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

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 ) 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 ) 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. OPEN ACCESSAtmosphere 2015, 6 1786

Fog Water Chemical Composition on Ailaoshan Mountain, Yunnan Province, SW China

“…In many studies, calcium (Ca 2+ ) has been found to be a major chemical component of fog water, mainly due to mineral dust from construction sites (Li et al, 2011) and land erosion (Liu et al, 2010;Klemm et al, 2015). However, in our study Ca 2+ contributes only slightly to the TIC, with a median of 3.7 ± 4.2%.…”

“…As shown in many previous studies, H 2 SO 4 and HNO 3 are the main acidifiers in fog water (e.g., Li et al, 2011;Degefie et al, 2015;Klemm et al, 2015;Simon et al, 2016). To measure the non-neutralized acidity of fog water, Hara et al (1995) proposed the quantitative index pAi, which is defined as the negative decimal logarithm of the nss-SO 4 2-concentration plus the NO 3 -concentration (Eq.…”

“…Calculating air mass backward trajectories from archived meteorological data is a common approach for deriving the origin of a certain air mass, and, thus, for identifying potential source regions of air pollutants (e.g., Yang et al, 2012;Klemm et al, 2015;Simon et al, 2015;Stein et al, 2015). For each fog sample, a 48-hour backward trajectory was calculated using the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model (Stein et al, 2015;Rolph, 2016) provided by the Air Resources Laboratory of the National Oceanic and Atmospheric Administration (NOAA) of the United States Department of Commerce (USA).…”

“…However, these acids were not measured in our study's protocol; so, even though these 30 samples did not meet the criteria for ion balance closing, there is a good chance that the ion analyses were of good quality. Therefore, instead of excluding the samples and losing valuable information, we followed the reasoning of Klemm et al (2015), who suggest not excluding data points from further analysis under such conditions. As such, we considered all samples that had not been flagged by the laboratories during chemical analysis as valid.…”

Surface Potential Driven Water Harvesting from Fog

“…Zeta potentials for PC membranes showed the greatest differences at pH values from 2.5 to 6, which is in the range of water harvested from typical fogs around the world (3.5−6 pH). 50,51 The highest level of zeta potential was observed for PC25+, with the lowest surface charge measured with KPFM. Interestingly, for pH values above 7, the difference in the zeta potential of the tested samples ceased to show significant changes.…”