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Emissions of NO2, CO, and Formaldehyde from Wildfires

Abstract: The byproducts of wildfires can have a significant impact on global air quality and increase health risk to the general public. Biomass burning byproducts can travel long distances from the source, bringing pollutants into cities far away from the fire and driving atmospheric chemical processes in the region. Satellite observations can provide information on wildfire emissions, complementing air and ground campaigns, and can help validate emission inventories. This research focuses on nitrogen dioxide (NO2), carbon monoxide (CO), and formaldehyde (HCHO) down-plume enhancements and emissions rates from wildfires using high-spatial-resolution TROPOspheric Monitoring Instrument (TROPOMI) satellite measurements. A 1-D advection-diffusion model is used to calculate emissions from distinguishable wildfire plumes, using TROPOMI vertical column densities (VCDs) and aerosol layer height (ALH). The estimated emission rates are compared to those of fires observed by the Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) aircraft campaign obesrvations (summer 2019). The method used in this work creates 4km x 4km grid of binned TROPOMI VCDs in the upwind/downwind direction of the plume and then fits a Gaussian distribution along the binned VCDs, with three standard deviations used to define the lateral boundary of the bins and rotate the grid downwind. The flux of each bin is then calculated with horizontal wind velocity, the area of the box, and the difference in VCD with background levels removed. Wind velocity is defined by determining plume height with the TROPOMI ALH data product and using European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5 reanalysis wind data for that height. The chemical processes within wildfire plumes are complex, e.g. NO2, despite its short lifetime, is capable of long-range transport through nitrous acid (HONO) and peroxyacetyl nitrate (PAN) formation. Increased NO2 concentrations can increase tropospheric ozone (O3), which is not naturally occurring in the troposphere. HCHO, a secondary byproduct of 1 NOx (NO + NO2), is capable, in the presence of volatile organic compounds (VOCs), of producing ozone and atmospheric radicals, such as OH and HO2, which further atmospheric chemistry processes. These atmospheric radicals are also capable of reacting with CO to produce CO2 and ozone. Additionally, HCHO/NOx ratios have also been shown to be indicators of VOC- or NOx-concentration dependence on ozone levels. Our research observes TROPOMI measurements of HCHO, CO, and NO2 in wildfire plumes to investigate correlations between the emissions of each species downwind of the fires.

Host: Eylon Vakrat
Event series  Brewer-Wilson Seminar Series