Precipitation Chemistry Observed at Five Island Stations in East Asia

Ya-Ching Jao and Neng-Huei (George) Lin*

The precipitation chemistry observed at five island stations in East Asia, including Gosan (126.27°E, 33.48°N, 72 m asl), Cheju Island, Korea; Cape Hedo (128.2°E, 26.8°N, 60 m asl), Okinawa, Japan; Peng-Jia Islet (122.07°E, 25.63°N, 101.7 m asl), Matsu Island (119.92°E, 26.17°N, 97.842 m asl), and Kinmen Island (118.29°E, 24.41°N, 47.88m asl), Taiwan, will be compared. Gosan, Cape Hedo and Peng-Jia Islet are considered as remote and background stations (group A), while, the other two stations are very close to China (group B). This work will elucidate the geographical distribution of chemical composition of rainwater in East Asian oceanic region, and further to assess wet deposition fluxes of sulfate and nitrate in these stations. These datasets will be also characterized based on their corresponding source regions. The daily sampling period at Gosan, Cape Hedo and Peng-Jia Islet were from January 2003 to December 2007; for Matsu Island and Kinmen Island, it was from April 2005 to December 2008. Principal ions of group A in rainwater were seasalt ions, such as Cl- and Na+, accounting for more than 50%, and followed by SO4 2-. In group B, seasalt ions are still the principal ions in Matsu Island, followed by SO4 2- (16%) and H+(12%), while in Kinmen Island, the principal ions were SO4 2- (20%) and H+ (16%). For all five island stations, rain events containing higher SO4 2- were found to be associated with northeast monsoon and frontal systems, which are capable of transporting atmospheric pollutants to the sites via longrange transport. The stations in two groups have various chemical compositions with respect to different source regions. It was also shown the influences of long-range transport on group A, in which has very limited local emissions. Among five stations, Matsu Island had the lowest average pH of 4.5 and the highest nss-SO4 2- l-1, and it also had the highest frequency (84%) of acid rain (which is defined as pH < 5.0). The highest average pH of 4.95 was found at Cape Hedo, which had the lowest nss-SO42- l-1. The ratio of nss-SO4 2- / NO3-, somewhat reflecting the influences of long-range transport, was of 1.66 at Gosan, 1.93 at Cape Hedo, 1.41 at Peng-Jia Islet, 1.56 at Matsu Island, and 1.96, the highest ratio at Kinmen, respectively. More detailed statistic analyses will be also presented.

*Corresponding author: +886-3-4254069, Email: