FINE AEROSOL COMPOSITION IN NORTH AMERICA
Annual mean PM2.5 concentrations (NARSTO, 2004)
Current air quality standard is 15 mg m-3
SULFATE-NITRATE-AMMONIUM AEROSOLS IN U.S.
(2001)
Sulfate
Nitrate
Ammonium
Highest concentrations
in industrial Midwest
(coal-fired power plants)
Acidity
Ammonia and NOx emissions in the US (2006)
Zhang et al. [2012]
Distributions of HNO3 (g) and NO3- (aerosol) in surface air
EPA network data for 2006
HNO3 (g)
Zhang et al. [2012]
NO3- (aerosol)
FORMATION OF SULFATE-NITRATE-AMMONIUM AEROSOLS
Thermodynamic rules:
H 2O
H 2 SO4 ( g ) 
 SO42  2 H 
H 2O
NH 3 ( g ) 
 NH 4  OH 
H 2O
HNO3 ( g ) 
 NO3  H 
NH 3 ( g )  HNO3 ( g )
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
NH NO (aerosol )
4
3
Highest concentrations
in industrial Midwest
(coal-fired power plants)
HNO3 and excess NH3
can also form a solid aerosol
if RH is low
Condition
aerosol pH
Low RH
High RH
2[S(VI)] > [N(-III)]
acid
H2SO4•nH2O,
(NH4+ , H+, SO42- )
NH4HSO4 , (NH4 solution
)2SO4
2[S(VI)] ≤ [N(-III)]
neutral
(NH4 )2 SO4 ,
NH4 NO3
(NH4+ , SO42-, NO3- )
solution
U.S. SO2 EMISSIONS
GLOBAL
Industrial
UNITED STATES
Volcanoes
Sulfur emissions,
Tg a-1
Biomass
burning
78
Oceans
8.3
Observation of SO2 point sources in US by OMI oversampling
SO2 point sources, 2004-2007
3 km-resolution data enables
analysis of SO2 emission trends,
SO2 atmospheric lifetime
OMI SO2 (3 km oversampling)
AQAST PI: De Foy
SO2 columns observed from SCIAMACHY
Andreas.Richter@iup.physik.uni-bremen.de
GOME and SCIAMACHY SO2 over China
Volcanic
eruption
•
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 plants
Not all power plants have been equipped other sources are on the rise
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
Kasatochi volcano
Altitude: 314 m
Latitude: 52.16°N
Longitude: 175.51° W
http://www.avo.alaska.edu/
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.
BLACK CARBON (BC)
0.66 Tg yr-1
ORGANIC CARBON (OC)
Fossil fuel
Biofuel
Biomass burning
Vegetation
2.7 Tg yr-1
Annual mean concentrations (2001)
BC
Park et al. [2006]
OC
Long-term trends in BC and OC aerosol over the US
Annual mean
concentrations
National trends
Leibensperger
et al. [2011]
Observed
Model
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
Freshly emitted BC particle
Diesel engines are large BC sources
Atmospheric aging and scavenging of BC
Hydrophobic BC
resistant to scavenging
coagulation
gas condensation
Aging time scale
τ ~1d
Hydrophilic BC
coated with sulfate, nitrate
Scavenging
Emission
Implications for BC export from source continents:
long-range
aging
transport
Hydrophobic
BC
aging
scavenging
OCEAN
FREE TROPOSPHERE
BOUNDARY LAYER
BC and OC aerosol during ARCTAS
aircraft campaign (spring 2008)
Wang et al. [2011]
ORGANIC AEROSOL IN STANDARD GEOS-Chem MODEL
Global sources in Tg C y-1
VOC
K
OH, O3,NO3
20
SOG
SOA
secondary
formation
isoprene
alkanes
terpenes
alkenes
oxygenates… aromatics…
700
alkenes
aromatics
oxygenates…
30
50
vegetation
fuel/industry
POA
open fires
VOC EMISSION
SOA ≡ secondary organic aerosol
POA ≡ primary organic aerosol
20
fuel/industry
100
open fires
PRIMARY EMISSION
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:
Mo is the mass concentration
of pre-existing organic aerosol
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
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
As VOCs go through successive oxidation steps, products become more
oxygenated and less volatile, but eventually smaller and more volatile
Donahue et al. [2006]
IMPLEMENTING OC VOLATILITY CLASSES IN GEOS-Chem
“Primary” OC is actually semi-volatile
Mean wintertime OC concentrations:
IMPROVE data shown as circles
Combustion
Pye and Seinfeld [2010]
POSSIBLE MECHANISMS FOR DICARBONYL SOA FORMATION
GAS
AQUEOUS
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
oligomerization
Oligomers
KH* ~ 105 M atm-1
methylglyoxal
Altieri et al.
[2006, 2008]
OH
Organic acids
KH* ~ 103 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]
GLYOXAL/METHYLGLYOXAL FORMATION FROM ISOPRENE
+ NO3
+ OH
+ NO
+ NO
Isoprene
16%
16%
Organic
nitrates
84%
84%
25%
Organic
nitrates
O
12%
37%
26%
OH
O
N
and
isomers
O
O
Methylnitroxy butenal
O
O
Hydroxymethylvinyl ketone
C5 carbonyls
18%
52%
45%
6%
62%
16%
O
O
Glyoxal
O
O
OH
33%
32%
29%
Methylvinyl ketone Methacrolein
51%
24%
2%
0.5%
39%
87%
HO
O
Glycolaldehyde
O
25%
O
Methylglyoxal
O
OH
Hydroxyacetone
GEOS-Chem mechanism based on MCM v3.1
molar yields
Fu et al. [JGR, 2008]
Van Krevelen diagram for chemical aging of organic material
Heald et al. [2010]
Van Krevelen diagram: application to organic aerosol
-1 slope suggests aging by adding of –COOH functionalities
Heald et al. [2010]