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 ___1___ your car battery at night generates less ozone. The work appears in the journal Environmental Research Letters. [Tammy Thompson et al., "Air quality impacts of plug-in hybrid electric vehicles in Texas: evaluating three battery charging scenarios"]

Plug-in electric hybrids give off ___2___ 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 ___3___.

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 ___4___ 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 ___5___ is best. So to drive green, plug in, lay down and get some ozone-free Zs.
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