FINE AEROSOL COMPOSITION IN NORTH AMERICAAnnual mean PM2.5 concentrations (NARSTO, 2004)

Current air quality standard is 15 mg m-3

SULFATE-NITRATE-AMMONIUM AEROSOLS IN U.S. (2001)

Highest concentrations in industrial Midwest(coal-fired power plants)

Sulfate Nitrate

Ammonium

Acidity

Ammonia and NOx emissions in the US (2006)

Zhang et al. [2012]

Distributions of HNO3 (g) and NO3- (aerosol) in surface air

HNO3 (g) NO3- (aerosol)

EPA network data for 2006

Zhang et al. [2012]

FORMATION OF SULFATE-NITRATE-AMMONIUM AEROSOLS

2

2

2

22 4 4

3 4

3 3

3 3 4 3

( ) 2

( )

( )

( ) ( ) ( )

H O

H O

H O

H SO g SO H

NH g NH OH

HNO g NO H

NH g HNO g NH NO aerosol

Sulfate always forms an aqueous aerosol

Ammonia dissolves in the sulfate aerosol totally or until titration of acidity, whichever happens first

Nitrate is taken up by aerosol if (and only if)excess NH3 is available after sulfate titration

HNO3 and excess NH3 can also form a solid aerosol if RH is low

Thermodynamic rules:

Highest concentrations in industrial Midwest(coal-fired power plants)

Condition aerosol pH Low RH High RH

2[S(VI)] > [N(-III)] acid H2SO4•nH2O, NH4HSO4 , (NH4 )2SO4

(NH4+ , H+, SO4

2- ) solution

2[S(VI)] ≤ [N(-III)] neutral (NH4 )2 SO4 , NH4 NO3

(NH4+ , SO4

2-, NO3- )

solution

U.S. SO2 EMISSIONS

Industrial

Volcanoes

Biomassburning

Oceans

Sulfur emissions,Tg a-1

78 8.3

GLOBAL UNITED STATES

Observation of SO2 point sources in US by OMI oversampling

SO2 point sources, 2004-2007

OMI SO2 (3 km oversampling)

3 km-resolution data enables analysis of SO2 emission trends, SO2 atmospheric lifetime

AQAST PI: De Foy

SO2 columns observed from SCIAMACHY

SAA

Andreas.Richter@iup.physik.uni-bremen.deAndreas.Richter@iup.physik.uni-bremen.de

GOME and SCIAMACHY SO2 over China

• Large increase in SO2 loading observed from 2000 to 2007 Turnover in 2007

• Decrease to 2003 / 2004 levels but now increasing again.Result of legislation requiring flue-gas desulphurization of power plantsNot all power plants have been equipped other sources are on the rise

Volcanic eruption

Kasatochi eruption as seen in GOME-2 SO2

• After some smaller SO2 emissions, large eruption on August 8, 2008

• SO2 rapidly distributes over the NH

• GOME-2 integrated SO2 column indicates more than 1 Tg total SO2 emission

http://www.avo.alaska.edu/

Kasatochi volcano

Altitude: 314 mLatitude: 52.16°NLongitude: 175.51° W

OBSERVED TITRATION OF SO2 BY H2O2 IN CLOUD

First aircraft observations by Daum et al. [1984]

WORLDWIDE MEASUREMENTS OF FINE AEROSOL COMPOSITION

CARBONACEOUS AEROSOL SOURCES IN THE U.S.

Fossil fuel

Biofuel

Biomass burning

Vegetation

Fossil fuel

Biofuel

Biomass burning

Vegetation

ORGANIC CARBON (OC)

2.7 Tg yr-1

BLACK CARBON (BC)

0.66 Tg yr-1

Annual mean concentrations (2001)

BC OC

Park et al. [2006]

Long-term trends in BC and OC aerosol over the US

Annual meanconcentrations

National trendsObservedModel

Leibensperger et al. [2011]

RADIATIVE FORCING FROM BLACK CARBON (BC)

IPCC [2007]

BC is emitted by incomplete combustion“BC” or “soot” is optically defined and includes both graphitic elemental carbon (EC) and light-absorbing heavy organic matter

