I+ 1

;=-k

data and y is the least square fit. Therefore, the root-mean-square of the slope bis

32

https://error.in

s(y)

(3)

It is proportional to the root-mean-square (standard deviation) ofy, and inversely proportional to

the standard deviation of the range. That means the accuracy of the estimate of the slope

increases with smaller standard deviation of noise and greater range interval.

2. Parabolic least square fit

The parabolic least square fit curve has the form

y = a+ b(z - z) + c(z - z)2. (4)

The slope dz at z = z= Z; is b, which can be calculated by the following equation:

~zLk

j[y(z;+)- y(z;_ 1 )] Lk

j[y(z;+J)- y(z;_)] = J=Ib = J=I ~------,-k---- (5)

2~zI j 2

J=I J=I

The variance of b is then

(6)

33

It is interesting to see that Eq. (6) is the same as Eq. (2), i.e., at z = z = Z; the variance

of the estimated slope has the same mathematical expression for linear or parabolic fitting.

However, with a better least square fit, the standard deviation ofy will be smaller and the slope

will have higher accuracy.

3. Error in the ozone concentration due to the statistical uncertainty of the slope

It is straightforward to calculate the statistical error in ozone concentration caused by the

uncertainty in the slope of ln[F(z)]. Using Eq. (5) in Section II of the final report, we can easily

obtain the standard deviation of ozone concentration

(7)

When estimating the error in ozone concentrations, we multiply a(p03) by a factor of2 to

have 95% of the error estimates within this range.

Implementing the equations in our programs but keeping the other parameters unchanged,

we reprocessed part of the data files on September 28, 1997, to obtain the statistical errors of

ozone as a function of altitudes at different times of the day when signal-to-noise ratios (SNR)

varied. In order to see the effect of decreased transmitted laser energy on the statistical errors in

ozone concentrations, a part of the data in the evening of August 4, 1997 was also reprocessed.

The statistical error will be higher when the signal is lower. As shown in Eq. (1) in

Section II, the signal P(z) is proportional to the atmospheric transmission (related to the

attenuation by ozone and aerosol), the aerosol backscattering coefficient, and the instrument

constant (which is proportional to the transmitted laser energy). The late September episode was

the last major IOP in the SCOS97 field campaign. The scanning mirrors were seriously damaged

by the pollution. The errors in ozone concentrations in the evening of August 4, 1997 (the first

day of the first major IOP) were two times smaller (less than 5 ppb throughout most of the

34

detection range) than those in the evening of September 28, 1997 ( compare Figure A and Figure

E). This implies an energy loss by a factor of about 4 due to the decrease of reflectivity in the

scanning mirror coatings. In fact, in the last day of the experiment, we took off the mirrors and

found that the signals immediately increased by a factor of 5. Therefore, the errors calculated for

data taken on September 28 should be the upper limits of those during the field study.

Errors in ozone concentrations at different altitude ranges at different times during the

day of September 28 ( especially those with higher errors) are listed in Table 1, and examples of

the error profiles are plotted in Figures A-E. The errors are low from late evening to the next

morning throughout the measurement range. At altitudes above 1000-1500 m, the errors increase

fast from mid morning to noon, reaching a maximum in early afternoon when ozone

concentrations in the boundary layer were highest for the day. During this short time period

(about one hour), ozone data above -1500 m have errors of approximately 25 ppb or more and

thus may not be usable. But in the boundary layer (below-1000 m), the statistical errors in

ozone concentrations remains less than 10 ppb.

Table l. Statistical error in ozone concentration retrieval from lidar data (E 1 d . 9/28/1997)xamp es unng

0054-0119 PST 1229-1259 PST 1327-1407 PST 1429-1454 PST 1729-1754 PST

MSL(m) 2o (ppb) MSL(m) 2o (ppb) MSL(m) 2o (ppb) MSL(m) 2o (ppb) MSL(m) 2o (ppb)

