1. Future Inorganic Aerosol Levels 4th GEOS-Chem Users’ Meeting 9 April 2009 Havala Pye* 1, Hong Liao 2, Shiliang Wu 3,5, Loretta Mickley 3, Daniel Jacob 3, Daven Henze 4,6, John Seinfeld 1 1 California Institute of Technology, 2 Chinese Academy of Sciences, 3 Harvard University, 4 Columbia University 5 now at Michigan Technological University 6 now at University of Colorado at Boulder Havala Pye* 1, Hong Liao 2, Shiliang Wu 3,5, Loretta Mickley 3, Daniel Jacob 3, Daven Henze 4,6, John Seinfeld 1 1 California Institute of Technology, 2 Chinese Academy of Sciences, 3 Harvard University, 4 Columbia University 5 now at Michigan Technological University 6 now at University of Colorado at Boulder

2. Determine the effect of climate and emissions changes on future sulfate-nitrate-ammonium (SNA) aerosols with a focus on surface concentrations in the U.S. Objective GISS GCM meteorology (year 2000 or 2050) Anthropogenic emissions (year 2000 or 2050) GEOS-Chem with ISORROPIA II sulfate nitrate ammonium

3. Inorganic Aerosols From Gas Phase Precursors DMS gas phase chemistry SO 2 Chemistry SO 4 2- Aerosol Phase in Thermodynamic Equilibrium: ISORROPIA II DMS emission SO 4 emission SO 2 emission NH 4 + water NH 3 NH 3 emission NO 3 - HNO 3 Na + Cl - Ca 2+ Mg 2+ K+K+ NO X chemistry NO X emission Sea salt emission

4. Simulated Present-day Nitrate Concentrations [µg/m 3 ] DJFMAM JJASON

5. Nitrate Predictions Compared to Observations Simulated [µg/m 3 ] Measured [µg/m 3 ] Simulated [µg/m 3 ] Measured [µg/m 3 ] DJFMAM JJASON Agreement with observations improved compared to previous ISORROPIA Sensitivity tests performed for conditions representative of JJA in So. California –Predictions not very sensitive to total ammonia available –Possible model limitation at low RH

6. Predicted Change in total SNA due to Changes in Climate Alone (anthropogenic emissions at present-day levels) Multiple changes potentially important for aerosols including changes in: Windspeed/transport Oxidant levels (sulfate) Precipitation Frequency of mid-latitude cyclones [Wu et al., 2008] Temperature (nitrate) Dry deposition (nitric acid) Humidity Future climate: year 2050 (GHG follow IPCC A1B) from GISS GCM III [Wu et al., 2008] 522 ppm CO 2 1.6 K global mean surface temperature rise 8% increase in global annual mean precipitation

7. Future Anthropogenic Emissions Based on IPCC A1B scenario for 2050 NH 3 NO X SO 2 SO 4 40% -35% -74%-75%

8. Predicted Change due to Changes in Anthropogenic Emissions (climate at present-day conditions) SO 4 -2 NO 3 – NH 4 + Annual SNA levels decrease due to Lower sulfate levels as a result of lower SO 2 emissions Generally lower ammonium as a result of lower sulfate levels DJF SNA levels increase on the order of 1  g/m 3 due to Increased nitrate aerosol levels as a result of more ammonia and lower sulfate concentrations

9. Climate Change with Constant Emissions Sulfate more important for determining trend with present-day emissions Nitrate more important for determining trend with future emissions Present-day Emissions {(2050 Climate, 2000 Emissions) - (2000 Climate, 2000 Emissions)} Future Anthropogenic Emissions {(2050 Climate, 2050 Emissions) - (2000 Climate, 2050 Emissions)}

10. Conclusions Climate change alone is predicted to lead to improvements in air quality in the SE U.S. but degraded air quality in the MW and NE –Sulfate increases in the MW and NE –Nitrate generally decreases Predicted changes in SNA levels in the U.S. are more strongly influenced by changes in emissions than changes in climate (for the scenario considered here) –SNA levels are generally predicted to be lower due to domestic SO 2 emission reductions –Nitrate levels are generally predicted to be higher due to increased NH 3 emissions and lower sulfate despite decreasing NO X emissions The response of SNA aerosols to climate change depends on the anthropogenic emissions for the MW and NE For more information see: Pye et al. J. Geophys. Res. 2009

11. Acknowledgements This work was supported by the U.S. Environmental Protection Agency’s STAR Program (grants RD830959 and RD833370). Havala Pye was supported by a NSF Graduate Research Fellowship. Hong Liao acknowledges support from the National Natural Science Foundation of China (grant 40775083). Discussions with Becky Alexander and Athanasios Nenes are greatly appreciated.