Outdoors most of the particulate matter was in the coarse size fraction and fluctuated throughout the day; PM2.5 and PM1 were more stable. The concentrations are similar to those reported elsewhere for Lahore (e.g. Colbeck et al 2010c) and significantly above the WHO guidelines (25 μg m−3 for PM2.5 and 50 μg m−3 per 24 h (WHO 2006)).