Abstract
In order to identify the seasonal variability and source of carbonaceous aerosols in relation to haze occurrence, organic carbon (OC) and elemental carbon (EC) were continuously measured at the Taehwa Research Forest (TRF) near the Seoul metropolitan area from May 2013 to April 2014. For the entire experiment, the mean OC (5.1 µgC/m3) and EC (1.7 µgC/m3) concentrations of TRF were comparable to those of Seoul, with noticeably higher concentrations in winter and spring than in other seasons, and during haze days (6.6 ± 3.2 and 2.1 ± 1.0 μgC/m3) than during non-haze days (3.5 ± 2.2 and 1.3 ± 0.8 μgC/m3). The seasonal characteristics of OC and EC reveal the various sources of haze, including biomass combustion haze either transported for long distances or, in spring, from domestic regions, the greatest contribution of secondary organic carbon (SOC) in summer, and fossil fuel combustion in winter and fall. In addition, the seasonal OC/EC ratios between haze and non-haze days highlights that the increase in EC was more distinct than that of OC during haze episodes, thus suggesting that EC observed at a peri-urban forest site serves as a useful indicator for seasonally varying source types of haze aerosols in the study region.
Highlights
For the entire experiment period, mean and maximum organic carbon (OC), elemental carbon (EC), and TC concentrations were 5.1 ± 3.2 μgC/m3 and 1.7 ± 1.0 μgC/m3, 6.8 ± 3.9 μgC/m3 and 22.7 μgC/m3, 8.0 μgC/m3, and 27.3 μgC/m3, respectively. These average OC and EC concentrations were higher than those observed in Jeju (2.9 μgC/m3 and 0.8 μgC/m3 ) [28], the background of Northeast Asia, and comparable to those observed in Seoul
It is evident that OC and EC were inversely correlated with O3, which is usually higher from May to June
The average OC and EC concentrations were significantly higher on haze days (6.6 ± 3.2 and 2.1 ± 1.0 μgC/m3 ) than on non-haze days (3.5 ± 2.2 and 1.3 ± 0.8 μgC/m3 ), suggesting OC and EC as major constituents of haze aerosol
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. In Seoul, OC and EC concentrations were reported to be higher during winter and spring than in summer and fall [12] This type of seasonality is observed in major cities in Korea, where the ratio of OC to EC varies due to the influence of local sources. Forest (TRF) has been established near the Seoul metropolitan area (SMA) to investigate the effects of mixed emissions of anthropogenic and natural sources, mainly from vehicles and vegetation, on air quality [15]. We continuously determined OC and EC concentrations of PM2.5, along with reactive gases including O3 , NO2 , CO, and SO2, at the peri-urban TRF site for one year, and examined the seasonal variability and sources of carbonaceous aerosols with an emphasis on haze occurrence
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