This presentation will focus on the interplay between field measurements and the development of atmospheric chemical mechanisms. Atmospheric chemistry involves ozone formation, nitrogen oxides, volatile organic compounds (VOCs) and other trace gas species. Laboratory and field measurement data are used to develop and evaluate chemical mechanisms such as the Regional Atmospheric Chemistry Mechanism, Version 2 (RACM2). One example of a field is the Clark County Regional Ozone and Precursor Study (CCROPS). The field measurement program for CCROPS took place during the summer of 2005. As part of this program, concentrations of volatile organic compounds (VOCs) were quantified. The measured VOC can be compared with those in RACM2 to test its formulation. The RACM2 is an updated version of the Regional Atmospheric Chemistry Mechanism (Stockwell et al., 1997). It contains new biogenic and aromatic schemes based on recent literature data. It also contains the new speciated compounds methanol, benzene, and acetaldehyde, among others. The inorganic chemistry will be further tested through a new NSF supported field studies of the nitrate radical, “NO3 Induced Nighttime Air Chemistry”. The field campaign will take place in Reno, NV during the summer of 2008, during which NO3, a key nighttime oxidant, will be measured by the Differential Optical Absorption Spectroscopy (DOAS), as well as ancillary species including PM concentrations and meteorological parameters. This study should be able to produce a complete nitrate radical budget. In Reno the measurements will be collected under a wide range of relative humidities (10 – 90%); this will allow the indirect loss rate of the nitrate radical through the hydrolysis of N2O5 to be determined.