Global tropospheric measurements of mitric acid vapor and particulate nitrate

Measurements of HNO3 vapor and particulate NO3− were made over continental and marine areas, at altitudes from .2 to 7 km, as a part of Project Gametag. HNO3 vapor was found to be as common over marine areas, far from anthropogenic sources of NOx, as over remote continental regions, ranging from < .02 to .3 ppbv. Urban influenced continental values ranged from .3 to .86 ppbv. Comparable HNO3 was found both above and within the boundary layer, in contrast to theoretical predictions of a negative HNO3 gradient with altitude. In many regions of the troposphere there was more HNO3 vapor than participate NO3−, although the reverse is true in the marine boundary layer, where it appears that heterogeneous chemistry converts HNO3 and Cl− to HCl and particulate NO3−. This rather limited data set suggests an HNO3 lifetime on the order of a few days.