Science Illustrated

Exhaust Controls Air Pollution

Even if still charged by coal-fired electricit­y, at least an EV isn't belching exhaust fumes all over your kids as you drop them off. Car exhaust is toxic, and as we wait for battery tech to improve, we must rely on ever-more sophistica­ted filters to "cle

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On a Friday afternoon in January 2017, toxic smog veils Beijing, just like it has many times before, causing a red alert. Nursery schools and schools close, old polluting cars are not allowed on the streets, and heavy industry such as steel rolling mills are asked to close down. The huge city comes to a halt. During the next few days, people try to stay indoors, and wear masks if they venture outside. The citizens of Beijing know very well that this thick, acrid smog should not be underestim­ated.

In 2014, China’s prime minister, Li Keqiang, officially declared war against air pollution, promising the population to “make the sky blue again”. Now, the citizens of Beijing are beginning to see the results.

LETHAL BREATHING

In a lifetime, about 250 million litres of air pass through our lungs. That's a similar volume of gas as the amount of hydrogen in the Hindenberg. So If the air is even slightly polluted, the total quantity of toxins ending up in the body is tremendous.

For decades, scientists have known that smog causes diseases such as asthma, bronchitis, lung cancer, and other breathing difficulti­es. In recent years, other complicati­ons have been added to the list – including dementia, obesity, and arterioscl­erosis. Annually, some 7.2 million people die an early

death, because they breathe harmful substances, making air pollution one of the the world’s biggest environmen­tal problems.

Smog is big trouble in China. Sixteen of the world’s most polluted cities are located in the world’s most populous nation, which itself is home to a total of 1.4 billion people.

In Beijing, pollution exceeds internatio­nal threshold values of unhealthy air more than half of the year. On the worst days, the air is worse than chain smoking.

China’s extremely unhealthy air is due to a combinatio­n of emissions from different sources. From power station chimneys, carbon dioxide is emitted, the exhaust pipes of cars fill the air with nitrogen dioxide, and ammonia vapour the result of the use of artificial fertiliser­s. Several of the gases also combine in the air, producing even more toxins. In late 2016, a US-Chinese study showed that cities with both heavy industry and heavy traffic are tormented by extra many extremely harmful sulphate compounds, which form based on sulphur dioxide, when large quantities of nitrogen dioxide are present.

TINY PARTICLES – MAJOR PROBLEMS

But in recent years, the toxic gases in the atmosphere have been overshadow­ed by a much more worrying type of pollution: microscopi­c particles which are so small that they can enter deep into the lungs, passing

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