But even when governments were promoting diesel cars, we knew there were issues with toxic emissions (those immediately harmful to humans, not CO2). Heating air in an engine produces nitrogen oxides (NOx) which include the toxic nitrogen dioxide (NO2), greenhouse gas nitrous oxide (N2O) and nitric oxide (NO), which reacts with oxygen to form NO2. In a petrol car, these can be cleaned up by a three-way catalytic converter so that it emits on average around 30% less NOx than a diesel car, without after-treatment.
We know that long-term exposure to nitric oxide can significantly increase the risk of respiratory problems, and so these emissions have been regulated for some time. The fine particulate matter (PM) that diesel engines produce also causes cancer and can have acute respiratory effects.
Particulate filters in car exhausts can reduce PM emissions by more than 90%, but they require good operating conditions and regular maintenance. They can also produce more nitrogen dioxide, making diesel one of the main sources of this toxic gas.
And there’s this:
To protect the public from particle pollution, regulators have required diesel truck manufacturers to use filtering technology, which can cut out 85 percent or more of PM 2.5 [“a mix of soot and bits of organic compounds smaller than 2.5 micrometers in diameter”]. But these filters use a chemical reaction that sometimes generates more of another pollutant: nitrogen dioxide. It’s this extra NO2 that seems to make breathing filtered exhaust—at least in the short term—even harder on the lungs than straight diesel fumes. Nitrogen dioxide causes inflammation and tightening of airways, and thus cuts lung function. Over the long term, breathing it in can cause asthma and respiratory diseases. It also reacts in the atmosphere to form smog.
I reckon our City Representatives are saying, “So what? Respiratory problems? Cancer? Rub some dirt on it and walk it off.”
Remember that when the elections roll around.