EC-14. Investigating the effects of smoke masking on satellite retrievals of carbon monoxide in fresh biomass burning plumes

Abstract
The Biomass Burning Fluxes of Trace Gases and Aerosols (BB-FLUX) field campaign was carried out during the summer of 2018 with the primary goal of quantifying emission fluxes of trace gases by mass balance of actual wildfires. To characterize these fluxes, the University of Colorado Airborne Solar Occultation Flux (CU AirSOF) instrument was flown below biomass burning plumes to measure vertical trace gas columns, such as CO, along the direct solar beam at mid-infrared wavelengths. The Sentinel-5 Precursor satellite, which houses the TROPOspheric Monitoring Instrument (TROPOMI), provides a unique opportunity to quantify and validate emission fluxes from space. Through daily observations of area sources such as wildfires, TROPOMI provides measurements of trace-gas maps in the Ultraviolet-Visible (UV-Vis.) and shortwave-IR (SWIR) spectral regimes (e.g. CO, using the first overtone vibrational band). We first present radiative transfer modeling (RTM) calculations of air mass factors (AMFs) from both the aircraft and satellite perspectives. In the SWIR, TROPOMI measures backscattered solar photons, which we show through RTM simulations to be advantageous in reducing aerosol effects as compared to the UV-Vis. regimes. To evaluate this effect on satellite remote sensing instrumentation, selected research flights (RFs) from BB-FLUX, where observations were coincident spatially and temporally within ~1 hour of the TROPOMI overpass, are selected for comparison. Since CU AirSOF measures a vertical column density (VCD) along the direct solar beam, and TROPOMI also fits a VCD, integrated differential vertical column densities (dVCDs), are calculated across transects of the plume and compared. In building the foundation for divergence flux calculations, the FLEXible PARTicle (FLEXPART) dispersion model is used to bridge any spatial and temporal differences between the measurement platforms. Once integrated dVCDs are calculated, a priori information on profile shapes from BB-FLUX and TROPOMI are considered. The TROPOMI radiative transfer model calculates a surface averaging kernel (AVK) and can be used as a smoothing mechanism to correct the observed CO vertical column density (VCD) in altitude-binned partial columns. These AVKs are assessed relative to biomass burning plume profile characterizations performed during BB-FLUX. In situ profiles of CO, CO2, or aerosol concentrations are used to leverage information on the vertical profile shapes of these plumes. In combination with the prior RTM calculations and integrated dVCDs, differences between the satellite and aircraft measurement geometries across spectral regimes are explored to understand the effects of smoke masking on the satellite retrieval.