The Volkswagen (VW) scandal among many things highlights the issues of different types of emissions and what is clean and what is not.
There are two types of emissions. One type is air quality related and the other type is related to greenhouse gases. Air quality is about health. Greenhouse gases are about global warming.
Major primary air quality related emissions are nitrogen oxides (NOx), sulfur oxides (SOx), carbon monoxide (CO), volatile organic compounds (VOC), and particulates.
Anthropogenic (human induced) greenhouse gases is most of all carbon dioxide (CO2) but to a lesser extent also methane (CH4) and some industrial chemicals like chlorofluorocarbons (CFCs).
When designing a fossil fueled powered engine, whether it is a reciprocating engine, turbine or even a fuel cell with a reformer, one has to optimize both types of emissions. There are trade-offs. For example generally a high combustion temperature is more efficient, which means less CO2. However, high combustion temperatures tend to generate more NOx.
Diesel fuel compared with gasoline has close to 12 % higher energy density, which makes it a more efficient fuel. For a vehicle it results in better mileage, lower costs and less CO2. However, diesel engines emit more air toxic emissions. With a combination of cleaner diesel fuel (e g by reducing the sulfur content at the refinery), advanced engines and advanced emissions control technology there have been huge progress in reducing these emissions, but there is no such thing as “clean diesel”. It is cleaner, much cleaner than it used to be, but it is not clean equal to zero emissions.
“Clean diesel” has been a marketing slogan meaning clean enough to meet air quality standards. The most demanding air quality standards in the world for a long time have been set by California Air Resources Board (CARB), which was established in 1967 under then governor Ronald Regain to address the serious air quality issues California, especially Los Angeles, was facing. Frequently California has been the first state out on stricter standards and other states and countries have followed. It has also been the case with California’s Tier2/Bin 5 standard, which is the one VW is struggling with. This standard is also used by New York, Massachusetts, Vermont and Maine.
The US regulations on NOx are much stricter than the European regulations. Ironically it was for this very reason the International Council on Clean Transportation early 2014 enlisted West Virginia University Center of Alternative Fuels, Engines and Emissions (CAFEE). The intent was to build support for tightening European standards to get closer to the US standards. If the VW diesel cars could pass the CARB standards for NOx, why not require the same levels in Europe?
The CAFEE team started the road tests and found quite soon that VW cars in the test had NOx emissions much higher than the CARB numbers. For example for Jetta it was 15 – 35 times higher and for Passat 5 – 20 times. The results triggered CARB and the US Environmental Agency (EPA) in May 2014 to open an investigation on VW and the rest is now history.
Nicely put, it seems VW got overly focused on fuel efficiency and (power) performance. For some strange reason they downplayed the air quality emissions and engineered a “sophisticated software algorithm” enabling the engines to identify and pass the formal emissions tests. From a technical perspective VW should be able fix the emission problems. It may result in somewhat lower fuel efficiency and performance as well as slightly higher maintenance costs.
How VW can fix the legal, financial and reputational problems is a whole other matter. In any case, VW being a core part, if not the nucleus, of the German industry it will be too big to fail.
Going forward it will be even more important to understand the two types of emissions and not forget one for the other.
… and let’s stop talking about clean diesel or clean coal but instead talk about cleaner diesel and cleaner coal!