The Impacts of Wildfires on Ozone Production and Boundary Layer Dynamics
in California's Central Valley
Abstract
We investigate the role of wildfire smoke on ozone photochemical
production (P(O3)) and atmospheric boundary layer (ABL)
dynamics in California’s Central Valley during June-September,
2016-2020. Wildfire events are identified by the Hazard Mapping System
(HMS) and Hybrid Single Particle Lagrangian Integrated Trajectory Model
(HYSPLIT). Air quality and meteorological data are acquired from 10
monitoring sites operated by the California Air Resources Board (CARB)
across the Central Valley. During wildfire influenced periods, maximum
daily 8h averaged (MDA8) O3 was enhanced by about 5 ppb
(~10%) across the entire valley after the temperature
correction. The photochemical ozone production rate calculated from a
modified Leighton relationship was also found to be higher by 35% on
average compared to non-fire periods despite the average diminution of
by ~7% due to the shading effect of the wildfire
plumes. Furthermore, the in-situ ozone production rates are found to be
elevated due to an increase of both peroxyl radicals
(~24%) and NO (~11%). 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. Further, ABL height measured from a
radio acoustic sounding system (RASS) located in Visalia in the Southern
San Joaquin Valley were found to decrease 80 m and virtual potential
temperatures in ABL are higher on average by ~1.5 K when
wildfire smoke is present. The increased temperature is likely the
result of shortwave-radiation absorption by the additional aerosols in
the wildfire smoke.