1. Jingqiu Mao, Daniel Jacob, Jenny Fisher, Bob Yantosca, Philippe Le Sager, Claire Carouge Harvard University Xinrong Ren(U Miami), Bill Brune(Penn State), Paul Wennberg(Caltech), Mike Cubison(U Colorado), Jose Jimenez(U Colorado), Ron Cohen(UC Berkeley), Andy Weinheimer(NCAR), Jennifer Olson(NASA Langley), Alan Fried(NCAR), Greg Huey (Gatech)

2. We are trying to answer these questions: How important is the heterogeneous processes? How does the acidity of aerosol phase affect the aqueous chemistry? What are the major HO x sources and sinks here? Are transport and wet scavenging affecting the oxidation capacity of Arctic spring? HO x chemistry in Arctic spring POLARCAT

3. Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) Phase I: April 1 st ~ April 20 th NO,O 3 : Andy Weinheimer(NCAR) NO2, PAN: Ron Cohen(UC Berkeley) OH & HO 2 : Bill Brune(Penn State) H 2 O 2 & MHP: Paul Wennberg(Caltech) Aerosol composition: Jose Jimenez(CU) HCHO: Alan Fried(NCAR) Box modeling: Jennifer Olson (Langley) BrO: Greg Huey(Georgia Tech) ARCTAS POLARCAT

4. GEOS-Chem V8-01-04 GEOS-5 assimilated met field with reprocessed cloud OD FLAMBE emission Updated reaction rates with JPL06 and IUPAC06 Updated photolysis cross sections and quantum yield with Fast-JX 1 year spin up at 2x2.5 degree Use daily OMI ozone column to calculate photolysis module POLARCAT

5. Vertical Profile(Observation vs. GEOSChem)

6. Reconciling the discrepancy for HO 2 1. BrO? (No) ~5 ppt only changes OH.HO2 is highly buffered. 2. NO x ? (No) 1 molecule BrO = 3 molecule NO, 10ppt NO is not enough. 3. HO 2 uptake to aerosol? Mass accommodation coefficient is unity at low PH condition. Henry’s law constant exponentially increases with decreasing temperature. POLARCAT (Huey) (Courtesy of J. Olson) Limiting step: aqueous reaction HO 2 (aq)->???? HO 2 aerosol 0.52.1.0 With/Without BrO Calculated impact of BrO on OH and HO 2 Altitude, km OHHO 2 1.46

7. SO4 is as H2SO4 SO4 is as NH4HSO4 SO4 is as (NH4)2SO4 H AER + =2*SO 4 2- +NO 3 - +Cl - -NH 4 + The main form on average for SO4 should be HSO4 - (pKa(HSO4 - )=2, pH<2). It could also be another scenario: Half of aerosols are (NH4)2SO4, half of aerosols are H2SO4. Aerosol composition in Arctic spring

8. POLARCAT HO 2 (aq)+O 2 - (aq) → H 2 O 2 (g) Fe 2+ /Cu 2+ +O 2 - (aq) → H 2 O 2 (g) HO 2 (aq)+HSO 4 - (aq) → SO 5 - (Cooper and Abbatt, 1996) SO 5 - +HCOOH/HSO 3 - → H SO 5 - (Caro’s acid, stable) H SO 5 - +HSO 3 - → SO 4 2- (Jacob, 1986) HO 2 (aq)+H 2 SO 4 (aq) → HO 2 -H 2 SO 4 complex (Miller and Francisco, 2001) Surprisingly stable HO 2 -H 2 SO 4 complex Fate of HO 2 in the aerosol phase HO 2 (aq)+HO 2 (aq) → H 2 O 2 (aq) H 2 O 2 (aq)+H + → HOOH 2 + (Protonated Hydrogen Peroxides, extremely oxidative) HOOH 2 + +RH →ROH 2 + (Oiestad, 2001) γ~0.4 in UT

9. Why do we care H2O2? POLARCAT H 2 O 2 +hv The photolysis of H 2 O 2 is the dominating HO x source in Upper Troposphere of polar spring. How much transport? How much local cycling? O 1 D+H 2 O and the photolysis of HCHO dominates the lower troposphere.

10. Budget of peroxides(H 2 O 2 +CH 3 OOH) Are they in steady state in polar region? Processes to be taken into account: Chemical Production(HO 2 +HO 2 /CH 3 O 2 ) Chemical Loss(gas phase, photolysis, reacting with OH) Chemical Loss(aqueous phase, H2O2+SO2=>SO4) Transport Wet scavenging Dry Deposition POLARCAT

11. Chemical budget of H 2 O 2 in gas phase PH2O2(g)=k*[HO2]*[HO2] LH2O2(g)=k*[H2O2]*[OH]+J*[H2O2] Does not seem balanced either in observation or in model. What are we missing here?

12. Circumpolar budget in the model Design regional domain 60˚N~90˚N, 30 vertical layers(~11km) Includes gas phase and aqueous chemical production and loss Transport is calculated by northward fluxes from mid-lat, up-down net fluxes, convective fluxes, turbulence mixing fluxes. Wet scavenging is calculated by large scale and convective precipitation fluxes for the specified species (co- condensation for H 2 O 2 ). Dry deposition is calculated by dry deposition fluxes for the specified species. POLARCAT

13. Circumpolar budget from April 1 st to 20 th Avg(Gmol /day) H2O2MHP ChemP0.7150.386 ChemL(g)-0.565-0.448 Chem(aq)-0.115N/A WetDep-0.040-0.029 DryDep-0.042N/A Transport0.1280.081 Net0.080-0.01 They are in steady state! Chemical lifetime: H 2 O 2 :1~2 days MHP: 1~2 days HCHO: 3~6 hrs

14. Vertical distribution of each term Deficit for both H2O2 and MHP in upper troposphere could be compensated by transport if they are in steady state for the whole domain and in lower troposphere. Negative value for wet deposition could be due to the reevaporation.

15. Conclusions Cold temperature and highly acidic aerosols in Arctic spring leads to a totally different HO x chemistry. A new pathway for HO 2 uptake is proposed. H 2 O 2 becomes the major HO x source in UT of arctic spring. The aqueous loss of H2O2 becomes very important in lower troposphere. Transport plays an important role in balancing H 2 O 2 and MHP budget in UT, and thus affecting the oxidation capacity in Arctic spring. POLARCAT