Spatio-temporal variations of air pollutants and human health exposure impacts during 2023 haze through respiratory deposition analysis in Delhi-NCR, India

• The 2023 Haze episode in Delhi-NCR caused a disproportionate rise in pollution levels, exceeding air quality standards and significantly increasing respiratory health risks. • The haze episode was caused by a complex interplay of meteorology, regional transport of biomass burning, and local emissions. • Physical activity increases pollutant deposition in the respiratory system. • Males are more vulnerable to health risks than females. • PM 2.5 poses a greater risk to the deeper parts of the lungs, while PM 10 mainly affects the upper respiratory tract. This study investigated the impacts of the 2023 haze episode on air quality and respiratory health in the Delhi-National Capital Region (Delhi-NCR), India. Monitoring data for PM 2.5 , PM 10 , NO 2 , NH 3 , SO 2 , O 3 , and CO were collected at four representative sites (Delhi, Gurugram, Greater Noida, and Ghaziabad) and analyzed for spatiotemporal variations. Fire hotspot analysis, meteorological data, and backward trajectory analysis modeling revealed the elevated pollution levels during the haze episode were attributable to increased local emissions coupled with the transport of pollutants from biomass burning in neighboring states. To assess health risks, the International Commission on Radiological Protection (ICRP) modeling was used to estimate respiratory deposition dose (RDD) of PM 2.5 and PM 10 in the head airway (HA), tracheobronchial (TB), and alveolar (AL) regions for both males and females under three modes of metabolic activities of seated, walking and exercise. The results indicated a substantial increase in the total RDD (sum of HA, TB, and AL regions) across all sites, genders, and activity levels. For instance, PM 2.5 RDD in Delhi increased from 1.03 to 2.44 µg/min during the haze period for males under seated activity and from 0.72 to 1.69 µg/min for females. Overall, the study estimated a 130 % increase in health risk during the haze period across all activity levels and genders.