Temporal variations of O3 and NOx in the urban background atmosphere of the coastal city Jeddah, Saudi Arabia

Ozone is a pollutant of major concern because of its well recognized effects upon human health and crop yields. This study analyses in depth a new dataset for ozone from Jeddah, a coastal city in Saudi Arabia within the Middle Eastern region, for which very few ozone data are currently available, collected between March 2012 and February 2013. The measurements presented include NO, NO2 and ozone as well as relevant meteorological variables. The data show a marked seasonal variation in ozone with highest concentrations in the summer months and lowest average concentrations in the winter. Concentrations also show a substantial difference between weekdays and weekends, with higher NO and NO2 on weekdays, but lower concentrations of ozone. Plots of total oxidant versus NOx concentration indicate background concentrations of ozone (at zero NOx) ranging from 38.2 ppb in January to 59 ppb in May consistent with the northern hemisphere spring maximum in ozone concentrations. The slope of total oxidant/NOx varies from 0.13 in March to 0.68 in August. The two summer months of July and August are anomalous with slopes of around double that of other months, suggesting a higher efficiency of ozone production at lower primary pollutant concentrations arising from much reduced daytime traffic. A substantial weekend/weekday difference in ozone which is higher at weekends appears to be attributable to lower daytime traffic activity and hence reduced emissions of NOx to a “NOx-saturated” atmosphere.