Fatty acids in the marine atmosphere: Factors governing their concentrations and evaluation of organic films on sea‐salt particles

Abstract

Fatty acids (C 14 –C 32 ) in the marine boundary layer were measured in aerosols that were collected over the northern North Pacific from October 1996 to June 1997. Concentrations of lower molecular weight (C 14 –C 19 ) saturated fatty acids (LFAs, 0.8–24 ng m −3 ) showed a positive correlation with sea‐salt concentrations, suggesting that LFAs are released from the ocean surface to the atmosphere with sea‐salt particles. The averaged ratios of [LFAs] air /[sea salt] in autumn, winter, spring and summer seasons were 1.8 (±1.3) × 10 −4 , 2.1 (±1.3) × 10 −4 , 3.7 (±2.9) × 10 −4 , and 4.6 (±1.8) × 10 −4 , respectively. The results indicate the seasonal variation of the sea‐to‐air flux of LFAs relative to that of sea salt with a maximum in spring to summer. The enhanced LFA flux was consistent with the satellite images of chlorophyll a over the northern North Pacific, which showed high biological productivity from spring to summer. On the basis of the ratios of [LFAs] air /[sea salt], relative humidity, and modeled size distribution of sea‐salt particles, the coverage of LFAs on sea‐salt particles was estimated to range from 0.3 to 14%. This study suggests that the coverage of fatty acids, together with other film‐forming materials, may have a significant effect on the physicochemical properties of aerosols, which may be affected by the high biological productivity in the high latitudinal ocean.