In response to David’s question below about whether air quality is worse closer to busy roads, the short answer is: It depends. Certainly for some air pollutants, including ground-level ozone, ambient concentrations near busy roads or intersections can be higher than elsewhere in an urban areas, particularly at certain times of the day. Ozone readings in urban areas are often highest during the afternoon at extremely busy intersections in the summer (and ozone readings for the purposes of establishing violations of federal air quality standards are typically taken at the worst such spots in a given metro area). Though this can also be an oversimplification, as some cities now experience ozone spikes during the weekends, when the drop in emissions actually produces a hydrocarbon-nitrogen oxide ratio more conducive to ozone formation. Busy roads can produce “hot spots” for other pollutants as well. But, I would hasten to add that it is always “the dose that makes the poison,” and the fact that a given pollution level is measurably higher near a road does not mean that living in such a location entails any significant increase in risk. It all depends on the pollution levels in question (which, in turn, will typically depend on many site-specific factors).
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