A field study of the incorporation of atmospheric ion species into raindrops

Urban atmospheric ion species are incorporated into raindrops near the ground. Rain was collected from July 1993 through June i994 at the midtown in Kobe City and at the top of Mt. Maya which is located adjacent to the town at an altitude of 700 m. The incorporated H+ was about one-half of the total deposited amount of H+ at the midtown. The ratios of the incorporated ions other than H+ to the total deposited amount of ions at the midtown ranged from 0.09 to 0.3i. Therefore, the majority of ions deposited at the midtown was supplied from clouds. Sodium ion (Na+), Ca2+ and Mg2+ in suspended particulate matter (SPM) were more abundant during the rain period than the non-rain period. When the SPM concentration was high, the pH of raindrops was lowered by acidic components such as SO2 which had increased in the atmosphere. Generation of H+ ion in raindrops near the ground could be due to the incorporation of SO2 supplied from diesel exhaust gas.