Indoor air quality and its relationship with cluster type in urban Pakistani households

OBJECTIVE: To assess the levels and predictors of formaldehyde, nitrogen dioxide (NO₂), carbon monoxide (CO) and fine particulate matter with diameter less than 2.5 μm (PM2.5) in Karachi, Pakistan.METHODS: A total of 1629 households were selected through multistage cluster sampling in a community-based cross-sectional survey. Formaldehyde, NO₂ and CO levels were measured using YesAir Indoor air monitor and for PM2.5, UCB-PATS (University of California Berkeley Particle and Temperature Sensor) was used. Clusters were classified either as planned (areas of planned housing) or unplanned (informal settlements).RESULTS: We found the median concentrations to be as follows: formaldehyde, 0.03 ppm (IQR 0.00-0.090); CO, 0.00 ppm (IQR 0.00-1.00); NO₂, 0 ppm (IQR 0.00-0.00) and PM2.5, 0.278 mg/m³ (IQR 0.162-0.526). We found a significant association of the upper quartiles of formaldehyde and PM2.5 levels with type of cluster. The risk of obtaining formaldehyde and PM2.5 levels in the upper quartile was higher in unplanned clusters than in planned clusters (adjusted odds ratio [aOR] 33.0, 95% CI 4.02-271.5 and aOR 0.10, 95% CI 0.001-0.16, respectively). No significant association was observed between levels of CO and cluster type (aOR 0.84, 95%CI 0.62-1.14).CONCLUSION: This study reports high levels of indoor air pollutants in Karachi, with considerable variation across planned vs. unplanned clusters.