March 24, 2004 EAS 4/8803 1

EAS 4/8803: Experimental Methods in AQ

Week 11:

Air Quality Management (AQM)Clean Air Act (History, Objectives, NAAQS)

Emissions and Atmospheric Trends (Links)

Principal Measurement Techniques (NOx, CO, SO2)

Measurement of CO (Exp 5)NDIR Method (Interferences, Stability, DL, Precision, Accuracy)

Controlling O3 and PM2.5

Principal Measurement Techniques (O3, PM2.5)

Atmospheric Transport & Photochemistry (NOx vs VOC, SOA)

Ambient Measurements and Trends (World, USA, GA)

Measurement of O3 (Exp 6)

UV Absorption (Interferences, Stability, DL, Precision, Accuracy)

March 24, 2004 EAS 4/8803 2

Tapered Element Oscillating Microbalance

If PM of mass m deposit on piezoelectric quartz crystal, frequency changes by

f = Kq Q t cm

with sensitivity Kq, aerosol mass flow Q,

time t, and PM mass concentration cm

March 24, 2004 EAS 4/8803 3

TEOM Method

If PM of mass m deposit on piezoelectric quartz crystal, frequency changes by

f = Kq Q t cm

with sensitivity Kq, aerosol mass flow Q,

time t, and PM mass concentration cm

March 24, 2004 EAS 4/8803 4

TEOM Setup and Operation

Reducing H2O Interference

• Inclusion of Nafion dryer using

TEOM’s exhaust (low p, dry)

as sheath flow.

• Filter housing T-controlled

at 50 oC.

March 24, 2004 EAS 4/8803 5

Assessing Accuracy of PM2.5 Mass Measurements

Comparison of dry TEOM averages with dehydrated Teflon samples

Williams Tower is ~20 km west of LaPorte, which is close to Ship Channel

70

60

50

40

30

20

10

0

30 m

in T

EO

M (

ug

m-3

)

403020100

discrete PCM (ug m-3

)

Will. TowerMass r = 0.92slope = 0.96 +-0.07i-cept = 2.52 +-1.23

70

60

50

40

30

20

10

0

30 m

in T

EO

M (

ug

m-3

)403020100

discrete PCM (ug m-3

)

LaPorteMass r = 0.95slope = 1.01 +-0.05i-cept = 0.98 +-0.81

excl 1st 3 PCM

254 m agl 6 m agl

March 24, 2004 EAS 4/8803 6

High Resolution vs Integrated [PM2.5]at LaPorte and Williams Tower

60

40

20

0

μg

m-3

PM2.5 Mass PCM LP WT TEOM LP WT

Large [PM2.5] transients (spikes) at both sites: Chemistry or transport?

Transients (changes in [PM2.5]) larger at WT, esp. at night.

Averages of integrated samplers (8-24h) are very similar and follow a regional trend.

March 24, 2004 EAS 4/8803 7

Adding Photochemistry (O3)

60

40

20

0

μg

m-3

PM2.5 Mass PCM LP WT TEOM LP WT

200

150

100

50

0

pp

bv

O3 LP WT

NOy(LP)

80

60

40

20

0

-20

ne

m-3

8/29/2000 8/31/2000 9/2/2000 9/4/2000 9/6/2000 9/8/2000Date (CST)

PM2.5 Acidity (SO4=/NO3

-/NH4

+) LP WT

LP max [O3] on 08/30 is more than twice WT-[O3], which seems to follow a “rising tide”.

Fast P(O3) at LP (<200 ppb/h): high precursor emissions (Alkenes, NOx) in Ship Channel.

More regional influence from BB plume on 9/5 + 9/6: joint increase in [PM2.5].

March 24, 2004 EAS 4/8803 8

Average Diurnal Differences in [O3] and [PM2.5]

100

80

60

40

20

0

Ozo

ne

(p

pb

v)

00:00 06:00 12:00 18:00 00:00

LaPorteWill.Tower

WT-O3 levels are significantly higher at night and early mornings: Separation from nocturnal surface inversion; LP-O3 titration.LP-O3 higher at midday: >P(O3) from precursor mix and closer sources.

