The chemical composition of cloud and rainwater. Results of preliminary measurements from an aircraft

Using an aircraft, preliminary investigations have been carried out into the chemical composition of clouds. The emphasis was on testing the sampling devices under several conditions. The results clearly show a considerable spatial distribution in pollutant concentrations that must have been caused by the contribution of many plume sources and the inhomogeneity of cloudwater density as well. Rather high concentrations of H₃O⁺. Cl⁻, NO⁻₃, SO²⁻₄, NH⁺₄ and H₂O₂ were measured. Except for H₂O₂, these components are scavenged very fast during travel over short distances over source regions. Moreover H₃O⁺, NO⁻₃ and SO²⁻₄ are likely to be formed by chemical reactions of gaseous precursors with oxidants in the liquid phase. This may explain the marked decrease in high background H₂O₂ concentrations (ppm range). Relatively high (molar) NO⁻₃ /SO²⁻₄ ratios mainly varying from 1 to 2 were measured over The Netherlands near source areas. The lower values found during a flight over southern Scandinavia are in agreement with data from literature. Occasionally the chloride concentration was found to be much higher than could be expected from rain network data.