Correlation of ozone with NO_y in photochemically aged air

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, NO_y, 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 NO_y levels, from a background value of 30–40 parts per billion by volume (ppbv) at NO_y mixing ratios below 1 ppbv to values between 70 to 100 ppbv at NO_y levels of 10 ppbv. Ozone correlates even more closely with the products of the NO_x 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.