4. Conclusions
It is shown in this study that winter PM10 aerosol from Sao Paulo city is severely impacted by regional sugarcane burning, as is evidenced by the high concentrations of anhydrosugars and nitroaromatic compounds. The PM10, OC and EC concentrations were higher in 2013 than in 2012, and could be partly explained by more extensive sugarcane burning and a larger vehicle fleet in 2013 compared to 2012 in the state of Sao Paulo. The PM ~ 10 concentrations were below Brazilian legislation but much higher than those recommended by the World Health Organization. Levoglucosan,the major anhydrosugar and a primary marker for biomass burning formed by pyrolysis of cellulose and hemicelluloses, showed median concentrations of 260 ng m3 and 400 ng m3 in 2012 and 2013, which is much higher than the values reported for other Brazilian urban sites in previous studies. Examination of anhydrosugar ratios revealed that a levoglucosan/galactosan ratio lower than about 30 may be characteristic of sugarcane burning. The major nitroaromatic marker compounds, 4-nitrocatechol and the isomeric methyl nitrocatechols, secondary products formed by oxidation of cresols emitted during biomass burning, presented substantial concentrations (medians of 13.6 ng m3 and 14.1 ng m3 in 2012 and of 32 ng m3 and 20 ng m3 in 2013), which correlated well with those of levoglucosan, consistent with their biomass burning origin. Furthermore, other measured organic compounds including isoprene SOA markers, monosaccharides (fructose and glucose) and polyols (arabitol and mannitol) showed substantial concentrations, contributing to the OC mass with 0.63% in 2012 and with 0.42% in 2013. As to the isoprene SOA marker
compounds, the concentrations of 2-methylglyceric acid were higher than those of the 2-methyltetrols, consistent with its formation under polluted urban conditions.