Ground-based and aircraft measurements of trace gases in Phoenix, Arizona (1998)

In May and June of 1998, an extensive measurement campaign was fielded in the city of Phoenix and its environs. Measurements were made at ground sites and aboard the Department of Energyʹs G-1 research aircraft in an effort to understand the production of O3 in this area. Diurnal variations in O3 differed at the upwind Palo Verde, downtown Phoenix Super Site, and downwind Usery Pass surface stations. Air masses entering the metropolitan area had O3 concentrations greater than 40 ppbv. Maximum O3 concentrations near 100 ppbv were observed downtown at 14:00 local standard time; similar concentrations occurred much later in the day at the downwind site. One aircraft case study on 5 June, 1998 is presented to illustrate ozone production in the region. Calculated ozone production rate and efficiency varied from 1 to 7 ppbv h−1, and 1–3 molecules of O3 per molecule of NOz, respectively, for this flight. Hydrocarbon apportionment, based upon ground site and aircraft measurements, establishes that biogenic species are not significant contributors to O3 production in the Phoenix area. Therefore, carbon monoxide becomes a major contributor to OH reactivity as the more reactive anthropogenic hydrocarbons become depleted. The relatively low ozone production observed in this study is attributed to a low rate of radical production in the dry atmosphere.