Particle pollution

Everyone has had this experience: You’re sitting in traffic or driving down a highway behind a large truck with black fumes spewing from the tailpipe. You wonder just what that exhaust is doing to you. Scientists have been asking the same question for some time now. What we’re learning is that those fumes contain many complicated ingredients that can do more damage to your health than you might realize.

Not only can that black plume of smoke from the tailpipe or the graying haze settling over the city make you cough and blink, but it can do much worse—it could help take months to years off of your lifespan. The evidence accumulates as the results of new research studies pour in each month. Analyses conducted over the past seven years link air pollution to shorter lives, heart disease, lung cancer, asthma attacks and serious interference with the growth and work of the lungs.

The dirty, smoky part of that stream of exhaust is made of particle pollution. Eighteen percent of the nation—53 million people—live where the air they breathe has so much particle pollution day in and day out that their health can be at risk. Twenty-two percent—64.3 million—live in areas where frequent spikes in particles lasting hours to days places their health at risk as well. But what is particle pollution? What can these particles do to your health? Who is most vulnerable? And what can we do about it? What is Particle Pollution?

Particle pollution refers to a combination of fine solid particles and aerosols that are suspended in the air we breathe. But nothing about particle pollution is simple. First of all, the particles themselves are different sizes. Some are one-tenth the diameter of a strand of hair. Many are even tinier; some are so small they can only be seen with an electron microscope. Because of their size, you can’t see the individual particles. You can only see the haze that forms when millions of particles blur the spread of sunlight. Alarmingly, you may not be able to tell when you’re breathing particle pollution. Yet it is so dangerous it can shorten your life.

Because particle pollution ranges in size from the tiny to the microscopic, the differences in size make a big difference in how they affect us. Our natural defenses help us to cough or sneeze larger particles out of our bodies. But those defenses don’t keep out smaller particles, those that are smaller than 10 microns (or micrometers) in diameter, or about one-seventh the diameter of a single human hair. These particles get trapped in the lungs, while the smallest are so minute that they can pass through the lungs into the blood stream, just like the essential oxygen molecules we need to survive.

Researchers categorize particles according to size, grouping them as coarse, fine and ultrafine. Coarse particles fall between 2.5 microns and 10 microns in diameter and are called PM10-2.5. Fine particles are 2.5 microns in diameter or smaller and are called PM2.5. Ultrafine particles are smaller than 0.1 micron in diameter and are small enough to pass through the lung tissue into the blood stream, circulating like the oxygen molecules themselves. No matter what the size, particles can be harmful to your health.

Because particles are formed in so many different ways, they also can be composed of many complex compounds. Although we often think of particles as solids, not all are. Some are completely liquid; some are solids suspended in liquids. As the U.S. Environmental Protection Agency puts it, particles are really “a mixture of mixtures.” The mixtures differ between the eastern and western United States. For example, the eastern states have more sulfate particles than the west, largely due to the high levels of sulfur dioxide emitted by large, coal-fired power plants. By contrast, in Southern California, nitrate particles from motor vehicle exhaust form a larger proportion of the unhealthful mix.

Where Does Particle Pollution Come From?

Particle pollution is so complex in part because its components come from many sources. It is generally produced through two separate processes: mechanical and chemical. Both processes can produce particles of a range of sizes, but the each procedure produces predominantly one size.

The simplest process is mechanical, which means the breaking down of bigger bits into smaller bits with the material remaining essentially the same, only becoming smaller. Mechanical processes primarily form coarse particles. Dust storms, construction and demolition, mining operations, agriculture, and coal and oil combustion are among the activities that produce coarse particles. They generally are already formed as particles when they enter the air.

By contrast, chemical processes in the atmosphere create most of the tiniest fine and ultrafine particles. Combustion sources burn fuels and emit gases. These gases can simply vaporize and then condense to become a particle of the same chemical compound. Or, they can react with other gases or particles in the atmosphere to form a particle of a different chemical compound. Particles formed by this latter process come from the reaction of elemental carbon (soot), heavy metals, sulfur dioxide (SO2), nitrogen oxides (NOX) and volatile organic compounds with water and other compounds in the atmosphere. Burning fossil fuels in factories, power plants, steel mills, smelters, diesel- and gasoline-powered motor vehicles (cars and trucks) and equipment generate a large part of the raw materials for fine particles. So does burning wood in residential fireplaces and wood stoves and burning agricultural fields or forests.

What Can Particles Do to Your Health?

That irritating dark smoke coming out of the truck’s tailpipe is probably directly emitting carbon particles and the raw ingredients for other fine particles into the air. That dark stream mixes with exhausts from other cars, trucks and heavy equipment, as well as the exhaust plumes from power plants, factories and many other sources to create the particle pollution problem we have in many places in the United States today.

In the early 1990s, dozens of community health studies from cities throughout the United States and around the world indicated that short-term increases in particle pollution were associated with adverse health effects ranging from increased respiratory symptoms to increased hospitalization and emergency room visits, to increased mortality from respiratory and cardiovascular disease.

In 1993, a landmark study appeared in the New England Journal of Medicine, which documented the significant risk to human life from long-term exposure to particle pollution. Called the Harvard Six City study, it looked at six small towns in the eastern United States and found clear evidence of the increased risk of premature death from exposure to the particle pollution in the most polluted city studied, compared to the cleanest. Two years later, another group of researchers using the large nationwide database of personal histories from the American Cancer Society, came to similar conclusions. Additional thorough reviews have left no room for doubt: particles at the levels seen in the United States today are shortening lives.

Particle pollution causes a broad range of health problems. Exposure worsens asthma and causes wheezing, coughing and respiratory irritation in anyone with sensitive airways. It also triggers heart attacks, cardiac arrhythmias (irregular heartbeat) and premature death.

Because of its very small size, particle pollution gets right through the nasal passage, past the trachea and deep into the lungs. The smallest of the particles can even enter the bloodstream via the lungs.

Particle pollution can damage the body in ways similar to cigarette smoking, researchers have discovered. In a 2005 review of the research on how particles cause harm, researchers found that the body responds to particles in similar ways to its response to cigarette smoke. These findings help explain why particle pollution can cause heart attacks and strokes.

Article Courtesy American Lung Association