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

Abstract

Abstract. 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 ∘C). Substantial mass increase due to water uptake was observed for all the six pollen species, and at 25 ∘C the relative mass increase at 90 % RH, when compared to that at <1 % RH, ranged from ∼30 % to ∼50 %, varying with pollen species. It was found that the modified κ-Köhler equation can well approximate mass hygroscopic growth of all the six pollen species, and the single hygroscopicity parameter (κ) was determined to be in the range of 0.034±0.001 to 0.061±0.007 at 25 ∘C. 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, κ values decreased from 0.073±0.006 at 5 ∘C to 0.061±0.007 at 25 ∘C and to 0.057±0.004 at 37 ∘C for Populus tremuloides pollen, and decreased from 0.060±0.001 at 15 ∘C to 0.054±0.001 at 25 ∘C and 0.050±0.002 at 37 ∘C for paper mulberry pollen.

Bioaerosol field measurements: Challenges and perspectives in outdoor studies

“…The ability of aerosols to take up water at subsaturated conditions, i.e., hygroscopicity, can influence their direct climate effects (Boucher et al 2013). The hygroscopic properties of bioaerosols have been only rarely assessed (Tang et al 2019;Lin et al 2015;Griffiths et al 2012;Ghosal et al 2010;Lee, Kim, and Kim 2002;Ko, First, and Burge 2000;Rubel 1997;Reponen et al 1996), mainly due to technical challenges related to their relatively large sizes and their immense diversity. Indirect climate effects of bioaerosols are based on their interaction with clouds by acting as either cloud condensation nuclei (CCN), which nucleate liquid cloud droplets, or ice nucleating particles (INPs), which promote cloud droplet freezing.…”

A review of experimental techniques for aerosol hygroscopicity studies

“…A QCM was used to measure the DRH of a number of inorganic and organic salts, including NaCl, (NH 4 ) 2 SO 4 , CH 3 COONa and CH 3 COOK (Arenas et al, 2012), and the measured values agreed very well with those reported in previous work. Several studies (Thomas et al, 1999;Demou et al, 2003;Asad et al, 2004;Liu et al, 2016) have utilized QCM to explore hygroscopic properties of organic compounds of atmospheric interest. For example, Demou et al (2003) quantitatively determined the amount of water taken up by dodecane, 1-octanol, octanoic acid, 1,5pentanediol, 1,8-octanediol and malonic acid at room temperature.…”

Hygroscopic Properties of Saline Mineral Dust From Different Regions in China: Geographical Variations, Compositional Dependence, and Atmospheric Implications

“…Measurements were all carried out at room temperature (25 ± 0.1°C). Since instrumental and operational details can be found in our previous work Guo et al, 2019;Tang et al, 2019), here we only provide a brief description of key features. The mass measurement range and sensitivity were 0-100 mg and 0.01 μg, and the dry mass of samples examined in this work was in the range of 1-10 mg, depending on their hygroscopicity.…”

“…The sample was housed in a temperature-regulated chamber, and one dry nitrogen flow and one humidified nitrogen flow, regulated using to mass flow controllers, were mixed and then delivered into the chamber to control the RH (0-98%). The deliquescence of NaCl, KCl, and (NH 4 ) 2 SO 4 were routinely examined using this setup (Tang et al, 2019), and absolute differences were found to be <1% between the measured and theoretical deliquescence RH, suggesting that the accuracy in RH control could reach ±1%.…”