Lower U/R ratios have been interpreted as the impact of industrial and stationary local emissions from the city of Huelva on the regional monitoring station.
Moreover, the significant impact of local sources like road traffic present in the city, could increase the U/R ratios obtained for Snand Sb. The size distribution of main industrial elements is mostly fine at both sites (PM2.5/PM10 > 0.7; Table A.1).
The fine size distribution of the toxic elements, including arsenic (PM2.5/ PM10 = 0.8 at Campus and PM2.5/PM10 = 0.9 at El Arenosillo), represents an added health risk increasing the likelihood of transport to distant areas.