Dataset: Activities of 210Po and 210Pb in aerosol samples collected on Leg 2 (Hilo, HI to Papeete, French Polynesia) of the US GEOTRACES Pacific Meridional Transect (PMT) cruise (GP15, RR1815) on R/V Roger Revelle from October to November 2018

Aerosol samples were collected by Clifton Buck and colleagues, who were funded separately. Bulk aerosol samples were collected on 12-replicate acid-washed, 47-mm Whatman 41 (W41) ashless filter discs mounted in Advantec-MFS polypropylene open-face filter holders. Three filters with combined filter air volumes of ~360 to 1100 cubic meters were provided for 210Po and 210Pb. Aerosol filters were placed in microwave digestion vessels, spiked with 209Po tracer (1.76 dpm) and 10 mg stable Pb, and totally dissolved in a mixture of concentrated 5 mL of HCl, HNO3, and HF. Sample solutions were centrifuged, evaporated to dryness, redissolved in concentrated HCl, evaporated again, and picked up in 1.5N HCl for plating. Po was plated onto silver discs with heating for 3 hours. Residual Po was removed from the samples by suspending a piece of scrap Ag in them for 5 days, with periodic stirring, after which they were transferred to polycarbonate bottles for storage and ingrowth of additional 210Po. An aliquot of each stored solution was analyzed for Pb concentration by Inductively-Coupled-Plasma Mass Spectroscopy to determine Pb recoveries. Recoveries generally ranged from 83-100% (average 92 ± 6%). A second plating was carried out after ~6 months of storage to determine 210Pb from ingrown 210Po. All activities were corrected as appropriate to the time of sample collection, as described in Rigaud et al. (2013), and complete details are given in Wei (2021). Detector backgrounds and blanks were subtracted from all samples, and blank activities were less than 8% those of the aerosol samples. Errors were propagated using standard error propagation formulas (Rigaud et al., 2013) and included counting errors on sample, background and blank 210Po and 209Po, spiking errors, weighing errors (for water samples) and uncertainty of the 209Po tracer activity. Due to the long time interval between sampling and initial 210Po plating, the ingrowth and decay corrections for 210Po were large. As a consequence, the initial 210Po/210Pb activity ratio in most samples is small and scatters around 0.0 ± 0.2.