-30

-20

-10

0

10

20

Ozo

ne

WT-

LP

(

pp

bv

)

00:00 06:00 12:00 18:00 00:00

Δ-O3

center 67 %

30

25

20

15

10

5

TE

OM

mas

s

(µg

m-3

)

00:00 06:00 12:00 18:00 00:00Time (CST)

LaPorteWill.Tower

10

5

0

-5

-10

PM

WT-

LP

(

µg

m-3

)

00:00 06:00 12:00 18:00 00:00Time (CST)

Δ-PM2.5

center 67 %

Trend to higher WT-[PM2.5] mostly at night, similar to vertical gradients at Hendersonville, but note 20 km WT-LP distance!

March 24, 2004 EAS 4/8803 9

Vertical Gradients of PM2.5

Direct emissions and/or secondary formation of fine PM aloft.

Free Troposphere Source for PM2.5!

During SOS’99, 16 June - 22 July 1999,

measurements near Nashville, TN,

between 4 and 42 m agl showed

positive vertical gradients for

60-70 % of all daytime, and

70-80 % of all nighttime samples of

PM2.5 mass, SO4=, NO3

-, and NH4+!!

March 24, 2004 EAS 4/8803 10

Vertical Gradients of PM2.5

Free Troposphere Source for PM2.5!

BL Dynamics Important Influence on Ground-Based AQ Monitoring !!

12

10

8

6

4

2

0

-2

C

42m

-4m

(

g m

-3)

Daytime MASS SO4 NO3 NH4Nighttime MASS SO4 NO3 NH4

-6

-4

-2

0

2

4

WS

, T, R

H 4

2m-4

m

6/21/99 6/26/99 7/1/99 7/6/99 7/11/99 7/16/99 7/21/99Time (EST)

Daytime WS T RHNighttime WS T RH

March 24, 2004 EAS 4/8803 11

Vertical Wind Profile: Advection Horizontal Transport

Near logarithmic increase of WS and uniform WD within well-mixed BL.

Clockwise rotation with height near BL top to merge with more geostrophic winds.

Nighttime separation of layers with different wind speeds and directions.

March 24, 2004 EAS 4/8803 12

PM2.5 Wind Roses: Seasonal Differences Across GAIndications for Regional Advective Transport?

Period 2001+ 02MAY-OCT NOV-APR

34.4

34.2

34.0

33.8

33.6

33.4

33.2

33.0

32.8

32.6

32.4

32.2

32.0

-85.5 -85.0 -84.5 -84.0 -83.5 -83.0 -82.5 -82.0

Atlanta

FAQS measurement sites GA-EPD monitoring sites coal burning power plants point sources w/ CO:NOx > 1

20x20 km

N

E

S

W9 18

µg m-3

15.813.4Griffin

N

E

S

W9 18

µg m-3

16.715.5Macon SBP

N

E

S

W9 18

µg m-3

Columbus OLC 16.6 19.3

N

E

S

W9 18

µg m-3

15.014.2Augusta RP

N

E

S

W18 36

µg m-3

36.8

Aug’99

March 24, 2004 EAS 4/8803 13

…Similarity to Daytime O3

Period 2001+ 02MAY-OCT NOV-APR

34.4

34.2

34.0

33.8

33.6

33.4

33.2

33.0

32.8

32.6

32.4

32.2

32.0

-85.5 -85.0 -84.5 -84.0 -83.5 -83.0 -82.5 -82.0

Atlanta

FAQS measurement sites GA-EPD monitoring sites coal burning power plants point sources w/ CO:NOx > 1

20x20 km

N

E

S

W30 60

ppb

38.228.5Macon SBP

N

E

S

W30 60

ppb

Columbus OLC 30.7 19.8

N

E

S

W30 60

ppb

30.222.2Augusta RP

N

E

S

W30 60

ppb

44.236.1Griffin

N

E

S

W60 120

ppb

106

Aug’99

March 24, 2004 EAS 4/8803 14

Summertime PM2.5 – Max(O3) Relationship

Tighter correlation in July 2001.

“Downwind” Griffin site offset to higher PM2.5 mass.

