Abstract
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. One single fog sample (pH 3.17) was influenced by local volcanic activity, otherwise the pH ranged from 3.23 to 6.41 in fog and from 3.59 to 6.31 in rain. All the respective air masses arrived from the northeast, but exhibited two distinct groups: Group_1 had high concentrations of all ions (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 and industrialized regions of mainland China. Group_2 was from air masses with long travel times over the ocean and relatively low total ion concentrations (80–570 µeq.·L−1) and higher pHs (median 4.80). The cleanest samples are among the cleanest reported in the literature of worldwide 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 higher than the variability of 10−pH, which shows that the pH is a rather robust parameter in contrast to its drivers such as non-sea-salt sulfate.
Highlights
Acid precipitation has dominated atmospheric chemistry research over many years during the 1980s and 1990s but has lost some attention since
Each year in January and February, there is a well developed high surface pressure system over the cold East Asian continent, the Siberia High with its center at about 50°N and 100°E and a ridge extending towards southeast into China
While the mountain fog persisted over long time periods, rain was collected at a site that is situated about 200 m lower a.s.l
Summary
Acid precipitation has dominated atmospheric chemistry research over many years during the 1980s and 1990s but has lost some attention since It is the gaining importance of other topics such as greenhouse gas concentrations and chemistry, or the rapid development of instrumentation and remote sensing techniques to study more substances and to develop better spatial coverage of atmospheric conditions, and the increase of the pH of precipitation water that lead to the presumption that acid precipitation loses relevance. High emissions of air pollutants including precursors of atmospheric acidity lead to low pHs of rain, clouds, and fog (e.g., [4,5,6,7,8]) and to highly acidic aerosol particles (e.g., [9,10]). Is it feasible to assume that conditions of very clean cloud and rainwater can occur in this region? How will the pH be controlled under such conditions?
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