Measurements of CH4 Mixing Ratios Within the Planetary Boundary Layer From High Altitude Lidar Remote Sensing

Atmospheric methane is a prominent greenhouse gas that plays an important role in climate change and air quality due to rising emissions and their subsequent impact on radiative forcing and atmospheric composition. Accurate and routine observations of methane over a range of spatial and temporal scales are required to constrain both anthropogenic and biogenic methane emissions. Additionally, delineation between methane in the planetary boundary layer (PBL) and free troposphere is needed to better constrain transport models and increase the accuracy of near surface emissions. During the 2023 Synergistic TEMPO Air Quality Science (STAQS) mission, NASA Langley Research Center’s High-Altitude Lidar Observatory (HALO) was flown on the Gulfstream-III aircraft to provide quantitative air quality and greenhouse gas data over major U.S. cities, including Los Angeles, New York City, Washington DC, and Chicago. The spatiotemporal evolution of column and multi-layer methane, aerosol backscatter, extinction, depolarization, and PBL heights was observed by HALO during morning and afternoon flights. Within this presentation we will discuss several methodologies for apportioning PBL methane relative to the column abundance including traditional cloud slicing methods as well as utilization of the differential absorption lidar (DIAL) method employing aerosol and molecular scattering to retrieve PBL columns in clear air conditions.