Indoor PM2.5 Exposure, Source Contribution and Related Health Risks During Haze and Non- haze Episodes in Dhaka Cantonment, Bangladesh: A Comparative Study

Haze is a common phenomenon during winter (December- February) in Dhaka, Bangladesh. Fine particulate matter or PM_2.5 is considered the major component of haze. This study was conducted to evaluate the effect of haze on the concentration, chemical composition, source contribution and associated health risks of indoor PM_2.5 in a residential home of Dhaka Cantonment, located at the center of Dhaka city. During haze, the 24- hour average indoor PM_2.5 concentration was 139 ± 57.7 µgm^-3, whereas that during non- haze period was 96.3 ± 17.7 µgm^-3; both significantly exceeded the WHO guideline value (15 µgm^-3). Despite the same indoor environment, haze- time PM_2.5 concentration in Cantonment was 1.44 times higher than its non- haze counterpart. Mean I/O ratio (I/O_haze= 0.92 and I/O_{non- haze}= 0.96) and strong positive correlation (R²_haze= 0.89 and R²_{non- haze}= 0.85) between indoor and outdoor PM_2.5 suggested infiltration of polluted outdoor air into indoor environment. NOAA- HYSPLIT Backward Air Mass Trajectory Analysis indicated that north and northwestern air passing over the highly polluted Indo-Gangetic Plain (IGP) probably carried excessive air pollutants to Dhaka during winter, which might be responsible for creating haze and further increase of indoor PM_2.5 level owing to infiltration. 24- hour gravimetric sampling of Indoor PM_2.5 was carried out to quantify six heavy metals (Fe, Mn, Cu, Zn, Pb and Cr) by AAS analysis. Except Zn, haze- time concentration of all the heavy metals were 1.32 to 71.3 times higher than their non- haze concentrations. During haze, Pb (1022 ± 195 ngm^-3) and Mn (693 ± 62.3 ngm^-3) exceeded the WHO guideline values significantly. Enrichment factor analysis and source apportionment by Positive Matrix Factorization (PMF) revealed four sources of indoor PM_2.5, namely- industrial emission (4.4%), crustal sources (17.6%), vehicular emission (44.6%) and fugitive lead (32.9%). Health risk assessment indicated that hazard index (HI) for children during haze period was 31.19, whereas that during non- haze period was 0.57 only. Moreover, haze- time HI for adults was 13.68, which was 29 times higher than its non- haze value (0.47). Hence, indoor PM_2.5 exposure put children at much greater risk than the adults during haze, despite staying inside their home. Total cancer risk during haze and non- haze episodes exceeded the USEPA regulated target value (1 × 10^-6). The total cancer risk during haze was 1.33 times higher than that during non- haze weather. Therefore, haze increased the probability of developing cancer from 1 in 2146 individuals to 1 in 1608 individuals. The hazard ratio (HR) during haze (9.25) and non- haze (6.42) period indicated severely compromised indoor air quality in the sampling household of Dhaka Cantonment, so effective measures should be adopted to control indoor air pollution.