Characterization of Organic Aerosol across the Global Remote Troposphere: A comparison of ATom measurements and global chemistry models

Abstract

Abstract. The spatial distribution and properties of submicron organic aerosols (OA) are among the key sources of uncertainty in our understanding of aerosol effects on climate. Uncertainties are particularly large over remote regions of the free troposphere and Southern Ocean, where very little data has been available, and where OA predictions from AeroCom Phase II global models span a factor of 400–1000, greatly exceeding the model spread over source regions. The (nearly) pole-to-pole vertical distribution of non-refractory aerosols was measured with an aerosol mass spectrometer onboard the NASA DC8 aircraft as part of the Atmospheric Tomography (ATom) mission during the northern hemisphere summer (August 2016) and winter (February 2017). This study presents the first extensive characterization of OA mass concentrations and their level of oxidation in the remote atmosphere. OA and sulfate are the major contributors by mass to submicron aerosols in the remote troposphere, together with sea salt in the marine boundary layer. Sulfate was dominant in the lower stratosphere. OA concentrations have a strong seasonal and zonal variability, with the highest levels measured in the summer and over the regions influenced by the biomass burning from Africa (up to 10 μg sm−3). Lower concentrations (~ 0.1–0.3 μg sm−3) are observed in the northern mid- and high-latitudes and very low concentrations (