Respiratory deposition of particulate matter in Delhi: a five-year assessment of exposure patterns and health risks.

Air pollution poses a major health risk globally and is a leading cause of premature mortality. This study evaluates respiratory deposition and health impacts of particulate matter (PM10 and PM2.5) in Delhi, India, from 2019 to 2023. Using data from continuous air quality monitoring, we analysed daily and seasonal pollutant variations, with emphasis on Diwali and COVID-19 lockdown periods. PM10 and PM2.5 concentrations exceeded national and WHO guidelines on most days, with peak values of 826.7 µg/m³ (PM10) and 750.5 µg/m³ (PM2.5). The higher respiratory deposition doses (RDD) occurred in evening daily commuter periods, with PM2.5 and PM10 RDD values up to 39% and 23% higher than in the morning period, and maximum daily deposition was observed in 2019 (male, walking), which exceeded WHO air quality guideline-based values by nearly 40-fold. Among daily commuters, evening periods showed higher RDD values than mornings, indicating increased exposure during evening travel. Overall, these results highlight sustained high particulate matter exposure in Delhi and identify key periods and populations at increased risk. The findings underscore the urgent need for targeted interventions to reduce particulate matter exposure and protect public health in polluted urban environments.