Towards Accurately Measuring Atmospheric CO2 Enhancements from Wildfires an Airborne Demonstration with a Pulsed Multiwavelength Lidar

Wildfires are a major source of greenhouse gases. Recent western wildfires have had profound impacts on air quality and have emitted a record amount of CO2. The CO2 emissions from fires estimated with fire emission models or databases have large discrepancies and uncertainties. Ground-based and airborne measurements of fire emissions are few and difficult to obtain, and CO2 retrievals from passive spectrometers on satellites are significantly degraded by the scattering effects of smoke in the scene. NASA Goddard Space Flight Center has developed the CO2 Sounder lidar, an integrated-path, differential absorption lidar approach to measure global atmospheric column-averaged CO2 (XCO2) from space as a candidate for NASAs planned ASCENDS mission. This pulsed laser approach measures CO2 absorption at multiple wavelengths across the CO2 line centered at 1572.335 nm. Its simultaneous measurements of height-resolved laser backscatter profiles allow it to accurately estimate XCO2 through fire smoke plumes. We have demonstrated this capability using the lidar measurements from the summer 2017 ASCENDS/ABoVE airborne campaign. On July 21, a flight was conducted in the Central Valley, CA. Significant CO2 enhancements in lidar XCO2 retrievals were detected in the smoke plumes blown from the Detwiler wildfires near the Yosemite National Park. During the August 8 flight over Vancouver Island, there were dense smoke plumes from the large wildfires in the Canadian Rockies. The aircraft overflow this region at a 9-km altitude, the lidar XCO2 retrievals showed an average of 4 ppm enhancement. We validated the XCO2 retrievals against those computed from the vertical profiles of CO2 made with in situ sensors during the spiral maneuvers. We compared the measured enhancements with those from the Goddard chemistry transport models using the Global Fire Emissions Database and the Quick Fire Emissions Dataset. The comparison results suggest that the CO2 emissions for these wildfires were underestimated by more than a factor of 2. This is the first use of lidar to remotely sense CO2 enhancements from large wildfires. The results show that future airborne campaigns and spaceborne missions with this capability could significantly reduce the uncertainty in emissions modeling and can further benefit estimates of carbon fluxes.