Chemical characteristics of wet precipitation in urban and mountainous sites of Jeju Island

Abstract

Wet precipitation samples were collected in Jeju City and Mt. Halla-1100 site (a site at an altitude of 1100 m on Mt. Halla) during 2011−2013, and their major ionic species were analyzed to examine the chemical composition and characteristics. A comparison of ion balance, electric conductivity, and acid fraction of precipitation revealed correlation coefficients in the range of r = 0.950~0.991, thereby implying the high quality of analytical data. Volume-weighted mean pH and electric conductivity corresponded to 4.86 and 25.5 μS/cm for Jeju City, and 4.98 and 15.1 μS/cm for Mt. Halla-1100 site, respectively. Ionic strengths of the wet precipitation in Jeju City and Mt. Halla-1100 site corresponded 0.3 ± 0.5 and 0.2 ± 0.2 mM, respectively, thereby indicating that more than 30 % of total precipitation was within a pure precipitation criteria. The precipitation with a pH range of 4.5 − 5.0 corresponded to 40.8 % in Jeju City, while the precipitation with a pH range of 5.0 − 5.5 corresponded to 56.9 % in Mt. Halla-1100 site, thereby indicating slightly more weak acidity than that in Jeju city. The volume-weighted mean concentration (μeq/L) of ionic species was in the order of Na+ > Cl− > nss-SO4 2− > NO3 − > Mg2+ > NH4 + > H+ > nss-Ca2+ > PO4 3− > K+ > CH3COO− > HCOO− > NO2 − > F− > HCO3 − > CH3SO3 − at Jeju City area, while it corresponded to Na+ > Cl− > nss-SO4 2− > NO3 − > NH4 + > H+ > Mg2+ > nss-Ca2+ > PO4 3- > CH3COO− > K+ > HCOO− > NO2 − > F− > HCO3 − > CH3SO3 − at Mt. Halla-1100 site. The compositions of sea salts (Na+, Cl−, Mg2+) and secondary pollutants (NH4 +, nss-SO4 2−, NO3 −) corresponded to 66.1 % and 21.8 %, respectively, in Jeju City and, 49.9 % and 31.5 %, respectively, in Mt. Halla-1100 site. The acidity contributions in Jeju City and Mt. Halla-1100 site by inorganic acids, i.e., sulfuric acid and nitric acid, corresponded to 93.9 % and 91.4 %, respectively, and the acidity contributions by organic acids corresponded to 6.1 % and 8.6 %, respectively. The neutralization factors in Jeju City and Mt. Halla- 1100 site by ammonia corresponded to 29.8 % and 30.1 %, respectively, whereas the neutralization factors by calcium carbonate corresponded to 20.5 % and 25.2 %, respectively. From the clustered back trajectory analysis, the concentrations of most ionic components were higher when the airflow pathways were moved from the continent to Jeju area.