The results in general show positive air quality results due to the use of PHEVs regardless of charging scenario with the nighttime charging scenario showing the best results on average by a small margin. This further supports efforts to develop regulation to encourage nighttime charging; an example would be variable electricity pricing.
In particular, less ozone is emitted during nighttime charging. Ozone is the product of a chemical reaction between hydrocarbons & nitrogen oxides (both pollutants emitted by vehicles and electricity-generating power plants) and sunlight. As there is no sunlight at night (we did our research on this point), the chemical reaction that produces ozone cannot occur and the pollutants emitted will have dispersed by the time the sun rises. It is worth noting, though, that this schedule does produce the most nitrogen oxides. However, night charging will also help balance electricity demand meaning, in the long run, less power plants – and that's something that we can all agree is a good thing.[Source: PhysOrg]