The first step would be checking outdoor air quality as industry and traffic have a significant role in releasing hazardous chemicals into the air. The most health-relevant air pollutants are particulate matter (PM) with a diameter of 10 micron or less, which can penetrate deep inside the lungs and induce reaction of the surface and defense cells. Average particulate air pollution levels in many developing cities can be 4-15 times higher than WHO air quality guideline levels. Concentration of carbon monoxide (CO), particulate matters (PM10, and PM2.5), sulfur dioxide (SO2), Nitrogen dioxide (NO2), Ozone (O3), Nitrogen monoxide (NO) are important factors defining outdoor air quality. Outdoor air may have enough ozone to react with skin oils and is irritating to lung tissue and can produce toxic by-products in reaction with some cleaning products based on citrus and terpene extracts. However, indoor air quality is not only defined by the outdoor air. Airborne allergens, bacteria, fungi and viruses can still grow indoor. Volatile organic compounds (VOC) also need to be considered as their concentration can be several times more during winter when the windows are shut and they are trapped inside in absence of air exchange. VOCs can be found in paints and coating of walls, and furniture, cleaning products with cholorofluorocarbons and cholorocarbons, fossil fuels used directly and indirectly, benzene in tobacco smoke, and perchloroethylene used for dry cleaning. Most factors in the air have compounding long impact on health rather than an acute toxic effect. Hence, poor air quality can remain unrecognized without proper measurement apparatus. You may buy and install the required equipment to monitor air quality continuously or occasionally rent them which puts the latest technology in your hands at a lower cost. As the air quality change, the measurements need to be repeated and compare with the maximum allowed levels defined by the regional regulating agencies.