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Chemistry of hydrogen oxide radicals ( HO x ) in Arctic spring

Chemistry of hydrogen oxide radicals ( HO x ) in Arctic spring. Jingqiu Mao, Daniel Jacob Harvard University

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Chemistry of hydrogen oxide radicals ( HO x ) in Arctic spring

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  1. Chemistry of hydrogen oxide radicals (HOx) in Arctic spring Jingqiu Mao, Daniel Jacob Harvard University Jennifer Olson(NASA Langley), Xinrong Ren(U Miami), Bill Brune(Penn State), Paul Wennberg(Caltech), Mike Cubison(U Colorado), Jose L. Jimenez(U Colorado), Ron Cohen(UC Berkeley), Andy Weinheimer(NCAR), Alan Fried(NCAR), Greg Huey (Gatech)

  2. Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) Phase I: April 1st ~ April 20th ARCTAS-A DC-8 flight track

  3. Vertical Profile(Observation vs. GEOS-Chem) W. Brune(PSU), P. Wennberg(Caltech), R. Cohen(UCB), A. Weinheimer(NCAR), A. Fried(NCAR)

  4. HO2 uptake by aerosol ν is mean molecular speed A is surface area γ is reactive uptake coefficient Discrepancy cannot be solved by reasonable change of halogens or NOx. Temperature dependence of γ is expected by large enthalpy for HO2 (g) ↔ HO2(aq). Cu-doped Aqueous Solid To ensure effective HO2 uptake (γ>0.1): aqueous Cold or Cu-doped

  5. Arctic particles for HO2 uptake were likely aqueous Mass fraction • The majority is OC and sulfate. • Aqueous under Arctic condition from lab measurement. • The main form of sulfate is bisulfate, so generally acidic (pKa (HSO4-)= 2.0). • 95% surface area is contributed by submicron aerosols. • Refractory aerosols contribute less than 10% of surface area. Please see Jenny Fisher’s (Wed 310PM) and Qiaoqiao Wang ‘s talk (Thursday 930AM) for aerosol simulations in GEOS-Chem.

  6. Conventional HO2 uptake by aerosol with H2O2 formation

  7. Fate of HO2 in aerosol HO2 is weak acid (pKa ~ 4.7), not much O2-(aq) in acidic aerosols HO2(aq)+O2-(aq)→ H2O2 (aq) H2O2 (g) Pure HOy sink HO2 HSO4- HCOO-, HSO3- SO5- H SO5- OH(aq) ? HSO3- H2SO4 SO42- +2H+ HO2-H2SO4 complex

  8. Non-conventional HO2 uptake as a HOy sink This non-conventional HO2 uptake provides the best simulations for HOxand HOy.

  9. Sources and sinks for HOx and HOy (from observations) • HO2 uptake is needed to close HOx and HOy budgets above 5 km. • Large observed HCHO below 3 km is inconsistent with independently computed HOx sinks. • H2O2 + hv is dominant HOx source above 4 km (unique in Arctic). • OH+CH3OOH dominates HOy sink below 4km (unique in Arctic). HO2 uptake

  10. CircumpolarHOybudget by GEOS-Chem (60-90N) • Transport from northern mid-latitudes accounts for 50% peroxides in upper troposphere. • H2O2+SO2(aq) is a minor HOysink in lower troposphere.

  11. Schematic diagram of HOx-HOy chemistry in Arctic spring Masses (in parentheses) are in units of Mmol . Rates are in units of Mmol d-1. • Main driver of this chemistry is by O (1D)+H2O(70%) and transport (30%). • Amplification by HCHO is comparable to primary source from O (1D)+H2O. • Aerosol uptake accounts for 35% of the HOy sink.

  12. Possible aerosol effects of changing sources Acidic aerosol ?? Less SO2 emission and more NH3 emission Neutralized aerosol

  13. Conclusions Cold temperature, high aerosol loading and slow photochemical cycling suggest the important role of HO2 uptake in HOx chemistry in Arctic spring. With HO2 uptake as a HOy sink, we successfully reproduce HOx and their reservoirs in the model. HO2 uptake accounts for 35% of HOy sink. Successful simulation of observed HO2 and H2O2 in ARCTAS implies HO2 uptake that does not produce H2O2 – possible mechanism coupled to HSO4-/H2SO4 producing HSO5- . The photolysis of H2O2 becomes the dominant HOx source in middle and upper troposphere due to the long lifetime of HOy combined with the efficient cycling between HOx radicals and peroxide reservoirs. Future changes in aerosol acidity due to decreasing SO2 and increasing NH3 could lead to different chemistry and possibly increase OH.

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