New Developments in Heterogeneous Aerosol Processes Affecting NOx and SO2

Randall Martin

Reduced Rate of NReduced Rate of N22OO5 5 Hydrolysis (NHydrolysis (N22OO55 + aerosol + aerosol 2 HNO 2 HNO33))

• Reaction probability ( 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 NImplications of Reduced Rate of N22OO5 5 Hydrolysis Hydrolysis

JJA

Change in NOx (GEOS-Chem) Change in O3 (GEOS-Chem)

Evans and Jacob, 2005

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

Uptake of NOUptake of NO22 and NO and NO33 on Aerosols 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

Martin et al., 2003

Fraction of HNO3 production (~600 m) by uptake of NO2 and NO3 Calculated with GEOS-Chem

Uptake of HOUptake of HO22 on Aerosols ( 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 HOCombined Effect of Uptake of HO2 2

((and aerosol and aerosol

scattering and absorptionscattering and absorption

Values in mixed layer ~600 m

Martin et al., 2003

• 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)

HNOHNO33 scavenging by Dust scavenging by Dust

Bauer et al., 2004

Percent Change in Surface HNO3

[SO2] % decrease

[SO42-]

% increase

SO2 + OH % decrease

10 30 50 705

SOSO2 2 + H+ H22OO22 or O or O33 in Alkaline Sea-Salt in Alkaline Sea-Salt

Implications for Particle NucleationImplications for Particle Nucleation

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

ConclusionsConclusions

• 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