1. Aerosol Working Group The 7 th International GEOS-Chem User’s Meeting May 4, 2015 Aerosol WG Co-Chairs Colette Heald: heald@mit.edu Jeff Pierce (outgoing): jeffrey.pierce@csu.edu Peter Adams (incoming): petera@andrew.cmu.edu To join email list send email to: geos-chem-aerosols-join@seas.harvard.edu

2. Why Aerosols in GEOS-Chem? Air Quality Ecosystem Health Climate Local Visibility LRT Acid Rain Nutrients Why in GEOS-Chem rather than stand-alone aerosol model? Benefits from coupled oxidant simulation, enables multi-pollutant approach.

3. Why Aerosols (if I really only care about gas-phase)? Heterogeneous Chemistry Effect on Photolysis Rates [Martin et al., 2003] Original: [Martin et al., 2003] N 2 O 5 : [Evans and Jacob, 2005] HO 2 : [Thornton et al., 2008] Gas-Particle Partitioning ISORROPIA II: [Foutoukis and Nenes, 2007] Implementation in GC: [Pye et al., 2009]

4. The History of Aerosols in GEOS-Chem Carbonaceous Aerosols and Sulfate-Nitrate Ammonium based on GOCART [Park et al., 2003][Park et al., 2004] Sea Salt Dust (DEAD Scheme with SOA (biogenic GOCART source map) anthropogenic, semi-vol POA) [Alexander et al, 2005; Jaeglé et al., 2011] [Fairlie et al., 2007] [Liao et al., 2007; Henze et al., 2008; Pye et al., 2010] mass based scheme, assumes fixed log-normal size distributions full-chemistry with or without SOA (only without is benchmarked), also aerosol-only

5. Sectional Scheme Option: TOMAS TwO-Moment Aerosol Sectional microphysics scheme (maintained by Marguerite Marks, Jack Kodros, Jeff Pierce and Peter Adams) Explicit simulation of the aerosol size distribution. Features Aerosol number and mass simulated in 12, 15, 30 or 40 size sections Explicit aerosol number balance 4x5, 2x2.5 and 0.5x0.666 nested grid GEOS-Chem aerosol species incorporated into size sections Sulfate, primary OC, SOA, EC, sea salt, dust In the Pipeline: HEMCO compatability tagging Aerosol/climate effects and aerosol-size/heath effects

6. Sectional Scheme Option: APM (maintained by Gan Luo and Fangqun Yu, UAlbany) Secondary particles (SP) : 40 bins Sea salt particles: 20 bins Dust: 15 bins BC : 4 log-normal modes.  Size-resolved microphysics with variable size resolution for particles of different types and sizes  Recent advances (1)Integrated aerosol optical depth (AOD) and surface area based on APM aerosols with photo-chemistry and heterogeneous chemistry (2)Integrated cloud optical depth (COD) based on APM aerosols and explicit cloud droplet activation scheme with photochemistry (3)Added tracers and processes to predict global concentrations of amines (4)Updated APM has been integrated into v9.2.0 (5)APM works with 0.25 o x0.3125 o nested domains  GC-APM AeroCom II participation 1)Aerosol direct radiative forcing (Myhre et al., 2013) 2)Host model uncertainties in aerosol radiative forcing estimates (Stier et al., 2013) 3)Aerosol microphysics (Mann et al., 2013) 4)Aerosol organics (Tsigaridis et al., 2014) Primary OC: 4 log-normal modes  Mixing states: Semi-externally mixed, with coating of primary particles by secondary species explicitly simulated

7. Research Topics Being Investigated in the WG Aerosol chemistry (eg. sulfate formation, SOA, aqueous chem) Black carbon and combustion aerosol Regional AQ Historical aerosol trends, future aerosol projections (AQ and climate) Satellite-based PM 2.5 estimation Inverse PM 2.5 estimation Long range transport and impacts Precursor emission estimation, including for new satellite products (eg. NH 3, SO 2 ) Estimating associated health impacts Aerosol microphysics: New particle formation, optics, mixing state, direct effect, indirect effect, geoengineering Removal processes Sea-salt impacts on tropospheric chemistry

8. Progress since IGC6 v9-02 ● TOMAS parallelization and speed-up options (Pierce/Adams) ● Heterogeneous chem updates... HO 2, N 2 O 5 ) (Mao) ● NH 3 emissions updates (Zhang/Lo) ● GFED3 emissions through 2011 (Kasibhatla) ● SOA with semi-volatile POA (Pye) ● Cloud-water pH for sulfate formation (Alexander) Coming soon: v10-01 ● Stratospheric aerosol chemistry through UCX (Barrett/Eastham) ● Lots of emissions updates relevant to aerosols (HEMCO, GFED,4 EDGAR4.2, MIX, NEI2011, EMEP)

9. Important Capabilities in the Pipeline RRTMG online (Ridley/Heald, v10-01) Simplified description of uptake of SO 2, nitric acid and sulfuric acid on mineral dust (Fairlie, v10-02) Aerosol thermodynamics and microphysics from MOSAIC (Eastham, TBD) Impaction scavenging for hydrophobic BC and homogeneous IN removal (Wang, TBD) Others? Challenges Ahead, Topics for Discussion Maintaining 3 rd party code (TOMAS, APM, RRTMG, ISORROPIA, MOSAIC) Full integration of gas and particle phase chemical mechanism Modernizing aerosol optics The future of SOA (multiple options?) BC aging Others??