The impact of local sources and meteorological factors on nitrogen oxide and particulate matter concentrations: A case study of the Day of Atonement in Israel

Measurements of the atmospheric concentrations of NO_x and particulate matter (PM) in three urban centers in Israel before, during, and after the Day of Atonement were performed for nine consecutive years (2000-08). This enabled to investigate the significance of local versus long-range sources of pollution and probe the effect of meteorological conditions (synoptic systems, ventilation rates, height of surface boundary layer, and wind speed) on level of pollution. During the Day of Atonement all traffic and most of the industrial activities cease in the Jewish populated parts of the country. We observed that in spite of this, concentrations of particulate matter (PM_2.5 and PM₁₀) are very similar in all three urban centers during the Day of Atonement to the days before and after. Moreover, PM levels during the Day of Atonement are generally higher during Red Sea trough synoptic conditions which carry air from the Saudi and Jordanian deserts in the east and southeast relative to Persian Trough synoptic conditions which bring air from the eastern Mediterranean and the Black Sea region in the north-west. In addition, 55% of the variation in PM values during the nine days of Atonement included in this study can be explained by changes in ventilation rates of the atmosphere, namely the product of the mixing depth and a representative boundary layer wind speed. Thus, long-range sources and local mixing conditions determine the concentrations of PM in the atmosphere of Israel as expected from their long residence time. On the other hand, NO_x concentrations during the Day of Atonement are significantly lower than the days before and after, reflecting NO_x short residence time in the atmosphere and the strong influence of local emission sources. Furthermore, the difference in concentrations of NO_x in different Days of Atonement cannot be accounted for either by different synoptic conditions or by variations in ventilation rates, height of surface boundary layer, and wind speed. They are determined by the combination of local and regional sources of emission and the meteorological conditions which control their transport from these nearby sources to the sampling station.