August 99 in Atlanta was hotter, dryer, more polluted with O3-precursor species.

March 24, 2004 EAS 4/8803 15

Seasonal & Regional Comparison of PM2.5 Composition

Summer Months

Regional Difference: Higher OM/OC and OC/EC at more rural site!Seasonal Difference: Lower OM/OC and (higher) OC/EC in winter.

More SOA in August 99? More oxygenated POCs away from Atlanta?

Winter Months

March 24, 2004 EAS 4/8803 16

Atlanta JST Griffindownwind

120

100

80

60

40

20

0

O3

(

pp

bv

)

35302520151050

NOz (ppbv)

July 2001Sunny daytimesNortherly flowslope = 13.7 +-0.59intcept= 34 +-1.5r = 0.86incl "lost" HNO3

slope = 2.9 +-0.21intcept= 34 +-2.4r = 0.72

120

100

80

60

40

20

0

O3

(

pp

bv

)

35302520151050

NOz (ppbv)

Sunny daytimesAugust 1999slope = 3.6 +-0.14intcept= 59 +-1.5r = 0.59July 2001slope = 2.7 +-0.28intcept= 38 +-2.7r = 0.50December 2001slope = -0.6 +-0.09intcept= 33 +-1.1r = -0.42

Elevated regional O3 background reflected in regression’s intercept: higher in Aug 99!

At JST higher intercept and slope during Aug ’99 (OPE= 4 vs 3): more efficient P(O3).

OPE in air mass arriving at Griffin is likely larger given by upper and lower limits.

Lower limit assumes 1st order loss of HNO3 due to surface deposition at k ≈ 0.22 h-1.

Air mass transitions from VOC-limited to NOx-limited regime due to Biogenic HC.

High photochemical activity P(O3) allows for high P(SOA): rural/urban gradient.

Photochemical ActivitySource – Receptor Considerations: O3/NOz as “OPE”

March 24, 2004 EAS 4/8803 17

Photochemical Processes Leading to O3 and PM

SOA

NOz

An Assessment of Tropospheric Ozone Pollution, A North American Perspective, NARSTO, National Acad. Press, 2000.

March 24, 2004 EAS 4/8803 18

Ozone Isopleths

Area of effective VOC control (most often highly populated areas)

Volatile Organic Compounds (VOC)

Nit

rog

en O

xid

es

(NO

x) Constant [O3]

Low [O3]

High [O3]

NOx control effective(areas with high biogenics)

March 24, 2004 EAS 4/8803 19

SOA & O3 Formationand Transport

PM, SO2, NOx

Emissions

VOCEmissions

Wind

DepositionRainout

O3, HNO3

PM

NO

hv

RO2 /HO2 RO,OH

NO2

O2

O3

HNO3

OH

OH

Fine PM, SOA

March 24, 2004 EAS 4/8803 20

Planetary Boundary Layer Dynamics

Comparison of PBL and Free Troposphere Characteristics

Property PBL FT

Turbulence Near continuous over Zi. Convective clouds; sporadic

in thin layers extending horizontally.

Friction Large drag & energy dissipation. Small viscous dissipation.

Dispersion Rapid in vertical & horizontal. Small molecular diffusion; rapid

horizontally by mean wind.

Winds WS log profile in surface layer. Nearly geostrophic.

Vertical Transport Mainly turbulence. Mean wind, cumulus-scale.

Thickness 100 – 3000 m, f (time/space). 8 – 18 km, less variable.

Diurnal oscillations over land. Slow time variations.

PBL strongly influenced by Earth’s surface, responding to surface forcings within 30-60 min

March 24, 2004 EAS 4/8803 21

Turbulence in PBL

Assuming an air parcel rises or sinks adiabatically, i.e. no energy is supplied nor removed, it expands and cools as it reaches lower ambient pressure aloft, or compresses and warms as it reaches higher pressure below. If the ambient vertical temperature profile (lapse rate) is less steep, the air parcel will continue to rise or fall once in (vertical) motion.

Superadiabatic T profile (unstable layer)

March 24, 2004 EAS 4/8803 22

Consequences for Dispersion/Dilution

Weakly instable to neutral layer: Dispersion driven by advection (horizontal WS).

