The role of fire in atmospheric chemistry Discussion with Susquehanna University “Green Chemistry” class Sonia Kreidenweis Colorado State University

Worldwide occurrence of fire

Mean annual fire emissions, (g C m -2 year -1 ) (van der Werf et al., ACP, 2006) Which locations are mostly WILDFIRES? Which are PRESCRIBED fires? Why do people use prescribed burning?

Burning in North America (Image: from van der Werf et al., ACP, 2006) In the U.S., about 2 million acres per year of federal forests were burned by prescribed fires from 1998 to 2006, in comparison to around 6 million acres of wildfires (Tian et al., ES&T, 2008) Which are prescribed burning?

In a typical year, how much of the CARBONACEOUS particulate matter in the US can be attributed to fire?  About 1%  About 10%  About 50%

Biomass burning can contribute ~50% of annual mean carbonaceous aerosol in U.S.

Sugar cane burn, LA

Prescribed fire in Georgia Joseph W. Jones Ecological Research Center wiregrass and longleaf pine needles and underbrush

Lightning-started peat fire Firefighters battle burning peat at Pocosin Lakes National Wildlife Refuge in North Carolina, January USFWS, posted at Typical of swampy areas, peat soils consisting of organic matter burned and held intense heat. Soaking the peat with water was the only way to fully extinguish the underground fire. (reported at ans_road.shtml)

Chaparral Chaparral canyon fire near Rancho Peñasquitas (1995) Reported by The San Diego Wildfires Education Project,

Alaska boreal forest wildfire

How far does a “smoke plume” travel?  About 50 km  About 100 km  Several hundred km  Question is not worded properly

NOAA Smoke Forecasting

Aerosol optical depth in Boulder summer 2012 AP Photo/Ed Andrieski

True or false?  The mix of emitted species changes from the beginning to the end of a fire.  Most of the mass of burned biofuels is emitted as particles.  Fires always emit a lot of black carbon (“soot”).  A fire will always result in a high-ozone episode in the nearby areas affected.  The particles that are emitted might evaporate as the smoke plume is diluted.

Composition of emissions from biomass burning (where does the carbon in the plant go?) Andreae & Merlet, Global Biogeochemical Cycles, 2001 carbon dioxide (CO 2 ) [92 – 96 %] carbon monoxide (CO) [3 – 7 %] everything else [ < 2 %]

What’s in the “everything else”? Andreae & Merlet, Global Biogeochemical Cycles, 2001 methane (CH 4 ) [10 – 30 %] non-methane hydrocarbons [20 – 40 %] particulate matter [ > 30 %]

Yokelson et al., J. Geophys. Res., 1996 Where does N in the plants go…?

Pyrolysis  Pyrolysis is a thermochemical decomposition of organic material at elevated temperatures in the absence of oxygen (or any halogen). It involves the simultaneous change of chemical composition and physical phase, and is irreversible. The word is coined from the Greek-derived elements pyro "fire" and lysis "separating".thermochemical decompositionorganic material oxygenhalogenchemical composition Greekelementslysis  Pyrolysis is a type of thermolysis, and is most commonly observed in organic materials exposed to high temperatures. It is one of the processes involved in charring wood, starting at 200–300 °C (390–570 °F) [Wikipedia]thermolysisorganiccharring

Conceptual picture new particle formation

Conceptual picture new particle formation OZONE FORMATION

Direct evidence for health impacts of smoke

Study Finds Peat Wildfire Smoke Linked to Heart Failure Risk In the summer of 2008, a lightning strike started a wildfire in eastern North Carolina that burned for weeks, blanketing nearby communities in smoke. An EPA study shows for the first time that smoke from this wildfire, which was fueled by peat (decayed vegetable matter found in swampy areas) can lead to an increase in emergency room visits for both respiratory and cardiovascular effects. This was the first study to report increased visits for symptoms of heart failure in counties exposed to wildfire smoke. The study found a 37 percent increase in emergency room visits for people with symptoms of heart failure during a three day period of dense smoke exposure and the following five days. The EPA study also showed an increase in emergency department visits for problems relating to asthma, chronic obstructive pulmonary disease (COPD), pneumonia, and bronchitis, which are similar to studies of other wildfires.

Ozone also rises when plumes arrive… “Air pollutants from a prescribed fire about 80 km southeast of metro Atlanta on February 28, 2007 led to parts of the city being exposed to unhealthy levels of PM 2.5 for several hours. Observed 1-h PM 2.5 concentrations at several monitors in the city reached higher than 145 μ g/m3 (U.S. National Ambient Air Quality Standard (NAAQS) for 24-h PM2.5 is 35 μg/m3), increasing by over 100 μg/m3 in two hours. In addition, as the plume hit, 1-h average ozone concentrations increased markedly from 63 to 95 ppb at one monitor.” Tian et al., ES&T, 2008

Air Quality Impacts

National Ambient Air Quality Standards: smoke impacts? Fire influence is UNDER DEBATE (fire probably leads to increased ozone downwind)

National Ambient Air Quality Standards: smoke impacts? No direct impact, but together with other emitted gases, can lead to high ozone levels

National Ambient Air Quality Standards: smoke impacts? Very important, not only locally but over large regions! Standards are being lowered in response to health data….

Strategies for the future? “Wildland fire is a complicated subject when considered under the Regional Haze Rule (RHR). While prescribed fire emits pollutants which contribute to haze, a series of prescribed fires may emit less pollutants than one wildfire.” smoke/educational-resources/tutorial/lesson-2/regional-haze/