Investigating the role of photochemistry and impact of regional and local contributions on gaseous pollutant concentrations (NO, NO2, O3, CO, and SO2) at urban and suburban sites

Gaseous pollutant concentrations were monitored for one year in urban (NO, NO₂, O₃, CO, and SO₂) and suburban (NO, NO₂, and O₃) sites. Common characteristics were identified at both sites, such as higher concentrations during typical winter months for all pollutants except O₃. Increased NO, NO₂, CO and SO₂ concentrations during wintertime were linked to residential heating emissions, with pairwise correlations showing CO as marker for the study site. O₃ production was lower in wintertime but higher in summertime at both sites based on its seasonal cycle and the impact of sunlight. Furthermore, diurnal variations showed that traffic emissions during rush hours most profoundly affected CO and NO. Nevertheless, NO_x were characteristically higher at the urban site based on the burdened environment, whereas O₃ was higher at the suburban site due to the lower destruction rates. O₃ was the dominant oxidant at both sites, with a linear regression between OX and NO_x revealing a negative relationship. This observation suggested a dominant regional contribution to oxidant concentrations. In addition, abnormally high O₃ concentrations in relation to the season were reported for the first time at the study sites. Elevated concentrations were measured in parallel with Sahara dust events indicating noteworthy atmospheric conditions that require further assessment. Other O₃ burdened periods were driven by regional transport of polluted plumes from the northeast. Lastly, nocturnal increases in O₃ were observed and associated with enhanced vertical mixing.