| dc.description.abstract | This study used Positive Matrix Factorization (PMF) and Conditional Probability Function (CPF) to identify PM2.5 source contributions of the six stations in the “PM2.5 chemical composition monitoring and analysis study” in 2017 (henceforth referred to “2017 Study”). In addition, the Potential Source Contribution Function (PSCF) was applied to investigate the trajectory origins of sulfates through long-range transport to each site. Given the proportion of PM2.5 nitrate ion was higher in a high PM2.5 event (≧35 μg m-3) and frequent occurrence of high PM2.5 in the western area of Taiwan in the midnight in “2017 Study”, this study summarized the pollutant concentrations and environmental conditions associated with the above findings. Moreover, this study estimated primary and secondary organic carbon concentrations to understand the relative distribution of each other.
The source apportionment results showed that F3 (secondary sulfate and industrial boiler) was the main source factor under the influence of the Shulin Industrial Zone at the Banqiao station. For the Zhongming station, F4 (secondary nitrate) was the most important source factor caused by Freeway 1 and other traffic emissions. F3 (secondary nitrate) was the most significant source factor affected by Yunlin Technology Industrial Park and Freeway 3 during poor ventilation of the Douliu station. Similarly, F1 (secondary nitrate) was the source factor contributed the most and was related to Jiatai Industrial Zone plus intensive traffic emissions at the Chiayi station. For the Xiaogang station, F3 (secondary nitrate and soil dust) was the major source factor under the influences of the Dafa and Linhai Industrial Zones. Specifically, ship emissions from the sea and Meilun Industrial Zone accounted for the worst source factor of F4 (secondary sulfate and Industrial boiler) at the Hualien Station.
PSCF modeling for the trajectory origins of “secondary sulfate” of various stations only to find that the Banqiao Station was under the influence of Shandong and Jiangsu Provinces in China. In contrast, local pollution sources affected other stations. For example, Taichung Incineration Plant, as well as Taichung and Changbin Industrial Zones affected the Zhongming Station. The mixed sources including Douliu Industrial Zone influenced the Douliu Station. The Southern Taiwan Science Park might have affected the Chiayi Station. Moreover, a mix of sources affected the Xiaogang Station such as Renwu Refuse Incineration Plant, Dafa Industrial Zone, China Steel Corporation, and Linyuan Industrial Zone. The ship emissions in the northeastern direction to the Hualien station might have caused the pollution.
The high NO3- proportion in high PM2.5 concentration events were mainly under the influences of pollutant accumulation due to low wind speed and the pollutant left-overs from the previous day. ISORROPIA modeling indicated the abundance of NH4+ such that the main compound forms were (NH4)2SO4 and NH4NO3 of the water-soluble inorganic ions. This was evidenced by the excellent correlations (R2) between excess molar concentrations of NH4+ and NO3- were 0.79, 0.89, 0.89, 0.89, and 0.90 in the five stations from north to south in Taiwan. For the outliers that deviate from the linear relationship between excess NH4+ and NO3- might be related to the occurrence of N2O5 hydrolysis under high NO3- and NO2 concentrations at night. Apparently, the pollutant concentrations of the previous days affected the midnight high PM2.5 concentrations. Among various gas pollutants, NOX concentrations were the highest with great deviations with that of the previous day; however, the control of NOX and SO2 were of equal importance as SO2 was also with great deviations with that of the previous days.
The estimates from the EC-Tracer method showed that the proportions of secondary organic carbon over organic carbon (OC) were 32-38% at the Banqiao station, 23-41% at the Zhongming station, 44-56% at the Douliu station, 30-47% at the Chiayi station, 30-47% at the Xiaogang station, and 28-46% at the Hualien station, respectively. It implies that primary OC is the major OC in Taiwan. The sources are mainly associated with emissions from transportation activities and biomass burning.
In summary, local pollution sources are mainly responsible for PM2.5 concentration especially for NO3- in the western area of Taiwan except part of SO42- transported from northern China. Low wind speed and higher NOX were associated with the high proportion of NO3- in high PM2.5 concentration events. As for the high concentration of NO3- at night, it might be related to N2O5 hydrolysis under high NO2 and relative humidity in the environment. | en_US |