Particulate matter (PM) contains microscopic solids or liquid droplets that are so small that they can be inhaled and cause serious health problems. Some particles can get deep into your lungs and some may get into your bloodstream. The size of particles has been directly linked to their potential for causing health problems. Small particles of concern include “inhalable coarse particles” with a diameter of 2.5 to 10 μm and “fine particles” smaller than 2.5 μm in diameter.
Outdoor PM outdoor can be originated from a heavy trafﬁc, resuspension of street and soil dust, emissions from industries, railway station emissions and construction activities close by. Outdoor PM enters into buildings at varying efficiencies, becoming indoor PM. Controlling indoor PM2.5 concentration is presently more feasible and economic than decreasing outdoor PM2.5 concentration. Outdoor PM enters buildings by infiltrating through cracks and gaps in the building envelope as well as via natural ventilation and mechanical ventilation. Mechanical ventilation is likely to be a bigger source of outdoor PM in commercial buildings than in homes.
Important indoor sources of PM include combustion, candles, and cooking. Combustion is a major source of indoor PM. Combustion PM consists of a wide variety of organic compounds along with varying amounts of soot, depending on the combustion process and source. The physical and chemical characteristics of some sources of indoor PM, including cigarette smoke, incense burning, and wood combustion in stoves and fireplaces, have been well characterized by research. The combustion and heating sources of indoor PM include cooking, natural gas stoves and ovens, and electronic cigarettes.
Secondhand smoke can be a significant source of indoor PM in multiunit housing.If you live in an apartment or condominium and you have neighbors next door or underneath you who smoke, infiltration of secondhand smoke into your unit can be quite substantial. Secondhand smoke can infiltrate from outdoor areas, such balconies, patios, and open windows, through walls and via ducts that can move air from one residence to the next.
The indoor PM emission rate from cooking, for example, depends greatly on the food being cooked, the cooking method (whether the food is being grilled, fried or baked and the type of cooking oil being used, for example), and the type of ventilation. Many people who have ventilation fans above their stoves actually turn them on in a consistent manner. Burning food can very quickly introduce large quantities of PM into the indoor environment. Natural gas stoves and ovens emit mainly ultra fine particles (UFP), but how long they persist in indoor air is unclear, and their chemical composition is not well characterized. UFPs pose a health risk, as they generally enter the body through the lungs, but translocate to essentially all organs.
The indoor environment can also be a rich source of allergens. Pets can be a significant source of shed skin flakes, or dander, which by itself can be an allergen, because of its dog or cat saliva content. Dander also contains bacteria that can be allergenic. Various components of house dust, such as mold spores, bacteria, mite proteins, and cockroach proteins can be allergenic. House dust is one key source of PM and vacuuming is a way to increase exposure to PM2.5. Study suggests that PM2.5 levels increase two- to five-fold during vacuuming, with the variation resulting largely from how well the exhaust filter fits in the filter frame.