Phoenix, Arizona, Revisited: Indications of Aerosol Effects on O3, NO2, UV-B, and NO3

During the early summer of 1998, the Department of Energy's Atmospheric Chemistry Program conducted tropospheric field studies in Phoenix, Arizona. As part of that effort, measurements were taken at one-minute intervals for a number of key pollutants, as well as UV-B radiation and temperature. Pollutants measured included NO2 and PAN by using a luminol-based chemiluminescence detector with fast gas chromatography, ozone by UV absorption, and CO by nondispersive infrared detection. These measurements were taken at a field station located near Usery Mountain Recreation Area, on a saddleback overlooking Phoenix and Mesa, Arizona. This site was found to be suitable for examining the urban plume from Phoenix during nocturnal boundary layer flow situations. During a portion of this study, the area was also affected by smoke from regional biomass burning in Mexico. This smoke resulted in the reduction of UV-B and a subsequent reduction in ozone. Low values for NO2 were also noted. These data are compared to values more usual for air masses sourced in the San Diego-Los Angeles area, which indicated long-range transport of photochemical oxidants. The results are discussed in light of the potential effects of aerosols on the air pollutants measured and the production of nitrate radical at night.