Some things are best done after dark， such as setting off fireworks， telling scary stories， and charging your plug-in hybrid electric vehicle. Because a new study shows that topping off your car battery at night generates less ozone. The work appears in the journal Environmental Research Letters.

Plug-in electric hybrids give off less exhaust than gas guzzlers， and when they’re running on battery power， they generate no fumes at all. But there’s a catch. The power plants that make the electricity you use to recharge the battery produce plumes of pollution. But how much ozone gets produced depends on when you reach for that plug.

Electric power plants that burn fossil fuels release hydrocarbons and nitrogen oxides. And when sunlight hits those compounds， ozone forms. At night， however， well， it’s dark， and the compounds disperse in large part before the sun comes up.

Scientists modeled how much ozone would be generated if the cars were charged at three different times： overnight， just before they’re driven or just after. And they found that drawing electricity from the grid after-hours is best. So to drive green， plug in， lay down and get some ozone-free sleep.

有些事情在暗夜做才有效果，比如放焰火、講鬼故事，還有為你的插電式混合動力電動汽車充電。一項新的研究表明夜間為汽車充電產(chǎn)生的臭氧較少。該研究成果刊登在《環(huán)境研究快報》上。

插電式混合動力電動汽車排放的廢氣要比油耗大的車少，而且在使用電池能時不會產(chǎn)生任何濃煙。不足之處在于，為你的充電電池提供電能的發(fā)電廠產(chǎn)生的污染相當(dāng)嚴(yán)重。不過，產(chǎn)生多少臭氧則取決于你在何時充電。

通過燃燒化石燃料提供電能的發(fā)電站會釋放大量碳?xì)浠衔镆约暗趸?，?jīng)陽光照射，就形成了臭氧。不過在夜間，因為沒有陽光，大部分的化合物在太陽出來之前就消散了。

科學(xué)家們分別在夜間、用車前以及用車后這三個時間段為汽車充電，以估算在這三個時間段內(nèi)產(chǎn)生的臭氧量。他們發(fā)現(xiàn)在夜間充電效果最好。為了綠色出行，插上電源，然后躺下來睡個好覺吧，無臭氧的哦。