TROPOSPHERIC OZONE AND OXIDANT CHEMISTRY Troposphere Stratosphere: 90% of total The many faces of atmospheric ozone: In stratosphere: UV shield In middle/upper troposphere: greenhouse gas In lower/middle troposphere: precursor of OH, main atmospheric oxidant In surface air: toxic to humans and vegetation 00

The atmosphere as an oxidizing medium EARTH SURFACE Emission Reduced gas Oxidized gas/ aerosol Oxidation Uptake Reduction Atmospheric oxidation is critical for removal of many pollutants, e.g. methane (major greenhouse gas) Toxic gases such as CO, benzene, mercury… Gases affecting the stratosphere

CO and methane account for most of reduced gas flux to atmosphere Methane observed from space: ppb CO observed from space: ppb

Production of O( 1 D) in troposphere takes place in narrow band [ nm] solar flux I at sea level ozone absorption cross-section  O( 1 D) quantum yield   I

Stratospheric ozone mechanism doesn’t apply to troposphere O 2 +hv O 3 +hv By contrast, in troposphere: no photons < 240 nm  no oxygen photolysis; neglible O atom conc.  no XO + O loss In stratosphere:

Ozone production in troposphere Photochemical oxidation of CO and volatile organic compounds (VOCs) catalyzed by HO x and NO x HO x ≡ H + OH + HO 2 + RO + RO 2 NO x ≡ NO + NO 2 Oxidation of CO: Oxidation of VOC: Carbonyl products can react with OH to produce additional ozone. CO emitted by combustion VOCs emitted by biosphere, combustion, industry NO x emitted by combustion, biosphere, lightning

Chemical mechanism for tropospheric ozone and OH O3O3 HO 2 H 2 O NO H2O2H2O2 CO NO 2 h O( 1 D) h M OH HNO 3 NO x -limited regime: ~ [O 3 ] 1/2 [H 2 O] 1/2 [NO] ~ [O 3 ] 1/2 [H 2 O] 1/2 [NO]/[CO] NO x -saturated regime: ~ [O 3 ][H 2 O][CO]/[NO 2 ] ~ [O 3 ][H 2 O]/[NO 2 ] P(O 3 ) [OH]

GLOBAL BUDGET OF TROPOSPHERIC OZONE O3O3 O2O2 h O3O3 OHHO 2 h, H 2 O Deposition NO H2O2H2O2 CO, VOC NO 2 h STRATOSPHERE TROPOSPHERE 8-18 km Chem prod in troposphere, Tg y Chem loss in troposphere, Tg y Transport from stratosphere, Tg y Deposition, Tg y Burden, Tg Lifetime, days Present-day Preindustrial

ATMOSPHERIC CARBON MONOXIDE Source: incomplete combustion Sink: oxidation by OH (lifetime of 2 months) Satellite CO data at 500 hPa

ATMOSPHERIC METHANE LIVESTOCK LANDFILLS GAS COAL RICE TERMITES WETLANDS BIOMASS BURNING methane emissions Global sources, Tg a -1 Sink: oxidation by OH (lifetime of 10 years)

METHANE: #2 ANTHROPOGENIC GREENHOUSE GAS Greenhouse radiative forcing of climate between 1750 and 2005 [IPCC, 2007] Referenced to concentration Referenced to emission

HISTORICAL TRENDS IN METHANE The last 1000 years The last 30 years

Methane column observed by SCIAMACHY,

NO x EMISSIONS (Tg N a -1 ) TO TROPOSPHERE FOSSIL FUEL 23.1 AIRCRAFT 0.5 BIOFUEL 2.2 BIOMASS BURNING 5.2 SOILS 5.1 LIGHTNING 5.8 STRATOSPHERE 0.2

LIGHTNING FLASHES SEEN FROM SPACE (2000) DJF JJA

SATELLITE OBSERVATIONS OF TROPOSPHERIC NO 2 SCIAMACHY data. May- Oct 2004 (R.V. Martin, Dalhousie U.) detection limit

TROPOSPHERIC NO 2 FROM THE OMI SATELLITE INSTRUMENT (MARCH 2006) March 2006

NO x EMISSION TRENDS SEEN FROM SPACE Hillboll et al. [2012]

GLOBAL DISTRIBUTION OF TROPOSPHERIC OZONE Zhang et al. [2010] TES thermal IR satellite observations for 2006, seasonal means at 500 hPa Maximum values at northern mid- latitudes in spring-summer due to anthropogenic pollution; High values in tropical regions affected by seasonal biomass burning; Minimum values over tropical oceans due to chemical loss

OBSERVED RISE IN TROPOSPHERIC OZONE OVER 20 th CENTURY Observations at mountain sites in Europe [Marenco et al., 1994]

