Impact of Global NOx Sources on the Northern Latitudes

Nitrogen oxides (NO_x), through their control of tropospheric ozone production, play a major role in determining the global reactivity of the atmosphere. The concentration of these oxides varies by as much as a factor of 1000 between continental source regions and remote locations and fluctuates significantly with season at high latitudes. While NO_x levels appear to be rather low (<50 pptv) away from local sources, high levels of PAN, an important reservoir for NO_x, have been measured at the surface in the winter polar regions [Barrie and Bottenheim, 1991] and in the free troposphere north of 30°N [Singh, Salas and Viezee, 1986]. Furthermore, our recent global chemical transport model (GCTM) study finds PAN to be the major reactive nitrogen species in the northern latitudes [Kasibhatla et al., 1992].