![]() The risk estimates for New Mexico presented by Pope et al. ![]() (2007) did not differentiate their results by distance from the smelters, but some information in their article is relevant because mortality is associated mainly with population centers (cities). If the smelter SO 4 was present regionally, exposure to concentration gradients of SO 4, SO 2, and metals would be expected with distance from the plants ( Eldred et al. ![]() However, the accompanying association with non–weather-related visibility change is problematic (e.g., Hidy 1984). NASN data indicate a strike reduction in SO 4 (0.1–3.6 μg/m 3) at sites in the region ( Trijonis and Yuan 1978 Table 16) and not Pope et al.’s uniform 2.5 μg/m 3. Ambient SO 4 includes SO 4 from oxidation of sulfur dioxide in air (secondary) and that emitted directly (primary). They attributed improved visibility across the Southwest to SO 4 reduction during the strike. (2007) is a study by Trijonis and Yuan (1978), who analyzed the National Air Surveillance Network (NASN) SO 4 and visibility. Although I found the thesis interesting, there is confounding that should be noted involving a) inconsistencies in state mortality relationships b) the trace metal role, and possibly carbon exposure from the plant complexes and c) ambiguities associated with SO 4 sampling. They ascribed mortality reduction to a decrease in ambient sulfate from the smelters. ![]() (2007) provide results for reduced mortality during the 1967–1968 smelter strike in the U.S. ![]()
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