Los Angeles was blanketed by a thick gas that stung people's eyes

洛杉磯被一層濃厚、使人眼睛感到刺痛

and blocked out the Sun.

且遮蔽陽光的氣體所壟罩

Panicked residents believed their city had been attacked using chemical warfare.

驚恐的居民相信他們的城市被化學武器攻擊了

But the cloud wasn't an act of war.

但這些烏雲並不是出於戰爭

It was smog.

那是霧霾

A portmanteau of smoke and fog,

就是煙和霧混合構成的詞

the word smog was coined at the beginning of the 20th century

霧霾這個詞是在20世紀初被創造出來的

to describe the thick gray haze that covered cities

來解釋壟罩城市的厚重灰霾

such as London,

像是倫敦、

Glasgow,

格拉斯哥、

and Edinburgh.

以及愛丁堡

This industrial smog was known to form

這些工業的煙霧

when smoke from coal-burning home stoves and factories

是由家中爐子和工廠燒煤

combined with moisture in the air.

混合濕氣進到大氣中

But the smog behind the LA panic was different.

但洛杉磯的霾害不一樣，

It was yellowish with a chemical odor.

是微黃色的，且混雜著化學臭味

Since the city didn't burn much coal, its cause would remain a mystery

但這個城市並沒有燒很多煤，它的成因一直是個謎

until a chemist named Arie Haagen-Smit identified two culprits,

直到一位名叫 Arie Haagen-Smit 的化學家發現了兩個兇手

volatile organic compounds, or VOCs,

揮發性的有機化合物，或稱 VOCs，

and nitrogen oxides.

以及一氧化二氮

VOCs are compounds that easily become vapors

VOCs 是一種容易揮發

and may contain elements, such as carbon,

可能包含其他物質的混合物，像是碳、

oxygen,

氧、

hydrogen,

氫、

chlorine,

氯

and sulfur.

和硫磺

Some are naturally produced by plants and animals,

有些是由動植物自然產生的，

but others come from manmade sources,

但其他則是人造的

like solvents,

像是溶劑、

paints,

塗料、

glues,

膠

and petroleum.

和石油

Meanwhile, the incomplete combustion of gas in motor vehicles

同時，摩托車未燒完全的氣體

releases nitrogen oxides.

會釋放一氧化二氮

That's what gives this type of smog its yellowish color.

那就是讓霧霾變黃色的原因

VOCs and nitrogen oxide react with sunlight

VOCs 和一氧化二氮對陽光起反應

to produce secondary pollutants called PANs and tropospheric,

並製造出第二種污染物，稱作 PANs 和位於對流層

or ground level, ozone.

或是陸地上的臭氧

PANs and ozone cause eye irritation and damage lung tissue.

PANs 和臭氧會刺激眼睛，並造成肺部的傷害

Both are key ingredients in photochemical smog,

這些都是光化學霧霾的主要成分

which is what had been plaguing LA.

也是洛杉磯的霾害來源

So why does smog affect some cities but not others?

那為何霾害只出現在幾個城市呢？

Both industrial and photochemical smog combine manmade pollution

工業和光化學霧霾都包含了

with local weather and geography.

當地天氣及地理環境的人造污染

London's high humidity made it a prime location for industrial smog.

高濕度讓倫敦成了累積工業霧霾的地方

Photochemical smog is strongest in urban areas with calm winds

光化學霧霾在有著微風、

and dry, warm, sunny weather.

乾燥、溫暖、晴天的都會地區最為嚴重

The ultraviolet radiation from sunlight provides the energy necessary

太陽的紫外射線提供了必需的能量

to breakdown molecules that contribute to smog formation.

來分解形成霧霾的分子

Cities surrounded by mountains, like LA,

像是洛杉磯這種山地環繞的城市

or lying in a basin, like Beijing,

或像是北京這種坐落在盆地的城市

are also especially vulnerable to smog since there's nowhere for it to dissipate.

也都特別容易受霾害，因為沒有地方可以讓霧霾消散

That's also partially due to a phenomenon known as temperature inversion,

其中一部分原因，是所謂的逆溫現象所造成的

where instead of warm air continuously rising upward,

就是熱空氣不斷的上升，

a pollution-filled layer of air remains trapped near the Earth's surface

被汙染的空氣層被囚禁在地球表面

by a slightly warmer layer above.

被一層輕薄的暖空氣覆蓋在上面

Smog isn't just an aesthetic eyesore.

霧霾不只是造成朦朧美

Both forms of smog irritate the eyes,

這些霾的形成會刺激眼睛、

nose,

鼻子

and throat,

和喉嚨

exacerbate conditions like asthma and emphysema,

還會使氣喘、肺氣腫病情加劇

and increase the risk of respiratory infections like bronchitis.

並增加肺部感染的危險，像是支氣管炎

Smog can be especially harmful to young children and older people

霧霾對小孩及老人會有特別大的傷害，

and exposure in pregnant women has been linked to low birth weight

孕婦暴露在霾害中會使肚子裡的寶寶體重減輕

and potential birth defects.

和潛在的缺陷

Secondary pollutants found in photochemical smog

光化學霧霾中的第二種汙染物質

can damage and weaken crops and decrease yield,

會傷害作物，使產量減低

making them more susceptible to insects.

並讓作物更容易遭受蟲害

Yet for decades, smog was seen as the inevitable price of civilization.

到目前幾十年，霾害看來是文明無法避免付出的代價

Londoners had become accustomed to the notorious pea soup fog

倫敦人已經習慣了惡名昭彰的霧霾

swirling over their streets until 1952,

盤旋在他們的街道間

when the Great Smog of London shut down all transportation in the city for days

直到1962年倫敦煙霧事件，迫使所有交通工具停止

and caused more than 4,000 respiratory deaths.

並造成超過4000人因呼吸疾病死亡

As a result, the Clean Air Act of 1956

因此，1956年的清潔空氣法

banned burning coal in certain areas of the city,

禁止在城市的特定區域燒煤

leading to a massive reduction in smog.

這大量減少了霧霾

Similarly, regulations on vehicle emissions and gas content in the US

美國也對交通工具的排氣量頒布了類似的法案

reduced the volatile compounds in the air and smog levels along with them.

減少空氣中的揮發化合物及霧霾的汙染程度

Smog remains a major problem around the world.

霧霾在世界上是個很大的問題，

Countries like China and Poland that depend on coal for energy

像是中國、波蘭這些仰賴煤炭作為能源的國家

experience high levels of industrial smog.

遭受嚴重的工業霾害

Photochemical smog and airborne particles from vehicle emissions

交通工具產生的光化學霾害和懸浮粒子

affect many rapidly developing cities,

影響許多快速發展的城市

from Mexico City and Santiago

從墨西哥市、聖地牙哥

to New Delhi and Tehran.

到新德里和德黑蘭

Governments have tried many methods to tackle it,

許多政府已經嘗試了許多解決方法

such as banning cars from driving for days at a time.

像是規定一天車輛行駛的特定時間

As more than half of the world's population crowds into cities,

當超過世界一半的人口擠進城市

considering a shift to mass transit and away from fossil fuels

就要思考如何排除大量化石燃料汙染

may allow us to breathe easier.

才能使我們呼吸得更輕鬆