You have to read between the lines to even get the hint that much (most?) of this pollution comes from vehicle use — both from entrained dust (dust that is kicked up by cars/trucks whooshing by) or emissions (NOX -> ozone, and fine particulates from combustion, particularly from “clean” diesel engines. )
Experts warn of poor Valley air quality The Arizona Republic. A familiar brown cloud is settling over a cool, dry Valley, prompting air-quality experts to warn that residents could be in for a particularly dirty winter.
Bad air expected for Valley through the holidays Bob McClay/KTAR PHOENIX — The Valley’s brown cloud season has arrived, with poor air quality that irritates respiratory systems … Mark Shaffer with the Arizona Department of Environmental Quality. …said the high pressure creates an air bubble that collects ozone below 5,000 feet.
For those of you who don’t follow such minutia, the Phoenix area is what is termed a “Serious Non-Attainment Area” for various forms of air pollution. This leads to, of course, some amount of human misery especially via various lung diseases, but it also brings the specter of loss of federal funds if the air isn’t cleaned up. Some local (state, or maybe county?) agency must produce a plan to clean up the air to the satisfaction of the EPA; that plan (critique here dated 9/13/2010: EPA Disapproves Air Quality Plan for Phoenix ) was rejected in part because “EPA has determined that the SIP (State Implementation Plan) over-emphasized emission reductions needed from construction-related activities and de-emphasized emission reductions from other sources”, you know, other source like, for example, those produced as a result of using motor vehicles.