0-1000 2-5 0-1000 1-8 0-800 3-8 0-1000 1-8 0-1000 1-6

1000-1500 3-5 1000-1200 8-15 800-1000 8-23 1000-1500 6-10 1000-1500 2-6

1500-2000 5-9 1200-1600 15-20 1000-1500 20-25 1500-1700 15-20 1500-2000 6-12

2000-2500 7-11 > 1600 >25 >1500 >25 1700-1900 20-25 2000-2500 12-16

The low accuracy in high altitudes at noon time were primarily due to the low signal level

when laser beams and backscattered radiation traveled through a thick layer of high ozone

concentrations (about 200 ppb during that time period), and also may be due to the damage of the

scanning mirrors which remained in the polluted air of Los Angeles for four months. These

errors presented are among the worst during SCOS97. We are now improving the far-range

35

signals of OP AL by adding another wavelength. The range resolution will be lower as a trade

off for longer range ozone monitoring when ozone concentrations in the boundary layer are high.

2500

2000

g500 ..J en ~000

500

0 0

2500

2000

:[1500

..J en :i: 1000

500

0 0

Average STD of Ozone Concentrations 8/04/97 1744-1759 PST

5 10 2*STD (ppb)

Figure A

15

Average STD of Ozone concentrations 9/28/97 0054-0119 PST

5 10 2*STD (ppb)

Figure B

15

20

20

36


2500

2000

g500 . . ~

_J . (/J . _.:,-2000

..--V 500

~ 0

0 5 10 15 20 25 30 2*STD (ppb)

Figure C


2500

2000

E5oo _J

~000

500

0

" " " "

" -" " "

~~ 0

~

~ ~

5 10 15 20 25 30 2"STD (ppb)

Figure D


2500

2000

€500 _J

~000

500

0 200 5 10 15

2*STD (ppb)

Figure E

37

2500 ~~~~--------~--~~-OZONE MIXING RATIO (ppb)OZvru. rvi1/\11,,.,. ""' ,v \J-')-'U/

2500 -----1;--7 ~I • 20002000~

~

"1 ■ 1~2 1

j 15001 5r-r I l1

1

1

1~• 1000

- .... ' i

- -

$• 1000

i ~

,,' SOOr -r 500

1

oL -10 15 2010 15 20

Time {Hours PST}Time (Hours PST) FJ Monie. CA 6/ 5/ 97£1 Monte. CA 8/ 4/ 97

~ROSOL EXTINCTIO~~E~F"ICIENT .~! ~~? _n~ ~.O~ ~m) _ km·' AEROSOL EXTINCTION COEFFICIENT AT 355 nm (.01/km) _ km·•01 01 25 250083

o~--_,.---~~~-~---~~~

ao 77 74

'' 71

2000 65

59 56 " 53 i 150050 47 44 .s 41 38 35 32 29 26 23 20

1000 1000

500 17 500 14 11

' LJ ~ 0 10 15 20

Time (Hours PST} £1 Monte. CA 8/ 4/ 97

i 1500

5. 0

~

oc.....___,.____,__~--'----'----'-_,_J

ppb

0 5 10 15 ,o Time (Hours PST)

El Monte. CA 8/ 6/ 97

ii I i1

r--

°' °'-'D

I 'tj-._. <f)

5'o ~ ...... 0

.g 0 <f) ·s.. <l.l <l.l -5 bl) C

·;:: .g 0 <fl

8 1;J

ifiatit" ~ ti,,,..., 7 83 2soo~:w■■■■■■■llil■■■■■ -.-.-,

1500

n~

ao 83 §80

77 77 74 <l.l74 71 71 C

0 65

059 59" "

56 " ••65

...... N

56 53 j 53 0 50 50 <f)47 47

1a44 5 44 41 38 35 " 38 ..c:

35 u32 32 29

26 2623

29

"fili23 20 20 17 1714 ]

14 11 11 8 8 5 5 2 2 ~

IO 15 20 10 15 20 r;me (Hours PST) Time (Hours PST)

~ El Monte. CA 8/ 5/ 97 Et Monte. CA 8/ 6/ 97

oilrr:

AEROSOL EXTINCTION COEFFICIENT AT .355 (.01/km) .o, km·• "O

ppb 162500 -- -ii ,. 2ooor •l

1 1 11 11

'·~t -· -Ii1000 l'1

soor

80 0 5 10 15 20 -

Time (Hours PST) Fl Monte. CA 9/ 5/ 97

:a~ROSOL EXTINCTION COEFFICIENT AT 355 nm (.01/km) .o, i.:m·• 2 83

BO 77 74 71

2000 68 65 62 59 56 SJi 1500 50 47 44..s 41 36~ 35';: 1000 32< 26 " 23 20

500 17 14 11 6 5

o~~~~~--~~~~~~~~~~~ l_J 2 10 15 20

Time (Hours PST) El Monte. CA 9/ 5/ 97

ppb 165~2500

14 1 1 1iil1 11 10 1i 1500

!;~8..s

~

~

500 Il! 0

5 10 15 20 Time (Hours PST)

Et Monte. CA 9/ 6/ 97

::~=iiiii~,,••I•••li ~ "56

~1500 ' ::" i~ E • • I 44

.._, ; 411,-1 IM_JI ~1111,~ !9! i -

.. !I 26 23 20

500r 1714 11

•5 OL..~~'-'~---'-~~~--'--~~.,__,~~ l_J 2

O 5 10 15 20 Time (Hours PST)


OZONE •t1~ING RATIO (ppb) 2500

2000

i 1500

..s ~ ~ 1000 <

soo

0 0 5 10 15 20

Time (Hours PST) El Monte. CA 9/ 7 / 97

AEROSOL EXTINCTION COEFFICIENT AT 355 nm (.01/km) 2500~

2000

i 1500

.§,

1000

500

10 15 20 Time (Hours PST)

El Monie. CA 9/ 7/ 97

ppb 656gig

I4i

lg i~

J~

'! 4~

0

_ km·'01 _ 83

60 77 74 71 68 65 62 59 56

.. SJ 50 47

41 38 35 32 29 26 23 20 17 14 11•5 2

...... °' ~

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0

AEROSOL EXTINCTION COEFFICIENT AT 355 nm (.01 /km) _ km·'~ROSOL EXTINCTION COEFFICIENT AT 355 nm {.01 /km) .ot km-' AEROSOL EXTINCTION COEFFICIENT AT 355 _nm _(:01/km) 01 km·' 01 2500 r iiii!'l- · I - 63 :J

2500 ppb lll

20002ooor- -·1~ 1500 j 1500

0 t -'-.i1000 11~ S .

1000

"ii 5oor -■-I' : ij

500

0 0 10 15 20 0 5 10 15 20

Time (Hour:i PST) Time (Hours PST) El Monte. CA 9/27 / 97 El Monte. CA 9/28/ 97

2

2000

i 1500

-'-~ :Z 1000

"

500

o~~~~~--~~~~~-~~~~~ 10 15 20

Time (Hours PST) Er Monte. CA 9/27 / 97

BJ "ift"iif- """j,I~ , ~.7 , 2soo~·~-,~~;,··~ _ "Cl BO BO 77 77 §77

74 71 71 74

71 <l) SB 20001 i 6B 2000

" 6B C65 62 62 55 65

62 0 59 59 59 N 56 56 56 0

5353 53 4-<i 1500 .. 5050 50 04747..., . " 44 -'-,. JBJB ~ ~ " 3535 ~ 1000 35 ~ 1000 32

" ]32 32

29 (.)

26 26 29 " 29 "

" 26

17 -§i2020 20

17 17 " " 500 500 14 ,. 14 -~

1111 11 ..cB 5 5 B B

5 2 2 2 ~

~ C'"l

ob ~

10 15 20 Time (Hours PST}

El Monte. CA 9/29/ 97


El Monte, CA 9/28/ 97

ppb 2500

ff H

2000

1500I i,

ii14

-'-~ ~ 1000

71 "

It 500

1, 0 0 5 10 15 20

Time (Hours PST) El Monte. CA 9/29/ 97

t---0\

-< °' ppb N °' I I I ~

~

"s .... <l)

i Cl) .... 0

.g 0 "' ·a <l)

-s 00 C·c:: .g 0 "' ~

OZONE MIXING RATIO~ .. ~·~ ppb ppb180 2500 180 174 168 162 156 150 144 138 132

r=r 11 Im 126

108 vi' 102 96 " 90

_§, 84 . 78 ]

"' 1000 72 ~ 66 ~

-48

60 54

36500f- --1 42

30 24 18 - 12 6

0 I 0

2500

2000

~ 1500

_§,. u ;E l000 <

AEROSOL EXTINCTION COEFFICIENT AT 355 nm (,01/km) km·• AEROSOL EXTINCTION COEFFICIENT AT 355 nm (.01 /km) km-•

;,>re 1'