Diesel engines are large BC sources

Freshly emitted BC particle

Atmospheric aging and scavenging of BC

Emission

Hydrophobic BCresistant to scavenging

coagulationgas condensation Hydrophilic BC

coated with sulfate, nitrate

Scavenging

Aging time scaleτ ~ 1 d

Implications for BC export from source continents:

OCEAN

aging

scavenging

HydrophobicBC

aginglong-range transport FREE TROPOSPHERE

BOUNDARY LAYER

BC and OC aerosol during ARCTASaircraft campaign (spring 2008)

Wang et al. [2011]

ORGANIC AEROSOL IN STANDARD GEOS-Chem MODEL

fuel/industry open fires

OH, O3,NO3SOG SOA

POA

K

vegetation fuel/industry open fires

700

isopreneterpenesoxygenates…

30

alkenesaromaticsoxygenates…

alkanesalkenesaromatics…

VOC EMISSION PRIMARY EMISSION

VOC

5020 100

20

Global sources in Tg C y-1

secondaryformation

SOA ≡ secondary organic aerosolPOA ≡ primary organic aerosol

TERPENES

Terpenes are biogenic hydrocarbons produced in plants by combination of isoprene units (C5H8)

• Monoterpenes: C10H16

β-pinene

• Sesquiterpenes: C15 H24

δ-cadinene

SOA MODELING AS GAS-AEROSOL EQUILIBRIUM

VOC oxidation generates semi-volatile products:

…which then partition between the gas and aerosol phase:

where the partitioning coefficient is given by

…and is a strong function of temperature. Values of a and p0 are fitted to smog chamber data

Chung and Seinfeld, 2002

Mo is the mass concentrationof pre-existing organic aerosol

SOA MODELING USING VOLATILITY BASIS SETS

Partition semi-volatile VOCs (SVOCs) between aerosol and gas:

Aerosol fraction for SVOCi

Define SVOCs by their stability class:

Donahue et al. [2006]

SOA VOLATILITY BASIS SET: EFFECT OF DILUTION

Donahue et al. [2006]

SOA VOLATILITY BASIS SET: CHEMICAL AGING

Donahue et al. [2006]

As VOCs go through successive oxidation steps, products become more oxygenated and less volatile, but eventually smaller and more volatile

IMPLEMENTING OC VOLATILITY CLASSES IN GEOS-Chem

Pye and Seinfeld [2010]

Combustion

“Primary” OC is actually semi-volatile Mean wintertime OC concentrations:IMPROVE data shown as circles

POSSIBLE MECHANISMS FOR DICARBONYL SOA FORMATION

GAS AQUEOUS

Oligomers

OHOrganic acids

KH* ~ 105 M atm-1

Ervens et al. [2004]Crahan et al. [2004]Lim et al. [2005]Carlton et al. [2006, 2007]Warneck et al. [2005]Sorooshian et al. [2006, 2007]

Altieri et al. [2006, 2008]

Schweitzer et al. [1998]Kalberer et al. [2004]Liggio et al. [2005a,b] Hastings et al. [2005] Zhao et al. [2006]Loeffler et al. [2006]glyoxal

KH* ~ 103 M atm-1

methylglyoxal

oxidation

oligomeriz

ation

oli

go

mer

izat

ion

GLYOXAL/METHYLGLYOXAL FORMATION FROM ISOPRENE

ON

O

O

O OH

OOH

O O O

OO

HO

OO

O

O

OH

Isoprene

C5 carbonylsHydroxy-

methylvinyl ketone Methylvinyl ketone Methacrolein

Glyoxal Glycolaldehyde Methylglyoxal Hydroxyacetone

Methyl-nitroxy butenal

25% 12% 37% 26%

18%33% 32%62%

29% 51% 24%39%

87%16%

45%52%

+ OH+ NO3

+ NO + NO

16%

84%

16%

84%

2%

andisomers

0.5%

Organicnitrates

Organicnitrates

GEOS-Chem mechanism based on MCM v3.1

Fu et al. [JGR, 2008]

6% 25%

molar yields

Van Krevelen diagram for chemical aging of organic material

Heald et al. [2010]

Van Krevelen diagram: application to organic aerosol

Heald et al. [2010]

-1 slope suggests aging by adding of –COOH functionalities