NPFVERTSTUDY

The formation of 1-nm-sized atmospheric clusters is an important environmental nanoscale process, with field measurements and modeling studies indicating that freshly nucleated particles can contribute significantly to the global population of aerosol and cloud condensation nuclei (Kerminen et al. 2005; Kuang et al. 2009; Lihavainen et al. 2003; Merikanto et al. 2010). While there have been an increasing number of atmospheric cluster measurements from surface-based platforms, very few measurements have been made of the vertically resolved ambient cluster size distribution from aerial platforms. Vertically resolved atmospheric cluster measurements are needed because aerosol formation in the upper troposphere may be a significant source of cloud condensation nuclei (Chen et al. 2018; Wang et al. 2016). Furthermore, these vertically resolved measurements are needed to: • Connect the atmospheric conditions that drive atmospheric new particle formation (NPF) with large-scale boundary-layer transport processes and meteorology, and • Evaluate the extent to which surface-based aerosol measurements are representative of the atmospheric aerosol aloft. Vertically resolved profiles of the atmospheric aerosol cluster concentration and size distribution will be obtained via the deployment of a pair of water-based condensation particle counters (CPCs) on board the ARM Tethered Balloon System (TBS). The water-based CPCs will be modified to detect aerosol down to 3 nm and below according to established protocols (Kuang et al. 2012). Proposed measurements will take place at the Central Facility of the ARM SGP site, which is ideal for studying NPF due to the frequent observations of NPF at the surface as well as NPF observations aloft (Chen et al. 2018; Hodshire et al. 2016). The proposed measurements of the atmospheric aerosol clusters will improve upon the measurements made during previous campaigns (NPFS and HI-SCALE) by extending the aerosol size detection limit down to 3 nm and below, more directly measuring the atmospheric cluster population.

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