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Hourly measurements of PM 2.5 , organic and elemental carbon (OC and EC), inorganic ionic species, and elemental constituents were made between February 1 and March 31, 2011, at a South Area Supersite at Gwangju, Korea. Over the two-month study period, daily PM 2.5 mass concentration exceeded the 24-hr average Korean NAAQS of 50.0 μg/m 3 on 20 days, of which two pollution episodes (episodes I and II) are investigated. Episode I (February 01-08) is associated with regional pollution along with wild fire smoke emissions over southern China, and also characterized by high CO/NO x ratios and high K + concentrations. While episode II (March 11-12) is characterized by locally produced pollution with low CO/NO x ratios, and broad variations in OC, EC, and NO 3 -concentrations. For episode I, the 1-hr PM 2.5 mass concentration ranged from 27 to 159 μg/m 3 with a mean of 88 μg/m . Hourly maximum contributions of SO 4 2-and NO 3 -to the PM 2.5 mass were 54 and 66%, respectively. An elevated NO 3 -concentration was observed along with high OC and EC concentrations, suggesting the influence of local emissions. The pattern of SO 4 2-variations in relation to wind direction and the strong correlation between SO 2 and SO 4 2-suggest local SO 2 emissions were likely an important source of SO 4 2-at the site.

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