Assessing the oxidation capacity in Arctic spring

Jingqiu Mao, Daniel Jacob, Jenny Fisher, Bob Yantosca, Philippe Le Sager, Claire Carouge

Harvard UniversityXinrong 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)

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 HOx sources and sinks here?

• Are transport and wet scavenging affecting the oxidation capacity of Arctic spring?

HOx chemistry in Arctic spring

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Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) Phase I: April 1st ~ April 20th

NO,O3: Andy Weinheimer(NCAR)NO2, PAN: Ron Cohen(UC Berkeley)OH & HO2: Bill Brune(Penn State)H2O2 & MHP: Paul Wennberg(Caltech)Aerosol composition: Jose Jimenez(CU)HCHO: Alan Fried(NCAR)Box modeling: Jennifer Olson (Langley)BrO: Greg Huey(Georgia Tech)

ARCTAS

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GEOS-ChemV8-01-04GEOS-5 assimilated met field with

reprocessed cloud ODFLAMBE emissionUpdated reaction rates with JPL06 and

IUPAC06Updated photolysis cross sections and

quantum yield with Fast-JX1 year spin up at 2x2.5 degreeUse daily OMI ozone column to calculate

photolysis modulePOLARCAT

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Vertical Profile(Observation vs. GEOSChem)

Reconciling the discrepancy for HO2

1. BrO? (No)~5 ppt only changes

OH.HO2 is highly buffered.

2. NOx? (No)1 molecule BrO = 3

molecule NO, 10ppt NO is not enough.

3. HO2 uptake to aerosol?Mass accommodation

coefficient is unity at low PH condition.

Henry’s law constant exponentially increases with decreasing temperature.

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(Huey) (Courtesy of J. Olson)

Limiting step: aqueous reactionHO2 (aq)->????

HO2 aerosol

0.5 2.1.0With/Without BrO

Calculated impact of BrO on OH and HO2

Altit

ude,

km

OHHO2

1.46

0 50 100 150-50

0

50

100

150

200

SO4(nmol/cm3)

H+ (n

mol

/m3 )

y = 1.049*x + 1.883

SO4 is as H2SO4

SO4 is as NH4HSO4

SO4 is as (NH4)2SO4

•HAER+ =2*SO4

2-+NO3-

+Cl--NH4+

•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

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HO2(aq

)

HO2(aq)+O2-(aq)→ H2O2 (g)

Fe2+/Cu2++O2-(aq) →H2O2 (g)

HO2(aq)+HSO4-(aq) →SO5

-

(Cooper and Abbatt, 1996)

SO5-+HCOOH/HSO3

- →H SO5

-(Caro’s acid, stable)H SO5

- +HSO3- → SO4

2-

(Jacob, 1986)

HO2(aq)+H2SO4 (aq) →

HO2-H2SO4 complex(Miller and Francisco, 2001)

Surprisingly stable HO2-H2SO4 complex

Fate of HO2 in the aerosol phase

HO2(aq)+HO2(aq)→ H2O2

(aq) H2O2

(aq)+H+ → HOOH2+

(Protonated Hydrogen Peroxides, extremely oxidative)HOOH2

++RH →ROH2+

(Oiestad, 2001)

γ~0.4 in UT

Why do we care H2O2?

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H2O2+hv

•The photolysis of H2O2 is the dominating HOx source in Upper Troposphere of polar spring. How much transport? How much local cycling?

•O1D+H2O and the photolysis of HCHO dominates the lower troposphere.

Budget of peroxides(H2O2+CH3OOH)

Are they in steady state in polar region?Processes to be taken into account:

Chemical Production(HO2+HO2/CH3O2)Chemical Loss(gas phase, photolysis, reacting

with OH)Chemical Loss(aqueous phase,

H2O2+SO2=>SO4)TransportWet scavengingDry Deposition

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Chemical budget of H2O2 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?

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 H2O2).

Dry deposition is calculated by dry deposition fluxes for the specified species.

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Circumpolar budget from April 1st to 20th

Avg(Gmol/day)

H2O2 MHP

ChemP 0.715 0.386ChemL(g)

-0.565 -0.448

Chem(aq)

-0.115 N/A

WetDep -0.040 -0.029DryDep -0.042 N/ATransport

0.128 0.081

Net 0.080 -0.01They are in steady state!

Chemical lifetime:H2O2:1~2 days MHP: 1~2 daysHCHO: 3~6 hrs

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.

Conclusions

Cold temperature and highly acidic aerosols in Arctic spring leads to a totally different HOx chemistry.

A new pathway for HO2 uptake is proposed. H2O2 becomes the major HOx source in UT of

arctic spring.The aqueous loss of H2O2 becomes very

important in lower troposphere.Transport plays an important role in

balancing H2O2 and MHP budget in UT, and thus affecting the oxidation capacity in Arctic spring.

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