We report here on a meteorological and chemical trace-gas observations made from two levels of a skyscraper in downtown Phoenix, Arizona. These observations were made as part the U.S. Department of Energy's Phoenix Sunrise Campaign of June 2001. The focus of this campaign was to study the chemical and meteorological transition as the urban atmosphere went from stable to a convective state. The observations to be presented here were designed to evaluate changes to the concentration of NOx, VOCs, PAN and other species involved in the production of ozone at sunrise with the onset of both mixing and chemistry. These observations were one component of a broader set of measurements designed to characterize the vertical structure of the lower urban atmosphere. The motivation for this campaign stems from studies in other urban areas that found peak ozone values above the ground that appeared to play an important role in governing the surface ozone concentrations in the early morning. Measurements at the skyscraper were continuously made over a two-week period that include several distinct meteorological regimes.

While the expected depletion of ozone through its titration with NO was observed at the lower floor, resulting in a large gradient in this specie, other species were observed to have a comparably large vertical gradient. Nitrous acid was measured with an atmospheric pressure ionization mass spectrometer and a differential optical absorption system (DOAS), allowing us to evaluate the vertical gradient of this important species using two independent techniques. Formaldehyde levels at night will also be reported. These and other observations will be related to the vertical structure of the atmosphere as measured by rawinsondes, profilers and sodars that were deployed in close vicinity to the skyscraper.