What is PM2.5?
Particulate matter, or PM, is the term for particles found in the air, including dust, dirt, soot, smoke, and liquid droplets. Particles can be suspended in the air for long periods of time. Some particles are large or dark enough to be seen as soot or smoke. Others are so small that individually they can only be detected with an electron microscope.

Many manmade and natural sources emit PM directly or emit other pollutants that react in the atmosphere to form PM. These solid and liquid particles come in a wide range of sizes.

Particles less than 10 micrometers in diameter (PM10) pose a health concern because they can be inhaled into and accumulate in the respiratory system. Particles less than 2.5 micrometers in diameter (PM2.5) are referred to as "fine" particles and are believed to pose the greatest health risks. Because of their small size (approximately 1/30th the average width of a human hair), fine particles can lodge deeply into the lungs.

Where does PM2.5 come from?
Sources of fine particles include all types of combustion activities (motor vehicles, power plants, wood burning, etc.) and certain industrial processes. Particles with diameters between 2.5 and 10 micrometers are referred to as "coarse." Sources of coarse particles include crushing or grinding operations, and dust from paved or unpaved roads. Other particles may be formed in the air from the chemical change of gases. They are indirectly formed when gases from burning fuels react with sunlight and water vapor. These can result from fuel combustion in motor vehicles, at power plants, and in other industrial processes.

How does PM2.5 affect human health?
Because these particles are so small they are able to penetrate to the deepest parts of the lungs.  Scientific studies have suggested links between fine particulate matter and numerous health problems including asthma, bronchitis, acute and chronic respiratory symptoms such as shortness of breath and painful breathing, and premature deaths. Most of these premature deaths are the elderly who's immune systems are weaker due to age or other health  problems such as cardiopulmonary diseases.
Children are more susceptible to the health risks of PM2.5 because their immune and respiratory systems are still developing. The average adult breaths 13,000 liters of air per day and children breath up to 50 percent more air per pound of body weight than adults.  The breathing of fine particles by children is believed to cause both acute and chronic respiratory problems such as asthma.  Forty percent of all asthma cases are children who make up only 25 percent of the population.

Threats of PM2.5
Particle pollution - especially fine particles - contains microscopic solids or liquid droplets that are so small that they can get deep into the lungs and cause serious health problems. Numerous scientific studies have linked particle pollution exposure to a variety of problems, including:
• premature death in people with heart or lung disease
• non-fatal heart attacks
• irregular heartbeat
• aggravated asthma
• decreased lung function
• increased respiratory symptoms, such as irritation of the airways, coughing or difficulty breathing

People with heart or lung diseases, children and older adults are the most likely to be affected by particle pollution exposure. However, even if you are healthy, you may experience temporary symptoms from exposure to elevated levels of particle pollution.

How does PM2.5 affect the environment?
These same fine particles that lead to health effects are also a major cause of visibility impairment in most parts of the region.  Because these particles are so small they can travel great distances affecting areas in the regions. These fine particles also have a great affinity for water thus contributing to acid rain.  Acid rain affects all things biological or man made and by thus affecting the environment, can have repercussions to human health.

Who is most at risk?
Roughly one out of every three people is at a higher risk of experiencing PM2.5 related health effects. One group at high risk is active children because they often spend a lot of time playing outdoors and their bodies are still developing. In addition, oftentimes the elderly population are at risk. People of all ages who are active outdoors are at increased risk because, during physical activity, PM2.5 penetrates deeper into the parts of the lungs that are more vulnerable to injury.