1. Loretta J. Mickley, Harvard University Shiliang Wu, Eric Liebensperger, Moeko Yoshitomi, Dominick Spracklen, Brendan Field Daniel Jacob, David Rind, Cynthia Lin, David Streets Effects of Climate Change on U.S. Air Quality Projected trends in global temperature

2. Probability of ozone exceedance vs. daily max. temperature Day-to-day weather plays a large role in surface air quality (1). Northeast Ozone is strongly correlated with temperature in observations; this is due to (1) chemistry, (2) biogenic VOC emissions, (3) joint association with stagnation. 1988, hottest on record Average num. of days Number of summer days with ozone exceedances (> 84ppb) over northeast U.S. Lin et al., 2001 1992, coldest on record, due to Pinatubo eruption

3. Day-to-day weather plays a large role in surface air quality (2). Stalled high pressure system increases ozone due to: increased biogenic emissions clear skies weak winds high temperatures. cold front EPA ozone levels 3 days later Cold front pushes smog poleward and aloft on a warm conveyor belt. cold front L L 85-104 ppb105-124 ppb cyclone

4. Nitrogen oxide radicals; NO x = NO + NO 2 combustion, soils, lightning Methane wetlands, livestock, natural gas Nonmethane volatile organic compounds (NMVOCs) vegetation, combustion, industry CO (carbon monoxide) combustion, VOC oxidation O3O3 O2O2 h O3O3 OH HO 2 h, H 2 O Deposition NO H2O2H2O2 CO, VOC NO 2 h STRATOSPHERE TROPOSPHERE 8-18 km Tropospheric ozone precursors generally limiting Chemistry of tropospheric ozone What processes will climate change affect? transport

5. A decrease in cyclone frequency across mid-latitudes has been observed (and calculated) for recent decades. Observed trend in winter cyclone frequency over Northern Hemisphere. McCabe et al., 2001 Calculated trend in summer cyclone frequency, from GISS 2x2.5 GCM, 23 layers Climate models tend to predict decrease in mid-latitude cyclogenesis in future due to: decrease in meridional temperature gradient more efficient poleward transport of latent heat Leibensperger et al., 2007

6. Ozone exceedances over eastern United States anti-correlate with cyclone frequency over Southern Canada/ Great Lakes region. Correlation of 1980-2006 summertime ozone exceedances with cyclone number in the red and green boxes for each summer. weak correlation Strong anti-correlation sample summertime storm tracks, 1979-81 NCEP/NCAR reanalysis

7. Cyclone trend works against improvements in emissions. Number of summertime ozone exceedance days in Northeast dropped from 38 in 1980 to ~8 in 2006, but would have dropped to 0 in absence of cyclone trend. Leibensperger et al., in prep. Observed 1980-2006 trend in summertime cyclone number, 40-50 N Number of O 3 exceedances in Northeast Interannual variability of cyclone frequency and ozone exceedance is highly anticorrelated (r = - 0.64). Cyclone trend from NCEP/NCAR reanalysis would imply large effect on ozone trends.

8. Global change and air pollution (GCAP): Five models working together to provide information on climate change impacts Model for precursor emissions archive met fields GEOS-CHEM Global chemistry model CMAQ Regional chemistry model MM5 Mesoscale model archive chemistry archive met fields 1950 2000 2025 2050 2075 2100 GISS general circulation model Spin-up changing greenhouse gases

9. Pollution episodes double in duration in 2050s due to decreasing frequency of cyclones ventilating the eastern U.S. 2045-2052 1995-2002 July - August GISS GCM simulations for 2050s vs. present-day climate. CO tracer: constant, present-day anthropogenic emissions + sink of present-day OH fields. Fewer cold front passages allow pollutants to build up. Changes at high end of distribution due to 10-20% decrease in summertime cyclogenesis. Mickley et al., 2004

