Suspended Particulate Matter: What It Is & Why It Matters
Discover how the size and source of microscopic airborne particles determine their distinct impacts on human health and environmental systems.
Suspended particulate matter is a complex mixture of microscopic solid particles and liquid droplets, like soot and dust, that hang in the air. Many of these particles are invisible to the naked eye and can only be detected with an electron microscope. Composed of hundreds of different chemicals, this airborne material is a form of air pollution that impacts human health and the environment.
Sources of Suspended Particulate Matter
The origins of suspended particulate matter are diverse. Natural sources include volcanic eruptions that release ash, windstorms that carry soil and dust, and sea salt spray from oceans. Forest fires and the decomposition of organic materials also release large quantities of particles into the atmosphere.
Human-made, or anthropogenic, sources are widespread and often concentrated in populated areas. Contributors include industrial processes, power plants that burn fossil fuels, and vehicle exhaust. Other activities that generate particulate matter include construction, demolition, and agricultural practices like tilling fields. Some particles are emitted directly, while others form in the atmosphere through chemical reactions between pollutants like sulfur dioxide and nitrogen oxides.
Classifying Particulate Matter by Size
Particulate matter is classified by physical size, as this determines how it interacts with the human respiratory system. Regulatory agencies focus on two main categories: PM10 and PM2.5. PM10 refers to inhalable coarse particles with a diameter of 10 micrometers or smaller. For comparison, a human hair has an average diameter of about 70 micrometers.
The second category, PM2.5, consists of fine inhalable particles with a diameter of 2.5 micrometers or less. To visualize this scale, a single human hair is about 30 times wider than the largest of these fine particles. Beyond these regulated categories, an even smaller class known as ultrafine particles (UFPs) has a diameter of less than 0.1 micrometers.
Consequences for Human Health
The size of particulate matter correlates with its potential to cause health problems. Larger particles, or PM10, can be inhaled but are often trapped in the upper respiratory tract, causing irritation in the nose and throat. The greater health risks are associated with smaller particles that bypass the body’s natural defenses.
Fine particles, or PM2.5, are dangerous because their small size allows them to travel deep into the lungs. From there, these particles can pass into the bloodstream, circulating throughout the body and affecting various organs. This penetration can trigger inflammation in the lungs, heart, and blood vessels.
Exposure to these fine particles is linked to a range of health issues. Short-term exposure can lead to eye, nose, and throat irritation, coughing, and shortness of breath. Long-term exposure can result in conditions like aggravated asthma, bronchitis, and decreased lung function. The impact on the cardiovascular system includes links to irregular heartbeat, heart attacks, and strokes. Children, older adults, and individuals with pre-existing heart or lung conditions are more vulnerable to these effects.
Environmental Impacts
Suspended particulate matter has consequences for the environment, with one of the most noticeable impacts being the reduction of visibility. Particles in the air scatter and absorb light, creating haze that can obscure landscapes and degrade scenic views in areas like national parks. This phenomenon is also responsible for the formation of atmospheric brown clouds observed in various parts of the world.
Particulate matter also plays a complex role in influencing climate patterns, and the effect varies by particle composition. Dark particles, like soot or black carbon, absorb sunlight and contribute to atmospheric warming. Conversely, lighter-colored particles can reflect sunlight away from the Earth, producing a localized cooling effect. This dual role complicates predictions of the overall impact on global temperatures.
When these particles settle out of the atmosphere, they can harm terrestrial and aquatic ecosystems. Deposition onto soil and water can alter their chemical balance by changing nutrient levels. Particulate matter coating the leaves of plants can interfere with photosynthesis, which can stunt plant growth and affect entire ecosystems.