| dc.description.abstract | Water-soluble inorganic ions (WSIIs) of atmospheric aerosol have a significant effect on the atmospheric environment. These inorganic ions need to observe with high time-resolution as they change their properties rapidly in the environment. This study measured PM2.5 WSIIs with the semi-automated method at the Fengyuan High School (FHS) in November 2017, Lulin Atmospheric Background Station (LABS) in March-April 2018, and at National Central University (NCU) in April-May 2018. The measurements were toward PM2.5 most of the time; however, for some time, the system switched to PM10 WSIIs. The results accompanying related monitoring data at the stations were suitable for investigating aerosol chemistry, physics, optical properties, and source contributions.
The averages of PM2.5 mass concentrations for the events of biomass burning (BB) and mountain-valley (M-V) wind were 21.8 ± 6.6 and 20.1 ± 1.3 μg m-3, respectively, in contrast to that of non-event PM2.5 mass concentration of 10.2 ± 6.8 μg m-3. Meanwhile, the averages of PM2.5 WSIIs at non-event period, BB, and M-V wind events were 4.9 ± 3.1 μg m-3, 5.7 ± 2.0 μg m-3, and 9.9 ± 0.7 μg m-3, respectively. Obviously, pollution events brought more PM2.5 WSIIs from the comparison. In high concentration events at the FHS and NCU (May), the averages of PM2.5 mass concentrations were 23.7 ± 6.8 and 21.2 ± 2.6 μg m-3, respectively. In contrast, the high concentration event at NCU (April) was as high as 80.6 ± 5.5 μg m-3 in PM10. The PM2.5/PM10 ratios were 0.3-0.6 and 0.2-0.4 at NCU and FHS, respectively. Evidently, coarse particles were more in PM10 at both sites. Comparing the fraction of NO3- and SO42- in particles, NO3- is higher than SO42- in PM10, but the reverse is true in PM2.5. It implies that a lot of coarse NO3- existing in PM10. For monitoring results in the ground level, NO2- observed to form during nighttime and correlated well with relative humidity (RH) and NO2 concentration. The PM2.5 events were under the influences of long-range transport of BB smoke and anthropogenic pollution transports at LABS. In contrast, the land-sea breeze was mainly responsible for high particulate concentrations at NCU and FHS, especially for pollution accumulation from low wind speed and shallow boundary layer at night.
As revealed from this study, low RH, non-calm wind, and non-fog environment provided a good correlation between aerosol chemical properties and aerosol optical depth (AOD) at the summit of LABS (R2=0.7, p< 0.05). Even in the ground level, aerosol chemical properties and AOD correlated moderately with each other under a non-calm wind environment (R2=0.5, p< 0.05). The application of the ISORROPIA II model for aerosol acidity simulation indicated that mountain aerosol was acidic, and the aerosol in the ground level was more toward acidic or neutral. The computations of molar concentrations of the correlated WSIIs to infer aerosol compound form resulting in more potassium sulfate and potassium nitrate in BB events at LABS and ammonium nitrate in high particulate events in the plain area
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