Chemical composition of fine particles in Mexico City during 2003–2004

Abstract

Ambient samples of PM2.5 collected at three different land use sites (industrial, commercial and residential) within Mexico City during late fall and early spring in 2003 and 2004, were chemically characterized for water soluble ionic species, carbonaceous aerosols and trace elements to further determine their origin. The PM2.5 total mass concentration was consistently lower during spring compared to late fall at the three sites. The total mass concentration decreased from 45 ± 3 μg/m3 at the industrial site, through 36 ± 4 μg/m3 at the commercial site to 30 ± 2 μg/m3 at the residential site. The largest component by mass was the organic fraction followed by sulfates, elemental carbon, nitrates, geological material, trace elements and salts. Carbonaceous aerosol accounted for 47% of the PM2.5 total mass, (31% organic and 16% elemental carbon), suggesting an origin from incomplete combustion processes and biomass burning among others. Zinc and lead were related to open waste burning and incineration, and showed an overall average of 0.28% and 0.09%, respectively. The concentrations of nickel and vanadium, that are related to fossil fuel combustion, were lower than 0.02%; these two elements were associated with sulfates. The results show that Al, Cr, Ni, Pb and V have a clear seasonality with higher concentrations in the late fall and lower in the early spring. The highest concentrations of these elements were observed at the north of Mexico City where most of the industrial activities take place.