RESEARCH ARTICLES CURRENT SCIENCE, VOL. 118, NO. 11, 10 JUNE 2020 1816 *For correspondence. (e-mail: amtulbaritabinda@gcu.edu.pk) Seasonal variations in indoor air quality of urban and rural Asian households Amtul Bari Tabinda 1, *, Ruby Safdar 1 , Abdullah Yasar 1 , Rizwan Rasheed 1 , Adeel Mahmood 2 and Anum Iqbal 1 1 Sustainable Development Study Centre, Government College University, Lahore 54000, Pakistan 2 Department of Environmental Sciences, Government College Women University, Sialkot 51310, Pakistan Burning of fuel for cooking and heating purposes causes smoke and other pollutants within households, resulting in direct human exposure. The present study focuses on assessment of seasonal variations in indoor air quality, including temperature, humidity, light, CO, SO 2 , PM 10 and airborne bacteria. Gaseous emissions were analysed using digital metres and bac- terial analysis was done by Gram staining method. Health data were gathered through questionnaires. Humidity, light intensity and concentration of CO, SO 2 and PM 10 were observed to be comparatively higher (P < 0.05) during winter and bacterial colonies were found to be comparatively higher (P < 0.05) in rural areas. About 80% of airborne bacteria in both urban and rural areas were Gram-positive. The indoor air quality of rural households was more pol- luted than urban households, and pollution was more in winter compared to summer due to inefficient cook- ing techniques and burning of biomass fuel. Keywords: Health assessment, indoor air, particulate matter, seasonal variations, urban and rural households. AIR pollution is often considered as an urban issue, but it now extends to rural areas as well. Indoor air pollution causes greater health impacts than outdoor air pollution 1 . The most important factor that describes indoor air quali- ty is the exposure to air pollutants released during the solid fuel combustion, containing biomass or coal used typically for cooking and heating purposes, indoor tobacco smoke, poor ventilation system, construction materials, furnishings and polishing 2 . Biomass fuel refers to the burned plant or animal excretes like dung, and wood, charcoal or crop residue that is used by more than half of the households as energy resource in most of the develop- ing countries and more than 95% of low-income- generating countries 3 . The burning of these fuels is the major source of smoke and other pollutants in the vicinity of a household, resulting in direct human exposure; this is several times more polluted than unprocessed solid or gaseous fuel 4 . Inefficient earthen or small metal stoves, or open pits are typically used for the burning of biomass in inadequately ventilated kitchens by a majority of the rural community, which results in an elevated level of indoor air pollution. Open fires from biomass fuel pro- duce high levels of gaseous and particulate matter (PM), which is 10–20 times higher than the health guidelines available for typical urban outdoor concentrations 5 . Thus, indoor air pollution has a detrimental impact on human health and the environment. The combustion of biomass fuel produces a large amount of toxic pollutants, e.g. car- bon monoxide (CO), sulphur dioxide (SO 2 ), PM, viz. (PM 10 ), nitrogen oxide (NO 2 ) and many other harmful pollutants 3 . Due to the confined nature of indoor spaces with minimum turnover rates of air, pollutants released inside will not disperse quickly, thus resulting in poor in- door air quality 6 . Carbon monoxide is an asphyxiate which binds with haemoglobin and hinders the transport of oxygen throughout the blood. While old aged people foetuses, and asthmatic patients are vulnerable to high CO levels, women and children are at the risk of direct exposure due to uncleaned fuel combustion for heating and cooking activities 7 . SO 2 is produced due to the oxidation of sulphur during the biomass combustion process, which can be detected at 0.5 ppm (0.9 mg/m³) due to its strong pungent smell. SO 2 can also absorbs in the mucous mem- brane of upper respiratory tract, however, its absorbency depends upon the level of humidity 8 . Thus, there is a strong association between the risk of diseases and burn- ing of biomass fuel 6 . Although SO 2 concentration is generally lower indoors than outdoors, it can cause detrimental health impacts, i.e. reduced lung functioning and other respiratory problems 8 . PM 10 has significant health impacts and indoor smoking can add up to 300 μg/m³ PM even after smoking a cigarette. Cooking, i.e. frying can further increase its concentration indoors 9 . Many bio- logical contaminants (bacteria, fungi, dust mites, moulds and pests) have also been found in indoor air and induce infections, direct toxicity or atopic mechanism. A developing country like Pakistan is fighting to deal with such environmental problems which are directly re- lated to poverty and health 10 . About 62% of Pakistan’s population lives in rural areas, where the use of biomass fuel is widespread for cooking and heating purposes 11 . About 94% of the rural population use biomass fuel for heating and cooking thus, contributing to indoor air