Aircraft measurements of NOx over the eastern Pacific and continental United States and implications for ozone production

Abstract

Measurements of NO, NO2, O3, and CO are presented from 13 aircraft flights made over the eastern Pacific Ocean and the continental United States in August and September 1986 during the NASA GTE/CITE 2 program. Measurements of NO by three different groups (two different techniques) and of NO2 by three different groups (three different techniques) are presented and examined along with calculated NOx (NO+NO2) for correlations with O3, CO, and dew‐point temperature (DPT) primarily as a function of air mass category. Median values of NO and NO2 in the marine boundary layer were 4.0 and 10.4 pptv, respectively, and 12.4 and 18.0 pptv in the marine free troposphere. In the continental boundary layer, median values of NO and NO2 were 34.5 and 75.0 pptv, respectively, and 13.0 and 36.0 pptv at altitudes above 3 km in air masses having continental influence. In the maritime NOx data set a negative correlation is often observed between NOx and DPT, while positive correlations were typically observed between NOx and O3 and between NOx and CO. As expected, then, negative correlations were often observed between O3 and DPT and between CO and DPT, along with positive correlations between CO and O3. In the continental data set, positive correlations were typically observed between NOx and DPT, O3, and CO. Additionally, the various air masses were examined with respect to regions of net ozone production or net ozone destruction. In all but one case in the marine boundary layer, model calculations indicate that there is significant ozone destruction. In the continental boundary layer, however, calculations indicate significant ozone production. In the middle free troposphere at 5±1 km, the in situ ozone formation was most often nearly in balance with ozone destruction.