Emissions and Global Warming – Related BUT Different

The Challenge

Recently, I was approached by a logistics service providing company that is working hard to decrease its emissions and environmental impact. The company complained that pollutant classes in the European Union, the so-called Euro classes (E) did not sufficiently reduce carbon emissions: “Trucks from the highest class E-VI emit more carbon than those from the lower class E-V.” Ideally, a higher class should have lower emissions, not more, and the company feared that emissions would rise if it modernized its fleet and increased the proportion of E-VI class vehicles.

I felt it was hard to believe that a higher standard should be more environmentally harmful rather than less. As I am scientist and addicted to data, I asked the company to send the data upon which it based its observation. Maybe the problem was hidden in there. After I had received the data, I immediately knew it was! What happened?

The company sent the emissions data for 20 ton trucks which were as follows:

• Class E-IV: 472 grams CO2 and 2.4 grams NO2 emissions per km
• Class E-V: 472 grams CO2 and 3.9 grams NO2 emissions per km
• Class E-VI: 485 grams CO2 and 0.3 grams NO2 emissions per km

Indeed, E-VI, the highest class, has 485 grams CO2 emissions per km compared to 472 grams for the E-V class. However, the list also includes additional piece of information often neglected in discussions about the greenhouse impact of combustion engines: NO2 emissions. The problem of the logistics service providing company was that it couldn’t really understand the role of those NO2 emissions which it had left out of consideration.

Global Warming Potential

Holistically, the objective of the company was to reduce its impact on climate and reduce greenhouse gas emissions. Greenhouse gases are like a blanket warming Earth as they slow the speed with which energy can evaporate into space. The point is that different gases have different capacities or strengths in absorbing energy. To make the effects of these gases comparable, the concept of global warming potential (GWP) was developed. It is supposed to make differences in capacity to warm Earth comparable.

The baseline for all comparisons is CO2 which has a GWP of 1. Nitrous oxide has a GWP which is approximately 270 times (sic!) higher than that of CO2. So, one gram more NO2 emissions is much worse for climate than one gram more of CO2 emissions.

With this information, it is now possible to calculate the total global warming potential per km for each E class:

• Class E-IV: (472g CO2 * 1) + (2.4g NO2 * 270) = 1,111 GWP
• Class E-V: (472g CO2 * 1) + (3.9g NO2 * 270) = 992 GWP
• Class E-VI: (485g CO2 * 1) + (0.3g NO2 * 270) = 572 GWP

The highest pollutant class focuses on reducing NO2 emissions and ‘sacrifices’ CO2 emissions in the sense that these are slightly higher in E-VI compared to E-IV and E-V. But given that these NO2 emissions have a much higher GWP, the total global warming potential is indeed lowest for E-VI class trucks. So, the logistics service provider can be reassured that increasing the proportion of E-VI trucks in its fleet will lower its negative impact on climate.

In case you want to understand the GWP of different greenhouse gases, you may find the overview provided by the Greenhouse Gas Protocol helpful. For the logistics and transportation sector, many governments maintain detailed lists with emissions for specific types of vehicles which can be easily converted into GWP calculations. For instance, the British Government maintains detailed lists about emission conversion factors for various industries.