| dc.description.abstract | Aerosol hygroscopicity is one of the most fundamental properties of atmospheric aerosols. The variations of aerosol mass change (AMC) due to water uptake will affect aerosol deposition characteristics, size distribution, optical property, and heterogeneous chemical reactions. In this study, PM2.5 at rural (Shi-Men in Taipei County), urban (Hsin-Chuang Aerosol Supersite), and mountain (Lu-Lin Mountain) sites are collected for measuring aerosol water content at high humid (90% RH) by using an aerosol water mass measuring system (Chang and Lee, 2002 ; Lee and Chang, 2002). The rural and urban samples were affected by Yellow dust transported from Asian Continent, while mountain samples was influenced by transported biomass burning from Southeast Asia during the field trip conducted in March 2006.
To investigate aerosol properties in affecting AMC, this study analyzes water-soluble inorganic ions, dicarboxylic acids, organic and elemental carbons, and water-soluble organic carbon (WSOC) in the collected aerosols. The ISORROPIA model (Nenes et al., 1998) is then utilized to simulate AMC of water-soluble inorganic ions for the comparison with the measured AMC. This will enable the study on AMC from the influence of aerosol organic components.
The averages of WSOC and its fractions in in PM2.5 in the field observation are 2.52 μgC m-3 and 7.3±1.8% for the rural site, 4.38 μgC m-3 and 24.0±5.7% for the mountain site, 2.75 μgC m-3 and 9.1±2.8% for the urban site, respectively. For the investigation of the influence of aerosol organic components on AMC, the ratios of WSOC/(Sulfate+Nitrate) are calculated to result in 14% at rural site, 120% at mountain site, and 30% at urban site, respectively. The analyzed concentrations of low-molecular dicarboxylic acids in abundance are in the descending order of oxalic acid, malonic acid, succinic acid, and glutaric acid.
In the study of aerosol behavior in the efflorescence mode and AWC, the highest mixing ratio of WSOC/(Sulfate +Nitrate) at the mountain site shows an inhibition of aerosol hysteresis in the efflorescence mode. For an environment controlled at 25℃ and 30% RH, AMC is found ranging from 1.00-1.41 in this study. It suggests that filter-based aerosol mass determined from weighing may be overestimated unless the absolute humidity of the weighing room is tightly controlled. As the differences of measured and modeled AWC using ISORROPIA for all three sites are within ±4 μg m-3, it indicates inorganic species are mainly responsible for AMC. Among aerosol inorganic water-soluble ions, sulfate and ammonium ions are the highest anion and cation, respectively. The modeled AMC from ISORROPIA shows that concentrations of sulfate and ammonium ions are positively related to AMC. High fraction of WSOC in aerosol tends to help increase aerosol water uptake under low RH envieonment in the deliquescence mode. This high fraction of WSOC in aerosol also inhibits complete water release even in the 20% RH envieonment in the efflorescence mode. | en_US |