Toxic Air Contaminants in Porto Alegre, Brazil

Information on ambient levels of toxic air contaminants is a critical component of programs aimed at regulating air emissions to protect public health. Yet, this information is not available in many countries. Toxic air contaminants have been measured near a busy highway in downtown Porto Alegre, Brazil, from 3/20/96 to 4/16/97. Of the 42 compounds listed in U.S. EPA Method TO-14, 21 were not detected (concentrations < 0.1 ppb), 3 were detected in 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 other than vehicles for CH2Cl2 and Cl2CCCl2, and vehicles as the major source of 1,3-butadiene, styrene, and aromatic hydrocarbons. Ambient concentrations 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 correlations are used to estimate mid-1996 vehicle emission rates, e.g., (197 ± 50) × 103 kg/year for 1,3-butadiene. A comprehensive comparison is made of our results (halogenated compounds measured in Porto Alegre, halogenated compounds not 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.