Toxic air contaminants in Porto Alegre, Brazil

Information on ambient levels of toxic air contaminants is a critical compo nent of programs aimed at regulating air emissions to protect public health . Yet, this information is not available in many countries. Toxic air conta minants have been measured near a busy highway in downtown Porto Alegre, Br azil, from 3/20/96 to 4/16/97. Of the 42 compounds listed in U.S. EPA Metho d T0-14, 21 were not detected (concentrations < 0.1 ppb), 3 were detected i n only a few samples (CHCl3, HClC=CCl2, and p-dichlorobenzene), and 3 were present at concentrations typical of background locations (CH3Cl, CH3CCl3, and CFC-113). Comparisons of urban/background location concentration ratios and of urban concentrations vs those of CO indicate no local emissions for CCl4, small and variable sources for CFC-11 and CFC-12, local sources othe r than vehicles for CH2Cl2 and Cl2C-CCl2, and vehicles as the major source of 1,3-butadiene, styrene, and aromatic hydrocarbons. Ambient concentration s of 1,3-butadiene and aromatic hydrocarbons were well correlated to those of benzene (R = 0.92-0.98) and those of CO (R = 0.88-0.97). These correlati ons are used to estimate mid-1995 vehicle emission rates, e.g., (197 +/- 50 ) x 10(3) kg/year for 1,3-butadiene. A comprehensive comparison is made of our results (halogenated compounds measured in Porto Alegre, halogenated co mpounds nor detected in Porto Alegre, and aromatic hydrocarbons with focus on the toluene/benzene, (m + p)-xylene/benzene, and (m + p)-xylene/toluene ratios) with literature data for background and urban locations.