Behavior of Trace Metals in Marine Aerosols Over the Central North Pacific

Crustal and anthropogenic aerosols are transported from the Asian continent to the North Pacific. They influence chemical composition and biological activity in the marine surface layer. Thus, it is important to know the behaviors of chemical composition of aerosols for clarifying the linkage between surface ocean and lower atmosphere. The aim of this study is to determine the trace metals in marine aerosols over the central North Pacific during the summer and find out the typical concentration levels, the distribution pattern of these trace metals and their sources. Aerosol samples were collected every 12 hours on the R/V Hakuho-Maru KH05-2 cruise along the line of 160° W from 10.2° S to 53.6° N (8 August to 21 September 2005). They were segregated into coarse (D>2.5 μm) and fine particles (D<2.5 μm). Chemical components (Na, Mg, Al, K, Ca, Mn, Fe, Zn, Sr, SO4 2-) were determined by ICP-AES and IC. The mean concentrations in total particulate Fe, Mn, Zn and nss-SO4 2- were 14±11, 0.70±0.77, 1.9±2.4, and 450±310 ng m-3, respectively. Around 7° S, the peak concentrations in total particulate Zn and Mn were obtained to be 1.9 and 6.3 ng m-3, respectively. Their ratios of Mn/Fe (0.30) and Zn/Fe (0.65) were approximately four times higher than the mean ratios of Mn/Fe (0.08) and Zn/Fe (0.15), respectively. These ratios were approximately 15 and 700 times higher than crustal composition, respectively. According to the 7-day backward trajectory analysis, the air mass was originated from the region around Tahiti and/or South America. Thus, it was suggested that enriched trace metals such as Mn and Zn were emitted from some unique sources. High concentrations of particulate Fe and nss-SO4 2- were observed around Hawaii Islands. Simultaneously, high ozone concentration of 24 ppbv was observed and two times higher than the background concentration of 13 ppbv. By the backward trajectory analysis, air mass was from Hawaii Islands and may cause high concentrations by the island sources such as soils and volcano.