Reduction of Air Pollutants| Atmospheric Pollution| AP Environmental Science| Khan Academy

Hey there friends, today we're going to learn about air pollution, and to start off, we're going back in time to the small town of Donora, Pennsylvania, in October of 1948.

Walking into this small industrial town, you can immediately sense that something is wrong. It's the middle of the day, but there's a thick yellowish smog everywhere, enveloping everything and even blocking out the sun. It's so dark that street lights are on during the daytime. It stings your eyes, and it's hard, even painful, to breathe. What we're experiencing is the Donora death fog. One of the worst air pollution disasters in the United States, Donora was an industrial town full of steel plants and mills, which released toxic emissions such as hydrogen fluoride and sulfur dioxide when processing steel and other metals.

Normally, these poisonous gases would disperse into the atmosphere, but this time there was a temperature inversion, which caused a blanket of warm air to cover a layer of colder air near the surface and right over Donora. Consequently, the toxic emissions were essentially trapped under the warm air. Over the course of several days, from October 26th to October 31st, these toxic emissions had accumulated so much that half of the 14,000 people living in Donora suffered from respiratory problems, and 20 people died. Relief only came when the steel mills were shut down and a rainstorm alleviated the smog.

But following the deadly Donora smog, the public began to realize just how dangerous and life-threatening air pollution could be, and citizens demanded change. Donora became a turning point in U.S. history and was the start of the clean air movement. The Air Pollution Control Act of 1955 was the first piece of U.S. federal legislation involving air pollution and provided funds for research about air pollution. Then, in 1963, the Clean Air Act was passed, the first federal legislation to control air pollution, and later expanded in 1970, which resulted in the creation of the U.S. Environmental Protection Agency (EPA) to develop and enforce regulations to protect the general public from exposure to major outdoor air pollutants.

The Clean Air Act was expanded in 1977 and again in 1990, and throughout its nearly 60-year history, our air quality has drastically improved, and pollutants have dropped sharply since 1990. Major air pollutants such as carbon monoxide, nitrogen oxides, sulfur dioxide, and volatile organic compounds have greatly decreased, and that's just since 1990. These four main air pollutants that I highlighted are largely released as emissions from burning fossil fuels, which come from driving vehicles and operating coal-fired power plants and other industrial facilities.

So, as we've started to drive more efficient vehicles and obtain more energy from clean, renewable sources, we've decreased the amount of fossil fuels that we use and, in turn, we've reduced emissions from fossil fuels and associated air pollutants. But how does the Clean Air Act work exactly? How do we clean the air and limit emissions of harmful pollutants?

Clean Air Act regulations, implemented by the EPA, have led to new technologies that help to limit emissions and remove pollutants from the air. In particular, many of these technologies help to reduce air pollution from coal-burning power plants and vehicles. Each of these pollution control technologies functions to remove harmful components out of emissions and release a less harmful substance.

In the last decade or so, you've also probably noticed more and more electric vehicles on the road. Improving the fuel economy of vehicles and even using battery-powered electric vehicles can reduce the need to burn as much gasoline, thereby reducing emissions and giving us cleaner air. A good example is the growing demand for hybrid and purely electric vehicles.

Here, we have a simplified figure that explains the sources of energy for different types of vehicles and their respective emissions. On the left, we have conventional vehicles, which rely on fossil fuels such as gasoline or diesel, and when driven, produce lots of emissions like carbon dioxide and air pollutants. Hybrid and plug-in hybrid vehicles are similar to conventional vehicles in that they have an internal combustion engine, but they also have an electric motor which uses energy stored in batteries.

These batteries can be charged by regenerative braking, or in the case of plug-in hybrids, just by using a wall outlet or other charging equipment. In turn, because these hybrid cars are partially fueled by batteries, they produce fewer emissions than a conventional car. Finally, vehicles that rely solely on electricity, known as battery electric vehicles or BEVs, can use an alternative electricity source so that there's no emissions at the source of the electricity.

What else can we do to ensure cleaner air? We can reduce our reliance on fossil fuels and instead invest in cleaner renewable resources to generate electricity, such as geothermal, wind, and solar. We can make decisions in our day-to-day lives to reduce or prevent air pollution by using less energy and alternative fuels.

For example, walking, biking, or using mass transportation can reduce the need to burn fossil fuels, and there are plenty of other ways to reduce our electrical needs, in particular, using more energy-efficient appliances. For example, think of the LED bulb, which uses 75 percent less energy than incandescent lighting. So even switching out bulbs and the lights around your house or apartment can make a huge difference.

But there's still many other places out there like Donora and times folks living in cities with heavy air pollution literally can't afford to leave. There's still much work to be done in Donora, though. There's the Donora Smog Museum, which has the tagline "Clean air started here." The terrible incident suffered by Donora's community played a huge and pivotal role in opening the eyes of Americans to the hazards of air pollution and spur political action that's carried forth through today and will continue into the future.

Let's all take a deep breath and be glad that we can.