Polar organic marker compounds in atmospheric aerosol in the Po Valley during the Supersito campaigns - Part 2: Seasonal variations of sugars

摘要

Four intensive experimental campaigns were conducted in the Po Valley (Northern Italy) in different seasons through the years 2012 and 2013, in the framework of the "Supersito" project. As a part of a study on polar tracers in atmospheric PM_(2.5), the present paper describes the abundances and temporal variations of sugars, as primary biogenic biomarkers, being the major form of photosynthetically assimilated carbon in the biosphere. The study includes primary saccharides (glucose, sucrose, arabinose, galactose and mycose), sugar alcohols (arabitol and mannitol) and anhydrosugars (levoglucosan, gal-actosan and mannosan). Strong seasonality was observed with total sugars concentration nearly 10 times higher in the cold seasons (mean 377 ng m~(-3)) than in summer/spring (mean 36 ng m~(-3)). Also sugar composition profiles varied seasonally, being dominated by anhydrosugars in fall and winter, i.e., levoglucosan (mean 271 ng m~(-3)), followed by mannosan (mean 53 ng m~(-3)) and galactosan (mean 29 ng m~(-3)). These data indicate that in the cold seasons the biomass combustion for domestic heating is the main sugar source representing nearly 94% of the total saccharides mass measured in PM_(2.5). Accordingly, glucose, arabinose and galactose show the highest concentrations, since these saccharides are also emitted during the burning process as uncombusted biomass materials. In spring/summer the primary saccharides are dominant in PM_(2.5), with mannitol as the most abundant, followed by mycose, glucose and ribitol that are emitted by the terrestrial biomass, reflecting the higher sugar production and utilization by the ecosystem in the warm seasons. These results were confirmed by investigating other molecular markers, such as low-molecular-weight carboxylic acids and n-alkane homologs. Principal Component Analysis was applied to the data to extract three PCs that may be attributed to different saccharide sources, such as biomass burning and primary bio aerosol.