Park, S; Hong, HDT; Cho, SY; Bae, MS (2020). Chemical Composition and Light Absorption of PM2.5 Observed at Two Sites near a Busy Road during Summer and Winter. APPLIED SCIENCES-BASEL, 10(14), 4858.

To examine the difference in the major chemical composition of fine particulate matter (PM2.5) between two roadway sites, 24 h integrated PM(2.5)samples were simultaneously collected both 15 m (Buk-Ku District Office (BKO) site) and 150 m (Chonnam National University campus (CNU) site) away from busy roads during the summer and winter periods; these samples were taken to determine the concentrations of organic and elemental carbon (OC and EC), water-soluble organic carbon (WSOC), and water-soluble inorganic species. In addition, the real-time aerosol light absorption coefficients (Abs) were measured using a dual-spot seven-wavelength aethalometer at the CNU site to evaluate the influence of traffic and biomass burning (BB) emissions on the concentrations of organic aerosol particles. The hourly NO(2)concentration was also observed at an air pollution monitoring network that is about 2 km away from the CNU site. During summer, 24 h PM(2.5)concentrations (PM(2.5)episode) which exceeded the Korean PM(2.5)standard (35 mu g/m(3)) were linked to increases in organic matter (OM) and SO(4)(2-)concentrations that accounted for on average 35-41% and 26-30%, respectively, of the PM(2.5)at the two sites. The increased SO(4)(2-)concentration was most likely attributable to the inflow of long-range transported aerosols, rather than local production, as demonstrated by both the MODIS (Moderate Resolution Imaging Spectroradiometer) images and transport pathways of air masses reaching the sites. On the other hand, the OM, WSOC, and EC concentrations were directly attributable to traffic emissions at the sampling sites, as supported by the tight correlation between the OC and EC. A small difference between the absorption angstrom ngstrom exponent (AAE) values calculated at wavelengths of 370-950 nm (AAE(370-950nm)) and 370-520 nm (AAE(370-520nm)), and the poor correlation of absorption coefficient by brown carbon (BrC) at 370 nm (Abs(BrC370nm)) with K+(R-2= 0.00) also suggest a significant contribution of traffic emissions to OM. However, the wintertime PM(2.5)episode was strongly related to the enhanced OM and NO(3)(-)concentrations, which contributed 26-28% and 22-23% of the PM(2.5)concentration, respectively. It is interesting to note that there were two distinct OC/EC ratios in winter: a lower OC/EC (similar to 3.0), which indicates a significant contribution of traffic emissions to the OC and EC, and a higher OC/EC (similar to 6.5), which suggests an additional influence of BB emissions as well as traffic emissions at the sites. Strong correlations between the OC and EC (R-2= 0.72-0.83) and the enhanced AAE(370-520nm)values compared to the AAE(370-950nm)support that BB emissions were also an important contributor to the wintertime OM concentrations as well as traffic emissions at the two sites. A good correlation between the gaseous NO(2)and NO(3)(-)and meteorological conditions (e.g., low wind speed and high relative humidity) suggest that the heterogeneous oxidation of NO(2)on moist particles could be an important contributor to wintertime particulate NO(3)(-)formation at the sites. The OC concentrations during summer and winter were higher at the BKO site, with a higher traffic flow and a shorter distance from the roadway than at the CNU site. However, there were slight differences in the concentrations of secondary inorganic species (NO3-, SO42-, and NH4+) between the sites during summer and winter.