A case study of single hygroscopicity parameter and its link to the functional groups and phase transition for urban aerosols in Taipei City

作者：Hung Hui Ming^*; Hsu Chia Hung; Lin Wei Ting; Chen Yu Quan

来源：Atmospheric Environment, 2016, 132: 240-248.

DOI：10.1016/j.atmosenv.2016.03.008

• Urban aerosols
• CCN
• Hygroscopicity
• Phase transition
• ATR-IR

The hygroscopicity, functional groups and phase transitions of urban aerosol particles in Taipei City were studied using a cloud condensation nuclei counter (CCNc) with a scanning mobility particle sizer (SMPS) and an attenuated total reflectance with infrared (ATR-IR) detection technique. With the assumption of larger particles being activated first, the derived single hygroscopicity parameter (kappa) exhibited an increasing trend with particle size, i.e., from 0.022 +/- 0.01 at 87 +/- 10 nm to 0.13 +/- 0.03 at 240 +/- 20 nm. The collected size-selected particles were characterized using ATR-IR for the functional groups of alkyl, carbonyl, ammonium, sulfate and nitrate, which showed various size dependence patterns, linked to different formation mechanisms. The hygroscopic response based on the ratio (chi(W)_(solute)) for sample film of absorption by the enhanced water-stretching peak to that by the selected solute showed a better consistency with pure ammonium sulfate for sub-micron size particles. Based on the derived ammonium sulfate volume fraction from IR analysis, the kappa received from CCNc measurements was concluded mainly contributed by ammonium sulfate for sub-micrometer particles. The increasing trend of sodium nitrate absorbance at aerosol diameter >= 1 mu m was due to a reaction of nitric acid with sea salt particles. The micrometer sized particles were apparent not only in a significantly higher chi(W)_(solute) than pure sodium nitrate but also had a deliquescence RH of 69 +/- 1%, similar to that of sodium nitrate-sodium chloride mixtures. Overall, the organic species in this study exhibited a low hygroscopicity with less than 0.036 of contribution for the overall kappa, and the major hygroscopic material of urban aerosols consisted primarily of ammonium sulfate in the sub-micrometer particles and sodium nitrate with sea salt in the coarse particles.

• 出版日期2016-5