1. FIVE CHALLENGES IN ATMOSPHERIC COMPOSITION RESEARCH 1.Exploit satellite and other “top-down” atmospheric composition data to quantify emissions and export of environmentally important gases and aerosols 2. Quantify the role of intercontinental transport of pollution on regional environmental degradation 3. Understand the effects of air pollutants (ozone, aerosols) on climate, the related feedbacks, and the effects of climate change on air quality 4. Measure, understand, and predict long-term trends in the oxidizing power of the atmosphere 5. Use atmospheric composition data to improve numerical weather prediction

2. Exploit satellite and other “top-down” atmospheric composition data to quantify emissions and export of environmentally important gases and aerosols Need inverse models constrained by satellite and aircraft observations, and by bottom-up understanding of processes; geostationary satellites would increase capability tremendously “Bottom-up” source/sink inventories INFLOW OUTFLOW 3-D MODELS Hindcasts/forecasts (experimental design) Inversions “Top-down” constraints on emissions and export SATELLITES continuous monitoring AIRCRAFT MISSIONS covariances chemistry model errors satellite validation SURFACE SITES long-term trends surface fluxes

3. Quantify the role of intercontinental transport of pollution in regional environmental degradation Need global mapping (satellites), aircraft campaigns, long-term observations, integrated approach (ozone, aerosols, Hg, POPs…), new generation of models to resolve regional-global and ocean-atmosphere coupling PBL Free troposphere HEMISPHERIC/GLOBAL POLLUTION BACKGROUND (Ozone, metals, POPs) Oceanic transport (Hg, POPs) Continent 1 Continent 2 “Direct” intercontinental transport (aerosols)

4. Understand the effects of air pollutants (ozone, aerosols) on climate, the related feedbacks, and the effects of climate change on air quality Precursor emissions Aerosols Tropospheric ozone Inhomogeneous radiative forcing – is radiative forcing even an useful concept? Climatic effects on air pollution meteorology, emissions, chemistry Could be large (remember summer of ’88! Need better characterization of aerosol forcing, new generation of GCMs including aerosols/chemistry/biosphere and global/regional coupling

5. Measure, understand, and predict long-term trends in the oxidizing power of the atmosphere ? ? ? Lightning Nitrogen oxides (NO x ) CO, Hydrocarbons h Ozone (O 3 ) h, H 2 O Hydroxyl (OH) Complex non-linear chemistry Tropopause (8-18 km) Stratospheric ozone STRATOSPHERE TROPOSPHERE O 2 + h the main atmospheric oxidant Need better global OH proxies, better understanding of HO x /NO x /O 3 chemistry (partial derivatives), better understanding of related emissions STE (poorly understood)

6. Use tropospheric composition data (CO, ozone) to improve numerical weather prediction CO combustion source CO is conserved in wet processes; 2-month lifetime  tracer of long-range transport Ozone UT lifetime ~ months LT lifetime ~ days Tropospheric ozone has complicated chemistry but is a good tracer of vertical transport Satellite observations of CO, O 3 Chemical data assimilation Need to develop chemical data assimilation tools, integrate correlated atmospheric composition data and surface data (e.g. fire maps)