The origin of particulate organic carbon in the marine atmosphere as indicated by its stable carbon isotopic composition

Abstract

Organic carbon concentration and isotopic composition were determined in samples of atmospheric particulate matter collected in 1979 at remote marine locations (Enewetak atoll, Sargasso Sea) during the SEAREX (Sea‐Air Exchange) program field experiments. Atmospheric Particulate Organic Carbon (POC) concentrations were found to be in the range of 0.3 to 1.2µg.m −3 , in agreement with previous literature data. The major mass of POC was found on the smallest particles (r<0.5µm). The 13 C/ 12 C of the small particles is close to the one expected (δ 13 C = 26 ± 2‰) for atmospheric POC of continental origin. For all the samples analysed so far, it appears that more than 80% of atmospheric POC over remote marine areas is of continental origin. This can be explained either by long‐range transport of small sized continental organic aerosols or by the production of POC in the marine atmosphere from a vapor phase organic carbon pool of continental origin. The POC in the large size fraction of marine aerosols (<20% of the total concentration) is likely to have a direct marine origin since its carbon isotopic composition is close to the expected value (δ 13 C = −21 ± 2‰) for POC associated with sea‐salt droplets transported to the marine atmosphere.