Aerosol processes and interactions with cloud play an important role in the climate system and radiative budget; they are the largest individual source of uncertainty in assessing the Earth’s radiative balance. To constrain aerosol’s climate impacts, it is critical to understand the vertical distributions of aerosol compositions. Organic material accounts for about 20 – 80% of total aerosol mass in the atmosphere and is known to play a key role in aerosol processes and cloud formation. Although organic species have much smaller hygroscopicity than inorganics in general, important compounds such as organosulfates and organonitrates have been reported to be quite hygroscopic owing to the hydrophilic sulfate and nitrate functionalities. Therefore, organosulfates and organonitrates are crucial constituents in aerosol transformation and cloud formation processes. In prior research, characterization of organosulfates and organonitrates have been mostly carried out for aerosols collected at ground level. However, they have also been shown to be in substantial amount in cloud water, but their vertical distribution is not well understood. Hence, it is important to understand how organosulfates and organonitrates in aerosols are distributed, transformed, participate in aqueous-phase processes, and interact with clouds with elevated altitudes.
In the proposed FICUS project, we aim to carry out a field campaign at the Southern Great Plains (SGP) ARM site and utilize the tethered balloon systems (TBS) to collect vertically-resolved aerosol samples during a few flights in the winter, summer, and fall of 2024. During the flights, aerosol samples will be collected from ground level to up to ~ 1 km altitude. The SGP ARM site is chosen because recent studies have successfully deployed the TBS at the site and collected aerosol samples. Ground-level measurements at the SGP site also showed aerosol composition substantially comprised of organosulfates and organonitrates due to local agricultural activities. Moreover, the long-term real-time measurements of aerosol concentrations, bulk composition, and hygroscopicity at the ground level will nicely complement the proposed field campaign. The collected samples will be analyzed using the Environmental Transmission Electron Microscopy (TEM) and the nanospray desorption electrospray ionization coupled to high-resolution mass spectrometry (nano-DESI-HRMS) available at the EMSL facility and the ion mobility spectrometry time-of-flight mass spectrometry (IMS-MS) in the PI’s laboratory to characterize organosulfates and organonitrates in the collected aerosols on the molecular and isomeric levels. The analysis will provide vertical distributions of organosulfates and organonitrates, hence helping examine the hypothesized aerosol processes such as organosulfate formation through multiphase reactions and organonitrate hydrolysis in aqueous aerosols with increased elevation and reveal the different aerosol compositions in ground level and upper troposphere near clouds. The results could provide key insights into aerosol-cloud interaction affected by these two classes of hygroscopic species and help constrain aerosols’ climate impacts.