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.
The aerosol characteristics between haze episode and Asian dust event were identified in January and March, 2013 in Gwang-ju of Korea to investigate the metal elements, ionic concentrations and carbonaceous particles of PM 2.5 and PM 10 . In the haze episode, the concentrations were increased 1~3.2 times of ionic species and 1.6~2.7 of metal elements. Especially, the concentration of NO 3 -, SO 4 2-and NH 4 + + consists of 50 percent in ionic species during haze episode that was higher than Asian dust event. This suggests that secondary aerosols from anthropogenic air pollution were mainly contributed by haze episode. During the Asian dust event, increase of metal concentrations was higher than haze episode because of remarkable increase of Ti, K and Fe originated from soil. The concentrations of carbonaceous particles were increased 2.5 times during haze episode, and 2.4 times of OC and 2.1 times of EC during Asian dust event in PM 2.5 . However, these aerosol mass concentration does not affect the OC/EC ratio. The average equivalence ratios of cations/anions in PM 2.5 were 0.99 in haze episodes and 0.94 during non-event day. The neutralization factor of NH 3 was higher than that of CaCO 3 . Futhermore, NH 4 + + aerosol was aged due to atmospheric stagnation that might be affected by the haze episode.
In order to provide a better knowledge of visibility degradation during the PM2.5 event day (episodic high PM2.5 level, hereafter called as “event day”), the relationship between visibility and the chemical species of PM2.5 measured in Gwangju, Korea was estimated. Moreover, a visibility forecasting model was constructed by a statistical approach. The diurnal variation of visibility and PM2.5 concentration on the event day indicated that as the concentration of PM2.5 increased, more light was absorbed and scattered, resulting in visibility deterioration. The averaged visibility during the event day was 7.9 km, which was almost three times lower than that observed during a non-event day. Although the hygroscopic growth of aerosol was not considered in this study, it has been proved that NH4NO3 and organics dominantly contributed to the light scattering during the PM2.5 event day in Gwangju, Korea. The visibility determined in this study had also a negative correlation with PM10, nitrate, relative humidity, EC, OC, and sulfate. Meanwhile, visibility was positively linked with wind speed and temperature. The results of interrelationship and a multiple regression model suggest that among the meteorological variables, temperature was the main variable that influenced visibility.
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