An Air-Quality-Based Analysis of NO, NO2, and O3 at a Suburban Mediterranean Site

NO, NO2, and O3 were measured for 1 year at a suburban site in the southeast Mediterranean. NO preserved no seasonality, but significant seasonal variations were obtained for NO2 and O3. These pollutants exhibited inverse trends with higher NO2 levels measured during wintertime, whilst higher O3 levels were measured during summertime. Photochemistry was the primary reason for the opposing variations in both pollutants, although O3 levels were frequently increased due to O3-rich plumes travelling from northeast Europe, highlighting the impact of regional contributions in the measured concentrations. Nevertheless, anthropogenic sources were identified and contributed to both NO and NO2. Diurnal variations analysis showed that NO increased usually in the early morning and was linked with primary emissions from traffic. NO2 increased simultaneously with NO in the early morning, and besides primary vehicle emissions, it was associated with secondary formation from the emitted NO. Moreover, a significant contribution from domestic heating emissions on NO2 was identified in the late evening during wintertime. Overall, a relative burden of weekdays was associated with NO (morning rush hours) and NO2 (morning rush hours, evening), whereas weekends were burdened by O3 due to the weekend effect. Comparison with European Union air quality standards showed that NO2 was considerably lower than the limit values, but a significant number of exceedances were identified for O3, especially during the warmer months. This finding suggested the relative burden of the study site from O3. In conclusion, NO at the study site was influenced by primary traffic emissions, whereas NO2 had both primary and secondary contributions, and together with photochemistry, both pollutants governed O3 diurnal and seasonal cycles.