GLOBAL OZONE AND OH TRENDS Mean mass-weighted tropospheric values computed from GEOS-Chem model for present-day (PD), pre-industrial (PI), and last glacial maximum (LGM) Ozone, ppb OH, 10 5 molecules cm -3 PD PI LGM two different climate reconstructions Lee Murray, Harvard

Inferring recent OH trends from methylchloroform data Global trends in methylchloroform concentrations Global trends in OH concentrations Montzka et al. [2011]

LONDON FOG Aerosols a.k.a.particulate matter (PM) from domestic+industrial coal combustion “Killer fog” of December 1952 resulted in 10,000 excess deaths Coal combustion Temperature Altitude inversion sulfate organic carbon black carbon particles < 1km

LOS ANGELES SMOG Respiratory problems, vegetation damage due to high surface ozone troposphere stratosphere 8-18 km temperature inversion ozone altitude Nitrogen oxides (NO x ≡ NO + NO 2 ) Volatile organic compounds (VOCs) UV radiation Ozone (O 3 ) vehicles, industry, vegetation produced by photolysis of oxygen (O 2 )

AIR POLLUTION IN THE US TODAY: Ozone is the #1 pollutant 75 ppb (8-h average)

4 th -highest annual maximum for daily 8-h average ozone,

The 2012 ozone season

ppb Europe AQS (seasonal) U.S. AQS (8-h avg.) U.S. AQS (1-h avg.) Preindustrial ozone background Present-day ozone background at northern mid-latitudes Europe AQS (8-h avg.) Canadian AQS (8-h avg.) Mexican AQS (1-h avg.) Ozone air quality standards in the US and in the world ? 1997

OZONE CONCENTRATIONS vs. NO x AND VOC EMISSIONS Air pollution model calculation for a typical urban airshed NO x - saturated NO x -limitedRidge

LARGE SUPPLY OF BIOGENIC VOCs – unrecognized until the 1990s Isoprene (biogenic VOC)Anthropogenic VOCs Jacob et al., 1993 Switches polluted areas in U.S. from NO x -saturated to NO x -limited regime! recognized in Revised Clean Air Act of 1999

MAPPING OF VOC EMISSIONS FROM SPACE using satellite measurements of formaldehyde confirms dominance of biogenic over anthropogenic VOCs Millet et al. [2008]

TREND OF U.S. EMISSIONS Focus until past decade was on VOC emission controls

OZONE TRENDS IN U.S. Boston trend National trend The national trend is heavily weighted by California sites; other parts of the country have seen marginal improvement

DECREASE OF POWER PLANT NO x EMISSIONS OVER THE PAST DECADE Decreasing US NO x emissions from power plants

Decrease of North American NO x emisssions, as seen with annual mean NO 2 columns from the OMI satellite instrument Shailesh Kharol (Dalhousie) Decreases in both the eastern US and eastern Canada

Ozone trends in the Northeast,

EVEN IN NO x -LIMITED REGIME, THE TOTAL O 3 PRODUCED IS ONLY A WEAK FUNCTION OF NO x NO NO 2 HNO 3 hv HO 2,RO 2,O 3 OH, O 3 P(O 3 ) L(NO x ) EmissionDeposition Assuming NO x steady state, efficient HO x cycling, and loss of NO 2 by reaction with OH: OPE  as NO x  strong nonlinearity; in models, decreasing NO x emissions by 50% reduces ozone only by ~15% Define ozone production efficiency (OPE) as the total number of O 3 molecules produced per unit NO x emitted.

Median surface ozone, : emerging problem in the Intermountain West Cooper et al. [2012] Spring Summer

Daytime surface ozone trends, Spring Summer Cooper et al. [2012]

8-h daily maximum ozone in the intermountain West (2006) 56.3 ppb53.2 ppb 12.3 ppb 58.1 ppb 56.4 ppb 15.0 ppb GEOS-Chem model US pollution contribution Zhang et al., 2011

North American ozone background over the US 4 th highest annual North American background ozone (GEOS-Chem model) Zhang et al. [2011] defined as the surface ozone concentrations that would be present in the absence of North American anthropogenic emissions

Growing NO x emissions from Canadian oil sands Oil sand recovery In Alberta Satellite NO 2 columns, NO 2 increase of 10.4 ±3.5% per year McLinden et al. [GRL 2012]

Ozone trends in remote air at northern mid-latitudes D.D. Parrish, NOAA

Rising surface ozone pollution in China D.D. Parrish, NOAA

INTERCONTINENTAL OZONE POLLUTION INFLUENCES Surface O 3 enhancements from North American anthropogenic emissions from European anthropogenic emissions from Asian anthropogenic emissions Lin Zhang, Harvard GEOS-Chem model results for 2006