Charging electric cars at night eases a smog problem caused by fossil-fuel plants that provide the power for these vehicles, according to a research paper that appeared in the journal Environmental Research Letters.
In the study, scientists in the US simulated the local impact from plug-in hybrid electric vehicles (PHEVs), which are cars that can switch from battery power to gasoline. Their computer model was based on predictions for 2018 of emissions of nitrogen oxides, the basic ingredient for ground-level ozone, in four major cities in Texas—Dallas/Forth Worth, Houston, Austin and San Antonio. The study compared likely pollution levels when 20 percent of mileage in the region was carried out either by PHEVs or by vehicles that were only gas-powered.
Regardless of the scenario, ozone pollution improved when PHEVs were used because they did not emit nitrogen oxides. As for when these vehicles should be recharged, the paper found it was smarter to plug in the vehicle at night.
That’s because extra demand from fossil-fuel power stations at night did cause levels of nitrogen oxides to rise compared to the typically shorter recharging periods in daytime. But much of the gas emitted at nighttime had dissipated by daybreak. This eased the smog problem by a small but detectable margin.
PHEVs are viewed as a key tool in the fight for a cleaner planet as these do not emit tailpipe pollution when these run on electricity. But the vehicles contribute indirectly to pollution, as well as global warming, if their electricity comes from a power station that runs on coal, oil or gas.