Vertical Accumulation of Ozone and Aerosol during the 2016 Southeastern
U.S. Wildfires
Abstract
The vertical accumulation of ozone and aerosol during an episode of the
2016 Southeastern United States Wildfires is analyzed by integrating a
regional chemical transport model with ozonesonde, O$_3$ Differential
Absorption Lidar (DIAL), ceilometer, surface monitors, and satellite
products. The results indicate that measurements capture the vertical
extent of the smoke plumes affecting the surface and upper air over
Huntsville, AL, and also the enhanced ozone lamina in the plumes.
Sensitivity simulations and tendency diagnostics characterize the
chemical and physical processes affecting the vertical profiles
downstream of the wildfires. The model results show that the net
chemical ozone production (PO$_3$) dominates the daytime ozone
accumulation by up to 19 ppb/10 hrs in the upper air over Huntsville. At
the surface, the negative PO$_3$ is offset by positive O$_3$
contributions from vertical mixing and advection. Fire emissions
increase the vertical ozone by affecting local chemical reactions,
transportation, and vertical exchange. The dominant processes exhibit
daily, diurnal, and vertical variability. Quantitatively, fire emissions
increase the daytime positive PO$_3$ by up to 25\% in
the upper air, and increase the daytime PM2.5 by up to
77\%. The capability of the regional model for
reproducing the observations is explored. Increasing the fire aerosol
emissions improves the model performance on domain-averaged PM2.5. The
model captures the well-mixed aerosol in the boundary layer but fails to
fully reproduce the densest plumes seen in the DIAL and satellite. The
discrepancies are associated with poor satellite observing condition due
to clouds and with uncertainties in emission inventories.