pH Control in Fog and Rain in East Asia: Temporal Advection of Clean Air Masses to Mt. Bamboo, Taiwan

Klemm O, Tseng W-T, Lin C-C, Klemm K I, Lin, N-H

Zusammenfassung

Fog and rain was collected during an 18-day period in January 2011 at Mt. Bamboo,northern Taiwan. Almost 300 hourly fog samples and 16 daily rain samples were taken. Onesingle fog sample (pH 3.17) was influenced by local volcanic activity, otherwise the pH rangedfrom 3.23 to 6.41 in fog and from 3.59 to 6.31 in rain. All the respective air masses arrivedfrom the northeast, but exhibited two distinct groups: Group_1 had high concentrations of allions (median interquartile range of total ion concentrations 3200-6200 μeq.·L-1) and low pHs(median 3.52), the respective air masses had travelled over densely populated andindustrialized regions of mainland China. Group_2 was from air masses with long traveltimes over the ocean and relatively low total ion concentrations (80-570 μeq.·L-1) and higherpHs (median 4.80). The cleanest samples are among the cleanest reported in the literature ofworldwide fog and rain. In both groups, the pH was governed by the balance of sulfate,nitrate, ammonium, and, in some cases, calcium. The variability of these ions was higherthan the variability of 10-pH, which shows that the pH is a rather robust parameter in contrastto its drivers such as non-sea-salt sulfate.