Seasonal variation of fine particulate matter in residential micro–environments of Lahore, Pakistan

Shifting seasons greatly influence the use and management practices in residential built environments which subsequently affect the level of exposure to various pollutants indoors. The levels of fine particulate matter (PM2.5) were monitored in fifteen households of Lahore, Pakistan during different seasons. DustTrak aerosol monitors (model 8520, TSI Inc.) were run simultaneously in the kitchens and living rooms of the selected sites for seventy two hours each. To aid analysis, houses were categorized in three groups according to floor area. For non–smoking houses there was little variation between 24 h average PM2.5 concentrations in kitchens (270 to 295 μg/m³) although there was an increase in concentrations in living rooms as floor area increased. Across all houses the average PM2.5 concentration was observed to vary during the seasons. In the kitchens the average PM levels were 326 μg/m³ during the spring falling to 133 μg/m³ in summer, 180 μg/m³ in monsoon, 395 μg/m³ in autumn and 448 μg/m³ during the winter. Similarly, in the living rooms, the mean PM levels observed were 190 μg/m³ in spring, 101 μg/m³ in summer, 158 μg/m³ in monsoon, 458 μg/m³ in autumn and 590 μg/m³ in winter. Factors contributing towards these levels were cooking (involving frequent frying), floor sweeping, and also movement of the occupants. Smoking at two sites and use of gas heaters during the winter were also identified as contributing sources. Apart from these sources, ventilation was identified to be the most singular attributing factor to the above mentioned variations in PM levels. Ventilation during the warm season ranged from 3.51 air changes per hour (ACH) to 7.68 ACH. On the contrary, ventilation decreased during the autumn and winter season (2.5 to 5.64 ACH) and this resulted in an accumulation of PM indoors. The levels of fine particulate matter were observed to be 3 to 23 times higher than the WHO established standard of 25 μg/m³.