Assessment of indoor and outdoor air quality using low-cost sensors and analysing ventilation effect

Air pollution, driven by rapid urbanization and industrialization, poses serious health risks, particularly in densely populated cities where individuals spend most of their time indoors. This study assessed indoor and outdoor air quality in residential houses in Okhla, South Delhi—a recognized high-pollution hotspot—during spring 2023 (February–April) using calibrated low-cost sensors. A total of 24 houses were monitored and categorized as well-ventilated or poorly ventilated based on the presence of mechanical ventilation systems. Concentrations of particulate matter (PM2.5 and PM10) were measured indoors and outdoors, and indoor/outdoor (I/O) ratios were calculated to evaluate the role of ventilation. Results revealed that indoor PM10 levels in poorly ventilated houses reached approximately 320 µg/m3, far exceeding the WHO guideline of 45 µg/m3, while indoor PM2.5 levels were nearly five times above permissible limits. PM2.5 and PM10 exhibited similar temporal patterns, with I/O ratios consistently greater than one, indicating substantial indoor contributions to exposure. Poorly ventilated houses demonstrated higher ratios, underscoring the influence of inadequate ventilation in exacerbating indoor air quality. These findings highlight the urgent need for improved ventilation practices and sustainable urban planning to mitigate health risks. Beyond providing evidence of high indoor exposures in a critical urban hotspot, the study demonstrates the utility of low-cost sensors for monitoring. It contributes to policy discussions on scalable, affordable tools for managing indoor air quality in rapidly urbanizing regions.