We spend most of our time indoors, at work, home and school or even at the shopping mall. There are many sources of air indoor pollution, building materials, cigarettes, consumer products, gas appliances, and furniture can all add to the problem. However, the toxic emissions from many of these contributors are not measured or are only partially measured by local, state or federal laws. Pollution from power plants, cars, and other transportation is a well-known source of outdoor air pollution, but sometimes our indoor air quality is worse; it can be up to ten times worse for you than the outside air.
The revised United States Environmental Protection Agency National Ambient Air Quality Standards (US EPA NAAQS) for Particulate matter PM2.5 and other air pollutants could be exceeded not only outdoors but also indoors. This is based on the different studies on indoor and outdoor particulate matter in the inner-city environment or even in the neighborhood of busy major roads.
In these recent years indoor air quality (IAQ) has gained excessive attention. The main reason is we spend a significant amount of time indoors in modern times. Urban people spend on average 87% indoors and only 6% outdoors. We also believe that the indoor environment is better and more livable than the outdoors. We also believe indoor air is cleaner, more relaxed and healthier and the building will shelter us from harmful substances in the ambient environment. For this reason a number of air quality indication systems in the world, which are designed for outdoor use also, gives warnings or advice during episodes of poor air quality, to stay indoors. Yet, the important question is: Is indoor air actually cleaner? Is it cleared of outdoor pollutants?
First of all, it must be acknowledged that indoor air is simply an extension of the ambient air. Air enters indoors through air conditioners, doors, windows and so on. If we suppose there is no indoor source of pollution, the entering air would be filtrated by whatever it passes through. Yet, we are still uncertain whether this process efficiently removes any pollutant, not to mention the fact that it could actually add other pollutants into the airstream.
In addition, due to the considerable difference in the environment between indoors and outdoors, this could bring much different pollution environment and dispersion characteristics in the two settings. For instance, in a rainy or humid day, outdoor pollutants tend to be washed out while, because of the relative constant humidity indoor, indoor air quality could be much worse, without even looking at any indoor activity.
Moreover, indoor–outdoor relationships are a complex collaboration of various factors like pollutant depletions, meteorological factors, indoor sources and sinks, combustion gases from fireplaces, filtrations and ventilations, etc. The air pollutants indoors and outdoors differ in characteristics, types, absorptions and sources. For example,...