An assessment of tropospheric photochemistry over the central/eastern North Pacific

The study has focused on a region of the Pacific Ocean that has been labeled the central/eastern North Pacific (CENP). This region covers latitude range of 0°–45°N and a longitude range of 180°–120°W. Data from ten airborne programs dating from 1978 to 1999 has been collected to allow for the creation of an atmospheric chemical climatology. The data ensemble includes observations collected on 66 different flights.; Seasonal, latitudinal, and altitudinal trends for several critical photochemical precursor species (e.g., O₃, CO, NO, H₂O, NMHC's) are described. The sharpest gradients in ozone occurred in what has been defined as the “transition zone” (15°–30°N) which represent a shift from tropical to midlatitude air masses. There is a seasonal component to this shift, with the transition zone resembling mid-latitudes during spring, but during fall it appeared to reflect tropical latitudes. Significant CENP seasonal and latitudinal trends were also noted for CO. NO_x data revealed that low levels predominated throughout the CENP region.; The date ensemble was used as input for a time-dependent photochemical box model. The model allowed for the determination of the concentration of short-lived radical species, particularly those that make up HO_x (OH and HO₂). Model results also allowed for the determination of the local ozone photochemical tendency. This tendency was strongly negative at low altitudes for both seasons. While the tendency shifted to positive in the 4–6 km range, the net column tendency was negative for both seasons at all latitudes examined.; Studies performed previously in the western North Pacific which show a neutral column during fall, and a strong net production in spring. A comparison between the western and central/eastern North Pacific results in the determination that the key difference driving the change in ozone photochemical tendency is the low concentration of NO_x, in the CENP. The lifetime of NO _x is not sufficient for significant amounts to be transported to be the CENP via direct means. This would then suggest that the CENP region might serve as a buffer for any future increases in emissions from Eurasia.