New Developments in Heterogeneous Aerosol Processes Affecting NOx and SO2 Randall Martin

Reduced Rate of N2O5 Hydrolysis (N2O5 + aerosol  2 HNO3) Reaction probability (g) 0.1 (Jacob et al., 2000) Recent model and laboratory measurements suggest lower with species and RH dependence Updated Reaction Probabilities (GEOS-Chem) Evans and Jacob, 2005

Implications of Reduced Rate of N2O5 Hydrolysis Change in NOx (GEOS-Chem) Change in O3 (GEOS-Chem) JJA Reduces model bias - vs NOx climatology (Emmons et al., 2000) from -14 pptv to -8 pptv - vs ozonesonde climatology (Logan et al., 1998) -2.9 ppbv to -1.4 ppbv Evans and Jacob, 2005

Uptake of NO2 and NO3 on Aerosols NO2  0.5 HONO + 0.5 HNO3; reaction probability 10-4 (Jacob, 2000) NO3  HNO3; reaction probability 10-3 (Jacob, 2000) NO2 uptake dominates over land Fraction of HNO3 production (~600 m) by uptake of NO2 and NO3 Calculated with GEOS-Chem Martin et al., 2003

Uptake of HO2 on Aerosols (HO2  0.5 H2O2) Recommendation of 0.2 based on availability of Cu(II) (Jacob, 2000) Requires Cu(II) > 10-3 M (Mozurkewich et al., 1987) Reaction probability <0.01 in absence of Cu(II) (Thornton and Abbatt, 2005) Copper Emissions ~100 Gg yr-1 (crustal and combustion) Cu 0.1% of aerosol mass at northern midlat (likely sufficient if not bound with organics) Only 0.004% of aerosol mass in biomass burning plumes (likely insufficient) GEOS-Chem calculation (~600m) Reaction could be a large fraction of HOx budget if sufficient Cu(II) Martin et al., 2003

Combined Effect of Uptake of HO2 (g=0 Combined Effect of Uptake of HO2 (g=0.2), NO2 (g=10-3), NO3 (g=10-4), and aerosol scattering and absorption Values in mixed layer ~600 m Martin et al., 2003

HNO3 scavenging by Dust CaCO3 + 2HNO3  Ca(NO3)2(s) + CO2(g) + H2O(g) Reaction probability of 10-4 (Goodman et al., 2000) - 0.1 (Hanish and Crowley, 2001) Negligible effect on NOx in North America, but may be important for Sahara (Bauer et al., 2004; Liao and Seinfeld, 2005) Percent Change in Surface HNO3 Bauer et al., 2004

SO2 + H2O2 or O3 in Alkaline Sea-Salt Implications for Particle Nucleation [SO2] % decrease [SO42-] % increase SO2 + OH % decrease 10 30 50 70 5 GEOS-Chem Marine Boundary Layer Alexander et al., 2005 Similar Reactions May Also Occur in Dust (Ullerstam et al., 2002) However, field measurements of Asian (Ooki and Uematsu, 2005) and Saharan (Umann et al., 2005) found little evidence of SO2 uptake

Conclusions Recent updates <10% effect on surface NOx in North America Most significant: reduced rate of N2O5 hydrolysis potential role of HO2 uptake Oxidation of SO2 in alkaline sea-salt important over ocean