Measuring Atmospheric CO2 Enhancements from Wildfires with a Pulsed IPDA Lidar

Wildfires are a major source of greenhouse gases. Fires were responsible for up to a fifth as much as carbon released in 2019 from burning fossil fuels. The estimates of CO₂ emissions from fires from 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 atmospheric column-averaged CO₂ (XCO₂) retrievals from satellite measurements are significantly degraded by the scattering of smoke in the scene.

NASA Goddard Space Flight Center has developed an integrated-path, differential absorption (IPDA) lidar approach to measure global XCO₂ from space as a candidate for NASA's Active Sensing of CO₂ Emissions over Nights, Days, and Seasons (ASCENDS) mission (Kawa et al., 2018). Measurements of time-resolved laser backscatter profiles from the atmosphere allow this technique to estimate XCO₂ and range to any significant reflective surfaces with precise knowledge of the photon path-length even in the presence of atmospheric scattering (Abshire et al., AMT, 2018).

We demonstrate this measurement capability using airborne lidar measurements from summer 2017 ASCENDS/ABoVE airborne science campaign. During the August 8 return flight from Alaska to California over Vancouver Island, there were dense smoke plumes from fires in the Canadian Rockies. Over this region, the retrievals from our lidar measurements showed ~5 ppm enhancements in XCO₂. For validation, a spiral-down comparison to in situ CO₂ measurements was performed at Moses Lake airport in the central Washington just after the region of XCO₂ enhancement. We have also compared this enhancement with that from the Goddard Parameterized Chemistry Transport Model (PCTM) using the Global Fire Emission Database (GFED) and found the CO2 emissions from the record-breaking wildfires in British Columbia in 2017 were underestimated in GFED4 by about a factor of 2.

The results show that a future spaceborne XCO₂ lidar mission with these capabilities will improve fire emission modeling and carbon flux estimation. More details will be shown in the presentation.