Study On The Mechanism Of Particle Size Affecting The Lower Airways Exposure Of Particulate Matter

With the development of the society and the increasingly serious environmental pollution problems,more and more attention is paid to indoor air quality(IAQ).Particulate matter(PM)exposed to the air has gradually become the focus of indoor air quality because it can enter the human respiratory system with the respiratory airflow and thus cause a series of health threats to the human body.WHO and many countries have formulated corresponding indoor air quality standards for this issue to regulate the content of particulates in indoor air.The lower airways(including airway structures such as bronchioles,terminal bronchioles,alveolar ducts and alveoli)exposure of particulates represents the amount of particulate matter that can reach the human lower airways tract during human respiration.Some studies have shown that particle size is one of the most important factors which can affect the transport of particles and it has a great influence on the movement and deposition of particles in the lower airways.Considering the significant impact of particulate matter exposure in the airways,this paper starts from the control of indoor air quality to measure the exposure of particles with different aerodynamic diameter in the lower airways and analyzes the internal relationship between particle size and particle exposure.It has been found that the movement and deposition of particulates after entering the human respiratory tract are affected by factors such as gravity,inertia,and Brownian movement.Based on the experience and deficiencies in previous studies,this paper designed and implemented a particle exposure measurement of the lower airways: Firstly,the three-dimensional reconstruction of CT scan images of upper airways.Secondly,using the 3D printing technology,a physical model of the upper airways which is highly similar to the human airways geometric boundary is produced.Finally,using an artificial lung and particulate sampling device,the lower airways exposures of particles with aerodynamic particle sizes between 0.5-20?m in two active states of male sitting and male standing were measured in a full-size ventilation chamber.The measurement results of the lower airways exposure at different levels of particulate matter in the respiratory zone show that the PM2.5 mass concentration in the human lower airways showed a significant upward trend with the increase of PM2.5 particulate matter concentration in the respiratory zone,while the PM10 mass concentration in the human lower airways was significantly affected by particle size distribution and the trend of increase was not as pronounced as PM2.5.The particle size distribution in the lower respiratory tract was similar to that in the respiratory zone.The percentage of lower respiratory tract exposure between 0.5-2.5 ?m particles was increased first and then decreased with decreasing particle size,the highest percentage of lower respiratory tract exposure was at about 1.0?m.By comparing the quantity and mass distribution of particles in different particle size ranges(0.5-2.5?m,2.5-10?m,10-20?m)in the lower respiratory tract,it was found that there were significant differences in the quantity and mass distribution of particles in different particle size ranges.