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

2. 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

3. 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

4. Uptake of NO2 and NO3 on Aerosols
NO2  0.5 HONO 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

5. 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

6. 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

7. HNO3 scavenging by Dust CaCO3 + 2HNO3  Ca(NO3)2(s) + CO2(g) + H2O(g)
Reaction probability of 10-4 (Goodman et al., 2000) (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

8. 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

9. 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