Evaluating the influence of air pollution on solar radiation observations over the coastal region of Alicante (Southeastern Spain).

The present study evaluates ground-based downward surface shortwave radiation (Rs) over the coastal region of Alicante (Southeastern Spain). Hourly measurements collected over the eleven-year period 2010-2020 are used. Two weather stations located over the region capital, Alicante, have been selected as representative of urban and suburban typologies. Two additional weather stations far from the city have been selected representing rural typologies. Rs is significantly reduced over the urban station during the morning hours within the winter season compared to the observations recorded over the suburban and rural stations, with a global mean difference of -81 and -120 W/m2 at 10 LT, respectively. However, no significant differences are obtained during the midday sun, with a global mean difference of -20 W/m2 between the urban and rural stations. With the aim of explaining these differences, the current paper investigates the relationship between Rs and different air pollutants: NOx, SO2, and fine particulate matter (PM2.5 and PM10) as well as the wind field measured at the urban and suburban stations. The results found in this work point towards a close relationship between Rs and NOx concentrations annual cycles, which are also influenced by the prevailing wind circulations observed over the study area. A global mean NOx concentration of 107 µg/m3 is observed over the urban station at 10 LT during the winter season. In contrast, these high concentrations are significantly reduced over the suburban station, with global mean value of 40 µg/m3 at 10 LT, for this period of the year.