During the summer of 1988, measurements of photochemical trace species were made at a coordinated network of seven rural sites in the eastern United States and Canada. At six of these sites concurrent measurements of ozone and the sum of the reactive nitrogen species, NOy, were made, and at four of the sites a measure for the reaction products of the NO x oxidation was obtained. Common to all sites, ozone, in photochemically aged air during the summer, shows an increase with increasing NOy levels, from a background value of 30-40 parts per billion by volume (ppbv)at NOy mixing ratios below 1 ppbv to values between 70 to 100 ppbv at NOy levels of 10 ppbv. Ozone correlates even more closely with the products of the NOx oxidation. The correlations from the different sites agree closely at mixing ratios of the oxidation products below 5 ppbv, but systematic differences appear at higher levels. Variations in the biogenic hydrocarbon emissions may explain these differences. IntroductionElevated and potentially harmful levels of ozone are being found in many rural areas of North America during summer. Daily maximum 03 levels measured in rural areas are often comparable to those found in urban areas and daily average levels can exceed urban levels. There is substantial evidence from field measurements and model calculations that most of this ozone is being produced photochemically from ozone precursors emitted within the region [Research Triangle Institute, 1975; Vukovich et al., 1977Vukovich et al., , 1985Cleveland et al., 1977;Spicer et al., 1979;Wolff and Lioy, 1980;Fehsenfeld et al., 1983;Kelly et al., 1984;Liu et al., 1987]. A similar situation appears to exist for western Europe [Cox et al., 1975;Guicherit and Van Dop, 1977;Hov, 1984]. The photochemical processes responsible for these high levels are thought to be quite similar to the processes that operate in urban photochemical smog but with important differences. In

Measurements of light hydrocarbons, ozone, peroxyacetyl nitrate (PAN), HNO3, NO3−, NOx, NOy, and meteorological parameters were made during a 10‐day period in April and May 1985 at Point Arena, a coastal inflow site on the Pacific Ocean in northern California. The meteorological measurements indicate that during this study the sampled air was usually from the marine boundary layer with little land influence on the meteorological parameters. In this marine air the mixing ratios of the alkanes, ozone, PAN, and HNO3 showed strong correlations coincident with variations in the origins of calculated air parcel trajectories and with variations in the ratios of the light alkanes. This variation in the ratios is attributed to different degrees of photochemical aging of the alkanes that are generally consistent with the calculated trajectories. This behavior indicates that the alkane levels are determined by transport to the marine area from continental sources, most likely Asian, followed by photochemical removal over the Pacific Ocean. Since the concentrations of PAN and ozone correlate well with the alkane ratios, it is concluded that the observed PAN and ozone were dominated by continental sources and removal processes in the marine areas. This and other marine studies have observed a strong correlation of PAN and ozone, and it is suggested that production over the continents, transport to the marine areas, and parallel removal processes account for much of the observed correlation. From the correlation of these two species with the measured alkane ratios, approximate net lifetimes of PAN and ozone in the marine troposphere of ≤2.5 and ≥19 days, respectively, are derived. The primary conclusion is that the alkanes, ozone, and PAN in these air parcels from the Pacific marine troposphere are dominated by transport from continental sources and removal by photochemical processes. Direct emissions of the alkanes and in situ photochemical production of PAN and ozone from precursors emitted into the marine region from the surface or the stratosphere must play less important roles. Similar indications of continental influence in marine areas have been seen in other studies of ozone, the sulfur cycle, oxidized nitrogen, and hydrocarbons. It is suggested that the ratios of the light alkanes provide photochemical “clocks” that are useful for gauging the importance of continental influence in a particular marine measurement.

Measurements of NO, NO2, HNO3, particulate nitrate, peroxyacetyl nitrate (PAN), O3, and total reactive odd nitrogen (NOy) were made in the nonurban troposphere during the summer and fall of 1984. The field site was located near Niwot Ridge, Colorado, at an elevation of 3 km. NOy was measured by catalytic reduction to NO, followed by the detection of NO with a chemiluminescence instrument. The other species were measured with conventional techniques. The data and interpretation presented focus primarily on the relationships between a measurement of NOy and concurrent measurements of the individual species, as examined through ratio and correlation plots. Through the separate display of daytime and nighttime data, the plots provide insight into the photochemical nature of the individual species. In addition, the composition of NOy is addressed through a comparison of the measured NOy level with that found for the sum of the measured component species. The NOy level systematically exceeded the sum level, with the difference being larger in the summer than in the fall. The presence of organic nitrate species other than PAN is proposed as one way to account for the observed difference.

Abstract. An informal intercomparison of NOy measurement techniques was conducted from

NO3 has been measured in slightly polluted Colorado mountain air up to a few hundred ppt. There is clear evidence that it is removed by scavenging reactions in less than one hour. The identity of the scavenger is not yet established in mountain air, nor is it yet known whether the reaction removes odd nitrogen from the troposphere. In urban air the scavenging occurs in less than a few hundred seconds and may in part be due to the reaction of NO3 with NO.