The impacts of wildfires on ozone production and boundary layer dynamics in California's Central Valley
<p>We investigate the role of wildfire smoke on ozone photochemical production (P(O<span class="inline-formula"><sub>3</sub></span>)) and atmospheric boundary layer (ABL) dynamics in California's Central Valley during June–September from 2016 to 2020. Wil...
| Main Authors: | , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2022-07-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/22/9681/2022/acp-22-9681-2022.pdf |
| Summary: | <p>We investigate the role of wildfire smoke on ozone
photochemical production (P(O<span class="inline-formula"><sub>3</sub></span>)) and atmospheric boundary layer (ABL)
dynamics in California's Central Valley during June–September from 2016 to 2020.
Wildfire events are identified by the Hazard Mapping System (HMS) and the
Hybrid Single Particle Lagrangian Integrated Trajectory Model (HYSPLIT). Air
quality and meteorological data are analyzed from 10 monitoring sites
operated by the California Air Resources Board (CARB) across the Central
Valley. On average, wildfires were found to influence air quality in the
Central Valley on about 20 % of the total summer days of the study. During
wildfire-influenced periods, maximum daily 8 h averaged (MDA8) O<span class="inline-formula"><sub>3</sub></span> was
enhanced by about 5.5 ppb or 10 % of the median MDA8 (once corrected for
the slightly warmer temperatures) over the entire valley. Overall, nearly
half of the total exceedances of the National Ambient Air Quality Standards
(NAAQS) where MDA8 O<span class="inline-formula"><sub>3</sub></span> <span class="inline-formula"><i>></i></span> 70 ppb occur under the influence of
wildfires, and approximately 10 % of those were in exceedance by 5 ppb or
less indicating circumstances that would have been in compliance with the
NAAQS were it not for wildfire emissions. The photochemical ozone production
rate calculated from the modified Leighton relationship was also found to be
higher by 50 % on average compared with non-fire periods despite the average
diminution of <span class="inline-formula"><i>j</i>(NO<sub>2</sub>)</span> by
<span class="inline-formula">∼</span> 7 % due to the shading effect of the wildfire smoke
plumes. Surface heat flux measurements from two AmeriFlux sites in the
northern San Joaquin Valley show midday surface buoyancy fluxes decrease by
30 % on average when influenced by wildfire smoke. Similarly, afternoon
peak ABL heights measured from a radio acoustic sounding system (RASS)
located in Visalia in the southern San Joaquin Valley were found to decrease
on average by 80 m (<span class="inline-formula">∼</span> 15 %) with a concomitant reduction of
downwelling shortwave radiation of 54 Wm<span class="inline-formula"><sup>−2</sup></span>, consistent with past
observations of the dependence of boundary layer heights on insolation.</p> |
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| ISSN: | 1680-7316 1680-7324 |