MULTI-METRIC EVALUATION OF INDOOR AIR POLLUTANTS AND HEALTH RISKS ACROSS DIFFERENT MICROENVIRONMENTS IN A UNIVERSITY CAMPUS OF DELHI, INDIA

Abstract

Indoor air quality (IAQ) has become an important environmental and public health issue, especially in densely built-up urban educational institutions where students and teachers are often confined for extended hours. In this study, the concentration level of indoor air pollutants has been assessed comprehensively across seven representative microenvironmental studies of the Delhi Technological University (DTU) campus in Delhi, India using multiple metrics. The aim of the study was to determine particulate matter (PM1, PM2.5, PM10), size-resolved particle number concentrations (PNCs), carbon dioxide (CO2) and related health risks based on Respiratory Deposition Dose (RDD) and Lung-Deposited Surface Area (LDSA). Grimm aerosol spectrometer and HOBO CO₂ logger were used for continuous monitoring during active occupancy. The chosen microenvironments were classrooms, hostels, offices and library spaces with different levels of occupancy and with different ventilation attributes. The spatial and temporal variations of indoor pollutants, indoor-to-outdoor (I/O) relationships and the impact of ventilation systems were assessed. The results showed high spatial variability of pollutants concentrations in various indoor environments. The quasi-ultrafine particles (qUFPs) in the particle number concentrations in all monitored microenvironments were in the highest concentration range, from ~2.5 × 10⁵ to 1.0 × 10⁶ particles cm⁻³. The Central Library (ME4) had the highest concentration of PM2.5 (~145 µg m⁻³) even surpassing the WHO 24-hour Air Quality Guideline by nearly 9 times, mostly because of the high occupancy and recirculation-based HVAC operation. The highest values of lung deposited surface area (LDSA) (~118,587 µm² cm-3) and the highest qUFP particle exposure occurred in the Non-AC Hostel (ME1) which was naturally ventilated. During occupied time, high CO₂ concentration was found in the classrooms with the highest CO₂ concentration in the classroom was about 1,880 ppm indicating poor v vi

ventilation conditions in the classrooms during occupied time. Ventilation configuration, user density, and indoor activities (e.g., burning incense), which led to short-term increases in indoor particle levels, were among the most important factors that affected indoor air pollution. The health risk assessment showed that exposure risk via PM mass concentration may not be a good indicator for exposure risk to the respiratory system. Combining the integration of particle number concentration (PNC), Respiratory Deposition Dose (RDD), and Lung-Deposited Surface Area (LDSA) gave a more comprehensive picture on the possible health effects from fine and quasi-ultrafine particle exposure. The findings emphasize the significance of using multi-metric approach to indoor air quality assessment in the educational institutions situated in high polluted urban areas. The outcomes of this study can support the development of evidence-based ventilation and exposure mitigation strategies to improve occupant health and indoor environmental quality.