Credits: Pollution over Beijing image courtesy the NASA MODIS Rapid Response Team.

Particle pollution or particulate matter (PM) are mixtures of solid particles or liquid droplets in the air. Some, such as dust, dirt, soot, or smoke, are large or dark enough to be seen with the naked eye. These tiny particles come in many sizes and shapes and can be made up of hundreds of different chemicals. In general, they consist of a mixture of larger materials, “coarse particles”, with diameters between 2.5μm and 40 μm and smaller particles, “fine particles.” with diameters below 2.5 μm.

They come from natural sources e.g. dust or sea salt from wind erosion or wave breaking, human-made processes mainly in urban or industrial areas (agriculture, construction, industrial and energy processes, motor vehicles) and chemical reactions in the atmosphere. Particle pollution and their chemical composition vary by time of year, location and are affected by the weather (temperature, humidity, and wind).

They are an environmental concern as they lower visibility, contribute to acid rain, and adversely affect human health. Largest particles do not get very far into the lungs and tend to cause fewer harmful effects. Coarse and fine particles however pose the greatest problems by getting deep into the lungs, and some may even get into the bloodstream. Long-term exposures of people living for many years in areas with high PM levels are associated with decreased lung function, chronic bronchitis development and premature death. Short-term exposures of hours or days are associated with decreased lung function, increased respiratory symptoms, cardiac arrhythmias, heart attacks, hospital admissions, emergency room visits and premature death. Sensitive groups at greatest risk include people with heart or lung disease, older adults, and children.

Fortunately, many countries have instituted control programs to reduce particulate levels and strategies in place to combat smog, acidic deposition, and smoke releases are also effective in reducing particle levels and thus the risks of health effects.

Tanguy Griffon