Who that car is following and how long the spend sitting at red lights (or in traffic leaving a light) would likely have a larger effect. If you have enough data points you can reliably correct for it but there's still gonna be exception cases like the industrial area that's polluted during the day and the adjacent down that the wind blows the pollution to at night (Google doesn't drive street view cars at night AFAIK).

I don't know how much Google takes season into account when routing street view cars but areas with a tourism industry would be cleaner in the off season and colder areas will be dirtier in the winter (more fuel used for heating, less trees). Also something that could be accounted for...