FIRE AND BIOFUEL CONTRIBUTIONS TO ANNUAL MEAN AEROSOL MASS CONCENTRATIONS IN THE

UNITED STATES

ROKJIN J. PARK, DANIEL J. JACOB, JENNIFER A. LOGAN

AGU FALL MEETING, DECEMBER 11, 2006

OBSERVED TREND IN WILDFIRE FREQUENCY AND AREA BURNED IN NORTH AMERICA

THE IMPORTANCE OF FIRE FOR U.S. AIR QUALITY WILL INCREASE IN THE FUTURE AS U.S. ANTHROPOGENIC EMISSIONS DECREASE.

[Westerling et al., 2006]

[Soja et al., 2006]

OBJECTIVE AND METHODS

[TC]BM = ε(TC / K)BM × [ns-K]OBS,

[ns-K] ≡ [K] – 0.6 × [Fe], TC ≡ OC + EC

where ε = emission ratio from biomass burning and 0.6 = mass ratio of

K/Fe measured on coarse aerosols (Malm et al., 1994)

• Use the seasonal variation of ns-K concentrations and satellite fire data

to segregate different types of burning contributions

• ε(TC / K)BM ranges from 10 TO 110 (Andreae and Merlet, 2001)

• Use correlation statistics between TC and ns-K aerosol concentrations

from the nationwide IMPROVE network to compute enhancement ratios

from fires

ε(TC / K)FIRE ≈ d[TC] / d[ns-K]

• Use emission ratios of 100 for residential biofuel burning (Fine et al.,

2001) and of 10 for industrial biofuel burning (U.S. EPA, 2001)

QUANTIFY THE MORE DIFFUSE AND NATIONWIDE EFFECTS OF BIOMASS BURNING (WILDFIRES, OTHER FIRES, RESIDENTIAL BIOFUEL AND INDUSTRIAL BIOFUEL) ON SEASONAL AND ANNUAL AEROSOL CONCENTRATIONS IN THE U.S. FOR 2001-2004

Interagency Monitoring of PROtected Visual Environments (IMPROVE) network

• Started in 1987 to monitor visibility degradation in Federal Class I areas (large national parks and wilderness areas)• Measure 24-h speciated aerosol mass concentrations every third day including organic carbon (OC), elemental carbon (EC), potassium (K), iron (Fe).

Sites > 150 in 2001

MONTHLY MEAN TC CONCENTRATIONS AVERAGED AT CONTIGUOUS U.S. IMPROVE SITES FOR 2001-2004

[TC] ≡ [OC] + [EC]

SUMMERTIME TC CONCENTRATIONS ARE HIGHEST DUE TO FIRES AND SOA AND MORE VARIABLE THAN VALUES IN WINTER. SOA VARIABILITY IS NOT EXPECTED TO BE THIS LARGE (Palmer et al., 2006)

TC

(μ

g C

m-3)

DRY MASS BURNED IN NORTH AMERICA FOR JUNE-AUGUST, 2001-2004

van der Werf et al., 2006

MONTHLY MEAN ns-K CONCENTRATIONS FOR 2001-2004

2001 2004

West East

Background ns-K 1. Background ns-K concentrations are computed by taking averages of the lowest three monthly mean concentrations over 2001-2004 to minimize other burning influences.

2. Summer ns-K in excess of background represents summer wildfire contributions.

3. For other fires we use monthly gridded satellite fire data to constrain time and location of open burnings.

4. Remaining ns-K represents residential biofuel contributions.

DERIVED d[TC]/d[ns-K] ENHANCEMENT RATIOS FROM WILDFIRES FOR JUN-AUG, 2001-2004

SITES WITH R ≥ 0.7

VALUES ARE GENERALLY HIGHER IN THE NORTHERN U.S. WHERE MOST OF THE BURNING IS OF FOREST, THAN IN THE SOUTH, WHERE BURNING OF BRUSH AND GRASSLAND DOMINATES.

(μg C m-3 / μg m-3)

WILDFIRE CONTRIBUTIONS TO TC AEROSOL CONCENTRATIONS IN THE SUMMERS OF 2001-2004

1) USE RATIOS AT SITES WITH R ≥ 0.7 FOR A SPECIFIC YEAR2) AT SITES WITH R < 0.7, USE VALUE AVERAGED OVER SITES WITH R ≥ 0.7 IN

EACH STATE FOR A SPECIFIC YEAR3) IF NO SINGLE SITE WITH R ≥ 0.7 IS AVAILABLE WITHIN STATE, USE AVERAGE

OF OTHER YEAR VALUES FOR THAT STATE.

[TC]WILDFIRE = d[TC]/d[ns-K] × ([ns-K]SUMMER-[ns-K]BACKGROUND)

• HIGHEST WILDFIRE CONTRIBUTIONS ARE FOUND IN THE WESTCOAST WHERE 2002 IS HIGHEST.• IN THE NORTHEAST, TC CONCENTRATIONS ARE MOSTLY DUE TO TRANSBOUNDARY TRANSPORT FROM CANADIAN WILDFIRES.

TC ( μg C m-3)

FIRE AND BIOFUEL CONTRIBUTIONS TO ANNUAL TOTAL CARBON AEROSOL CONCENTRATIONS

Wildfires are the most important contributor to TC aerosol concentrations in the west while prescribed burns and residential biofuel are equally important in the east.

ANNUAL MEAN BIOMASS BURNING AEROSOL CONCENTRATIONS IN THE UNITED STATES FOR 2001-2004

μg C m-3 West East

SUMMER WILDFIRES 0.26 0.14

OTHER FIRES 0.27 0.31

RESIDENTIAL BIOFUEL 0.08 0.32

INDUSTRIAL BIOFUEL 0.07 0.18

SUM 0.68 0.95

OBSERVED TC AEROSOL 1.24 1.90

Annual mean concentrations of fine aerosols from biomass burning are 1.2 and 1.6 μg m-3 in the west and the east, respectively, accounting for 30% (west) and 20% (east) of observed total fine aerosol concentrations and represent a significant increment toward the NAAQS for annual mean concentrations of fine aerosols (15 μg m-3 ).

• The year-to-year variation of summer wildfires largely drives the observed interannual variability in TC aerosol concentrations in the United States.

• Wildfires are the most important contributor to annual concentrations of TC aerosol in the west while prescribed burns and residential biofuel are equally important in the east.

• Our estimates of annual mean contributions from biomass burning are 0.68 and 0.95 μg C m-3 in the west and the east, accounting for about 50% of observed annual mean TC concentrations.

• Annual mean concentrations of fine aerosols from biomass burning are 1.2 and 1.6 μg m-3 in the west and the east, respectively, accounting for 30% (west) and 20% (east) of observed total fine aerosol concentrations.

• Fire and biofuel contributions to annual aerosol concentrations represent a significant increment toward the NAAQS for annual mean concentrations of fine aerosols (15 μg m-3 ).

CONCLUSIONS

CORRELATION STATISTICS BETWEEN TC AND ns-K AEROSOL CONCENTRATIONS FOR JUNE-AUGUST, 2004

REGRESSION SLOPE AT SITES (R ≥ 0.7) R

HIGH SLOPE INDICATES SIGNIFICANT BOREAL WILDFIRE INFLUENCES.

SITES IN NEW MEXICO SITES IN MONTANA

TC

(μ

g C

m-3)