Terrestrial lipid biomarkers in marine aerosols over the western North Pacific during 1990-1993 and 2006-2009

Terrestrial lipid biomarkers are one of the key tracers in the studies of atmospheric aerosols. Here, we investigated such organic compounds in marine aerosols collected at Chichijima Island, the western North Pacific for two 4-year periods: 1990-1993 and 2006-2009. A homologous series of lipid biomarkers including C-18-C-37 n-alkanes, C-9-C-34 fatty acids, and C-14-C-35 fatty alcohols were determined by gas chromatography/mass spectrometry (GC/MS). The atmospheric levels of these tracers increased from 1990-1993 to 2006-2009. Their seasonal trends were clearly characterized by winter-spring maxima and summer-fall minima. The relative abundance of the high-molecular-weight (HMW) n-alkanes (C-25-C-37) and n-alcohols (C-20-C-35) in total HMW lipids peaked in winter and winter/fall, respectively, whereas those of HMW fatty acids (C-20-C-34) peaked in summer. Air-mass backward trajectory analyses suggest that the Asian continent, Southeast Asia including tropical regions, and the Central Pacific are the main source regions. The seasonal shift and distribution of the carbon preference index and average chain length for the HMW lipids were controlled by the changes in climatic factors and source regions. The higher abundance of terrestrial lipids during 2006-2009 than 1990-1993 indicates a higher emission from terrestrial plantation in the 2000s than in the early 1990s in upwind regions of East Asia. Furthermore, HMW lipid compounds exhibited much stronger positive correlations with levoglucosan, a biomass-burning tracer, during 2006-2009 than 1990-1993, suggesting that biomass-burning emissions contributed more significantly in this century. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The study investigated terrestrial lipid biomarkers in marine aerosols collected at Chichijima Island in the western North Pacific for two 4-year periods. The results showed an increase in atmospheric levels of these tracers from 1990-1993 to 2006-2009, with seasonal trends characterized by winter-spring maxima and summer-fall minima. The main source regions of HMW lipids were identified as the Asian continent, Southeast Asia, and the Central Pacific, with stronger positive correlations observed between HMW lipid compounds and levoglucosan during 2006-2009, suggesting a significant contribution from biomass-burning emissions in this century.