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

We analyzed fog and bulk precipitation chemistry at a cloud
forest in central Taiwan where mountain agriculture activities
are highest. Th ere 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). Th e total fog duration was 2415 h, representing 28% of the
sampling period. Compared with bulk precipitation, fog was
disproportionally enriched in NO3– and SO42– relative to K+,
Ca2+, Mg2+, and NH4+, 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). Th e very high input
of NH4+ (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.
Th e 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 SO2, the
precursor of SO42–, is an island-wide environmental issue.