Compositional Analysis of Cloud Droplet Residuals by High Resolution Time-of-Flight Aerosol Mass Spectrometry: A CAMP2Ex Case Study

There is a need to understand the role of biomass burning events on air quality and cloud formation, not only near the emission source, but in the transported aged emissions as well. Determining the chemical composition and carbon oxidation state of sub-cloud aerosols and their corresponding cloud droplet residuals helps us further understand the overall formation of clouds and the corresponding effect on the radiative budget of the atmosphere. The Cloud, Aerosol and Monsoon Processes-Philippines Experiment (CAMP2Ex) is a collaborative field campaign between NASA and the Philippines research community that flew during the 2019 southwest monsoon season. One of its primary focuses was to characterize aerosol and cloud microphysics in the study region utilizing a complex suite of instrumentation on the NASA P-3B aircraft. Here, we present a case study examining on-line High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) data from CAMP2Ex. This specific flight was conducted on 15 September 2019 (UTC) over the Sulu Sea targeting biomass burning aerosol originating from the Borneo region. The HR-ToF-AMS sampled from a forward-facing isokinetic inlet for the majority of the flight, but was switched to sample from a Counter-Flow Virtual Impactor (CVI) inlet when passing through clouds in order to characterize cloud droplet residual composition. Clouds sampled during the flight were a mixture of shallow marine cumulus (i.e., with cloud tops reaching approximately 1 km) and a more-developed convective cell reaching 4-5 km altitude. This sampling set-up allows us to observe the effects of cloud processing on the chemical composition of biomass burning organic aerosol and to determine if altitude and spatial variability play a role in compositional differences during the flight.