We address three major questions using this subset of the NE-OPS data. The covariance of NOy and CO in ambient air yields an estimate of the primary emission ratios for urban pollution sources, and provides a test of emission inventories. Apparent depletion of NOy relative to CO provides a measure of pollutant aging. Background ozone levels can be estimated by selecting data with the lowest levels of primary pollutants NOy and CO. By background, we mean the concentration of O3 in air not significantly impacted by recent addition of pollutants.
We infer an emission ratio of 0.18 molecule NOy per molecule of CO in the Philadelphia source region. Periods of intense NOy removal are evident in the data. These periods indicate significant contribution from aged pollutants or very rapid processing of local emissions. An episode of maximum NOy loss stands out as a period having the highest O3 concentrations (30-min. average O3 up to 150 ppb).. The O3 concentration during mid-day periods with the lowest 10% of CO or NOy concentrations is 47 ppb at the Baxter site. The corresponding value for Harvard Forest is 41 ppb.