What is PM2.5?

PM2.5 stands for Particulate Matter less than 2.5 micrometers. It is a measure of the amount of very small particles (2.5 micrometers or smaller in diameter) that are in the air. PM2.5 is measured in micrograms (µg) per cubic meter of air (m3). Essentially, PM2.5 tells us how much mass of fine particles are in a given quantity of air. 2.5 micrometers is very small – less than 1/10th the width of a human hair! PM2.5 can only be seen with an electron microscope.

Where does PM2.5 come from?

PM2.5 is most commonly produced by human activity. These fine particles can be produced by all types of combustion including motor vehicles, smoking, wood burning, power plants as well as certain industrial processes. Outdoors, motor vehicles are the most significant source of PM2.5 in most of the US. Indoors, smoking, cooking, fire places, candles, oil lamps and fuel-burning space heaters are common sources of PM2.5.

What are the health effects of PM2.5?

PM2.5 is hazardous due to its small size and ability to penetrate deeply into the lungs, PM2.5 is so small that our bodies cannot filter out the particles effectively. Larger particles are generally filtered out in the nose and throat (via cilia and mucus) before they reach the lungs. However, PM2.5 is sufficiently small enough that it can bypass our
body’s defense mechanisms and get into our lungs. PM2.5 can slide past the sticky mucus layer that protects our lungs, and reach the smallest and deepest parts of our lungs, thus penetrating the gas exchange regions in the lung (the alveolus).

In the short-term, high PM2.5 exposure can cause sneezing, coughing, a runny nose and shortness of breath, as well as irritation to the eyes, nose, throat and lungs. PM2.5 exposure can also exacerbate certain medical conditions including asthma and heart disease. In the long-term, PM2.5 exposure is associated with increased risk of mortality from lung cancer and heart disease. PM2.5 exposure is also associated with increased rates of chronic bronchitis and reduce lung function.

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