2 0 5 10 15 20 0 5 10 15 20 ob

Time {Hours PST) TTme (Hours PST) ti: El Monte. CA 8/22/ 97 El Monte. CA 8/23/ 97

0L...~~~...L.~~~--'-~~~"--"L...~~~~~~~ L_J 2

01 012500~. i'-~ - _.---,--- . 122 "O

.... ., _ ~- -, l m 118 §114I 110 0

106 1M i= 102 1m 02000 % N98 94 M 0 90 ~ '+-< 82 86 ~ 0

m ~ cJ)78 N74 i 1500

70 ro ~ ~66 _§, ..c:: ~ u62 . ~58 u54 ~50 ~ 1000 M -§i

46 ~Ill < ~42'<I ]~38

34 ~

n ~ ~ 30 ~26 500►

22 18

■ 18

14 14 ~ 1010

-- a 6 6 'SI"

174 168 &;162 156 ,-;150 "' 144

(")-. 138 N132

126 I N120

114 N 108 ...

cJ)102 96 §i90 84 78 ~ 72 66 '+-< 60 054 48 42 ~ 36 0

cJ)30 24 18 .fr 12 6 £0

OJ) i=·.:: .g 0

cJ)

8 ~

500

ppb 150 145 140 135 130 125 120 115

105

;I95

i,--I

90 85 80.·~r

110

100

75 70 65

-40

50

60 55

45

35 500f"- 30

25 20 15 - 10 5

0 0_J

0 5 10 15 20 Time (Hours PST)


AEROSOL EXTINCTION COEFFICIENT AT 355 nm (.01/km) 01 km·' 2500 152

147 142 137 132

2000'

. T " ~1Jit~ . . 127

122 117 112 107 102

-::; 97 92 87 82

~ 1500

5 77. 72 67u 62-~ 1000 57 52 " 47 42 37

500 32 27 22 17 12 7

0 2 5 10 15 20

Time (Hours PST) El Monte. CA 10/ 3/ 97

2500

2000

i 1500

-. E

u

~ 1000

"

500

0

2500

2000

f -::; rg 1500

5. u

~ 1000

"

500

0 0

0 5 10 15 20 Time (Hours PST}


AEROSOL EXTINCTION COEFFICIENT AT 355 nm (.01 /km) •r-.,-~~~

·, ~ ~~\.~;~·?.ii· 1~1f/f"~~:• ' t' . ·/' (, iii ~ '-- .• ,..., .. •---• • a i.

5 10 15 20 Time (Hours PST)


ppb 150 145 140 135 130 125 120 115 110 105 100 95 90 85 80 75 70 65 60 55 50 45 40 35 30 25 20 15 10 5 0

01 km·'• 152

147 142 137 132 127 122 117 112 107 102 97 92 87 82 77 72 67 62 57 52 47 42 37 32 27 22 17 12 7 2

&; .-< °' "t r'l ... <I)

.g 8 ._ 0

~ 0 "' ·a <I)

<I)

.s t>J)c::

"§ -0

0 "' 8 ~ -0 § <I)c:: 0 N 0 ._ 0

"' 'g ..c:: u

.1:: ] t>J)

~ ~ \r)

t,() ii;

0

OZONE MIXING RATIO (ppb) 2500 rT"li-iiiii ppb 170

165 160 155 150 145

2000 140 135 130 125 120

'.:i' (/) ::;

s Cll -a .a :;, <(

1500

1000

;,. 115110 105 100 95 90 85 80 75 70 65 60 55 50 45 40

500 35 30 25 20 15 10 5 0

17 18 19 20 21 22 Time (Hours PST)


AEROSOL EXTINCTION COEFFICIENT AT 355 nm (.01 /km~ 1 km_,

2500 · 62 60 58 56 54 522000 50 48 46 44 42

'.:i' 40(/) 1500::; 38

36 E 34

32 -a Cll 30

28 ~ 1000 26 <( 24

22 20 18 16 14 12 10 8 6 4 2

17 18 19 20 21 22 Time (Hours PST)


