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Projected trends in global temperature Effects of Climate Change on U.S. Air Quality Loretta J. Mickley, Harvard University Shiliang Wu, Eric Liebensperger, Moeko Yoshitomi, Dominick Spracklen, Brendan Field Daniel Jacob, David Rind, Cynthia Lin, David Streets Day-to-day weather plays a large role in surface air quality (1). Northeast Average num. of days Number of summer days with ozone exceedances (> 84ppb) over northeast U.S. Probability of ozone exceedance vs. daily max. temperature 1988, hottest on record 1992, coldest on record, due to Pinatubo eruption Ozone is strongly correlated with temperature in observations; this is due to (1) chemistry, (2) biogenic VOC emissions, (3) joint association with stagnation. Lin et al., 2001 Day-to-day weather plays a large role in surface air quality (2). cyclone cold front EPA ozone levels L Stalled high pressure system increases ozone due to: • increased biogenic emissions • clear skies • weak winds • high temperatures. cold front 85-104 ppb 105-124 ppb L 3 days later Cold front pushes smog poleward and aloft on a warm conveyor belt. O2 hn STRATOSPHERE 8-18 km O3 Chemistry of tropospheric ozone What processes will climate change affect? TROPOSPHERE transport hn O3 NO2 NO OH HO2 hn, H2O Deposition CO, VOC Nitrogen oxide radicals; NOx = NO + NO2 generally limiting combustion, soils, lightning Tropospheric ozone precursors H2O2 Methane wetlands, livestock, natural gas Nonmethane volatile organic compounds (NMVOCs) vegetation, combustion, industry CO (carbon monoxide) combustion, VOC oxidation 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. Calculated trend in summer cyclone frequency, from GISS 2x2.5 GCM, 23 layers McCabe et al., 2001 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 Ozone exceedances over eastern United States anti-correlate with cyclone frequency over Southern Canada/ Great Lakes region. sample summertime storm tracks, 1979-81 weak correlation Strong anti-correlation NCEP/NCAR reanalysis Correlation of 1980-2006 summertime ozone exceedances with cyclone number in the red and green boxes for each summer. Cyclone trend from NCEP/NCAR reanalysis would imply large effect on ozone trends. Observed 1980-2006 trend in summertime cyclone number, 40-50 N Interannual variability of cyclone frequency and ozone exceedance is highly anticorrelated (r = - 0.64). 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. Number of O3 exceedances in Northeast Leibensperger et al., in prep. Global change and air pollution (GCAP): Five models working together to provide information on climate change impacts GISS general circulation model 1950 Spin-up 2000 changing greenhouse gases 2025 2050 2100 MM5 Mesoscale model archive met fields Model for precursor emissions 2075 GEOS-CHEM Global chemistry model archive chemistry archive met fields CMAQ Regional chemistry model Pollution episodes double in duration in 2050s due to decreasing frequency of cyclones ventilating the eastern U.S. July - August 2045-2052 GISS GCM simulations for 2050s vs. present-day climate. CO tracer: constant, present-day anthropogenic emissions + sink of present-day OH fields. 1995-2002 Changes at high end of distribution due to 10-20% decrease in summertime cyclogenesis. Fewer cold front passages allow pollutants to build up. Mickley et al., 2004 2000-2050 A1 climate change increases summertime ozone. Changes in summer 8-h avg. daily maximum ozone from 2000-2050 climate change Higher temperatures, stagnation ppb Increased water vapor sink • 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 Maximum JJA temperatures Maximum JJA 8-h avg ozone Increased maximum temperatures during heat waves leads to increased ozone. 99th percentile 2050s 2000s Midwest Cumulative probability (%) Wu et al., 2008 Max. 8-hr-avg ozone Daily maximum temperature (K) Effect of 2000-2050 climate change on pollution episodes. 2050s climate 2000s climate 40% decrease in NOx 2050s climate + DNOx Cumulative probability (%) Amplification of temperatures at extreme due to • soil moisture feedbacks • 17% decreased cyclone frequency. We can use ozone-temperature correlations as a test of model sensitivity to climate change, esp in Southeast US Correlations of daily max-8h-avg ozone with daily max temperature in Jun-Aug GCAP model present-day climate (3 years) Regions of strongest correlation in model and observations. Observations (1980-1998) correlation coefficient R -1 -.5 0 .5 1 Yoshitomi et al., in progress EPA wildfire project: How will changing forest fire frequency affect future air quality over the United States? Area burned and temperature in Canada over the last century 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. Gillet et al., 2004 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 Results show far: Future 2040-2050 biomass consumption by wildfires over the western United States is ~50% greater than for present-day. Annual total biomass consumed by forest fires, 1996-2055 Plot shows standardized departures from the 1996-2055 mean. Rynda Hudman at Harvard is investigating effect of future forest fires on surface ozone concentrations. Spracklen et al., in progress. Increased 2050s wildfire activity leads to 3-6 ppb increase in afternoon mean ozone in July over western U.S. JJA surface ozone Biomass burning NOx emissions 2000 Mean of 5 ppbv enhancement due to fires a > 2 SD 2051 [Gg NO] Hudman et al., in progress [ppbv] 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. Extra slides Why is ozone in the Southeast insensitive to climate change? Isoprene has competing effects on ozone Isoprene + OH RO2 (OH sink) RO + NO2 (O3 formation) O3 RO2 + NO RONO2 Isoprene + O3 M (sink for NOx) (O3 sink) Isoprene emissions 2000 Wu et al., 2008 2050 / 2000 O3 Sensitivity test: Isoprene emissions +30% Δ(O3)