The Chemistry of Fires at the Wildland-Urban Interface (2022) / Chapter Skim
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4 Atmospheric Transport and Chemical Transformations
4 Atmospheric Transport and Chemical Transformations
Pages 69-98
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From page 69... ...
This chapter explores this impact, emphasizing atmospheric chemistry that informs inhalation exposures and the resulting health effects associated with emissions from WUI fires. It is important to recognize that, in addition to chemical processes, the physical processes of wet and dry atmospheric deposition can also be a source of contaminated water and soil and thus impact exposures through ingestion.
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From page 70... ...
The possibility that other loss processes dominate in WUI fire plumes (e.g., oxidation by chlorine radical, multiphase chemistry, cloud chemistry) is discussed in the next section, "Atmospheric Transformations." ATMOSPHERIC TRANSFORMATIONS The Downwind Fate of WUI Fire Emissions A wide range of plume studies including studies of wildland fire plumes provide confidence that WUI smoke concentrations decrease with distance downwind through dilution and surface deposition and undergo chemical and phase changes in the atmosphere (Figure 4-1)
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From page 71... ...
in particulate form Primary species with toxic potential: Toxic substance that is emitted directly from the source (e.g., WUI fire) Secondary organic aerosol: Organic particulate matter that is formed in the atmosphere from precursor gases Secondary species with toxic potential: Toxic substances that are formed through atmospheric chemistry (continued)
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From page 72... ...
. These species and radicals derived from their atmospheric chemistry could alter the rate of chemical transformations in WUI plumes, changing the lifetime of primary species with toxic potential and the formation of secondary species with toxic potential.
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From page 73... ...
Limited atmospheric transport. Reacts with hydroxyl radicals.
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From page 74... ...
Oxidized rapidly in atmospheric waters and Oxidized by OH radicals in the gas phase and Depending on the hydroxyl removed from the atmosphere by precipitation or in clouds/fogs by peroxides, NO2, and transition radical concentration, sulfur dioxide dry deposition, mainly as sulfuric acid (acid rain)
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From page 75... ...
from the air.a and taken up by particulate matter or dust.a Per- and Found in both the gas and particle phases. PFASs include thousands of compounds across The lifetimes are days to weeks (Ellis polyfluoroalkyl several compound classes.
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From page 76... ...
Photochemical reactions involve NOx, N2O5, OH, PAHs having two to three rings are present in air O3, SO2, and peroxyacetyl nitrate. predominantly in the vapor phase; those with four rings exist both in the vapor and particulate phase; Reactions of PAHs, including fluoranthene and and those having five or more rings are found pyrene, with the OH radical (in the presence of predominantly in the particle phase.
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From page 77... ...
. NOTES: Based on laboratory and field measurements from wildland fires, WUI fires, and structure fires, as well as information about materials.
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From page 78... ...
78 THE CHEMISTRY OF FIRES AT THE WILDLAND-URBAN INTERFACE Atmospheric Transport and Chemical Transformations Plume Rise Plume Dilution & Dispersion Wet & dry deposition Gas phase, aqueous, catalytic & multiphase chemistry Near-field exposure Local exposure to Regional exposure to fresh emissions fresh emissions to the transformed WUI plume SPATIAL 1–10 KM 10–100 KM >100 KM SCALE TEMPORAL MINUTES HOURS DAYS SCALE FIGURE 4-1 The movement and changes of WUI emissions over space and time. The processes, shown in the top half above the structures, are discussed in this chapter.
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From page 79... ...
While little is known about secondary species with toxic potential from WUI fires, elevated concentrations of the hydroxyl radical, reactive nitrogen, reactive chlorine, and transition metals are likely to exist in WUI plumes (see "Major Atmospheric Oxidants Driving Gas-Phase Chemistry" below) and will react with a variety of unsaturated organic compounds to form more oxygenated, chlorinated, and nitrated products that may have increased toxicity (Tuet et al., 2017; Wong et al., 2019)
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From page 80... ...
. Much is left to learn about the formation of secondary species with toxic potential downwind of WUI fires.
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From page 81... ...
