As the world began to learn in September, when the U.S. Environmental Protection Agency issued a shocking «notice of violation,» the vehicles met emissions standards for
dangerous oxides of nitrogen, known collectively as NOx, only when running their paces in an artificial, indoor lab setting.
As if sweltering heat weren't bad enough, Europeans also suffered through a higher - than - normal number
of days with
dangerous smog levels that year.6 Smog — with ground - level ozone as the main component — forms when sunlight reacts with chemicals such as volatile organic compounds, carbon monoxide,
nitrogen oxides, and water vapor.