Estimations of primary and secondary organic carbon formation in PM2.5 aerosols of Santiago City,Chile

High concentration of fine airborne particulates is considered one of the major environmental pollutants in Santiago, the Chilean Capital city, which in 1997 was declared a PM₁₀ saturated zone. To date there is no control of the amounts of fine and coarse aerosols concentrations and the source and chemical characterizations of the PM_2.5 particulates in the carbonaceous fractions are not well known even though this fraction could be represented almost the 50% in mass of the PM_2.5.In this work, we present for the first time determinations of primary organic aerosol (POA) and secondary organic aerosol composition (SOA) fractions of the total mass of PM_2.5 particulates collected in the urban atmosphere of Santiago City. Our purpose is to know the anthropogenic contributions to the formation of SOA. To accomplish this we used the elemental carbon (EC) and organic carbon (OC) determinations developed by automatic monitoring stations installed in the city during the period 2002–2005, with a particular analysis of the summer time occurred in February 2004. Based on the EC tracer method, we have estimated the POA and SOA fraction and our data permit us to estimate the SOA reaching up to 20% of total organic aerosol matter, in good agreement to other measurements observed in large cities of Europe and U.S.A.     

Distribution and temporal variation of trace metal enrichment in surface sediments of San Jorge Bay, Chile

Cu, Pb, and Hg concentrations were determined in surface sediment samples collected at three sites in San Jorge Bay, northern Chile. This study aims to evaluate differences in their spatial distribution and temporal variability. The highest metal concentrations were found at the site “Puerto”, where minerals (Cu and Pb) have been loaded for more than 60 years. On the other hand, Hg does not pose a contamination problem in this bay. Cu and Pb concentrations showed significant variations from 1 year to another. These variations seem to be a consequence of the combination of several factors, including changes in the loading and/or storage of minerals in San Jorge Bay, the dredging of bottom sediments (especially at Puerto), and seasonal changes in physical–chemical properties of the water column that modify the exchange of metals at the sediment–water interface. Differences in the contamination factor and geoaccumulation index suggest that pre-industrial concentrations measured in marine sediments of this geographical zone, were better than geological values (average shale, continental crust average) for evaluating the degree of contamination in this coastal system. Based on these last two indexes, San Jorge Bay has a serious problem of Cu and Pb pollution at the three sampling locations. However, only Cu exceeds the national maximum values used to evaluate ecological risk and the health of marine environments. It is suggested that Chilean environmental legislation for marine sediment quality—presently under technical discussion—is not an efficient tool for protecting the marine ecosystem.