The 2001 Phoenix Sunrise Experiment: what's been learned since then

The objectives of the 2001 Phoenix Sunrise Campaign were to i) characterize the local nighttime accumulation of O3 precursors within the nocturnal boundary layer (NBL), ii) to study the subsequent interactions of these compounds the next morning as the NBL began to break up, and iii) to examine the role of vertical mixing on the chemistry within the developing convective boundary (CBL) during the morning hours. To meet these objectives, Chris Doran and colleagues made an extensive set of simultaneous meteorological and chemistry measurements within the Phoenix area from platforms that included an instrumented aircraft, two levels of a tall building in downtown Phoenix and a surface air chemistry network. In addition, the structure of the CBL was characterized with radiosondes, sodars and wind profiling radars. Many of the resulting profiles of CO, O3 and NO/NOy were consistent with a simple conceptual model of nighttime trapping of pollutants in a shallow stable layer with the subsequent release at sunrise. However, on several occasions significant vertical mixing was found to occur before sunrise. This mixing appeared to be associated with density currents arriving in the downtown Phoenix area before sunrise which in turn destabilized the lower atmosphere. Observations from the campaign also found that entrainment into the CBL of clean air from aloft and differential advection produced a non-uniform chemical structure in the CBL. We will review how the results from this campaign have been used in subsequent research and present an update of related results since the campaign.