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AIR POLLUTION IN THE US TODAY:Ozone and PM are the major pollutants
http://epa.gov/airtrends
75 ppb (8-h average)
Milllions of people exposed to air pollutants in excess of national ambient air quality standards (NAAQS), 2012
Any pollutant
PM2.5
Ozone
PM10
SO2
Lead
12 µg m-3 (annual average), 35 µg m-3 (24-h average)
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TYPICAL AEROSOL SIZE DISTRIBUTION
by volume
PM2.5
PM10
PM2.5 ≡ concentration of particulate matter less than 2.5 µm diameter
PM10 ≡ concentration of particulate matter less than 10 µm diameter
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Wiley Interdisciplinary Reviews
obstacle
impaction
diffusion
interception
Airflow
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County life expectancies at birth for white males and females;1997–2001
CJL Murray et al, Eight Americas: Investigating Mortality Disparities across Races, Counties, and Race-Counties in the United States. PLoS Med. 2006 Sep;3(9):e260
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Life Expectancy vs annual PM2.5
1978-82
71
72
73
74
75
76
77
78
79
80
81
5 10 15 20 25 30 35PM2.5 (mg/m3)
Lif
e E
xp
ec
tan
cy
Steubenville, OH
Topeka
Boston
EPA NAAQS
Pope, Ezzati, Dockery. NEJM 2009; 360:376
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Life Expectancy vs annual PM2.5
1997-2001
71
72
73
74
75
76
77
78
79
80
81
5 10 15 20 25 30 35PM2.5 (mg/m3)
Lif
e E
xp
ecta
ncy
Topeka
Boston
Steubenville
EPA NAAQS
Pope, Ezzati, Dockery. NEJM 2009; 360:376
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Life Expectancy vs annual PM2.5
1980-2000
71
72
73
74
75
76
77
78
79
80
81
5 10 15 20 25 30PM2.5 (mg/m3)
Lif
e E
xp
ec
tan
cy
Steubenville
Boston
Topeka
Pope, Ezzati, Dockery. NEJM 2009; 360:376
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Annual PM2.5 distributions in US, 2005-2007 [EPA, 2009]
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ANNUAL MEAN PM2.5 CONCENTRATIONS (2002)derived from MODIS satellite instrument data
Beijing US embassy current PM2.5 levels
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WORLDWIDE MEASUREMENTS OF FINE AEROSOL COMPOSITION
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FINE AEROSOL COMPOSITION IN NORTH AMERICAAnnual mean PM2.5 concentrations (NARSTO, 2004)
Current air quality standard is 15 μg m-3
11
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U.S. SO2 EMISSIONS
Sulfur emissions,Tg a-1
78 8.3
GLOBAL UNITED STATES
Main source is coal combustion
12
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SO2 columns over Midwest observed from space, 2005-2010
Ben De Foy, Saint Louis U.
