Geographical distribution and sources of phosphorus in atmospheric aerosol over the North Pacific Ocean

Abstract

Atmospheric aerosol samples with two size fractions (Da ≤ 2.5 μm and Da ≥ 2.5 μm) were collected in the subtropical region of the western North Pacific (WNP) and over the central North Pacific (CNP) Ocean in summer and geographical distributions of particulate concentrations of total phosphorus (TP), water soluble fraction of phosphorus, and tracer elements (Fe, Zn, Na) were investigated. Average concentrations (in ng m−3) of TP, Fe, Zn, Na in the WNP region were 7.3 ± 4.3, 16.2 ± 17.1, 5.5 ± 7.5, and 1450 ± 700, while they were 2.5 ± 1.2, 5.9 ± 5.1, 0.9 ± 1.2, and 1480 ± 610 along the 160°W line in the CNP, respectively. Source apportionment using the tracer elements exhibited that contribution of anthropogenic source was estimated to be 38% and 18%, while that of crustal source was estimated to be about 5% for both WNP and CNP regions, respectively. Oceanic source was estimated to have a little contribution. Half or less fraction of the TP could be accounted for by the anthropogenic and crustal sources. Water solubility of the TP was found to be higher in the WNP region than the CNP region. The similar fractions of water soluble and anthropogenic contribution to the TP found in both WNP and CNP regions suggested that anthropogenic phosphorus was water soluble and dominant in the WNP region, although the unaccounted fraction occupied a large portion of the TP (47% and 76% for WNP and CNP, respectively) as insoluble form.