Highly instable layer: Dispersion driven by thermal looping (vertical & horizontal).

March 24, 2004 EAS 4/8803 23

Effects of Terrain (Friction)

March 24, 2004 EAS 4/8803 24

Temperature Inversion

Assuming an air parcel rises or sinks adiabatically, i.e. no energy is supplied nor removed, it expands and cools as it reaches lower ambient pressure aloft, or compresses and warms as it reaches higher pressure below. If the ambient vertical temperature profile (lapse rate) is steeper, the air parcel will return to its original position.

Subadiabatic T profile (stable layer)

March 24, 2004 EAS 4/8803 25

Inversion Types and Formation

Elevated

Surface

Subsidence inversion: Large scale sinking of cold (but warming) air meets rising cooling air (thermals) under regional high pressure conditions.Frontal inversion: Warm moist air from S glides over cold dry air from N.

Radiational inversion: Radiative heat loss at night from the Earth’s ground into space according to Tg

4.

March 24, 2004 EAS 4/8803 26

Typical PBL Evolution in Summer

Stull, R. B., 1988: An Introduction to Boundary Layer Meteorology. Kluwer Academic, 666 pp.

March 24, 2004 EAS 4/8803 27

Potential Temperature () Profiles…is T an air parcel at P and T would have if it were at Ps (conserved for adiabatic motions, i.e., d/dt = 0).

Afternoon After sunset Before sunrise After sunrise Before noon Noon

March 24, 2004 EAS 4/8803 28

PBL Winter vs Summer

March 24, 2004 EAS 4/8803 29

00:00 03:00 06:00 09:00 12:00 15:00 18:00 21:00 00:00

Time (EST)

WINTER HALF NOV-APRMac '01/'02 '00/'01Col '01/'02 '00/'01Aug '01/'02 '00/'01

25

20

15

10

5

0

PM

2.5

(

g m

-3)

00:00 03:00 06:00 09:00 12:00 15:00 18:00 21:00 00:00

Time (EST)

SUMMER HALF MAY-OCTGrif '02Mac '02 '01 '00Col '02 '01 '00Aug '02 '01 '00

Seasonal Differences in Diurnal Cycles of PM2.5

Midday minimum due to BL mixing seems compensated by SOA in summer.

PM2.5 sources near Columbus drive nighttime averages in winter 2001/02.

Summer stagnation with high O3 also leads to high PM2.5 (e.g. 2000).

Annual PM2.5 NAAQS (15 g m-3) sensitive to:

- SOA formed under regional stagnation in summer;

- Primary PM2.5 from local sources at night in winter.

WinterSummer

March 24, 2004 EAS 4/8803 30

30

20

10

0WS

(m

/s)

Tm

ax-

Tm

in(C

)

3000

2000

1000

0

BL

H-d

ay

(m)

1000

800

600

400

200

0

Ft B

ac

r bu

rne

d B

LH

-nig

ht (m

)

10/17/01 10/21/01 10/25/01 10/29/01 11/2/01 11/6/01 11/10/01 11/14/01 11/18/01 11/22/01 11/26/01

Time (EST)

4

68

10

2

4

68

100

2

4

24

h -

PM

2.5

(

µg

m-3

)

Columbus OLCGriffin Macon Augusta

wild firesprescribed

-10

0

10

Win

d B

arb

PM2.5 Exceedances at Columbus in Oct-Nov 2001

March 24, 2004 EAS 4/8803 31

PM2.5 at Columbus in Oct-Dec 2001

2.52.01.51.00.5

24h - WS (m s-1

)

448

142

600500400300200100GFC-BLHnight (m agl)

448142

300020001000GFC-BLHday (m agl)

448142

10008006004002000

FtB total acr burned

448142

80

60

40

20

0

24h

- P

M2

.5

(µg

m-3

)

2015105Tmax- Tmin (K)

448

142

Critical parameters driving [PM2.5]:

• size of burn, distance and plume trajectory

• atmospheric divergence (horizontal wind speed)

• {vertical} boundary layer stability (T difference)

• BL mixing depth at night (BLHnight)