Emissions and Effects Susan M

SMOKE PLUMES: EMISSIONS AND EFFECTS Susan M. O’Neill, Shawn Urbanski, Scott Goodrick, and Narasimhan K. Larkin moke can manifest itself as a towering plume rising against Smoke can affect public health, Sthe clear blue sky—or as a vast transportation safety, and the health swath of thick haze, with fingers that settle into valleys overnight. It and well-being of firefighters. comes in many forms and colors, from fluffy and white to thick and black. Smoke plumes can rise high 1). Overall, dry air is made up of 78 affect visibility, degrading vistas and into the atmosphere and travel percent nitrogen (N2), 21 percent creating transportation hazards. great distances across oceans and oxygen (O2), and about 1 percent Smoke combined with high humid continents. Or smoke can remain trace gases (about 0.9 percent ity can produce whiteout conditions close to the ground and follow fine- argon (Ar) and 0.1 percent other known as superfog (Achtemaier scale topographical features. trace gases). Water vapor in the 2002). air ranges from almost nothing to Along the way, the gases and par 5 percent. Yet the trace amount Wildland Fire Emissions ticles in the plumes react physically of smoke in the air can have sig If fire were 100-percent efficient, and chemically, creating additional nificant impacts, such as making the only products released would particulate matter and gases such the air smell bad; limiting vis be carbon dioxide, water vapor, as ozone (O3). If atmospheric water ibility; and affecting the health of and heat. However, the combus content is high, smoke plumes can vegetation and animals, including tion of wildland fuels is never also create “superfog” (Achtemeier humans. Smoke can affect public 100-percent efficient. In addition 2002). Over the past decade, health, transportation safety, and to carbon dioxide and water vapor, researchers have studied the suite the health and well-being of fire the process transforms some of of trace gases and aerosols emitted fighters. by wildland fires, along with the the fuel into ash, char, particulate matter, carbon monoxide, and physical and chemical reactions and Due to health and safety concerns, other carbon-containing gases—a transformations that occur within the Clean Air Act regulates aspects rich and complex mixture of gases a plume. of atmospheric smoke. If smoke and particles. Figure 1 shows the concentrations in a region exceed distribution of carbon emitted by Why Do We Care? the national ambient air qual Smoke gases and particles con ity standards (NAAQSs), then the stitute only a tiny fraction of the region is designated as “nonattain air (less than 0.1 percent of the ment.” Nonattainment triggers reg atmosphere in any location, even ulatory actions, such as controls on under the worst conditions) (table smoke emissions; fees/charges for emissions; restrictions on industry; Susan O’Neill is an air quality scientist and, in some cases, restrictions for the Forest Service, Pacific Northwest on the use of fire. Currently, the Research Station, Seattle, WA; Shawn NAAQS threshold for particulate Urbanski is a research physical scientist for the Forest Service, Rocky Mountain matter finer than 2.5 micrometers Research Station, Missoula, MT; Scott in diameter (PM2.5) is 35 micro- Goodrick is a research meteorologist for grams per cubic meter (24-hour Figure 1—The distribution of carbon the Forest Service, Southern Research average); for ozone, the threshold Station, Athens, GA; and Sim Larkin is emitted by a typical low-intensity a research scientist and team leader for is 75 parts per billion (8-hour aver understory prescribed fire in light fuels the Forest Service AirFire Team, Pacific age). Even at levels below these (based on Urbanski (2014)). CO2 = carbon Northwest Research Station, Seattle, WA. dioxide; CO = carbon monoxide; PM = standards, smoke can significantly particulate matter. Fire Management Today 10 Table 1—Gases and particles in the atmosphere, including those related to biomass burning. Chemical/particle Symbol Name Description Ar Argon About 0.9 percent of the atmosphere. BC Black carbon Particles from combustion that strongly absorb incoming solar radiation and emit longwave radiation. CO Carbon monoxide Emitted from the incomplete combustion of biomass. CO2 Carbon dioxide A primary product of biomass burning. H2O Water A primary product of biomass burning. N2 Nitrogen About 78 percent of the atmosphere. NH3 Ammonia A precursor of inorganic particle formation; trace amounts emitted from biomass burning. NOX Oxides of nitrogen NO and NO2, precursors to ozone and particle formation. NO Nitrogen oxide Part of NOX; released from biomass burning as a function of the fuel nitrogen content and combustion phase. NO2 Nitrogen dioxide Part of NOX. O2 Oxygen About 21 percent of the atmosphere. O3 Ozone Created by the reaction of NOX and VOCs in the presence of sunlight; regulated under the Clean Air Act. OC Organic carbon Carbon and hydrogen compounds, oxygenated carbon/hydrogen compounds, and other trace elements; a major constituent of particulate matter from biomass burning. PAN Peroxyacetyl nitrate Can sequester NOX and travel long distances in the atmosphere; mixed back down near the surface, warmer temperatures break it apart, freeing up NOX to generate more O3 far from the fire. PM2.5 Particulate matter Fine particulate matter; can comprise organic and inorganic (aerodynamic compounds; regulated under the Clean Air Act. diameter < 2.5 μm) SO2 Sulfur dioxide A precursor of inorganic particle formation; trace amounts emitted from biomass burning. SOA Secondary organic Particles formed by a series of physical and chemical reactions. aerosol VOC Volatile organic Precursors of O3 and SOA formation; hundreds identified from compound biomass burning, hundreds yet to be identified; examples: methane, ethane, benzene, furan, formaldehydes, methanol, monoterpenes. Volume 75 • No. 1 • 2017 11 a typical low-intensity understory trace elements. Black carbon is the Secondary organic aerosols are prescribed fire in light fuels. Minor fraction of the particle that strongly particles formed in the atmosphere smoke constituents such as carbon absorbs incoming solar radiation through a series of gas-phase chem monoxide, particulate matter, and and emits longwave radiation into ical reactions that lower the volatil “other gases” are mainly respon the atmosphere. It is a product of ity of VOCs to the point where they sible for smoke impacts on visibility combustion; in its purest form, it can condense into or onto particu and air quality. would be graphite. It has been iden lates. These organic compounds tified as a short-lived climate forcer, can continue reacting until the car Over the past decade, scientists bolstering the greenhouse effect; bon is oxidized to carbon monoxide have made tremendous progress deposition of black carbon on snow or carbon dioxide or until the par in identifying the “other gases” accelerates snowmelt. ticles are removed from the atmo produced by wildland fires (fig. sphere through deposition. Cooler 1). Multiple research projects temperatures help semivolatile have gotten support from the gases condense into particulates. Forest Service’s Research and Smoke particles are As compounds react and age in Development, the multiagency quite small, making the atmosphere, they tend to more Joint Fire Science Program, the them very efficient at readily attach to water, increasing U.S. Department of Defense scattering light, thereby the amount of water in the particu Strategic Environmental Research late. Most semivolatile compounds and Develop Program, and oth reducing visibility and formed in the atmosphere remain ers. Researchers have studied generating “haze.” to be identified. Secondary organic the composition of smoke from aerosols are an important area of simulated fires in the large-scale current research. combustion facility operated by the Particles rarely exist solely as Rocky Mountain Research Station’s organic or black carbon. Instead, Most smoke particles are quite Missoula Fire Sciences Laboratory they form a continuum, rang small, often less than 1 micrometer and from operational prescribed ing from pure graphite to mostly in diameter. They are very efficient fires in the Southeastern and organic compounds. Smoke par at scattering light, reducing visibil Southwestern United States. Recent ticles from wildland fires tend to ity and generating “haze.” Smoke advances in instrumentation and have a higher percentage of organ plumes lofted high into the atmo chemical analytical techniques have ics than do particles from anthro sphere can also interact with cloud- allowed scientists to identify nearly pogenic combustion sources, which forming processes. 200 volatile organic compounds tend to have a higher black carbon (VOCs) in fresh smoke. The gases content. Smoke and Ozone include methane, ethane, benzene, Ozone is created in the atmosphere furan, formaldehydes, methanol, New particles form in the atmo through the reactions of oxides of monoterpenes, and more. Despite sphere through gas-to-particle nitrogen (nitrogen monoxide and such advances, a large percent reactions involving VOCs, oxides nitrogen dioxide) with VOCs in the age of VOCs remain unidentified, of nitrogen (nitrogen monoxide presence of sunlight. Nitrogen diox including 30 to 40 percent of them and nitrogen dioxide), ammonia, ide undergoes photolysis (the sepa in forest fuels and over 70 percent and sulfur dioxide. Factors such ration of molecules by light)

Load more