Assessment of exposure to airborne aerosol and bio-aerosol particles and their deposition in the respiratory tract of subway metro passengers and workers

This research paper presents an investigative study of airborne aerosol particles (PM2.5) and bio-aerosol particles (bacteria and fungi) inside subway metro stations and their deposition dose in the respiratory tract of exposed passengers and workers. In this study, aerosol monitoring and bio-aerosol sampling were conducted along the metro line and inside metro stations to determine the daily average exposure levels of passengers and workers. The deposition of aerosol and bio-aerosol particles in the respiratory tract of healthy adult males and females was calculated using Multipath Particles Dosimetry Model. The exposure assessment revealed that exposure to fine airborne particles (<1 μm) was dominant; more than 40% of total aerosol deposition and 10–16% of bio-aerosol deposition were found in the pulmonary region of the respiratory tract. Higher deposition dose of particles was observed in males in comparison to females. In the journey along the metro line, a high deposition dose was found during in-train travel and in the underground metro station. Severalfold higher deposition doses were found in the respiratory tract of subway metro workers due to the longer exposure duration. Recent studies have confirmed the spread of COVID-19 virus through airborne particles of size <2.5 μm and airborne transmission was found to be significantly more in indoor spaces. Thus, it is critical to study the exposure levels and deposition dose of fine airborne particles in the human respiratory tract to assess the possible health risks and devise ways to maintain a healthy metro environment.