Fig. 6 Time-height charts of ozone concentrations and aerosol extinction coefficients in the evening of August 4

OZONE MIXING RATIO (ppb)

21.35 21.40 21.45 Time (Hours PST)


AEROSOL EXTINCTION COEFFICIENT AT 355 nm (.01 /km~ km- 1

21.30 21.35 21.40 21.45 21.50 Time (Hours PST)


Fig. 7 Time-height chart of ozone concentrations and aerosol extinction coefficients during one scanning at about 2120 PST on August 4, 2997

2500

2000

~ _J

<fl 1500::;;

sS ., -0

.3 1000:;:; <(

500

ppb 135 130 125 120 115 110 105 100 95 90 85 80 75 70 65 60 55 50 45 40 35 30 25 20 15 10 5 0

12500 .

2000

~ _J

<fl 1500::;;

sS ., -0

.3 1000:;:; <(

500

62 60 58 56 54 52 50 48 46 44 42 40 38 36 34 32 30 28 26 24 22 20 18 16 14 12 10 8 6 4 2

Fig. 8 Time-height charts of ozone concentrations and aerosol extinction coefficients from late afternoon to evening on September 5, 1997

OZONE MIXING RATIO (ppb) 2500

2000

~

_j

U1 1500::;;

s (l)

-0

.2 :;:; 1000 <i'

500

AEROSOL 2500

2000 I

'.::j' U1 1500::;;

s (l)

-0

~ 1000 <i'

500


El Monte. CA 9/ 5/

EXTINCTION COEFFICIENT AT

,,,.,..


El Monte. CA 9/ 5/

22

97

355 nm

22

97

ppb 105 100 95 90 85 BO 75 70 65 60 55 50 45 40 35 30 25 20 15 10

5 0

km_, 86 83 80 77 74 71 68 65 62 59 56 53 50 47 44 41 38 35 32 29 26 23 20 17 14 11 8 5

2500 OZONE

:rrr-......acr.r: MIXING RATIO (ppb)

p-,---..--r-.-.. ppb

90

85

80 2000 75

70

65

-::,- 60 U1 ::. 1500 55

-S 50

Q) 45 "O

.3

.;:; ;;'

1000 40

35

30

25

500 20

15

10

5

0 17.60 17.70 17.80 17.90 18.00 18.10

Time (Hours PST) El Monte. CA 9 / 5/ 97

AEROSOL EXTINCTION COEFFICIENT AT 355 nm (.01 /kmti1 km-1

2500 · 25 24 23 22

2000 21 20 19 18 17~

_J

U1 1500 16 ::. 15

-S 14

Q) 13 "O 12 .3 ·.;:; 1000 11 ;;' 10

9 8 7

500 6 5 4 3 2 1

17.60 17.70 17.80 17.90 18.00 18.10 Time (Hours PST)


Fig. 9 Time-height chart of ozone concentrations and aerosol extinction coefficients during one scanning at about 1800 PST on September 5, 1997

3000 OZONE MIXING RATIO (ppb)

ppb 135 130 125 120 115 110 105 100

,=, (/]

:::.

2000 95 90 85 80

E 75 70

" 65 -0

.3 :;:;

60 55

<( 50 1000 45

40 35 30 25 20 15 10 5 0

17.5 18.0 18.5 19.0 Time (Hours PST)


km_, 66 64 62 60 58 56 54 52 50 48

2000 46 44 42 40 38 36 34 32 30 28 26 24 22 20 18 16 14 12 10 8 6

17.5 18.0 18.5 19.0 Time (Hours PST)

El Monte. CA 9 /28 / 97

Fig. 10 Time-height charts of ozone concentrations and aerosol extinction coefficients in the evening on September 28, 1997


17.30 17.32 17.34 17.36 17.38 17.40 Time (Hours PST)

El Monte. CA 9 /28 / 97

AEROSOL EXTINCTION COEFFICIENT AT 355 nm (.01/km km- 1613000

2000 42-:;- 40 ::, 38

36

(/)

-S 34 32

"O"' 30.2 .;:; 28 :;;: 26

1000 24

3000

2000 ~

_J (/) ::,

-S " "O

.2 ·.;:; :;;:

