Fog and Precipitation Chemistry at a Mid‐land Forest in Central Taiwan

Abstract

We analyzed fog and bulk precipitation chemistry at a cloud forest in central Taiwan where mountain agriculture activities are highest. There were 320 foggy days (visibility <1000 m) recorded between April 2005 and March 2006. Fog was most frequent between April 2005 and July 2005 and in March 2006 (153/153 d) and least frequent in January 2006 (21/31 d). The total fog duration was 2415 h, representing 28% of the sampling period. Compared with bulk precipitation, fog was disproportionally enriched in NO(3)(-) and SO(4)(2-) relative to K(+), Ca(2+), Mg(2+), and NH(4)(+), resulting in higher a content of nitric acid and sulfuric acid than weak acids or neutral salts and, therefore, higher acidity (median pH, 4.9) in fog than in bulk precipitation (median and mean pH, 5.5). The very high input of NH(4)(+) (47 kg N ha(-1) yr(-1)) through bulk precipitation suggests that the use of fertilizer (ammonium sulfate and animal manure) associated with mountain agriculture has a major impact on atmospheric deposition at the surrounding forest ecosystems. The input of inorganic N reached 125 kg N ha(-1) yr(-1) and likely exceeded the biological demand of the forest ecosystem. Sulfate is the most abundant anion in fog at Chi-tou and in precipitation at various forests throughout Taiwan, suggesting that the emission and transport of large quantities of SO(2,) the precursor of SO(4)(2-), is an island-wide environmental issue.

Chemical Composition of Fog Water at Four Sites in Taiwan

“…Similar conditions are reported for other sites in Taiwan (Beiderwieden et al, 2007;Liang et al, 2009;Lin et al, 2010) as well as many sites all over the world (e.g., Wrzesinsky and Klemm, 2000;Collett et al, 2002;Tago et al, 2006;Li et al, 2011;Giulianelli et al, 2014;Herckes et al, 2015;Wang et al, 2015).…”

“…Besides tourism, the high-lying region of Xitou is intensively used for agriculture, along with heavy fertilizer input (Liang et al, 2009). The site is characterized by a quite regular daily wind regime.…”

“…The acidity was largely neutralized by the formation of ammonium from ammonia. This is related to sources from agriculture (Liang et al, 2009) and traffic in the larger region. High concentrations of K + , which are good indicators for biomass burning, underline the strong influence of agricultural-waste burning, in all likelihood burning of rice straw (Chen et al, 2008).…”

“…Yu (Liang et al, 2009). Studies of fog chemistry in Taiwan did not start until the 1990s, while only limited data is published from Mount Bamboo (Lin and Peng, 1998;Lin et al, 2010), Chilan Mountain (Chang et al, 2002;Beiderwieden et al, 2007), and Xitou Experimental Forest (Liang et al, 2009). Lin and Peng (1998) collected fog water on an hourly basis during 1996 and 1997 at Mt.…”

“…At the same site, nowadays known as Chilan Mountain Site (CLM), Beiderwieden et al (2007) presented median and minimum pH values of 4.13 and 2.24, while H + , NH 4 + , NO 3 -and SO 4 2-contributed 85% to the total equivalent ion concentration. For Xitou (XT), Liang et al (2009) reported an annual median pH of 4.9 of fog water with SO 4 2-and NH 4 + being the dominating ions. Overall, the data available for Taiwan is still relatively sparse.…”