Coordinated measurements, including the use of tracers of chemical processes, have played an important role in improving our understanding of atmospheric chemistry. Atmospheric oxidants transform the smoke mixture as it travels downwind, forming more oxidized and functionalized gases and secondary organic aerosols (e.g., wildland fire aerosol; Zhou et al., 2017)
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From page 82... ...
. Finding: The increase in reactive nitrogen and halogen emissions in WUI fires relative to wildland fires, and the VOC-to-NOx ratios of WUI fire emissions, are not well characterized; this information could improve prediction of ozone from WUI fires.
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From page 83... ...
Phenol, guaiacol, dioxins, and synthetic polymer degradation products are among the potential WUI precursors to SOA formation through gas-phase oxidation and vapor pressure–based partitioning. SOA Formation via Aqueous, Heterogeneous, or Multiphase Chemistry Chemistry in WUI fire plumes can also occur on the surfaces of aerosol particles (heterogeneous)
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From page 84... ...
Many of the most important processes are controlled by radical chemistry. Because WUI fires have the potential to have significantly different radical reactivities than wildland fires, due to the increased presence of halogen radicals, metals, and other species, critical chemical pathways have the potential to have different rates and to be qualitatively different than in wildland fires.
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From page 85... ...
Different types of models are used to characterize chemical transformations in wildland fire and WUI plumes over local, regional, and continental scales. The complex gas-phase chemical transformations, particle-phase chemical transformations, and gas-to-particle partitioning associated with wildland fires and WUI fires, outlined in this chapter, are tracked using computationally intensive models that couple chemical transport and transformation.
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From page 86... ...
86 THE CHEMISTRY OF FIRES AT THE WILDLAND-URBAN INTERFACE FIGURE 4-2 Example of daily fire locations (top) and fire plume projections (bottom)
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From page 87... ...
. Chemical transport models have generally not been optimized to address the unique chemistries and transport characteristics of wildland fire plumes.
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Finding: Current models lack the chemical specificity needed to track in detail the types of toxicants associ ated with wildland fires and WUI fires. Research need: Development of condensed chemical mechanisms is needed for use in applying chemical transport models to WUI fires.
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From page 89... ...
• Development of sub-grid-cell models that could be used to model the mixing of fire plumes with ambient air and the structure of single-structure or neighborhood-scale plumes • Development of chemical transport models that could be used in prognostic mode to facilitate first-responder activity during environmental crises, and communication/decision-making coordination (a technology link to communicate predictions at the different scales of responders) Research need: A combination of research approaches is needed to understand and predict toxicant concen trations downwind of WUI fires and ultimately mitigate their health risks.
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From page 90... ...
2016. "Secondary Organic Aerosol Formation from Isoprene Photooxidation during Cloud Condensation–Evaporation Cycles." Atmospheric Chemistry and Physics 16(3)
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2021. "Nighttime and Daytime Dark Oxidation Chemistry in Wildfire Plumes: An Observation and Model Analysis of FIREX-AQ Aircraft Data." Atmospheric Chemistry and Physics 21(21)
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From page 92... ...
2017. "Multi-instrument Comparison and Compilation of Non-methane Organic Gas Emissions from Biomass Burning and Impli cations for Smoke-Derived Secondary Organic Aerosol Precursors." Atmospheric Chemistry and Physics 17(2)
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From page 93... ...
2013. "Chemical Insights, Explicit Chemistry, and Yields of Secondary Organic Aerosol from OH Radical Oxidation of Methylglyoxal and Glyoxal in the Aqueous Phase." Atmospheric Chemistry and Physics 13(17)
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From page 94... ...
2020. "Quantification of Organic Aerosol and Brown Carbon Evolution in Fresh Wildfire Plumes." Proceedings of the National Academy of Sciences 117(47)
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2010. "Insights into Secondary Organic Aerosol Formed via Aqueous-Phase Reactions of Phenolic Compounds Based on High Resolution Mass Spectrometry." Atmospheric Chemistry and Physics 10(10)
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From page 96... ...
2018. "Photochemical Cloud Processing of Primary Wildfire Emissions as a Potential Source of Secondary Organic Aerosol." Environmental Science & Technology 52(19)
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From page 97... ...
2013. "Secondary Organic Aerosol Formation from Biomass Burning Intermediates: Phenol and Methoxyphenols." Atmospheric Chemistry and Physics 13(16)
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