Chemical and strontium isotope characterization of rainwater in Beijing during the 2008 Olympic year

To improve the air quality during the 2008 Beijing Olympic Games, the Beijing Municipal Government enforced a series of emission control measures. This provided a valuable case study to evaluate the effectiveness of these aggressive measures on mitigating air pollution and improving the atmospheric environment. In this paper, we report the first results of the chemical and Sr isotopic compositions of the rainwater in Beijing during the 2008 Olympic year. The ionic composition of samples show that Ca2 + and NH4+ were the dominant cations, accounting for about 76–97% of the total cations, and that SO42 − and NO3− were the major anions, accounting for 61–91% of the total anions measured. Using Na as the indicator of marine origin and Al as that of terrestrial inputs, the proportions of sea salt and terrestrial elements were estimated from elemental ratios. The calculated results indicate that the major chemical components were mainly of non-sea-salt origin. Good correlation between Ca2 + and Sr2 + (R2 = 0.85) in rainwater samples indicates the potential of Sr as a provenance tracer for Ca. Sr2 + concentrations in rainwater samples ranged from 0.01 to 2.87 μmol l− 1, with 87Sr/86Sr ratios from 0.7092 to 0.7109. All of the samples had a 87Sr/86Sr ratio higher than that of seawater. The 87Sr/86Sr isotopic and elemental ratio systems show that the data set of rainwater was mainly distributed between the seawater end-member (~ 0.70917) and the soil dust end-member (0.7111–0.7115), and the analysis indicate that the effect of anthropogenic inputs could decrease in 2008. Comparisons of the chemical composition of the rainwater in different periods show that all chemical components, except NH4+, had the lowest concentration levels during the Olympic Game period. The VWM concentrations of major ions in the rainwater decreased significantly during the Olympic period by up to 29% for SO42 −, 39% for NO3−, 38% for Ca2 +, 51% for Mg2 +, 57% for K+, and 44% for Na+, compared with the pre-control period. The concentrations of almost all species decreased during the 2008 Olympics, most likely due to both strict emission controls and favorable meteorological conditions.