10. Models agree that 2000-2050 climate change will decrease background ozone but increase surface ozone. We find an increase of 3-5 ppb over large regions. Most but not all models find maximum effect during pollution episodes (up to 10 ppb in ours) due to increased stagnation and higher temperatures. Most models find significant effects in Northeast/ Midwest. Many models disagree in Southeast partly due to different mechanisms for oxidation of biogenic isoprene (the dominant VOC precursor) Wu et al., 2008 ppb Increased water vapor sink Higher temperatures, stagnation 2000-2050 A1 climate change increases summertime ozone. Changes in summer 8-h avg. daily maximum ozone from 2000-2050 climate change

11. Effect of 2000-2050 climate change on pollution episodes. Wu et al., 2008 Increased maximum temperatures during heat waves leads to increased ozone. Amplification of temperatures at extreme due to soil moisture feedbacks 17% decreased cyclone frequency. Cumulative probability (%) Max. 8-hr-avg ozone 2050s climate 99 th percentile Midwest Daily maximum temperature (K) Cumulative probability (%) 2050s 2000s Maximum JJA temperatures Maximum JJA 8-h avg ozone 40% decrease in NOx 2050s climate +  NOx 2000s climate

12. -1 -.5 0.5 1 correlation coefficient R GCAP model present-day climate (3 years) Correlations of daily max-8h-avg ozone with daily max temperature in Jun-Aug Observations (1980-1998) Yoshitomi et al., in progress We can use ozone-temperature correlations as a test of model sensitivity to climate change, esp in Southeast US Regions of strongest correlation in model and observations.

13. Most of the variability in wildfire frequency is due to year-to-year changes in surface temperatures and precipitation. Forest fires in western US have big impact on particle concentrations and on surface ozone. Area burned and temperature in Canada over the last century Gillet et al., 2004 EPA wildfire project: How will changing forest fire frequency affect future air quality over the United States? What will happen next? Dominick Spracklen has developed a fire prediction tool to calculate future area burned using GISS GCM meteorological variables.... 2050 and beyond

14. Results show far: Future 2040-2050 biomass consumption by wildfires over the western United States is ~50% greater than for present-day. Plot shows standardized departures from the 1996-2055 mean. Annual total biomass consumed by forest fires, 1996-2055 Spracklen et al., in progress. Rynda Hudman at Harvard is investigating effect of future forest fires on surface ozone concentrations.

15. Increased 2050s wildfire activity leads to 3-6 ppb increase in afternoon mean ozone in July over western U.S. 2051 [ppbv] Biomass burning NO x emissions 2000 [Gg NO] Mean of 5 ppbv enhancement due to fires a > 2 SD Hudman et al., in progress JJA surface ozone

16. Conclusions In the 1980-2006 NCEP/NCAR record, we find a decline in cyclone frequency of -0.15 cyclones/y, which may have limited the efficacy of air pollution regulations. For 2050-2000 A1B climate change, we calculate a10-20% decline in cyclone frequency, lengthening pollution episodes over Midwest and Northeast. Climate change is expected to degrade U.S. ozone air quality. The summer average daily max-8h ozone increases by 2-5 ppb over large areas due to 2000-2050 climate change with the IPCC A1B scenario. Largest effect is during pollution episodes, when ozone increases by as much as 10 ppb. Summertime ozone concentrations are predicted to increase by 3-6 ppb over parts of western US due to increasing wildfire frequency in the 2050s. Projected trends in global NOx emissions for a range of scenarios.

17. Extra slides

18. Why is ozone in the Southeast insensitive to climate change? Isoprene has competing effects on ozone Sensitivity test: Isoprene emissions +30%  Δ(O 3 ) 20002050 / 2000 Isoprene emissions RO 2 + NO RONO 2 (sink for NO x ) Isoprene + OH RO 2 (OH sink) Isoprene + O 3 M (O 3 sink) O3O3 RO + NO 2 (O 3 formation) O3O3 Wu et al., 2008