Chemical Composition and Light Absorption of [PM.sub.2.5] Observed at Two Sites near a Busy Road during Summer and Winter

• Published in: Applied sciences 2020-07, Vol.10 (14)
• Main Authors: Park, Seungshik, Hong, Hue Dinh Thi, Cho, Sung Yong, Bae, Min-Suk
• Format: Article
• Language: English
• Subjects: Automotive emissions; Chemical properties; Comparative analysis; Environmental aspects; Location; Observations; Optical properties; Particles; Roads; South Korea; Streets; Summer; Winter
• ISSN: 2076-3417; 2076-3417
• DOI: 10.3390/app10144858

To examine the difference in the major chemical composition of fine particulate matter ([PM.sub.2.5]) between two roadway sites, 24 h integrated [PM.sub.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 N[O.sub.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.sub.2.5] concentrations ([PM.sub.2.5] episode) which exceeded the Korean [PM.sub.2.5] standard (35 [micro]g/[m.sup.3]) were linked to increases in organic matter (OM) and S[O.sub.4.sup.2-] concentrations that accounted for on average 35-41% and 26-30%, respectively, of the [PM.sub.2.5] at the two sites. The increased S[O.sub.4.sup.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 exponent (AAE) values calculated at wavelengths of 370-950 nm ([AAE.sub.370_950nm]) and 370-520 nm ([AAE.sub.370_520nm]), and the poor correlation of absorption coefficient by brown carbon (BrC) at 370 nm ([Abs.sub.BrC370nm]) with [K.sup.+] ([R.sup.2] = 0.00) also suggest a significant contribution of traffic emissions to OM. However, the wintertime [PM.sub.2.5] episode was strongly related to the enhanced OM and N[O.sub.3.sup.-] concentrations, which contributed 26-28% and 22-23% of the [PM.sub.2.5] concentration, respectively. It is interesting to note that there were two distinct OC/EC ratios in winter: a lower OC/EC (~3.0), which indicates a significant contribution of traffi