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The most outstanding way to reduce indoor air pollution is to get rid of each pollution source, or at least lower their emissions. Sources that contribute to indoor air pollution should be removed if possible. If not, they should be sealed or somehow enclosed. Other sources, like gas stoves, can usually be adjusted to reduce emissions. Reducing indoor air pollution by attacking the sources is cheaper than increasing ventilation or air exchange with the outside. Increased ventilation usually increases energy costs.
That said, increasing ventilation will help lower indoor air pollution concentrations. You cannot count on central air systems to bring in sufficient outside air. If local weather or climate will enable, you can open windows & doors, or use ceiling and attic fans. Bathroom and kitchen exhaust fans can also help reduce indoor air pollution by removing contaminants directly and by increasing the outdoor air exchange rate.
If you are doing something like painting, heating with a kerosene heater, or engaging in other activities that increase short-term levels of indoor air pollution, you should try to increase ventilation as much as possible without undue concern about increased energy costs.
A third method for reducing indoor air pollution is using an air cleaner. While air cleaners can have a positive impact on particle levels in the air, very few are designed to reduce gaseous pollutants. When comparing air cleaners for buy, pay particular attention to the “percentage efficiency rate” (how well it removes pollutants from the air) and the air circulation rate (usually given in cubic feet per minute). Air cleaners are most effective with regular maintenance.
Effective reduction of indoor air pollution will most likely be achieved with a combination of the methods above. But the most effective is the first method described: controlling or removing the sources of indoor air pollution.