SUMMERTIME PARTITIONING AND BUDGET OF NOY COMPOUNDS IN THE TROPOSPHERE OVER ALASKA AND CANADA - ABLE 3B

As part of NASA's Arctic Boundary Layer Expedition 3A and 3B field mea surement programs, measurements of NOx, HNO3, PAN, PPN, and NOy were m ade in the middle to lower troposphere over Alaska and Canada during t he summers of 1988 and 1990. These measurements are used to assess the degree of closure within the reactive odd nitrogen (N-x O-y) budget t hrough the comparison of the values of NOy measured with a catalytic c onvertor to the sum of individually measured NOy(i) compounds (i.e., S igma NOy(i) = NOx + HNO3 + PAN + PPN). Significant differences were ob served between the various study regions. In the lower 6 km of the tro posphere over Alaska and the Hudson Bay lowlands of Canada a significa nt fraction of the NOy budget (30 to 60%) could not be accounted for b y the measured Sigma NOy(i). This deficit in the NOy budget is about 1 00 to 200 parts per trillion by volume (pptv) in the lower troposphere (0.15 to 3 km) and about 200 to 400 pptv in the middle free troposphe re (3 to 6.2 km). Conversely, the NOy budget in the northern Labrador and Quebec regions of Canada is almost totally accounted for within th e combined measurement uncertainties of NOy and the various NOy(i) com pounds. A substantial portion of the NOy budget's ''missing compounds' ' appears to be coupled to the photochemical and/or dynamical paramete rs Influencing the tropospheric oxidative potential over these regions . A combination of factors are suggested as the causes for the variabi lity observed in the NO budget. In addition, the apparent stability of compounds represented by the NOy budget deficit in the lower-altitude range questions the ability of these compounds to participate as reve rsible reservoirs for ''active'' odd nitrogen and suggest that some po rtion of the NOy budget may consist of relatively unreactive nitrogen- containing compounds.