Impact of the 2016 Southeastern U.S. Wildfires on the Vertical
Distribution of Ozone and Aerosol at Huntsville, Alabama
Abstract
We present an integrated analysis of measurements from ozonesonde, ozone
(O3) Differential Absorption Lidar (DIAL), ceilometer, surface monitors,
and space-borne observations in conjunction with the regional chemical
transport model Weather Research and Forecast Model with Chemistry
(WRF-Chem) to investigate the effect of biomass burning emissions on the
vertical distribution of ozone and aerosols during an episode of the
2016 Southeastern United States wildfires. The ceilometer and DIAL
measurements capture the vertical extent of the smoke plumes affecting
the surface and upper air over Huntsville, AL. The model evaluation
results suggest a scaling factor of 3-4 for the wildfire aerosol
emissions to better match observed aerosol optical depth (AOD), fine
particulate matter (PM2.5), and DIAL aerosol extinction. We use the
scaled emissions together with WRF-Chem tendency diagnostics to quantify
the fire impacts and characterize the processes affecting the vertical
ozone budget downstream of the wildfires. During the daytime at
Huntsville on 12 and 13 November, we estimate that fire emissions
contribute 12-32 μg/m3 (44-70%) to hourly surface PM2.5 and 7-8 ppb/10
hrs (30-37%) to the surface ozone increase (∆O3), respectively. Net
chemical ozone production (PO3) is the main contributor to upper-air
ozone, which reaches 17-19 ppb/10 hrs with 14-25% contribution from
fire sources. Vertical mixing and advection are the major drivers of
changes in surface ozone. Model analysis indicates that advection
dominates fire-related ∆O3 below 1 km on 12 November, while local
photochemistry dominates on 13 November. These results quantify the
different mechanisms through which fires can influence the vertical
ozone budget and point out uncertainties in fire inventories that need
to be addressed in light of the increasing role of wildfires on air
quality.