大气生物气溶胶花粉单颗粒的形貌特征及吸湿特性研究

Morphological Characteristics and Hygroscopicity of Atmospheric Bioaerosol Pollen Single Particles

近年来大气生物气溶胶颗粒吸湿性对气候和人体健康的影响引起了人们的广泛关注,而花粉颗粒是生物气溶胶的重要组成部分,为了解花粉颗粒吸湿性的变化趋势,在杭州市内收集了5种花粉颗粒(山茶花花粉、诸葛菜花粉、耧斗菜花粉、锦带花花粉、三色堇花粉),使用扫描电子显微镜观察花粉颗粒物的微观形貌,并使用单颗粒吸湿性系统研究了不同相对湿度(relative humidity,RH)条件下花粉单颗粒粒径的分布特征,获得了花粉颗粒吸湿增长因子(GF).结果表明:5种花粉颗粒的吸湿增长特征各异,RH=90%时山茶花、诸葛菜、耧斗菜、锦带花和三色堇花粉颗粒的吸湿增长因子分别为1.09、1.09、1.08、1.13和1.14,RH=95%时则分别为1.11、1.10、1.11、1.14和1.16,这些结果总体低于大气中无机盐颗粒的吸湿增长因子.在花粉颗粒的吸湿性增长过程中,不仅花粉颗粒表面有微弱的吸湿增长,一些花粉颗粒的整体结构和形态也会发生变化,如在扫描电子显微镜下,可以观察到锦带花花粉颗粒在干燥状态时表现为一种内部镂空的塌缩状态,而在相对湿度增大的过程中颗粒会鼓起并逐渐接近于球形.这表明花粉颗粒在大气中确实呈现出较弱的吸湿增长特性,且颗粒内部会吸水,从而改变其形貌结构,这对于理解花粉颗粒在人体呼吸道中的表面吸湿行为及其在大气中的成云凝结核能力有着重要的科学意义.研究显示,花粉种类、花粉萌发孔数目和花粉表面结构影响花粉吸湿性,低湿度下花粉吸湿增长缓慢,高湿度下花粉吸湿增长迅速.

In recent years,the impact of atmospheric bioaerosol particle hygroscopicity on climate and human health has attracted widespread attention,and pollen is an important component of bioaerosols.In order to understand the changing trend of hygroscopicity of pollen particles,five types of pollen particles were collected in Hangzhou,including Camellia,Orychophragmus violaceus,Aquilegia,Weigela florida,Viola tricolor.Scanning electron microscope was used to observe the morphology and structural characteristics of individual pollen particles.An individual particle hygroscopic system was used to observe the hygroscopic growth of pollen particles under different relative humidity(RH).Here we obtained the size distribution of individual pollen particles and their hygroscopic growth factors(GFs).The results show that hygroscopic GFs of Camellia,Orychophragmus violaceus,Aquilegia,Weigela florida,Viola tricolor pollen particles were 1.09,1.09,1.08,1.13 and 1.14 at 90%RH and the hygroscopic GFs were 1.11,1.10,1.11,1.14 and 1.16 at 95%RH,which is lower than the GFs of inorganic aerosols in the ambient atmosphere.We found that the surface of pollen particles had weak size growth through water uptake.In addition,we also noticed that the overall structure and shape of some pollen particles changed during particle hygroscopic growth.For example,scanning electron microscopy images showed that the weigela florida pollen particles in the dry state displayed internal hollow collapse,but the pollen particles transformed from collapsed particles to the spherical shape with increasing RH.These results suggest that pollen particles have weak hygroscopic properties in the atmosphere,and the absorption of water can alter their morphological structures,which is of great scientific significance for understanding pollen hygroscopicity in the human respiratory and cloud condensation nucleation activities in the atmosphere.Studies have shown that pollen types,the number of pollen germination pores and the surface structure of pollen affect the hygroscopicity of pollen,and the hygroscopicity of pollen increases slowly under low humidity and rapidly under high humidity.