During the late summer and early fall of 1988, measurements of many trace species of tropospheric photochemical interest including NO, NO2, PAN, HNO3, NO3, NOY, and ozone were made at seven surface stations in the eastern United States and Canada. The NOY (as well as ozone) levels and its partitioning were strongly influenced by the diurnal evolution of the boundary layer at the sites that are beneath the nocturnal inversion. At the higher elevation sites the median levels of all species were much more nearly constant. During the daytime the median NOY levels were 2 to 5 ppbv at all sites, which may be representative of rural areas in the populated regions of eastern North America. Each site showed variations in the NOY levels of an order of magnitude or more. Measurements from all of the sites are consistent with the major contributors to NOY being NOX (the sum of NO and NO2), PAN, and nitric acid with a minor contribution from aerosol nitrate.

At the lower elevation sites the median X> to Y> ratios were 70% or more during the night declined to minima of 25 to 40% during the day. During the daytime the ranges of the median contributions of PAN and HNO3 to NOY were 12 to 25% and approximately 20 to 30%, respectively. The distributions of the contributions about these medians are discussed. Results from all of the sites are consistent with the individually measured species accounting for about 90% of the simultaneously measured NOY. ¿American Geophysical Union 1993