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Kasatochi eruption as seen in GOME-2 SO2
• Lage eruption on August 8, 2008 injects SO2 to the upper troposphere
• SO2 lifetime of 1-2 weeks
http://www.avo.alaska.edu/
Kasatochi volcano
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In surface air, however, sulfate observations imply an SO2 lifetime ~ 1 day
Sulfate deposition, kg ha-1 a-1 Sulfate aerosol, µg m-3
Leibensperger et al. [2012]
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OBSERVED TITRATION OF SO2 BY H2O2 IN CLOUD
First aircraft observations by Daum et al. [1984]
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Ammonia and NOx emissions in the US (2006)Ammonia is mainly from agriculture
Zhang et al. [2012]
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Formation of sulfate-nitrate-ammonium (SNA) aerosol
SO2
NH3 NOx HNO3
NH3(aq), NH4=
H2SO4(aq), HSO4
-, SO42-
HNO3(aq), NO3-
High RH (aqueous) Low RH
NH4+,SO4
2=, NO3-
dry salts
EMISSIONS
oxidation
oxidation
• Uptake of NH3 and HNO3 by sulfate aerosol follows thermodynamics• This uptake affects the mass and phase of the aerosol
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Thermodynamic rules for SNA aerosol formation
22 4 4 4( ) 2H SO aq HSO H SO H
H2SO4 condenses to aqueous solution; dissociation to HSO4-, SO4
2- governed by pH
2
3 4( )H O
NH g NH OH NH3 condenses into acid aerosol until neutralization; no further uptake
3 3( )HNO g NO H
HNO3 condenses only if excess NH3 is available
4 4 4 3 4 2 4 2 4 4 3( ), ( ) ( ) , ( ) ( ), ( )NH HSO s NH H SO NH SO s NH NO s
At low RH, equivalent equilibria apply to the solid salts
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Three different regimes for SNA aerosol formation[S(VI] = [H2SO4(aq)] + [HSO4
-] + [SO42-]
[N(-III)] = [NH3(g)] + [NH3(aq)] + [NH4+]
[N(V)] = [HNO3(g)] + [HNO3(aq)] + [NO3-]
Equivalents per m3 of air
[S(VI)] > [N(-III)]
• Aerosol is acidic• N(-III) all in aerosol• No N(V) in aerosol
S(V
I)
N(-
III)
[S(VI)]+[N(V)] > [N(-III)] > [S(VI)]
• Aerosol is neutral• N(-III) all in aerosol• N(V) partly in aerosol
gasaerosol
S(V
I)
N(-
III)
N(V
)
N(V
)
gasaerosol
[S(VI)]+[N(V)] < [N(-III)]
S(V
I)
N(-
III)
gasaerosol
N(V
)
• Aerosol is neutral• N(-III) partly in aerosol• N(V all in aerosol
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SULFATE-NITRATE-AMMONIUM AEROSOLS IN U.S. (2001)
Highest concentrations in industrial Midwest(coal-fired power plants)
Sulfate Nitrate
Ammonium
Acidity
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CARBONACEOUS AEROSOL SOURCES IN THE U.S.
ORGANIC CARBON
2.7 Tg yr-1
ELEMENTAL CARBON
0.66 Tg yr-1
Annual mean concentrations (2001)
elemental organic
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FORMATION OF ORGANIC AEROSOL FROM VEGETATIVE EMISSIONS
(C5H8)
(C10H16)
OH, O3
AldehydesRC(O)H
KetonesRC(O)R
DicarbonylsRC(O)-C(O)R
absorptioninto aerosol
oxidation
Carboxylic acids RC(O)OH
polymerization
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Van Krevelen diagram for chemical aging of organic material
Heald et al. [2010]
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Van Krevelen diagram: application to organic aerosol
Heald et al. [2010]
-1 slope suggests aging by adding of –COOH functionalities
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LONG-TERM TREND IN US SO2 EMISSIONS
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Decline of sulfate aerosol in the US
1990
µg m-3
Observed sulfate concentrations (circles), GEOS-Chem (background)
Leibensperger et al. [2012]
2010
µg m-3
Scrubbers on coal power plants, transition to natural gas
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Long-term trends in BC and OC aerosol over the US
Annual meanconcentrations
National trendsObservedModel
Leibensperger et al. [2011]
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EPA REGIONAL HAZE RULE: WILDERNESS AREAS MUST ACHIEVE NATURAL VISIBILITY CONDITIONS BY 2064
GlacierNationalPark
7.6 µgm-3
12.0 µgm-3
21.7 µgm-3 65.3 µgm-3
U.S. annual air quality standard
Visibility degradation by aerosols at Glacier National Park, Montana
Natural aerosol concentrations are typically less than 2 μg m-3
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VISIBILITY IN U.S. WILDERNESS AREASStatistics for 20% worst visibility days
Deciviews
2001 observations Natural Background; includestransboundary pollution
300 150 80 40 20 Visual range (km)
Park et al. [2006]
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WILDFIRES: A GROWING AEROSOL SOURCES. California fire plumes,Oct. 25 2004
Total carbonaceous (TC) aerosol averaged over U.S. IMPROVE sites
Interannual variability is driven by wildfires