by Geraldine Freeman, M.D.*
The Arizona Department of Environmental Quality, through a delegation from the U.S. Environmental Protection Agency, enforces the Clean Air Act (CAA) in Arizona. The CAA was enacted by Congress over 25 years ago to monitor air pollutants, gas and solid, and attempts to reduce these factors to quality standards. Monitored elements are nitrogen oxide (NO2), ozone (O3), sulfur dioxide (SO2), and particulates (PM10—particles 10 microns or smaller in diameter), all of which have important specific effects on the respiratory tract, some immediate and some long-term.
Pollution is generally worse in wintertime due to temperature inversions, with better months in spring and October associated with wind that moves the pollutants away. The Phoenix “valley” is actually a plain—lower, hotter, and more extensive than Tucson to the south. Cold, dry air, an irritant for asthma, is less problematic than in many parts of the U.S. because of mild winters.
Most air pollution in Phoenix is produced from motor vehicle emissions. Carbon monoxide (CO) affects the oxygen-carrying capacity of blood and the cardiovascular system. SO2 from coal and oil burning and copper smelters (some distance from Phoenix) provokes asthma when breathed through the mouth. Ozone forms from photochemical reactions, primarily on nitrogen oxides and hydrocarbons from vehicular exhaust and industrial combustion, the latter minimal in Phoenix. The sunshine and hot temperatures of the summer (up to 115°F) make ozone a particularly tenacious summer problem. CO levels have improved whereas O3 levels have risen. Particulates include dusts and hydrocarbons. Brown haze is associated with particulates and NO2.
Overall, pollution levels are in a holding pattern in the Phoenix area long-term as the population using vehicles grows rapidly in a city without much progress in providing alternate transportation within it’s increasingly sprawling borders. Oxygenated fuels are required, and cars must be emission certified.
Allergists believe that asthma and allergic rhinitis are increasing worldwide. Both monitored and non-monitored airborne factors may be important causes. Research in the Los Angeles area has identified airborne diesel and gasoline exhaust products as well as plants debris, wood smoke, charbroiled meat smoke, paved road dust, and rubber particles. Rubber and plant fragments are allergenic. Research laboratories have identified multiple immune-allergic responses to diesel exhaust particles which may prove important. While individual diesel particles are minute they can aggregate to a size that will deposit in the human airway.
*Mark R. Santana, Administrative Counsel for the Arizona Department of Environmental Quality, provided air quality data and helpful advice.
Posted in: Urban Environment