Yearly Mean
1972 1973 1974 1975 1976 1977 1978 1979 1980 1981
* 5.4 * * * 5.3 5.2 6.5 6.3 6.6
1982 1983 1984 1985
6.8 6.5 6.7 6.5
1986 1987 1988 1989 1990 1991 1992 1993 1994 1995
5.4 4.3 4.6 4.5 4.4 4.7 5.3
1996 1997 1998 1999
5.9 5.8 5.2 5.3 4.8 5.0 4.6
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009
4.6 4.6 4.9 4.5 4.7 4.5 4.4 4.4
2010 2011 2012 2013
4.2 4.5 4.5 4.3 * *

According to the EPA's regulation, rainfall with pH value below 5.0 is classified as acid rain, indicated by red italics here. http://www.cwb.gov.tw/V7e/observe/phRain/index.htm

This is pretty disturbing. These are the figures for acid rain in Keelung - and it looks pretty grim. There are also daily figures that show that it's basically all acid rain up there. In fact, i was just in Taipei, and the whole city really does look grim and grimey. You can see this black rain stain on every building to various degrees according to age.
Taidong, however, is still ok - about the cleanest place on the island, not surprisingly.