干燥方法对人工制备生物气溶胶消光性能的影响

Effect of Drying Methods on Extinction Properties of Artificial Bioaerosols

通过建立具有丰富结构细节的生物颗粒形态模型,利用Kramers-Kronig算法、离散偶极子近似方法和蒙特卡罗算法计算了冷冻干燥和热风烘干两种干燥方法对BB0819生物气溶胶消光性能的影响,并通过傅里叶变换和红外光谱方法分析了由两种干燥方法所得孢子形成的生物气溶胶内部组成和蛋白质结构的差异,进一步解释了消光性能变化的原因。通过气溶胶室实验证明了仿真结果的可靠性,实验结果显示:在中红外波段,选用冷冻干燥孢子所形成的生物气溶胶可在3 min内将平均透过率从11.95%降至9.14%;在远红外波段,选用热风烘干孢子所形成的生物气溶胶可在3 min内将平均透过率从34.38%降至26.03%。研究结果阐明了干燥方法对人工制备生物气溶胶消光性能的影响,为在制备过程中提升生物气溶胶消光性能提供了有效参考。

Objective Bioaerosols are colloid systems formed by tiny biological particles floating in the atmosphere,such as bacteria,fungi,viruses,and pollen.Bioaerosol particles can scatter and absorb solar radiation,communication signals,and optical signals,and can also be suspended in the air and spread long distances with the wind.Therefore,they exert an effect on many fields such as climate change,optical communication,and optical remote sensing.They have also attracted widespread attention in research areas such as functional materials,environmental protection,and disease transmission and prevention.Bioaerosol particles have diverse morphologies and rich compositions and can absorb and scatter incident light in multiple wavelengths.Additionally,their artificial cultivation techniques are relatively mature,with low cultivation costs,simple operation,and short cultivation periods.As a result,the artificially prepared bioaerosols have great development potential in the research on optical functional materials.Drying is an essential step in the artificial preparation of bioaerosols,and it can affect the broadband extinction performance of artificially prepared bioaerosols.However,the influence of different drying methods on the extinction performance of bioaerosols has not been studied.Our paper aims to investigate the influence of different drying methods on the extinction performance of artificially prepared bioaerosols and provide references for improving the extinction performance of bioaerosols through preparation.Methods BB0819 spores are one of the common entomopathogenic fungal spores and have been proven to have significant broadband extinction performance.Therefore,BB0819 spores are selected as the research object to investigate the effect of drying methods on the extinction performance of artificially prepared bioaerosols.In our study,two common microbial treatment methods,freeze drying and hot-air drying,are chosen to dry BB0819 spores.The preparation process consists of four main steps,including spore suspension preparation,solid culture medium cultivation,drying,and spore collection.To investigate the effect of the two drying methods on the broadband extinction performance of BB0819 bioaerosol,we build a model with detailed structural information on bio-particle morphology,and the Kramers-Kronig algorithm,discrete dipole approximation,and Monte Carlo simulation methods are adopted to calculate the extinction performance.Furthermore,Fourier transform infrared spectrum and two-dimensional correlation infrared spectrum are employed to analyze the internal composition and protein structure differences of bioaerosols after drying,explaining the changes in extinction performance.The reliability of the simulation results is confirmed through experimental validation in an aerosol chamber,where transmittance data is obtained for bioaerosols produced by different drying methods in the midinfrared and far-infrared wavelengths.Results and Discussions The drying process can disrupt the internal composition of spores.This leads to changes in the absorption functional groups,protein secondary structures,and various component contents,which in turn affects the optical absorption of spores.Compared with freeze drying,hot-air drying results in a higher protein absorbance in BB0819 spores,about 7.19%.The increased protein content can enhance the optical absorption ability of spores in the 6-8μm wavelength range.Although the protein absorbance in BB0819 spores is relatively higher after hot-air drying,the fitting results of protein secondary structure indicate that the protein absorbance of α-helix structure in spores decreases by about 5%.The α-helix is the main structure maintaining protein conformation,indicating that although the protein content is not reduced by hot-air drying,it has a significant influence on the stability of protein structure.Additionally,the rising temperature during hot-air drying leads to significant denaturation of polysaccharide substances(mainly peptide polysaccharide layer)and changes in the content of polysaccharide groups inside the material.Polysaccharides contain abundant C—O and C—C bonds,and the stretching and vibration of these chemical bonds have a strong absorption peak at around 10μm,which may affect the optical absorption performance of spores around 10μm.As shown in Figs.7(c)-(f),in the 2.5-10.3μm wavelength range,freeze-dried spores have a larger extinction cross-section and stronger extinction performance for individual spores,while in the 10.3-15.4μm wavelength range,hot-air dried spores have a larger extinction cross-section and stronger extinction performance for individual spores.Both BB0819 bioaerosols dried by the two drying methods show significant optical attenuation ability.In the 2.5-10.3μm wavelength range,both bioaerosols can attenuate the transmittance of incident light to below 20%,with most of them below 15%.In the 10.3-15.4μm wavelength range,freeze-dried spores can attenuate the transmittance to between 20% and 35%,while hot-air dried spores can attenuate the transmittance below 30%.Conclusions Drying is an essential step in the artificial preparation of bioaerosols,and it affects the broadband extinction performance of artificially prepared bioaerosols.Research results show that bioaerosols after freeze drying have higher content of polysaccharides and more stable protein structures,which leads to better extinction performance in the farinfrared band.Bioaerosols obtained through hot-air drying contain more proteins for better extinction performance in the mid-infrared band.In the mid-infrared band,selecting bioaerosols obtained by freeze-dried spores can reduce the average transmittance from 11.95% to 9.14% within three minutes,while in the far-infrared band,adopting bioaerosols obtained by hot-air dried spores can reduce the average transmittance from 34.38% to 26.03% within three minutes.We clarify the effects of drying methods on the extinction properties of artificially prepared bioaerosols and provide references for improving their extinction properties through preparation.