Absorption properties and size distribution of aerosol particles during the fall season at an urban site of Gwangju, Korea

Abstract

To investigate the influence of pollution events on the chemical composition and formation processes of aerosol particles, 24-h integrated size-segregated particulate matter (PM) was collected during the fall season at an urban site of Gwangju, Korea and was used to determine the concentrations of mass, water-soluble organic carbon (WSOC) and ionic species. Furthermore, black carbon (BC) concentrations were observed with an aethalometer. The entire sampling period was classified into four periods, i.e., typical, pollution event I, pollution event II, and an Asian dust event. Stable meteorological conditions (e.g., low wind speed, high surface pressure, and high relative humidity) observed during the two pollution events led to accumulation of aerosol particles and increased formation of secondary organic and inorganic aerosol species, thus causing PM2.5 increase. Furthermore, these stable conditions resulted in the predominant condensation or droplet mode size distributions of PM, WSOC, NO3-, and SO4 2-. However, difference in the accumulation mode size distributions of secondary water-soluble species between pollution events I and II could be attributed to the difference in transport pathways of air masses from high-pollution regions and the formation processes for the secondary chemical species. The average absorption Ångström exponent (AAE370-950) for 370-950 nm wavelengths > 1.0 indicates that the BC particles from traffic emissions were likely mixed with light absorbing brown carbon (BrC) from biomass burning (BB) emissions. It was found that light absorption by BrC in the near UV range was affected by both secondary organic aerosol and BB emissions. Overall, the pollution events observed during fall at the study site can be due to the synergy of unfavorable meteorological conditions, enhanced secondary formation, local emissions, and long-range transportation of air masses from upwind polluted areas.

Size distribution and formation processes of aerosol water-soluble organic carbon during winter and summer in urban Beijing

“…The MMADs of SO 4 2− and NO 3 − in the coarse mode were slightly lower than those of Ca 2+ (Ca 2+ : 5.87 ± 1.82 μm; SO 4 2− : 5.21 ± 1.81 μm; NO 3 − : 6.28 ± 2.92 μm), indicating that NO 3 − and SO 4 2− were associated with base cations. This result suggested that part of the WSOC in coarse mode was possibly condensed on the surface of Ca(NO 3 ) 2 and CaSO 4 (Park and Yu, 2019). Furthermore, the backward trajectories (Fig.…”

“…Particularly, high RH conditions could enhance the formation of secondary organic carbon through aqueous-phase oxidations of VOC (Section 3.3), resulting in an increase in the WSOC concentrations. These meteorological conditions could accelerate the accumulation of organic carbon aerosols through VOC processes (Park and Yu, 2019).…”

A Regional Aerosol Model for the Oceanic Area around Eastern China Based on Aerosol Robotic Network (AERONET)

“…Though a slight shift of fine mode peak positions can be observed among sites' VPSDs in autumn and winter, shown in Figure 3c,d, the deviations of the radius location of fine mode peaks were small. The shifted fine modes suggest the appearance of smaller particles, such as black carbon from North China [8,32], which is an indicator of pollution [33]. The amplitudes of both fine and coarse mode peaks of VPSDs in these two seasons were similar to those in spring and summer.…”

“…The spectral ICRI of the summer was the lowest, and that of winter was the highest, while those of spring and autumn were medium and had roughly the same values. The high value of the imaginary part indicated pollution conditions in winter for the highly absorbing aerosols, which might be related to localized pollution sources such as North China [32,34,35]. The spectral curve of ICRI moved upwards synchronously, although there were slight discrepancies in spectral distributions as the time passed from summer to winter, implying changes in pollution compositions [36].…”