| dc.description.abstract | The environmental impact and health effects of atmospheric aerosols have drawn much attention. From time to time, people invest a great deal of money and efforts to understand the role of aerosols. Until recently, filter based sampling and laboratory analysis is still the mainstream to resolve aerosol properties. This could only provide a rough temporal and spatial resolution of aerosol chemical contents and is hard for quantification of sampling artifacts. The real-time continuous measurement for aerosol properties could provide the solution of acquiring precise results without incurring transportation and storge errors like filter samples. The installation of Taiwan supersite is to achieve the aforementioned objectives. Owing to the high atmospheric RH, it is necessary to assess liquid water content (LWC) of aerosols for their effects on mass measurement, acid deposition, light attenuation, global change, and health effects. Although there are several thermal equilibrium models to estimate aerosol LWC, however, they are all built by the LWC of laboratory generated known aerosols. These models need more data from aerosols in real atmosphere to test. To date, the data of aerosol LWC are scarce; this study adopted a developed measurement system to detect LWC from collected filters (Chang and Lee, 2002; Lee and Chang, 2002). Measurement results and model estimates are compared in this study to understand more on aerosol LWC in the real atmosphere.
The results of aerosol properties from continuous monitoring in the springtime of urban Taipei show as follows. PM2.5 and PM10 is with an average of 37.2mg/m3 and 54.9mg/m3, respectively. The average of organic carbon is higher at 7.6mg/m3 compared with 2.6mg/m3 for elemental carbon and 3.7mg/m3 for black carbon. The measured average for sulfates is 7.1mg/m3 and that of 3.6mg/m3 is for nitrates. For all these aerosol properties, excluding the data during yellow sand periods, the monthly averages vary very little from March to May.
The time history of aerosol mass and major chemical species are influenced by the time shift of on and off duty. Concentration pattern in working days and holidays is deviated from each other significantly. Wind speed has been expected to influence the dilution and dispersion of pollutants. This study agrees with the above inference by showing a linear relationship between PM2.5-10 and wind speed and a reverse relationship between wind speed and other measurements. At high relative humidity (RH), the predominant size fraction changed from equal weight of fine and coarse particles into fine particles. An apportionment of carbonaceous materials shows secondary organic carbon is predominant in occupying 56%, followed by elemental carbon with 25%, and primary organic carbon with 19%. By applying a “near-source aerosol chemical properties” source apportionment to PM2.5, the contributions from secondary reaction is found higher than that from mobile vehicles. The contributions from the two sources could be summed up to 35-95% of fine mass.
For the assessment of LWC of aerosol, aerosol LWC is found mainly determined by atmospheric RH and its chemical compositions. From the humidographs of aerosol LWC, the results will tend to underestimate if the measurement system is operated from dry state of arosol to the reconstructed RH. However, starting from a very high RH to the reconstructed RH will induce an overestimate in measuring aerosol LWC. The right procedure is to include aerosol LWC retained in the previous RH cycle. Meanwhile, for aerosol in the high RH stage, the measurements of aerosol LWC are close to each other. The aerosol LWC measured in this study is agreed well with ISORROPIA model estimate with a R2 at 0.86. However, the model underestimates aerosol LWC, which is probably due to not incorporating hygroscopic organics and all hygroscopic inorganic salts into the model. It is noteworthy to reveal that for temperature controlled in the range of 22-270C and RH within 26-34%, the conditioned particles before weighing still carry 3-29% LWC. The measurement of aerosol LWC at the RH when it was collected shows an average of 64% in the range of 86-30% of the fine mass. | en_US |