On the chemistry of fogwater sulfur (IV) and nitrogen (III)

摘要

Fog chemistry was studied with particular emphasis on the reduced species of sulfur and nitrogen, S(IV) and N(III), in a polluted source region in Germany. Immediately after sampling, S(IV) and N(III) were preserved by appropriate derivatization methods for later analyses. A differentiation was carried out between non-oxidizable S(IV) species and total Fogwater contained high concentrations of various pollutants but only little or no acidity. While significant concentrations of N(III) were found, namely 3 - 52 μmol L~(-1), oxidizable S(IV) was in the range 0.006 - 0.28 mmol L~(-1). A two-phase chemical box model is used to interprete the chemistry. In a ,first step simulations were performed under the assumption that phase equilibrium was continuously maintained. It is concluded that S(IV) enrichment occurred resulting from phase partitioning of gaseous SO_2. Fogwater N(III) was very sensitive to both gaseous HNO_2 and HCHO which were not measured. From the free S(IV) / HMS ratios simulated it is infered that HCHO most likely was low. Under these conditions the reaction between dissolved NO_2 and free S(IV) is an important N(III) source and could explain the high N(III) values found even in the absence of HNO_2. NO_2 dissolution obeying first order kinetics, as suggested recently based on cloud chamber experiments, would presumably lead to even higher N(III) concentrations.