air pollution in the us today: ozone and pm are the major pollutants 75 ppb (8-h average) milllions...
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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)
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
Wiley Interdisciplinary Reviews
obstacle
impaction
diffusion
interception
Airflow
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
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
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
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
Annual PM2.5 distributions in US, 2005-2007 [EPA, 2009]
ANNUAL MEAN PM2.5 CONCENTRATIONS (2002)derived from MODIS satellite instrument data
Beijing US embassy current PM2.5 levels
WORLDWIDE MEASUREMENTS OF FINE AEROSOL COMPOSITION
FINE AEROSOL COMPOSITION IN NORTH AMERICAAnnual mean PM2.5 concentrations (NARSTO, 2004)
Current air quality standard is 15 μg m-3
11
U.S. SO2 EMISSIONS
Sulfur emissions,Tg a-1
78 8.3
GLOBAL UNITED STATES
Main source is coal combustion
12
SO2 columns over Midwest observed from space, 2005-2010
Ben De Foy, Saint Louis U.
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
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]
OBSERVED TITRATION OF SO2 BY H2O2 IN CLOUD
First aircraft observations by Daum et al. [1984]
Ammonia and NOx emissions in the US (2006)Ammonia is mainly from agriculture
Zhang et al. [2012]
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
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
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
SULFATE-NITRATE-AMMONIUM AEROSOLS IN U.S. (2001)
Highest concentrations in industrial Midwest(coal-fired power plants)
Sulfate Nitrate
Ammonium
Acidity
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
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
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
LONG-TERM TREND IN US SO2 EMISSIONS
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
Long-term trends in BC and OC aerosol over the US
Annual meanconcentrations
National trendsObservedModel
Leibensperger et al. [2011]
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
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]
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