Saccharides in summer and winter PM2.5 over Xi'an, Northwestern China: Sources, and yearly variations of biomass burning contribution to PM2.5.

Abstract Saccharides are important constituents in atmospheric aerosols but studies in northwestern China are still very limited. Here, we have measured anhydrosugars (levoglucosan, mannosan and galactosan), primary sugars (glucose, fructose, sucrose and trehalose), and sugar alcohols (arabitol, mannitol, sorbitol and inositol) in ambient PM 2.5 samples during summer and winter in Xi'an city, northwestern China. The abundance of total saccharides showed no clear seasonal variation, but apparent distinctions on the levels of the three categories and individual saccharide compounds were found. Primary sugars and particularly sucrose were dominant in summer. In contrast, levoglucosan was the predominant species in winter, contributing 60% of total saccharides. Source apportionment by positive matrix factorization revealed that airborne pollen was a major source of PM 2.5 associated-saccharides in summer, accounting for 35% of total saccharides; while biomass burning activities contributed to 60% of the winter saccharides. Furthermore, an increasing trend of biomass/biofuel burning contribution to winter PM 2.5 was observed in comparison with previous studies in Xi'an, suggesting a change in emission sources may be underway in northwestern China. Graphical abstract Unlabelled Image Highlights • Sucrose dominates total saccharides during summer while levoglucosan was the dominant species during winter. • Biomass burning emissions are the predominant source of saccharides in winter. • A yearly increase of biomass burning contribution to PM 2.5 during winter was found over Xi'an. [ABSTRACT FROM AUTHOR]