The concentration on reducing the CO2 'greenhouse' gas emissions over the last decade in automotive terms has somewhat eclipsed the NOx issue, but these oxides produced in high temperature combustion react with ammonia, moisture, and other compounds to form small particles.
Such particles can penetrate deep into the lungs and can cause or worsen respiratory disease, like emphysema and bronchitis. They can aggravate existing heart disease, lead to increased hospital admissions and premature death.
A recent study by emissions measurement experts Emissions Analytics showed that diesel NOx emissions in city stop-start driving can exceed current nitrogen oxides targets by a factor of seven, even in Euro6-compatible engines. Petrol engines generally meet the NOx targets across the range of their use. And hybrids offer both better fuel consumption in urban driving, and less health issues.
Last March, Paris authorities issued a temporary restriction on petrol and diesel cars during a weather inversion that trapped pollutants to dangerous levels over northern France. Hybrid and electric vehicles were not restricted.
The NOx issue is not related to diesel particulates, sooty byproducts of combustion, which in modern diesels are removed by filters before exhaust fumes reach the outside.
