Seasonal characteristics of ambient nitrogen oxides and ground–level ozone in metropolitan northeastern New Jersey

Nitrogen oxides (NOx) and ground–level ozone (O3) were measured and meteorological parameters, wind speed, temperature, relative humidity and barometric pressure were monitored, to determine the seasonal variations of gas–phase pollutants in the Meadowlands. O3 and NOx were inversely related; the highest average NOx concentration (29 ppb) occurred in winter while average O3 concentrations peaked in summer up to 36.2 ppb. The seasonal variations of O3 were more distinct than NOx. In multiple linear and principal component regression analysis, ambient levels of NO2 and O3 were influenced primarily by wind speed. In time series and regression analysis, NO2 and O3 displayed an inverse relationship with wind speed but O3 paradoxically increased with wind speed downwind. The seasonality of O3 was amplified mainly by wind speed and temperature, while NOx displayed stronger dependence on diurnal source emissions. Concentrations of NOx and O3 were also influenced by differences in chemical processing through their complex emission–production and consumption mechanisms, making them interdependent. In intense solar radiation, O3 was NOx–dependent but as O3 levels were inhibited by lower temperatures, NOx concentrations increased. Higher O3 on weekends indicated an apparent sensitivity to VOC precursors. This study provides a basis for improved air quality standards primarily in summer and during daily O3 peaks. Additionally, plans for protection against health problems caused by O3 and NOX are feasible in this region.