Precipitation chemistry at a rural Mediterranean site: Between anthropogenic pollution and natural emissions

Abstract

The chemistry of weekly rainwater collected at a rural site (La Castanya, Montseny Mountains, northeast Spain), exposed both to anthropogenic pollutants and natural African dust, was analyzed for the period 1983–2000. On the basis of back trajectories and synoptic charts we distinguished four source regions: (1) African, (2) European, (3) Oceanic, and (4) Local. The chemical characteristics of each provenance were interpreted in relation to the emission processes at each source region. The temporal trends between 1983 and 2000 in the volume weighted mean (VWM) concentrations showed an upward trend for alkalinity in European, Local, and Oceanic provenances, while they showed a slight (nonsignificant) downward trend for African rains. All provenances exhibited a significant decline in excSO4−2, which was most pronounced for European rains (b = −5.7 μeqL−1 yr−1). Because NO3− remained about constant (except for European rains), NO3− acquired a more important role in the acid anion contribution. A reduction of the acid deposition for European, Local, and Oceanic rains was observed, as well as an increase in the global deposition of alkalinity. The role of African rains appeared as a determinant in the accumulated alkalinity during the period. A quantification of the transport of pollutant species (SO4−2, NO3−, and NH4+) from eight contributing European subregions was obtained on the basis of the residence time of the trajectories in each subregion. It suggested that not only subregions closer to the receptor point, such as the Iberian Peninsula, France, and the United Kingdom, were important contributors to the deposition of SO4−2, NO3−, and NH4+ but also distant sites such as Scandinavia contributed considerably.

Wet and dry African dust episodes over eastern Spain

“…These events are known as red rains for this reason. The chemistry of these episodes is characterized by very high pH and high concentration of Ca +2 [ Avila and Alarcón , 2003]. The African episodes had pH > 6 and [Ca +2 ] > 80 μeq/L.…”

Inventory of African desert dust events over the southwestern Iberian Peninsula in 2000–2005 with an AERONET Cimel Sun photometer

“…Wet desert episodes require other methods to be accounted for. As is shown by Escudero et al [2005], a criterion based on chemical analysis (pH > 6 and [Ca +2 ] > 80 μ eq L −1 ) allows the discrimination of these episodes [ Avila and Alarcón , 2003].…”

“…[2005], a criterion based on chemical analysis (pH > 6 and [Ca +2 ] > 80 meq L À1 ) allows the discrimination of these episodes [Avila and Alarcón, 2003].…”

Determination of the contribution of northern Africa dust source areas to PM10 concentrations over the central Iberian Peninsula using the Hybrid Single‐Particle Lagrangian Integrated Trajectory model (HYSPLIT) model

“…Furthermore, chemical compounds emitted from North African deserts, which represent a source of alkalinity that neutralizes atmospheric acidity, can influence the rainfall composition characteristics. This is particularly relevant over the Mediterranean basin [ Löye‐Pilot et al , 1986; Losno et al , 1991; Rodà et al , 1993; Camarero and Catalán , 1998; Alastuey et al , 1999; Avila and Alarcón , 1999, 2003; Avila and Rodà , 2002].…”