Assessment of Air-Borne Particulate Matter (PM2.5) and Bio-Aerosols in Different Residential Built Micro-Environments of Lahore, Pakistan

Abstract

The situation of air quality is worse in the developing countries where annually million lives are lost as a result of impaired air quality which stems from poor socio-economic conditions and lack of awareness. Although a few studies have been conducted regarding air pollution monitoring in Pakistan, no baseline data has been generated to gather information about the indoor air quality. Besides this, there is yet no practical implication to reduce and/or remove the load of pollutants present in the air. Moreover, the studies conducted so far have limited their focus on aerosol emissions from biomass burning and the associated health outcomes in rural areas. So far any detailed study on the indoor air quality of urban centers in Pakistan has not yet been reported. Particulate matter and bioaerosols are two of the most important components of the air we breathe as both of these are ubiquitous in the air. Many studies have reported a number of negative health outcomes owing to a prolonged exposure to these two pollutants and their synergistic effect is also documented to be detrimental for human health. Keeping in view the insufficient data regarding the concentration of fine particulate matter and bioaerosols in the indoor air of urban centers in Pakistan, the current study was designed to monitor the air quality of indoor micro-environments of residential houses (n = 30) of Lahore, Pakistan. The parameters monitored were fine particulate matter and bio-aerosols. PM2.5 was monitored using DustTrak aerosol monitor (model 8520, TSI Inc.) while Koch sedimentation method was employed for microbial sampling. The kitchens and living rooms were identified as two major micro-environments of any residential household and thus were marked to be monitored at each of the selected sites. The ventilation rates were also measured using the tracer gas method with carbon dioxide as the tracer gas. PM2.5 monitoring was carried out for 72 hours each with both micro-environments being monitored in parallel while agar coated Petri plates were exposed for twenty minutes at each location to collect the bacteria and fungi suspended in the air settling by gravity. Temperature and relative humidity were also noted during bio-aerosol sampling. Our results were indicative of poor air quality in the residential indoor environments of Lahore. The 24-h average PM2.5 levels at any of the monitored site were manifolds higher than the WHO recommended limits of 25μg/m³. Overall, the mean levels of fine particulate matter exceeded 13 times the WHO limits. It was observed that cooking, cleaning, movement of people, space heating (during winters) and smoking (in some houses) were the principal indoor sources of particulate pollution. Maximum and minimum air change rate per hour (ACH) was determined for each micro-environment to observe the influence of ventilation on the indoor air quality and was observed to have a significant impact upon PM levels. Low ventilation rates during winter season as well as meteorological factors resulted in elevated PM levels indoors during the colder months. The exposure risk of the inhabitants, most particularly women and small children, was greatly increased as they spent maximum time indoors. The micro-biota of the sampled sites was comprised of common genera which were also identified as opportunistic pathogens. The bacterial composition was consisting of seven species including Micrococcus spp., Staphylococcus spp., and Bacillus spp., with occasional record of Serratia spp. Among the eleven fungal species identified, the dominant ones were Alternaria alternata and Aspergillus spp., with Trichoderma, Mucor, Fusarium and Rhizopus also detected in less numbers. The colony forming units per cubic meter for bacteria ranged from 472 to 9,829 in the kitchens and from 275 to 14,469 in the living rooms. Likewise, the fungal cfu/m3 ranged between 234 and 1887 in the kitchen and from 314 to 1887 in the living room. A seasonal variation in bioaerosols was evident in the kitchens while being not so pronounced in the living rooms. Linear regression model exhibited a direct association of temperature with bacteria and fine particulate matter but not with fungi. Out of thirty monitored households, sixteen contained at least one individual with allergic reactions from dust or during wheat harvesting season. These findings highlight the enhanced risk of exposure to fine particulate matter as well as bioaerosols in the urban residential built environment in Pakistan. The study holds its significance in being the first of its kind as previously no data focusing on simultaneously measured PM and bioaerosol levels in the urban centres of Pakistan has been reported. With the lack of any definite policies, the area of indoor air quality has been ignored at large. It is recommended that more detailed studies must be conducted to monitor air quality in the built micro-environments and guidelines should be formulated to keep a check on the contaminant levels indoors.