Daily evolution of sulphate aerosols in a rural area, northeastern Spain—elucidation of an atmospheric reservoir effect

The present work is focused on the daily evolution in the levels and composition of total suspended particles and PM10 (particulate matter <10 microns) in rural areas around the Teruel power station in northeastern Spain, with special emphasis on sulphate aerosols. A daily cycle in the levels of natural and sulphate aerosol is evidenced by higher ratios of sulphate/soil elements during the diurnal stage when compared with the nocturnal period. The origin of this cycle is probably related to higher SO2 oxidation rates and a higher frequency of plume impacts on the surface during the diurnal period. However, this trend is frequently disturbed by local atmospheric dynamics which give rise to an atmospheric reservoir of sulphate aerosols which increase nocturnal sulphate levels without major SO2 plume impacts. These atmospheric dynamics are described in spring, summer and winter measurement campaigns which are characterised by different plume dispersion scenarios. The results indicate that the three following situations concerning the sulphate levels can be present in the study area: (1) direct plume impacts inducing high sulphate levels in short time periods; (2) a sulphate reservoir effect leading to relatively high sulphate background levels, homogeneously distributed at distances of 60 km from the power plant, without major SO2 impacts; and (3) a regional sulphate background giving rise to relatively low sulphate levels with a clear external origin and seasonal trend.