Deliquescence of nascent Sea Spray Aerosol (SSA) measured using VH-TDMA during the Surface Ocean Aerosol Production (SOAP) study to the Chatham Rise onboard the RV Tangaroa in 2012

The SOAP voyage examined air-sea interactions over the productive waters of the Chatham Rise, east of New Zealand onboard the RV Tangaroa (New Zealand National Institute of Water and Atmospheric Research, Wellington) from February 12 to March 7 (Law et al., 2017: doi:10.5194/acp-17-13645-2017). 23 seawater samples were collected throughout the voyage for the purpose of generating nascent SSA. Seawater samples were collected from the ocean surface during workboat operations (approximately 10 cm depth) or from the mixed layer (3 - 12 m depth, always less than the measured mixed layer depth) or deep water samples. Surface samples were collected in prewashed 5L PTFE bottles, subsurface measurements were colected in Niskin bottles onboard a CTD rosette. Nascent SSA was generated in-situ in a 0.45 m3 cylindrical polytetrafluoroethylene chamber housing four sintered glass filters with porosities between 16 and 250 μm (Cravigan et al., 2019: https://doi.org/10.5194/acp-2019-797). Dried and filtered compressed air was passed through the glass filters at a flow rate of 15.5 ± 3 L/min and resulting SSA was sampled from the headspace of the chamber. The volatility and hygroscopicity of nascent SSA was determined with a volatility and hygroscopicity tandem differential mobility analyser (VH-TDMA) (Johnson et al., 2004: doi:10.1016/j.jaerosci.2003.10.008, 2008: doi:10.1016/j.jaerosci.2008.05.005). A diffusion drier was used to dry the sample flow to 20 ± 5 % RH prior to characterisation by the VH-TDMA. The VH-TDMA used two TSI 3010 condensation particle counters. The aerosol sample flow rate for each scanning mobility particle sizer was 1 L/min, resulting in a total inlet flow of 2 L/min, the sheath flow for the pre-DMA, V-DMA and H-DMA were 11, 6 and 6 L/min, respectively. The dependence of HGF on RH at ambient temperature was measured for one water sample (workboat 9) to provide the deliquescence relative humidity (DRH). All VH-TDMA data were inverted using the TDMAinv algorithm (Gysel et al., 2009: doi:10.1016/j.jaerosci.2008.07.013). The seawater chlorophyll-a concentration was measured by filtering 2 litres of sample water onto GF/F Whatman filters, with immediate freezing in liquid nitrogen and subsequent analysis within 3 months of collection. […]