1000

ppb 135 130 125 120 115 110 105 100 95 90 85 80 75 70 65 60 55 50 45 40 35 30 25 20 15 10 5 0

60 58 56 54 52 50 48 46 44

22 20 18 16 14 12 10 8

0 6

17.30 17.32 17.34 17.36 17.38 17.40 Time (Hours PST)



'.:J' V1 ~

~ " " 3

:.::, ;;'

3000

2000

1000

0 '--'-.L......~...L_L....L~-'-----"~~.L.....L~...L_L....L~_,___.~~.L.....L~--'-----"

ppb 135 130 125 120 115 110 105 100 95 90 85 80 75 70 65 60 55 50 45 40 35 30 25 20 15 10 5 0

18. 18 18.20 18.22 18.24 18.26 18.28 18.30 Time (Hours PST)


AEROSOL EXTINCTION COEFFICIENT AT 355 nm (.01 /km61 km-•

18. 18 18.20 18.22 18.24 18.26 18.28 18.30 Time (Hours PST)

El Monte. CA 9 /28 / 97

~ _J

V1 ~

~ " " 3

:.::, ;;'

3000 - -,. •. - .

2000

1000

0---'-~~~~~~~...L_~~~~~~~...L_~~~

66 64 62 60 58 56 54 52 50 48 46 44 42 40 38 36 34 32 30 28 26 24 22 20 18 16 14 12 10 8 6


2500

2000

~ _j (/] 1500:::;;

sS " "O

~ 1000·.;, <(

500

ppb 170 165 160 155 150 145 140 135 130 125 120 115 110 105 100 95 90 85 80 75 70 65 60 55 50 45 40 35 30 25 20 15 10

8


6 8 10 12 14 16 18 Time (Hours PST)

El Monte. CA 9 /29 / 97

AEROSOL EXTINCTION COEFFICIENT AT 355 nm 2500 J-

~ _j (/]

:::;;

sS " "O

2000

2 1000 ~

500

km- 1

83 80 77 74 71 68 65 62 59 56 53 50 47 44 41 38 35 32 29 26 23 20 17 14 11 8 5 2

6 8 10 12 14 16 18 Time (Hours PST)

El Monte. CA 9 /29 / 97

Fig. 13 Time-height charts of ozone concentrations and aerosol extinction coefficients September 29, 1997

500

OZONE MIXING

I ppP

2500 55 50 55 50 45

~~ 2000

'" 15 10 05

~, 1500 00 cl,95

..s 90 85 ..s BO . u, 75 u,70

; 1000 55 60 ~< 55 50 45 ~g

15 10 5 0

6.JO 6.J2 6.34 6.36 6.38 6.40 6.28 6.30 6.32 6.34 6.36 5.38 6.40 Time (Hours PST) Time (Hours PST)

El \tonte. CA 9 /29 / 97 El Monte. CA 9/29/ 97

OZONE MIXING RATIO (pobl

I ppb

i65 i70

160 155:ig140 1~51 0 1 5 120 115 110 105 100 95 90 '5 ~Q

l5 15 10

6

Fig. 14 Time-height charts of ozone concentrations and aerosol extinction coefficients in three scanning operations at about 0620, 0720, and 0820 PST on September 29, 1997

2500

2000

~

~ 1500

..s

t 7.30 7.32 7.34 7.36 7.38 7.40 7.30 7.32 7.34 7.36

Time {Hours PST) Time (Hours PST) El ~Onie. CA 9/29/ 97 El ~onte. CA 9/29/

OZONE" MIXING R.'1'0 ( cpb)

I ppb

2500 155 150 145 140 135 130

2000 125 120 115 110 :os 100 95 90 '5 BO. 75

u, 70 65

~ 1000 60 55 50 45 40 35 30 25 20 15 10 5 0

8 ..30 8.32 8.34 8.J6 8.38 8.28 8.30 8.32 8.34 8.36 Time (Hours PST) Time (Hours PST)

El ~orile. CA 9/29/ 97 El ~ante. CA 9/29/

. u,

AERCSOL ':XTINCTIQN CoEi=-FICIE\IT A.T 355 "'TI

2500

2000

-~ 1000

500

7.38 7.40

97

8.38 8.40

97

Report: 1999-05-01 Measurement of the Ozone Concentration ...

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