The relative influence of the anthropogenic air pollutants on the atmospheric turbidity factors measured at an urban monitoring station.

This work is based on simultaneous measurements of direct solar radiation along with other chemical measurements, with the objective of investigating the diurnal and seasonal variations of atmospheric turbidity factors (i.e., Linke's factor, Angström's coefficient, and aerosol optical depth). Relationships between atmospheric turbidity factors, expressing the solar radiation extinction, and anthropogenic air pollutants were also evaluated. The frequency of occurrence of the individual indices has been established to describe the sky conditions. The preliminary results obtained indicate high variability of aerosol loading, leading to high turbidity for most of the year. Annual averages of 0.2 and 6 with standard deviations of 0.096 and 0.98 were found for Angström and Linke turbidities, respectively. On the base of the frequency of occurrence, it has been found that over 50% of the dataset are around 0.25 and 6.3 for Angström and Linke turbidities, respectively. On average, the month of September experienced the highest turbidity, while December experienced the lowest. A possible reason for this is that the vertical distribution of the aerosol particles moves up in September due to the extent of the Sudan monsoon trough. We also note that spring values of the turbidity factors are closer to summer values, whereas the pronounced difference between the summer values in comparison with the winter values may be attributed to relatively greater difference in the water vapor level in the atmosphere.