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

Abstract

[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 O 3 , CO, NO x , and H 2 O. 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 NO x and H 2 O showed trends quite different from that of CO and O 3 , 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.

An assessment of ozone photochemistry in the central/eastern North Pacific as determined from multiyear airborne field studies

“…The observational database used in this study is that reported by DiNunno et al [2002] and consists of data assembled from 10 aircraft missions in the CENP region whose time history spans 20 years. Five of these missions took place in the spring (defined here as March, April, May) and five were scheduled in the fall (defined as September, October, and November).…”

“…Five of these missions took place in the spring (defined here as March, April, May) and five were scheduled in the fall (defined as September, October, and November). (Details concerning the methods used to create this database, as well as the justification of these methods can be found in DiNunno et al [2002].) The geographical boundaries of the data used in this study are 0° to 45°N in latitude and 180° to 120°W in longitude.…”

“…Thus, we are here looking at air masses that have experienced even longer chemical processing times from their point of release. The effects from this chemical processing, as well as that from further mixing, will be assessed in this study, both by comparing the respective levels of ozone photochemical precursors for both regions [ Davis et al , 1996; Crawford et al , 1997b; DiNunno et al , 2002], and by contrasting the resulting photochemical ozone formation and destruction rates.…”

A UT/LS ozone climatology of the nineteen seventies deduced from the GASP aircraft measurement program

“…However, convective activity is suppressed in the downward branch of the Walker circulation over the eastern Pacific region, and therefore UT air masses are much less affected by ozonepoor air from the marine boundary layer. Another mechanism contributing to the elevated values over the eastern Pacific may be large-scale advection of higher-ozone air masses from northern and central America in association with southward flow along the eastern flank of the UT high pressure centre over the Western Pacific (e.g., Gregory et al, 1999;DiNunno et al, 2003).…”

“…Logan et al, 1999;Oltmans et al, 2001;Liu et al, 2002;Oltmans et al, 2004), evaluations of individual aircraft campaigns (e.g., Singh et al, 1996;Zhang et al, 2003;Wild et al, 2003), and tropospheric ozone residuals from satellite observations (e.g., Fishman et al, 2003). The climatology presented by DiNunno et al (2003) includes 10 aircraft campaigns in 20 years. However, it is based on individual flights separated by large time intervals.…”