PNNL

Abstract

We report here on combined 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 in June 2001. The motivation for this campaign developed from studies in other urban areas that found peak ozone values above the surface layer appeared to play an important role in governing the surface ozone concentrations in the early morning. The first examination of the data here suggests a) the vertical extent of the boundary layer before sunrise is below 200 m and the concentrations of trace gases are very sensitive to the stability of the atmosphere, as shown by the observed gradients. Capturing these processes with an air quality model will require a very high degree of vertical resolution. b) Typically at night, and sometimes during the day, we would see lower concentrations of ozone at the ground, as expected from the titration of O3 with NO. On June 26 this difference throughout much of the day was of order 10 to 15 ppb. It is not clear if this is a local effect associated with street canyons, or representative of what actually occurs over the entire city and environs. c) DOAS observations highlight the relationship between the gradient structure of reactive trace gases and meteorology at night.