Abstract
Formaldehyde (HCHO) is a carcinogenic pollutant, has an active role in tropospheric photochemistry, and can be affected by seasonal variations. To our knowledge, this is the first comprehensive study of the effect of seasonal variation on the levels and behaviours of HCHO in the atmosphere of a suburban area (15 May City) in Cairo. Daytime and nighttime measurements of HCHO were performed from March 2014 to February 2015. The highest average daily concentrations of HCHO were found in summer and the lowest in winter. The difference was statistically significant (p <= 0.001). Daily average HCHO concentrations in spring, summer, autumn and winter were higher than the corresponding values in many polluted cities in the world. This was true for both weekdays and weekends. HCHO was higher in daytime than nighttime on weekdays and weekends, and the differences in mean concentrations were statistically significant (p <= 0.001), except during the autumn and winter on weekends. Therefore, the contribution of photochemical reactions in the observed levels of HCHO might be greater than that of traffic emissions. This was further proved by the significant positive correlation found between daytime HCHO concentrations and temperature. HCHO concentrations were higher on weekdays than weekends, the differences in mean concentrations were statistically significant (p <= 0.001). This may be attributed to higher emission of HCHO from higher traffic intensity during daytime. Significant positive correlations (p <= 0.001) were found between daytime and nighttime HCHO concentrations, both on weekdays and weekends suggesting that HCHO comes from the same sources.