Central/eastern North Pacific photochemical precursor distributions for fall/spring seasons as defined by airborne field studies


  • 16 June 1997


[1] Data from 10 aircraft programs recorded over the central/eastern North Pacific (180°–120°W, 0°–45°N) were assembled for the purpose of assessing an atmospheric chemical climatology for this region. It represents an early effort at carrying out this task and, thus, it can be expected to undergo many updates in the future. Such a database is useful in both gaining further insights concerning the fundamental processes controlling the chemistry of this region as well as serving as an important baseline by which to evaluate future change. Critical photochemical precursors examined included O3, CO, NOx, and H2O. In addition, the distribution profiles for select nonmethane hydrocarbons were explored. The precursor data were analyzed according to latitude, pressure altitude, and season of the year. Contrasting the spring and fall measurements, major trends that surfaced in both ozone and CO included observing elevated levels in spring compared to fall, with the largest spring increase occurring at latitudes north of 15°N. Both NOx and H2O showed trends quite different from that of CO and O3, with an indication of higher mixing ratio levels during the fall season. Variations in precursor distribution patterns within a season will be explained based on climatological flow patterns for the region and the resulting connection to source regions. Where possible, comparisons were performed with other sampling strategies, including ground-based observations, sonde, and satellite data, and data collected during shuttle missions. Overall, these comparisons revealed a reasonably high level of correspondence between the airborne ensemble data and those collected using other sampling strategies.