Impact of the 2016 Southeastern US Wildfires on the Vertical Distribution of Ozone and Aerosol at Huntsville, Alabama

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 in order to better match observed aerosol optical depth, fine particulate matter (PM_2.5), 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 November 12 and 13, we estimate that fire emissions contribute 12–32 μg/m³ (44%–70%) to hourly surface PM_2.5 and 7–8 ppb/10 h (30%–37%) to the surface ozone increase (ΔO₃), respectively. Net chemical ozone production (PO₃) is the main contributor to upper-air ozone, which reaches 17–19 ppb/10 h with an estimated 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 ΔO₃ due to fire emissions below 1 km on November 12, while local photochemistry dominates on November 13. 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.