SSS 2011-05-05（在线收听）

This is Scientific American’s 60-Second Science. I’m Karen Hopkin. This will just take a minute.

Some things are best done after dark--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. 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 Zs.

Thanks for the minute. For Scientific American’s 60-Second Science, I’m Karen Hopkin.