Edward Longshanks lived in England during the Middle Ages. He hated the thick smoke that polluted London's air. Others did too, but Longshanks got a chance to do something about it: he became King. As Edward I, he ruled from 1272 to 1307. One of Edward's earliest actions was a law against burning imported coal, which seemed to smoke more than the English variety. To show he meant business, the king threatened offenders with a serious punishment—death.

Take a nice, deep breath. What just went into your lungs? If the air around you is clean, you inhaled a mix of nitrogen (78 percent), oxygen (21 percent), and tiny amounts of other chemicals (1 percent). You probably couldn't see, taste, or smell what you breathed.

And if the air isn't clean? Then you also inhaled invisible particles called aerosols. They could be as small as a micron in size. (There are a million microns in a meter, which gives you an idea how small these are.) Aerosols range from bits of dust or smoke to industrial chemicals with names ten times larger than the actual particle. Some aerosols are natural; others result from human activities. NASA’s Learning Center provides detailed information about aerosols.

Nature constantly puts aerosols into the atmosphere. Volcanoes belch dust. Forest fires create smoke. Trees and flowers give off pollen. Salt crystals break free from waves. Natural aerosols, especially in large amounts, can irritate our lungs and airways. But they're seldom fatal.

click to view animation

This animation shows aerosols released into Earth’s atmosphere during July, August, and September of 1988. The darker the brown, the larger the number of particles. The dark swirls covering the United States in late August and early September represent smoke from wildfires, especially at Yellowstone. Source: NASA

OUR ACTIONS AFFECT AIR QUALITY

Human activities also generate aerosols. Cigarettes and cars produce carbon monoxide. Burning fossil fuels—especially oil, gasoline, and coal—releases huge amounts of particulates, carbon dioxide, and sulfur dioxide into the atmosphere. As you'd expect, these greenhouse gases increase global warming.

Unhealthy air can lead to a variety of ailments, from headaches and sore throats to asthma and chronic bronchitis. In fact, some experts warn that air pollution may rank
as one of the worst environmental problems affecting human health.

SMOKE + FOG = SMOG

Human-made aerosols can also create smog, an unhappy marriage of smoke and fog. This happens when weather patterns cause smoke particles and sulfur dioxide to linger near the ground instead of floating high into the atmosphere. Water vapor clings to the aerosols, creating street-level clouds.

But this is no ordinary fog. The smoke and sulfur make for extra-thick clouds, often compared to pea soup. Visibility plummets, so walking, driving, or flying become unusually dangerous. Breathing does too. Inhaling smog can damage people's throats
and lungs. Large doses can lead to serious respiratory problems, even death.

Source: EPA: Smog

December 1952 brought a dramatic example of smog's dark power. Brownish clouds smothered London, England, for several days. Four thousand people died as a result. Since then, Londoners have sharply reduced the use of coal to heat their homes, so
smog is much less of a problem there.

THE FIGHT AGAINST AIR POLLUTION

London's ordeal alarmed other nations too. By the 1970s, many industrialized countries had passed laws to limit air pollution. Taller smokestacks, especially near cities, kept aerosols from gathering near the ground. That lessened smog, though it probably increased acid rain. More successful were new technologies that reduced the number
of aerosols released into the air.

People have also found ways to consume less energy. That lowers the amount of fossil fuel burned in the first place. Architects and engineers, for example, have designed buildings that require less energy to heat or cool. Automakers have created cars that can go 40 to 60 miles on a single gallon of gasoline. The EPA’s Green Vehicle Guide can help you find out which cars and trucks are the most Earth-friendly. Find out more about how EPA arrived at these ratings.

This logo appears on “energy-efficient” products, from answering machines to windows. Source: EPA: Energy Star

As often happens, however, these new technologies are generally too expensive for developing countries. So power plants and factories in poorer countries still discharge the same old aerosols—and health problems. Doctors in India, for example, estimate
that 40,000 people a year die prematurely as a result of smog.

Even allowing for all the new laws and technologies, air pollution remains a problem around the globe. The world gets 85 percent of its energy—to heat buildings, operate machines, generate electricity, run vehicles, and more—by burning fossil fuels. That's largely because fossil fuels are much cheaper than wind or solar power. But scientists, businesspeople, and government officials are exploring ways to create more Earth-friendly energy. After all, they need to breathe too!

	Will global warming make your allergies worse?
	What's setting the world on fire?