QUESTIONSQUESTIONS

1. How does the thinning of the stratospheric ozone layer affect thesource of OH in the troposphere?

2. Chemical production of ozone in the troposphere is much faster in summer than winter. Explain.

3. Why don’t reactions of hydrocarbons deplete (or titrate!) all the OH in the troposphere?

CHAIN MECHANISM FOR OCHAIN MECHANISM FOR O33 PRODUCTION: PRODUCTION:

CHCH44 OXIDATION OXIDATIONInitiation: source of HOx (OH production)Propogation:

CH4 + OH CH3 + H2OCH3 + O2 + M CH3O2 + M

CH3O2 + HO2 CH3OOH + O2

CH3O2 + NO CH3O + NO2

CH3OOH + OH CH2O + OH + H2O CH3OOH + OH CH3O2 + H2OCH3OOH + hv CH3O + OH

CH3O + O2 CH2O + HO2

CH2O + OH CHO + H2OCH2O + hv + O2 CHO + HO2

CH2O + hv CO + H2

CHO + O2 CO + HO2

(…then CO oxidation…)

Oxidation from C(-IV) in CH4 through to C(+IV) in CO2

*

*

**

*

O3

O2 h

O3

OH HO2

h, H2O

Deposition

NO

H2O2

CO, CH4

NO2

h

METHANE OXIDATION SCHEMEMETHANE OXIDATION SCHEME

CH4 CH3 CH3O2

CH3OOH

CH3O

CH2O CHO COOH O2, MNO

HO2 OH

O2

hv

hv, O2

OH

OH

O2

hv

HO2

HO2HO2

NO2

In clean troposphere, ~70% of OH reacts with CO, 30% with CH4

NONOxx EMISSIONS (Tg N yr EMISSIONS (Tg N yr-1-1) TO TROPOSPHERE) TO TROPOSPHERE

FOSSIL FUEL 23.1

AIRCRAFT 0.5

BIOFUEL 2.2

BIOMASSBURNING 5.2

SOILS 5.1

LIGHTNING 5.8

STRATOSPHERE 0.2

Zeldovich Mechanism: combustion and lightningAt high T (~2000K) oxygen thermolyzes:

O2 O + OO + N2 NO + NN + O2 NO + O

LIGHTNING FLASHES SEEN FROM SPACE (2000)LIGHTNING FLASHES SEEN FROM SPACE (2000)

DJF

JJA

USING SATELLITE OBSERVATIONS OF NOUSING SATELLITE OBSERVATIONS OF NO22 TO MONITOR NO TO MONITOR NOxx EMISSIONS EMISSIONS

SCIAMACHY data. May-Oct 2004

(R.V. Martin, Dalhousie U.)

detectionlimit

NONOXX CYCLING CYCLING

HO2

NONO2

h

O3

O3

O2

Combustionlightning

HNO3

OH, M

O3

NO3

N2O5

M

H2O

PANcarbonyloxidation

T

~ 1 day

Example of PAN formation from acetaldehyde:CH3CHO + OH CH3CO + H2OCH3CO + O2 + M CH3C(O)OO + MCH3C(O)OO+NO2 + M CH3C(O)OONO2 + M

PEROXYACETYLNITRATE (PAN) AS RESERVOIR PEROXYACETYLNITRATE (PAN) AS RESERVOIR FOR LONG-RANGE TRANSPORT OF NOFOR LONG-RANGE TRANSPORT OF NOxx

DECOMPOSITION OF PAN LEADING TO OZONE PRODUCTIONDECOMPOSITION OF PAN LEADING TO OZONE PRODUCTION

H

Origin: Warm Conveyor Belt over Asia

Evolution: Split by blocking high pressure

ECMWF

Chemistry: Changing NOy speciation

CO

O3

[Heald et al., 2004]

O3

O2 h

O3

OH HO2

h, H2O

Deposition

NO

H2O2

CO, VOC

NO2

h

STRATOSPHERE

TROPOSPHERE

8-18 km

Chem prod in troposphere,

Tg y-1

4300

1600

Chem loss in troposphere,

Tg y-1

4000

1600Transport from stratosphere,

Tg y-1

400

400

Deposition,

Tg y-1700

400Burden, Tg 360

230

Lifetime, days 28

42

Present-day Preindustrial

GLOBAL BUDGET OF TROPOSPHERIC OZONEGLOBAL BUDGET OF TROPOSPHERIC OZONE

3O 10 2 18 3 2P k [HO ] k [CH O ] [NO] NO+peroxy radicals is rate-limiting, so:

Climatology of observed ozone at 400 hPa in July from ozonesondes and MOZAIC aircraft (circles) and corresponding GEOS-Chem model results for 1997 (contours).

GEOS-Chem tropospheric ozone columns for July 1997.

GLOBAL DISTRIBUTION OF TROPOSPHERIC OZONEGLOBAL DISTRIBUTION OF TROPOSPHERIC OZONE

[Li et al., 2001]

1996-2005 NO1996-2005 NOxx EMISSION TREND SEEN FROM SPACE EMISSION TREND SEEN FROM SPACE

[Van der A et al., 2008]

POWER PLANT EMISSION REDUCTIONS IN THE EASTERN USPOWER PLANT EMISSION REDUCTIONS IN THE EASTERN USEffects of NOx controls on large point sources in the Eastern US beginning in the late 1990s

•Acid Rain Program, NOx SIP Call, NOx Budget Trading Program

•Focus on coal-burning power plants

•Improved burner technology, post-burner ammonia scrubbers

Ohio River Valley 1997

E(NOx) ~ 50% power plant

Northeast Urban Corridor

E(NOx) < 20% power plant

Ohio River Valley 2005

E(NOx) ~ 20% power plant Courtesy: Greg Frost (NOAA)[Kim et al., 2006]

POWER PLANT POINT SOURCES IN WESTERN POWER PLANT POINT SOURCES IN WESTERN US SEEN FROM SPACEUS SEEN FROM SPACE

North Valmy

Intermountain

Hunter /Huntington

Mohave

Navajo Four Corners/San Juan

Cholla/Coronado/ Springerville

Bonanza

Craig/Hayden

Jim Bridger/Naughton

Dave Johnston/Laramie River

Colstrip

Reid Gardener

Courtesy: Greg Frost (NOAA)[Kim et al., 2009]

IPCC [2007]

Tropospheric ozoneIs the third anthropogenicgreenhouse gas

IPCC RADIATIVE FORCING ESTIMATE FOR TROPOSPHERIC IPCC RADIATIVE FORCING ESTIMATE FOR TROPOSPHERIC OZONE (0.35 W mOZONE (0.35 W m-2-2) RELIES ON GLOBAL MODELS) RELIES ON GLOBAL MODELS

Preindustrialozone models

}

Observations at mountain sites in Europe [Marenco et al., 1994]

…but these underestimate the observed rise in ozone over the 20th century

Fitting to observations would imply a radiative forcing of 0.8 W m-2

RECENT TRENDS IN TROPOSPHERIC OHRECENT TRENDS IN TROPOSPHERIC OHinferred from methylchloroform observationsinferred from methylchloroform observations