本硏究於2001年在彰化市收集雨水並分析其主要離子濃度，再透過多變量 因子分析探討雨水之化學物質組成，以定量方式評估雨水中成份之來源。分析結 果發現2001年雨水平均pH値爲4.91，約有一半的降雨其pH小於一般判定酸雨 的5.0。雖然雨水中SO42-、NO3-的濃度只有臺北市的1/4，但因K+、Ca2+與Mg2+ 的濃度亦遠低於臺北，故pH與臺北市（4.91)十分相近。以特徵値大於1萃取出 三個主要因子，結果發現降雨深受海鹽飛沫的影響，其中Na+、Mg2+、Cl-、Ca2+ 解釋變異量很高，可能是因靠近海洋有關。降雨中人爲污染的影響，應與彰化市 農業及工業發達有關，NH4+、SO42-、NO3-在因子中的負荷量皆呈高度相關。酸 因子主要以H+單獨呈現，代表雨水並未受到酸雨的主要物質SO42-、NO3-的主導， 而是致酸性及致鹼性離子綜合造成的結果。而塵土因子Ca2+及K+則必須扣除海 鹽之後才能顯示出來。

The data and interpretations presented in this paper are based on an analysis of precipitation in Changhua City during 2001. Factor analysis was used to evaluate relationships of ions in the precipitation to provide a quantitative determination of sources of rainwater contamination. Approximately half of the precipitation events had a pH < 5.0 and could be classified as acid rain. Although the mean concentrations of SO4 2- and NO3 - were only 1/4 of those reported for Taipei, the annual mean pH of precipitation of 4.91, was very close to that of Taipei (4.89). This figure probably resulted from the very low concentrations of base cations Na+, K+, Ca2+, and Mg2+ in the precipitation of Changhua. Three main factors were extracted with eigen values > 1. The first factor has high loadings on Na+, Mg2+, Cland Ca2+ and could be attributed to sea salt aerosol influence. The second factor has high loadings on NH4 +
SO4 2-
NO3 - and clearly indicates anthropogenic pollution sources. The third factor has a high loading only on H+ indicating that the pH of precipitation in Changhua City was not dominated only by acidic pollutants, SO4 2-
NO3 but rather by all components, both acidic and base ions, and this is evident from the strong relationship between precipitation pH and a combination of SO4 2-
NO3 - and NH4 +
Ca2+ concentrations. The influences of soil and dust cannot be recognized without sea salt correction, but after the correction, Ca2+ and K+ factors can be interpreted as being associated with dust pollution.