Emissions

Abstract

This chapter assesses the current state of the science regarding the composition, intensity, and drivers of wildland fire emissions in the USA and Canada. Globally and in the USA wildland fires are a major source of gases and aerosols which have significant air quality impacts and climate interactions. Wildland fire smoke can trigger severe pollution episodes with substantial effects on public health. Fire emissions can degrade air quality at considerable distances downwind, hampering efforts by air regulators to meet air standards. Fires are a major global source of aerosols which affect the climate system by absorbing and scattering radiation and by altering optical properties, coverage, and lifetime of clouds. A thorough understanding of fire emissions is essential for effectively addressing societal and climate consequences of wildland fire smoke.

Wildfires Increase Concentrations of Hazardous Air Pollutants in Downwind Communities

“…10,12 In this study, five of the six HAPs consistently elevated on smoke-impacted days can be divided by their chemical properties into two groups: oxygenated and chlorinated species. The oxygenated species (formaldehyde, acetaldehyde, and acrolein) are emitted in the largest amounts by wildfire 20 and are some of the major products from the pyrolysis of biomass, the dominant process in smoldering combustion. Overall, oxygenated species comprise nearly 70% of the measured VOCs in wildfire plumes.…”

“…Hydrogen cyanide, dioxin, and polycyclic aromatic hydrocarbons are examples of HAPs not included in this study that may contribute to the health impacts of wildfire smoke. 20 In the HAPs reported, infrequent measurements (typically a 3 day sampling schedule for PM 2.5 components, 6 days for gas-phase HAPs, or 12 days in San Jose after July 1, 2018) prevented us from assessing the exposure duration experienced by downwind populations. Given more frequent sampling, it is possible that higher magnitude values would have been recorded.…”

“…This study of air quality monitoring data builds on a long history of research on emissions from biomass burning, which has identified a wide range of chemical species emitted from wildfires, in addition to the major combustion products (CO 2 , CO, CH 4 , and PM 2.5 ). 20 Apart from the major combustion products, wildfire emissions include organic species in the gas and particle phases, inorganic gases (e.g., HCl, NOx, NH 3 ), and inorganic species in the particle phase (e.g., sulfate, trace metals). 20 Numerous laboratory studies and field studies have quantified emission factors with much of the focus on VOCs since they are a major portion of the emissions and are important precursors for ozone and secondary organic aerosol formation.…”

“…Building on decades of research on ambient PM 2.5 exposures (i.e., exposures during a typical day, not extreme events), there is extensive epidemiologic evidence relying on different exposure indicators (e.g., total or wildfire-specific PM 2.5 and smoke density) that wildfire smoke is associated with a range of health effects including increases in respiratory- and cardiovascular-related emergency department visits, hospital admissions, and even death. − Therefore, while wildfire smoke is a complex mixture, the use of PM 2.5 has been shown to be a reliable surrogate for smoke exposure . However, as the acreage burned and smoke emitted from wildfires increases, and some wildfires enter the wildland–urban interface (WUI), burning human-made structures and materials (e.g., buildings, vehicles), additional toxic pollutants may be emitted from the combustion of both natural and nontraditional fuels. , This potential change in the smoke mixture is important to characterize as current approaches to protect public health rely on reducing PM 2.5 concentrations, and it is unclear if currently recommended interventions would be effective at reducing other increased pollutants. ,, …”

“…12,18 This potential change in the smoke mixture is important to characterize as current approaches to protect public health rely on reducing PM 2.5 concentrations, 19 and it is unclear if currently recommended interventions would be effective at reducing other increased pollutants. 15,20,21 Among pollutants potentially increasing due to the prevalence of wildfire smoke are those classified by the US Environmental Protection Agency (US EPA) as hazardous air pollutants (HAPs). HAPs are regulated under the Clean Air Act and are defined as "pollutants that are known or suspected to cause cancer or other serious health effects".…”