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 microm (PM_2.5) 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 PM_2.5, 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 PM_2.5, 0.278 mg/m³ (IQR 0.162-0.526). We found a significant association of the upper quartiles of formaldehyde and PM_2.5 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.