Effects of size resolved aerosol microphysics on photochemistry and heterogeneous chemistry Gan Luo and Fangqun Yu ASRC, SUNY-Albany

Introduction Aerosol Micro physics Photo chemistry COD Our purposes  Build up the relationships among aerosol, droplet/crystal, COD, and tropospheric photochemistry in GEOS-Chem/APM  Study how does the new COD parameterization impact photolysis, oxidants and aerosol microphysics in the troposphere Tie et al. (2003): the influence of COD on photolysis and oxidants Liu et al. (2006): assessed the radiative effect of clouds in GEOS-Chem Liu et al. (2009): studied the impacts of different met inputs (GEOS1-STRAT, GEOS-3, and GEOS-4) on tropospheric photochemistry Aerosol impacts: AOD on photolysis; Surface area: heterogeneous chemistry Mattin et al., JGR, 2003 Twomey effect: aerosol impacts COD and albedo Twomey, JAS, 1977 Influence of anthropogenic aerosol on COD and albedo shown by satellite measurements and CTM Schwartz et al., PNAS, 2001

Simulation of new COD in GEOS-Chem/APM GEOS-Chem: GEOS5.2.0 met inputs, NOx–Ox–hydrocarbon–aerosol simulation, UpToDate emission inventories APM: SP, Sea Salt, Dust, BC, POC, coating of SP on primary particles Cloud Optical Depth: Aerosol number  droplet/crystal number  Effective Radius (Yu et al., ERL, 2013) + In Cloud Water Content  In Cloud COD  Linear Mean COD, Radiative Mean COD Liquid Cloud: Hu and Stamnes, JC, 1993; Ice Cloud: Fu, JC, 1996 Size distribution, Yu, ACP, 2011CN10 number concentration Yu and Luo, ACP, 2009 CCN0.4 number concentration Yu et al., ACP, 2012

Comparison of COD (GEOS5 and NewCld) with MODIS and ISCCP Radiative Mean CODLinear Mean COD τ l = τ incld ∙CldFraction MODIS: GEOS5: 3.7 NewCloud: Radiative Mean COD τ r = τ incld ∙(CldFraction) 1.5 ISCCP: 4.14 GEOS5: 1.77 NewCloud: 5.44 GEOS5 significantly underestimated COD NewCld In better agreement with observed COD MODIS GEOS5 NewCld ISCCP GEOS5 NewCld

The difference between COD from GEOS5 and NewCld and the correlation with CCN and CDN number concentration MODIS CDNC: Bennartz, 2007; Gantt et al., 2014

Impact of COD on Boundary layer photochemistry and aerosol microphysics The Tropics: ↓ 30-50% Alaska, Siberia: ↓ 20% South Ocean: ↓ 20% Tropical clear sky regions: ↑1-5% PH 2 SO 4 : new particle formation and growth; PLVSOG: particle growth especially over luxuriant vegetation regions The Tropics: ↓ 10-30% △ CCN > △ CN3 ↓ particle growth Alaska, Siberia: ↓ 10% South Ocean: Sea salt J(O 1 D) H 2 SO 4 CN3 OH LVSOG CCN0.4

Impact of COD on photochemistry and aerosol microphysics: view from zonal cross section

Impact of size resolved aerosol on heterogeneous chemistry

Summary  We developed a new COD parameterization in GEOS-Chem/APM, considering the aerosol indirect effect on clouds. It improves the agreement with observed COD and enable us to consider interactions among aerosol, droplet/crystal, COD, and tropospheric photochemistry.  Low layers: COD ↑  J(O 1 D), [OH] ↓  1) PH 2 SO 4 ↓  nucleation ↓, condensation ↓  aerosol # & size↓ 2) PLVSOG ↓  condensation ↓  aerosol size↓  Vertical cross section: significant backscattering effect above cloud: enhancement; below cloud: reduction  changes of atmospheric oxidation capacity and tracers’ lifetime  We use APM simulated surface area instead of bulk aerosol surface and find substantial impacts which depend on seasons.

The End Thank You !

LWP, IWP and TWP from GEOS5 (Barahona et al., 2014) CloudSAT (Li et al, 2012) and GEOS5.2.0 Figures are from Barahona et al., GMD, 2014LWP, IWP and TWP from GEOS5.2.0