Effects of activity intensities, smoking habits, and respiratory infection on the size distribution of exhaled aerosols

Exhaled aerosols, as the pathogen source in the transmission of respiratory infection, are affected by both physical activity intensity and respiratory activity. Our understanding of the size distribution and concentration of exhaled aerosols remains incomplete, particularly due to the lack of measurements of nano-sized aerosols. The effects of smoking, acute respiratory infection, and individual parameters on aerosol generation have not been systematically studied. This study recruited 45 non-smokers and 10 smokers, of whom nine non-smokers returned to participate after experiencing an acute respiratory infection. We investigated the characteristics of aerosols ranging in size from 14.8 nm to 20 μm generated during respiratory activities at three activity intensities: sedentary, light, and moderate. We also analysed the influences of individual parameters, metabolic parameters, smoking habits, or respiratory infections on the concentration of aerosols. Our results show that the size distribution of exhaled aerosols followed a log-normal distribution, exhibiting two to three peaks within the ranges of 0.07–0.12 μm, 0.6–0.8 μm, and 1–1.5 μm. Aerosol concentration showed a significant linear correlation with METs. Differences in aerosol concentration between sexes decrease with increasing exercise intensity. WC and BMI were found to be the primary factors influencing aerosol concentration in males and females, respectively. In addition to respiratory activities, the changes of aerosol concentration were also influenced by activity intensity, BMI, and WC. This study provides new insights into aerosol generation patterns, offering valuable guidance for the prevention and control of respiratory infectious diseases.