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Global atmospheric changes and future impacts on regional air quality Will O3 produced elsewhere in the world affect local air quality? How will a changing climate affect surface O3 concentrations? Loretta J. Mickley Harvard University Number of people living in US counties violating National Air Quality standards, 1999 Good O3 vs Bad O3 NOx = nitrogen oxide radicals VOC = volatile organic carbon How has tropospheric O3 increased in last 100 years? Ozone measured on various mountaintops in Europe, 1870 to 1990 What could increase regional O3 in 21st century? • Increase of local emissions of O3 precursors (NOx, VOCs) • Transport of O3 or O3 precursors produced elsewhere Can use model with observed winds to calculate current influence • Climate change effects on O3 loss and production rates Need to use model that generates its own climate (GCM) How does intercontinental transport of O3 enhance local O3 surface concentrations today? North America Europe Asia GEOS-CHEM model, July 1997, Li et al 2002 How does N. American O3 affect O3 violations in Europe? Number of exceedance days for European standards (55 ppb, 8 hour average) Number of exceedance days due to North American sources GEOS-CHEM model, summer, Li et al 2002 Does Asian O3 enhance US surface O3 in summer? Subsidence of Asian pollution + production aloft Tropical air Maximum Asian enhancements (up to 14 ppb) occur at intermediate ozone levels (50-70 ppb) Stagnation Major concern if O3 standard decreases or Asian O3 increases Fiore et al. 2002 How important is methane to O3 and climate? Methane = overlooked precursor of ozone, has long lifetime (8-10 years) Cutting methane by 50% would: decrease incidence of ozone > 80 ppb in surface air by more than 50% decrease radiative forcing by both ozone and methane Trends in methane How might climate change affect O3 loss and production? O2 + hn Stratospheric ozone Complex non-linear chemistry ? Nitrogen oxides (NOx) hn Ozone (O ) hn, H2O Hydroxyl (OH) 3 CO, Hydrocarbons ? Fires ? Biosphere O3 source with high NOx O3 sink with low NOx Human activity Ocean physics chemistry biology How might changing climate affect surface O3? Temperature changes ? (not the whole story!) Changes in circulation frequency of stagnation? stratospheric influx of ozone? transport from other continents? Lightning frequency? Water vapor concentrations? Emissions of VOCs from trees, grasses? Sum of climate changes more ozone? less ozone? Chemistry, Aerosols, and Climate: Tropospheric Unified Simulation (CACTUS) Objective: to improve understanding of interactions between atmospheric chemistry, aerosols, and climate Approach: coupled chemistry-aerosol-climate General Circulation Model (GCM) CACTUS model emissions land use greenhouse gas Atmospheric chemistry GISS GCM Aerosol microphysics climate chemistry CACTUS model study of preindustrial O3 Monthly mean observations at two sites in Europe Two model attempts, with differing natural emissions, but same climate as present-day Mickley et al. 2000 How will atmospheric motions change in 2xCO2 climate? Use SF6 to show how atmospheric motions change with warmer climate • Stronger convective transport • Weaker interhemispheric exchange Rind et al., 2001 How can we calculate change in O3 due to climate? 1. 2000-2100: change well-mixed greenhouse gases year-by-year, calculate climate 2. 2000,2025,2050,etc: change emissions of O3 precursors, use current climate, calculate ozone 3. 2000,2025,2050,etc: recalculate ozone using climate from step 1. Diagnose in ozone due to climate change. (Step 3- Step2) Final thoughts Transport could have a big effect in future if Asian emissions increase. We need to learn how climate change may affect local ozone levels Ozone in July 2100, worst case scenario