Researchers at the University of Texas believe that the use of plug-in hybrid electric vehicles will increase ozone during night-time hours while decreasing ozone during the day.
Ozone is formed as hydrocarbons and nitrogen oxides react with sunlight as they are emitted into the air. Two of the largest emitters are vehicles and electricity generating units, with some areas of the US failing to meet National Ambient Air Quality Standards even after 30 years of regulation.
As such, the team looked at the air quality impacts of replacing around 20 per cent of petrol powered light duty vehicle miles travelled with electric vehicle miles travelled by the year 2018 in Dallas/Fort Worth, Houston, Austin and San Antonio. Three charging scenarios were also examined – charging the car at off-peak times during the night; charging to maximise battery life; and charging the battery when it was a convenient time for the driver.
Among the findings were that the potential air quality impact of plug-in hybrid electric vehicles is dominated by the impact of nitrogen oxide decreases from mobile sources. The general trend is to see decreases in eight hour average ozone concentrations during daytime hours and increases during the night.
In addition, plug-in hybrid electric vehicles are deemed likely to positively impact air quality with regards to attaining the eight hour ozone standard; and for all charging scenarios in San Antonio and Austin potential exposure was reduced, while the results are less clear in Dallas and Houston.
The study shows that while in most cases there is little difference in maximum ozone concentrations between the three charging scenarios, the convenience charging scenario is most likely to cause increases in daily ozone.
