Aerosol characteristics at the Southern Great Plains siteduring the HI-SCALE campaign

Abstract. Large uncertainties exist in global climate model predictions of radiative forcing due to insufficient understanding and simplified numerical representation of cloud formation and cloud-aerosol interactions. The Holistic Interactions of Shallow Clouds, Aerosols and Land Ecosystems (HI-SCALE) campaign was conducted near the DOE's Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site in north-central Oklahoma to provide a better understanding of land-atmosphere interactions, aerosol and cloud properties, and the influence of aerosol and land-atmosphere interactions on cloud formation. The HI-SCALE campaign consisted of two Intensive Observational Periods (IOPs) (April–May, and August–September, 2016), during which coincident measurements were conducted both on the G-1 aircraft platform and at the SGP ground site. In this study we focus on the observations at the SGP ground site. An Aerodyne HR-ToF Aerosol Mass Spectrometer (AMS) and an Ionicon Proton-Transfer-Reaction Mass Spectrometer (PTR-MS) were deployed, characterizing chemistry of non-refractory aerosol and trace gases, respectively. Contributions from various aerosol sources, including biogenic and biomass burning emissions, were retrieved using factor analysis of the AMS data. In general, the organic aerosols at the SGP site was highly oxidized, with OOA identified as the dominant factor for both the spring and summer IOP though more aged in spring. Cases of IEPOX SOA and biomass burning events were further investigated to understand additional sources of organic aerosol. Unlike other regions largely impacted by IEPOX chemistry, the IEPOX SOA at SGP was more highly oxygenated, likely due to the relatively weak local emissions of isoprene. Biogenic emissions appear to largely control the formation of OA during HI-SCALE campaign. Potential HOM (highly-oxygenated molecule) chemistry likely contributes to the highly-oxygenated feature of aerosols at the SGP site, with impacts on new particle formation and global climate.