Water adsorption and hygroscopic growth of six anemophilous pollen species: the effect of temperature

Tang, Mingjin; Gu, Wenjun; Ma, Qingxin; Li, Yong Jie; Zhong, Cheng; Li, Sheng; Yin, Xin; Huang, Ru-Jin; He, Hong; Wang, Xinming

Hygroscopicity largely affects environmental and climatic impacts of pollen grains, one important type of primary biological aerosol particles in the troposphere. However, our knowledge of pollen hygroscopicity is rather limited, and the effect of temperature in particular has rarely been explored before. In this work three different techniques, including a vapor sorption analyzer, diffusion reflectance infrared Fourier transform spectroscopy (DRIFTS) and transmission Fourier transform infrared spectroscopy (transmission FTIR) were employed to characterize six anemophilous pollen species and to investigate their hygroscopic properties as a function of relative humidity (RH, up to 95 %) and temperature (5 or 15, 25 and 37 inline-formulaC). Substantial mass increase due to water uptake was observed for all the six pollen species, and at 25 inline-formulaC the relative mass increase at 90 % RH, when compared to that at inline-formula<1 % RH, ranged from inline-formula∼30 % to inline-formula∼50 %, varying with pollen species. It was found that the modified inline-formulaκ-Köhler equation can well approximate mass hygroscopic growth of all the six pollen species, and the single hygroscopicity parameter (inline-formulaκ) was determined to be in the range of inline-formula0.034±0.001 to inline-formula0.061±0.007 at 25 inline-formulaC. In situ DRIFTS measurements suggested that water adsorption by pollen species was mainly contributed to by OH groups of organic compounds they contained, and good correlations were indeed found between hygroscopicity of pollen species and the number of OH groups, as determined using transmission FTIR. An increase in temperature would in general lead to a decrease in hygroscopicity, except for pecan pollen. For example, inline-formulaκ values decreased from inline-formula0.073±0.006 at 5 inline-formulaC to inline-formula0.061±0.007 at 25 inline-formulaC and to inline-formula0.057±0.004 at 37 inline-formulaC for Populus tremuloides pollen, and decreased from inline-formula0.060±0.001 at 15 inline-formulaC to inline-formula0.054±0.001 at 25 inline-formulaC and inline-formula0.050±0.002 at 37 inline-formulaC for paper mulberry pollen.

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Tang, Mingjin / Gu, Wenjun / Ma, Qingxin / et al: Water adsorption and hygroscopic growth of six anemophilous pollen species: the effect of temperature. 2019. Copernicus Publications.

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