Influence of meteorological factors and polluting environment on rain chemistry and wet deposition in a rural area near Chimay, Belgium

This paper focuses on a detailed analysis of the effects of meteorological factors explaining the variability of rain composition.Inorganic composition of 113 individual rain events was measured from May 2002 to October 2005 at a rural site near Chimay, in the western part of the Belgian Ardennes. Original models were fitted for each studied ion (H+, Mg2+, Ca2+, K+, NH4+, Na+, Cl−, NO3− and SO42−) to relate rain event concentration or wet deposition to the rainfall volume (R), the length of the antecedent dry period (ADP), the volume of the previous event (Rprev) as well as to the mean wind speed and the prevailing wind direction during both the dry and the rainy periods. These variables explained from 32% (H+) to 69% (NO3−) of rain concentration variability. Concentrations decreased logarithmically with increasing R values except in case of H+ for which a positive effect of rain volume on rain concentration was observed. ADP affected positively rain concentrations of all ions excluding K+ and H+ for which, respectively, a nonsignificant and a negative effect of this variable was observed. Increasing Rprev strengthened the effect of the variable R on H+, Mg2+, Ca2+, Na+, NH4+ and SO42− concentrations while it softened the effect of ADP on NO3− concentrations. Wind speed and direction during dry and rainy periods explained together from 8% (K+) to 38% (Na+) of rain concentration total variability. R2 coefficients of the wet deposition models ranged from 0.51 (K+) to 0.79 (SO42−). For all ions, wet deposition increased significantly with increasing R values while the effects of the other variables were similar to those on concentrations. Wind conditions during dry and rainy periods explained from 4% (H+) to 24% (Na+) of wet deposition total variability. On an annual scale, the total dry period duration, the total rainfall volume as well as the shape of the distributions of the length of the antecedent dry periods and of the rain event volume are important parameters that influence annual wet deposition.