1. 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

2. 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

3. CO and methane account for most of reduced gas flux to atmosphere Methane observed from space: 1700-1900 ppb CO observed from space: 50-200 ppb

4. Production of O( 1 D) in troposphere takes place in narrow band [290-320 nm] solar flux I at sea level ozone absorption cross-section  O( 1 D) quantum yield   I

5. 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:

6. 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

7. 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]

8. 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 -1 4300 1600 Chem loss in troposphere, Tg y -1 4000 1600 Transport from stratosphere, Tg y -1 400 Deposition, Tg y -1 700 400 Burden, Tg 360 230 Lifetime, days 28 42 Present-day Preindustrial

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

10. ATMOSPHERIC METHANE LIVESTOCK 80-90 LANDFILLS 40-70 GAS 50-70 COAL 30-50 RICE 30-110 TERMITES 20-30 WETLANDS 100-230 BIOMASS BURNING 10-90 2005 methane emissions Global sources, Tg a -1 Sink: oxidation by OH (lifetime of 10 years)

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

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

13. Methane column observed by SCIAMACHY, 2003-2009

14. 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

15. LIGHTNING FLASHES SEEN FROM SPACE (2000) DJF JJA

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

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

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

19. 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

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

21. 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

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

23. 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

24. 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 )

25. AIR POLLUTION IN THE US TODAY: Ozone is the #1 pollutant 75 ppb (8-h average) http://epa.gov/airtrends

26. 4 th -highest annual maximum for daily 8-h average ozone, 2008-2010

27. The 2012 ozone season

28. 0 20 40 60 80 100 120 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 2008 2014? 1997

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

30. 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

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

32. 1970-2003 TREND OF U.S. EMISSIONS Focus until past decade was on VOC emission controls

33. OZONE TRENDS IN U.S. http://www.epa.gov/airtrends/ Boston trend National trend The national trend is heavily weighted by California sites; other parts of the country have seen marginal improvement

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

35. Decrease of North American NO x emisssions, 2005-2009 as seen with annual mean NO 2 columns from the OMI satellite instrument Shailesh Kharol (Dalhousie) 20092005 Decreases in both the eastern US and eastern Canada

36. Ozone trends in the Northeast, 1997-2012

37. 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.

38. Median surface ozone, 2006-2010: emerging problem in the Intermountain West Cooper et al. [2012] Spring Summer

39. Daytime surface ozone trends, 1990-2010 Spring Summer Cooper et al. [2012]

40. 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

41. 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

42. Growing NO x emissions from Canadian oil sands Oil sand recovery In Alberta Satellite NO 2 columns, 2004-2010 NO 2 increase of 10.4 ±3.5% per year McLinden et al. [GRL 2012]

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

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

45. 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