Long-term observations of saccharides in remote marine aerosols from the western North Pacific: A comparison between 1990-1993 and 2006-2009 periods

摘要

Anhydrosugars (galactosan, mannosan and levoglucosan), sugars (xylose, fructose, glucose, sucrose and trehalose) and sugar alcohols (erythritol, arabitol, mannitol and inositol) were measured in the aerosol samples collected in a remote island (Chichi-Jima, Japan) in the western North Pacific from 1990 to 1993 and from 2006 to 2009. Total concentrations of anhydrosugars, the biomass burning tracers, were 0.01-5.57 ng m~(-3) (average 0.76 ng m~3) during 1990-1993 versus 0.01-7.19 ng m~(-3) (0.64 ng m~(-3)) during 2006-2009. Their seasonal variations were characterized by winter/spring maxima and summer/ fall minima. Such a seasonal pattern should be caused by the enhanced long-range atmospheric transport of biomass burning products and terrestrial organic matter (such as higher plant detritus and soil dust) from the Asian continent in winter/spring seasons, when the westerly or winter monsoon system prevails over the western North Pacific. Sugars and sugar alcohols showed different seasonal patterns. The monthly mean concentrations of erythritol, arabitol, mannitol, inositol, fructose, glucose and trehalose were found to be higher in spring/summer and lower in fall/winter during both 1990-1993 and 2006-2009 periods, indicating an enhanced biogenic emission of aerosols in warm seasons. Interestingly, saccharides showed a gradual decrease in their concentrations from 1991 to 1993 and an increase from 2006 to 2009. In addition, the monthly averaged concentrations of sugars and sugar alcohols showed maxima in early summer during 1990-1993, which occurred about 1-2 months earlier than those during 2006-2009. Such a clear seasonal shift may be attributable to the changes in the strength of westerly and trade wind systems during two periods.