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.) Ozone PM 2.5

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

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

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

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.

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

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

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

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

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

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

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