1. AIR POLLUTION IN THE US : Ozone and fine particulate matter (PM 2.5 ) are the two main pollutants 75 ppb (8-h average) 15  g m -3 (1-y av.) http://epa.gov/airtrends/2010/ Ozone PM 2.5

2. 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

3. 4 th -highest annual maximum for daily 8-h average ozone, 2008-2010

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

5. 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

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

7. 1970-2003 TREND OF U.S. EMISSIONS Focus until past decade was on VOC emission controls

8. 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

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

10. 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

11. 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.

12. MEAN AFTERNOON SUMMER OZONE (2006) ppb CASTNet sites (regional background) High ozone concentrations at sites in intermountain west

13. 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

14. 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

15. 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

16. Daytime surface ozone distributions, 2006-2010 Spring Summer Cooper et al. [2012]

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

18. Using OMI observations to monitor growth in emissions from Canadian oil sands Oil sand recovery In Alberta OMI NO 2 columns, 2004-2010 NO 2 increase of 10.4 ±3.5% per year McLinden et al. [GRL 2012] AQAST PI: DIckerson

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

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

21. 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