Ozone Budget

From: Jacob

Ozone in the Atmosphere

• Lifetime:– ~1 month– Highly variable – dependent on season,

latitude, altitude, etc.

• Background concentrations:– less than 40 ppbv– can reach over 200 ppb in urban areas

Ozone in the Atmosphere

From: Fishman et al., 2005, Atmos. Chem Phys. Discuss., 3, 1453

HOx Sources and SinksSource:

oxidation of VOCs:

Sinks:

OH2OHD)O(

320nm D);O( O O2

1

k2

1

12

j3

h

2k

2

2

HOO H

HCO H COH2

h

222

22222

32

OOHHOOH

OOHHOHO

HNO NOOH

HOx Cycle

HOx in the Atmosphere

• Lifetime:– ~1 second

– highly variable (same reasons as for O3)

• Typical concentrations:– ~5 x 106 molecules/cm3

– higher over oceans and southern hemisphere• less anthropogenic CO and methane

NOx Sources and Sinks

Sinks:

3252

32

HNO2OHON

HNO OHNO

From: Jacob

Nighttime NOx ChemistryThere is no NO at night:

sink

-when the sun comes upONO

ONOhNO

2HNOOHON

MONMNONO

ONOONO

ONO ONO

2

23

3252

5223

2332

223

Peroxyacetylnitrates (PANs)

Organic radicals of the form:

RO

ROO

R(O)OO

can sequester NO2.

The most common is PAN: CH3C(O)OONO2.

NOx Cycle

NOx in the Atmosphere

• The lifetime of NOx varies, but is about 1 day near the surface and about 1 week in the upper troposphere.

• Concentrations range from a few pptv to 10’s of pptv.– higher concentrations near the ground.

• Urban areas may reach concentrations of 10s of ppbv.

NOx in the Atmosphere

From: Lamsal et al., 2008, J. Geophys. Res., 113, D16308, doi:10.1029/2007JD009235

CO Budget

From: Jacob

CO in the Atmosphere

• The lifetime of CO is about 2 months with respect to oxidation by OH

• CO is not well mixed globally– remote concentrations: 50-150 ppbv– over populated continental regions: 100-300

ppbv– in urban centers: > 1ppmv

CO in the Atmosphere

From: Barret et al., 2005, Atmos. Chem Phys. Discuss., 5, 4599

CO in the Atmosphere

Methane Budget

From: Jacob

Methane in the Atmosphere

• The overall lifetime of methane is 8.5 yrs.

• Current concentrations are about 1.8ppmv.– up from 800 ppbv preindustrial

– methane and CO2 concentrations track each other over geological time periods.

Methane in the Atmosphere

Methane in the Atmosphere

Beyond CO and Methane

• There are literally thousands of volatile organic compounds (VOCs) present in the atmosphere in trace amounts (pptv-ppbv).

• Many have short lifetimes– Low concentrations– Big influence on chemistry

Biogenic VOCs

Terpene compounds are emitted by trees:

Isoprene

Monoterpene

Sesquiterpene

Biogenic VOCs

• Globally, about 80% of VOCs emitted to the atmosphere are biogenic.

• Anthropogenic VOCs dominate only in industrial or some urban areas.

Photochemical Smog

OH2OCHOR4ORH :net

OHNONOHO

HOCHORORO

NORONORO

OHROOHRH

OH2OHD)O(

OD)O(hO

232

2k

2

2k

2

2k

2

22k,O

21

21

3

4

3

2

12

Photochemical Smog

O3 OH

RO2 RO

HO2

H2O2HNO3

O3

O3

PHOx

k1

k2k3

k4

k5k6

Photochemical Smog

]OH][NO[k]HO[kP

HOfor state-steady Assume

NO]][[HOk2P

NO]][[HOkNO]][RO[k

NO]][[HOkNO]][RO[kP

262

25HO

x

24O

2422

2422O

x

3

3

Case 1: Low NOx

NO][k

Pk2P

k

P]HO[]HO[kP

2

1

5

HO4O

2

1

5

HO2

225HO

x

3

x

x

-O3 production varies linearly with NOx

-independent of hydrocarbons

NOx-limited regime

Case 2: High NOx

[RH]k

NO]][HO[k[OH]

OH][RH][kNO]][HO[k

OHfor state-steady Assume

][NOk

P[OH]]OH][NO[kP

1

24

124

26

HO26HO

x

x

Case 2: High NOx

][NOk

RH][P2kP

[NO]][NOkk

[RH]kP]HO[

][NOk

P

[RH]k

NO]][HO[k

26

HO1O

264

1HO2

26

HO

1

24

x

3

x

x

-O3 production varies linearly with hydrocarbons-varies inversely with NOx

Hydrocarbon-limited regime

Ozone Pollution

From: Jacob

Ozone Pollution

• In the background atmosphere:

])[NO]RO[k]O[CHk]HO[k(P

NORONORO

NOOCHNOOCH

NOOHNOHO

2c23b2aO

2k

2

23k

23

2k

2

3

c

b

a

Ozone Pollution

• In the urban atmosphere, there is a competition between NO2 and RH for the OH radical:

• As a rule of thumb:

3M

2

22O

HNONOOH

OHRORHOH 2

limited VOC limited NO

5.5][NO

VOC][5.5

x

x

Why too much O3 is a bad thing• Health effects:

– Irritation of the lungs (short exposure to high concentrations).

– Permanent lung damage (long-term exposure).– Effects are worst for the elderly and people with

asthma.

• Ecosystem effects:– Reduced photosynthesis (low crop yields).– Increased susceptibility to pests.– Leaf scarring.

Ozone Air Quality Standards

• Federal:– 1 hour maximum concentration = 120 ppbv– 8 hour average maximum concentration = 75 ppbv

• State of California:– 1 hour maximum concentration = 90 ppbv

Ozone Problem Areas

From: EPA

Air Quality Index

From: EPA

Air Quality Index

Peak Ozone for California

From: www.airnow.gov

1 - 50

51 - 100

101 - 150

151 - 200

201 - 250

Data Not Available

AQI

LA Region Maximum Ozone

From: California Air Resources Board

LA Region Ozone Exceedance

From: California Air Resources Board

Sacramento Region Max Ozone

From: California Air Resources Board

Sacramento Region Annual Ozone

From: California Air Resources Board

Sacramento Ozone Exceedance

From: California Air Resources Board

Sacramento Region Ozone

Ozone data from: California Air Resources Board

1 - 50

51 - 100

101 - 150

151 - 200

201 - 250

Data Not Available

Ozone data from: www.airnow.gov

AQI