Nighttime and daytime dark oxidation chemistry in wildfire plumes: an observation and model analysis of FIREX-AQ aircraft data
<p>Wildfires are increasing in size across the western US, leading to increases in human smoke exposure and associated negative health impacts. The impact of biomass burning (BB) smoke, including wildfires, on regional air quality depends on emissions, transport, and chemistry, including oxida...
Guardado en:
| Autores principales: | , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , |
|---|---|
| Formato: | article |
| Lenguaje: | EN |
| Publicado: |
Copernicus Publications
2021
|
| Materias: | |
| Acceso en línea: | https://doaj.org/article/02f70af05f9e4872ba632c70b6749087 |
| Etiquetas: |
Agregar Etiqueta
Sin Etiquetas, Sea el primero en etiquetar este registro!
|
| Sumario: | <p>Wildfires are increasing in size across the western US, leading to
increases in human smoke exposure and associated negative health impacts.
The impact of biomass burning (BB) smoke, including wildfires, on regional
air quality depends on emissions, transport, and chemistry, including
oxidation of emitted BB volatile organic compounds (BBVOCs) by the hydroxyl
radical (OH), nitrate radical (<span class="inline-formula">NO<sub>3</sub></span>), and ozone (<span class="inline-formula">O<sub>3</sub></span>). During the
daytime, when light penetrates the plumes, BBVOCs are oxidized mainly by
<span class="inline-formula">O<sub>3</sub></span> and OH. In contrast, at night or in optically dense plumes, BBVOCs
are oxidized mainly by <span class="inline-formula">O<sub>3</sub></span> and <span class="inline-formula">NO<sub>3</sub></span>. This work focuses on the
transition between daytime and nighttime oxidation, which has significant
implications for the formation of secondary pollutants and loss of nitrogen
oxides (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M6" display="inline" overflow="scroll" dspmath="mathml"><mrow><mrow class="chem"><msub><mi mathvariant="normal">NO</mi><mi>x</mi></msub></mrow><mo>=</mo><mrow class="chem"><mi mathvariant="normal">NO</mi></mrow><mo>+</mo><mrow class="chem"><msub><mi mathvariant="normal">NO</mi><mn mathvariant="normal">2</mn></msub></mrow></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="85pt" height="13pt" class="svg-formula" dspmath="mathimg" md5hash="f0add4bbe2151ecfa7cd944e28fa7e9e"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-21-16293-2021-ie00001.svg" width="85pt" height="13pt" src="acp-21-16293-2021-ie00001.png"/></svg:svg></span></span>) and has been understudied. We present
wildfire plume observations made during FIREX-AQ (Fire Influence on Regional
to Global Environments and Air Quality), a field campaign involving multiple
aircraft, ground, satellite, and mobile platforms that took place in the
United States in the summer of 2019 to study both wildfire and agricultural
burning emissions and atmospheric chemistry. We use observations from two
research aircraft, the NASA DC-8 and the NOAA Twin Otter, with a detailed
chemical box model, including updated phenolic mechanisms, to analyze smoke
sampled during midday, sunset, and nighttime. Aircraft observations suggest
a range of <span class="inline-formula">NO<sub>3</sub></span> production rates (0.1–1.5 <span class="inline-formula">ppbv h<sup>−1</sup></span>) in plumes
transported during both midday and after dark. Modeled initial instantaneous
reactivity toward BBVOCs for <span class="inline-formula">NO<sub>3</sub></span>, OH, and <span class="inline-formula">O<sub>3</sub></span> is 80.1 %, 87.7 %, and 99.6 %, respectively. Initial <span class="inline-formula">NO<sub>3</sub></span> reactivity is 10–<span class="inline-formula">10<sup>4</sup></span>
times greater than typical values in forested or urban environments, and
reactions with BBVOCs account for <span class="inline-formula">>97</span> % of <span class="inline-formula">NO<sub>3</sub></span> loss in
sunlit plumes (<span class="inline-formula"><i>j</i>NO<sub>2</sub></span> up to <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M16" display="inline" overflow="scroll" dspmath="mathml"><mrow><mn mathvariant="normal">4</mn><mo>×</mo><msup><mn mathvariant="normal">10</mn><mrow><mo>-</mo><mn mathvariant="normal">3</mn></mrow></msup><mspace linebreak="nobreak" width="0.125em"/><mrow class="unit"><msup><mi mathvariant="normal">s</mi><mrow><mo>-</mo><mn mathvariant="normal">1</mn></mrow></msup></mrow></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="59pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="75fd83c3fc1e7202c7ef5bff89e9ecd3"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-21-16293-2021-ie00002.svg" width="59pt" height="14pt" src="acp-21-16293-2021-ie00002.png"/></svg:svg></span></span>), while
conventional photochemical <span class="inline-formula">NO<sub>3</sub></span> loss through reaction with NO and
photolysis are minor pathways. Alkenes and furans are mostly oxidized by OH
and <span class="inline-formula">O<sub>3</sub></span> (11 %–43 %, 54 %–88 % for alkenes; 18 %–55 %, 39 %–76 %, for furans, respectively), but phenolic oxidation is split between
<span class="inline-formula">NO<sub>3</sub></span>, <span class="inline-formula">O<sub>3</sub></span>, and OH (26 %–52 %, 22 %–43 %, 16 %–33 %,
respectively). Nitrate radical oxidation accounts for 26 %–52 % of
phenolic chemical loss in sunset plumes and in an optically thick plume.
Nitrocatechol yields varied between 33 % and 45 %, and <span class="inline-formula">NO<sub>3</sub></span>
chemistry in BB plumes emitted late in the day is responsible for 72 %–92 % (84 % in an optically thick midday plume) of nitrocatechol
formation and controls nitrophenolic formation overall. As a result,
overnight nitrophenolic formation pathways account for <span class="inline-formula">56 <i>%</i>±2 <i>%</i></span> of
<span class="inline-formula">NO<sub><i>x</i></sub></span> loss by sunrise the following day. In all but one overnight plume
we modeled, there was remaining <span class="inline-formula">NO<sub><i>x</i></sub></span> (13 %–57 %) and BBVOCs
(8 %–72 %) at sunrise.</p> |
|---|