| dc.description.abstract | Biomass burning (BB) in Southeast Asia frequently occurs from March to May every year. The large-scale open burning produces tremendous amount of aerosol and gases to influence atmospheric radiation budget and the air quality in the downwind area. Taiwan is located in the downwind area of the air masses transported from Southeast Asia. This makes it one of the best places to observe the modification on atmospheric aerosol from BB plume. In order to avoid the interference from ground-level pollution, this study observed atmospheric aerosols at the Lulin Mountain site (2,862 m a.s.l.) for eight times from June 2006 to April 2007. The objective of this study is to investigate aerosol properties modified by BB plume.
The estimates of aerosol carbons were compared between sampling devices with and without a preceeding activated carbon denuder. The estimates of aerosol carbons from the sampling device without a preceeding activated carbon denuder but with three quartz filters in series during BB event and non-event period are 8.5 ± 3.89 μg-C m-3 and 1.78 ± 1.07 μg-C m-3, respectively. Meanwhile, the average of volatile organic carbons (VOCs) was estimated at 0.54 ± 0.24 μg-C m-3 in terms of equivalent organic carbon (OC). The VOCs evaporated from deposited particles were found negligible. However, the VOCs evaporated from deposited particles from sampling device with a preceeding activated carbon denuder were obvious. The aerosol water-soluble ions resolved from quartz filters were more abundant than those from Teflon filters except for chloride ion. This indicates some species might be retained by the extracted Teflon filters.
In the BB event, fine particle concentration was five times as much as that in the non-event period. Ammonium, nitrate, and sulfate ions are 1.37μg m-3, 1.58μg m-3, and 3.30μg m-3, respectively, during the event period. One of the BB tracers, potassium ion, is at 0.59μg m-3 during the event period, which is four times as high as that in the non-event period. The OC fractions increased significantly during the event period; however, only EC1-OP of EC fractions increased significantly. Meanwhile, aerosol levoglucosan was nine times higher in the event than that in the non-event period. In addition, aerosol oxalic acid was the dominant species of low-molecular-weight dicarboxylic acids; it correlated well with sulfate ion. This suggests both were from the same source origin.
The analyses of cloud interstitial aerosol collected at the Lulin site show secondary pollutants such as ammonium, nitrate and sulfate ions are the three major water-soluble ions. Among aerosol OC fractions, low-temperature evolved OC1 and OC2 increased more than the others, it suggests that low-vapor-pressure VOCs condensed on the surface of fine aerosol during transport.
In the classification of back-trajectory pathways, because of the pathway from the ocean during the background period belong to unpolluted, the concentrations of all of the components from there are lowest; the coarse mode particle concentrateion from China pathway during the background period increase significant, this suggest that the aerosol form China may be affected by dust storm; the result of comparison between source region and source region via southern China show that the latter concentrateion of coarse and fine aerosol, sulfate and oxalic acid enhance significant.
In order to compare the difference between fresh and aged aerosol, this study conducted an experiment of rice straw burning in the field. The results show that potassium chloride is significant in newly burned smoke. Part of chloride ion was lost soon after a short distance transport, but potassium ion remained abundant in aerosol water-soluble ions. In contrast, nitrate ion was not significant in both fresh and slightly aged aerosols. This reveals that nitrate ion is not produced in the BB process. | en_US |