The Evolution of Photochemical Smog in the Metropolitan Area of Santiago de Chile

Abstract

In November and December 1996 the PHOTOCHEMICAL CAMPAIGN took place in the Metropolitan Area of Santiago de Chile and covered a range of simultaneous measurements of meteorological parameters and air chemical compounds, including ozone, carbon monoxide, nitrogen oxides, peroxyacetyl nitrate (PAN), and online nonmethane hydrocarbons (NMHC) in the range of C4?C12. Measurements were obtained at a downtown site and a receptor site. In addition to high ozone concentrations, Santiago faces high PAN values that can reach to more than 20 ppbv. It is estimated that more than 50% of the daytime maximum of ozone and almost all PAN are formed within the urban plume. Ozone:PAN ratios for diurnal maxima were about 7.7. The behavior of PAN is linked strongly to anthropogenic species, especially aromatic compounds, whereas biogenic NMHC also may contribute to afternoon ozone concentrations. The ethylbenzene:m-xylene ratio can be used as a good indicator for the effect of anthropogenically related hydrocarbon chemical reactions that lead to the formation of secondary pollutants. Using this ratio, mixing ratios for hydroxyl radical (OH) were calculated. Mean diurnal maximum OH mixing ratios were about 2.9 ? 106 molecules per centimeter cubed.