Introduction: Air pollution is recognized as a dangerous consequence resulting from the expansion of urban populations and the increase in energy consumption in the present era, and numerous studies conducted in this regard have identified airborne particulate matter as one of the main threats to human health. Having the necessary information about the physico-chemical nature and understanding the behavior of suspended particles in the environment plays an important role in implementing control and management programs. One of the important topics raised in the field of air pollution is the concentration of particulate matter in indoor spaces, which can be affected by the infiltration of outdoor particles. The prolonged presence of individuals inside their homes increases the likelihood of long term exposure to indoor airborne particles.
Materials and Methods: In this study, four residential buildings located in the city of Tehran were used to examine indoor particulate concentrations, air quality, and the particle mass distribution. Additionally, sampling was conducted at one point in the Amirabad area in order to investigate the distribution of outdoor particles. A cascade impactor sampler with a constant flow rate of 28.3 liters per minute was used for a period of 4 to 6 hours at times when the residents were present in order to collect airborne particles.
Results: Based on the obtained results, 0.75% by weight of the collected particulate matter was composed of particles with diameters smaller than 0.4 micrometers. Although this may seem negligible in comparison to the mass of other suspended particles, considering the very small size of these particles and their ability to penetrate vital organs of the body through the lungs, they pose a greater degree of toxicity. Despite the fact that the mean concentration of collected particles smaller than 0.4 micrometers was about 0.46 µg/m3, in comparison to particles larger than 11 micrometers measured at 24.88 µg/m3 and comprising approximately 41% by weight the smaller particles represent a greater health risk. Meanwhile, 2.99% by weight (with an average concentration of 3.48 µg/m3) of the particles collected outdoors consisted of particles smaller than 0.4 micrometers. Also, approximately 13.83% by weight of the indoor particles were composed of particles with an effective diameter smaller than 3.3 micrometers, while this value was 86.17% for the outdoor environment. In all particle size ranges, statistically significant differences were observed between particle concentrations across the four sampling sites. This difference becomes more pronounced with increasing particle size.
Discussion: Considering the age of the buildings, the type of ventilation and cooling systems, and the activities of the occupants, the infiltration and distribution of airborne particles indoors were considerable, and environmental variables such as temperature and humidity influenced particle distribution. The distance of buildings from pollutant generating sources such as major roads and high traffic routes was also one of the most important factors affecting the increased concentration of indoor particles. This parameter was especially noticeable in indoor spaces lacking ventilation systems or having defective systems. Indoor cleanliness, movement of residents, and the type of cooling system used also played a significant role in indoor particle dispersion. Therefore, increasing public awareness among building design specialists as well as the general population can partially help prevent excessive infiltration and distribution of particles indoors and reduce the likelihood of long term exposure for individuals.