|dc.description.abstract||Atmospheric aerosol plays a significant role in global climate change. Up to now, many studies on atmospheric aerosol characteristics already shifted to focus on aerosol organics; however, the understanding of aerosol organic acids is still limited because aerosol organic acids are diversified. In this study, the analytical method for measuring low molecular weight monocarboxylic acids (MAs) and dicarboxylic acids (DAs) of atmospheric aerosols is established. Atmospheric aerosols were collected at a remote site (Cape Fuquay at Shimen village in Taipei County) and an urban site (the North Aerosol Supersite of Taiwan Environmental Administration at Hsinchuan City) during cold high-pressure period (Shimen), normal period (Hsinchuan), and Yellow Dust period (Shimen and Hsinchuan). The collected aerosols were taken back to the laboratory for organic acids analyses using ion chromatograph. The goal is to investigate the characteristics of aerosol organic acids contributed from different sources at different areas and times.
The results show that Oxalic acid (C2) was the most abundant species in DAs, followed by Succinic acid (C4), Malonic acid (C3), and Glutaric acid (C5) in both urban and remote areas during all three periods. Aerosol organic acids are mainly contributed from photochemical reactions and mobile vehicle emissions. When photochemical reactions were dominated, the ratio of Acetic/Formic acid (A/F) in MAs was around 0.7, while that of Malonic/Succinic acid (C3/C4) in DAs was above 1. In contrast, A/F was at 0.86 and C3/C4 was at 0.7 during non-photochemical reactions period. It implies that C3 is produced more than C4 when in photochemical reactions period.
The source contributions of organic acids were dominated by long-range transport of pollution in the remote area during cold high-pressure period. Formic acid was mainly affected by photochemical reactions during transport, while Acetic acid was influenced by a combination of transported primary emissions and secondary reactions similar to the processing of fossil fuel burning. The A/F values are around 1.95 during this period. In addition, concentration variations of MAs are found affected by ambient temperature. Analogously, the DAs were mainly produced by a process related to secondary reactions of fossil fuel burning. The ratio of C3/C4 was around 0.95. High linear correlation between C3 and C4 indicates their source contributions are similar.
During Yellow Dust period, aerosol organic acids were found related to sources from primary emissions and secondary photochemical reactions of long-range transport. Acetic acid is the preferable MAs in both urban and remote areas. The ratios of A/F were 1.2 and 1.9 in urban and remote areas, respectively. The source inferences in both urban and remote areas of DAs are a combination of primary emissions and secondary photochemical reaction during transport. The C3/C4 values were 0.96 and 1.0 in urban and remote areas, respectively.