Near-zero emissions : ICE or BEV ?

Battery electric vehicles (BEVs) promise to reduce CO2 emissions, but there is clearly a lot of debate on the actual reductions, which depends on the carbon intensity of upstream electricity reduction. The second benefit presented then, is the reduction in criteria pollutants. NOx emissions from ICE powered vehicles are especially under the lens given concerns with air quality in major cities. Let’s examine the reductions offered by BEVs in this regard.

At the 28th Aachen Symposium, in a paper titled “Zero-Impact Combustion Engine”, authors from FEV and Aachen University estimated based on 2016 numbers in Germany, that powerplant NOx emissions translated to 117.5 mg/km when the electricity is used to drive a BEV.

Here’s the equivalent calculation for US, with more recent numbers:

·        NOx emissions from power plants : 1.02 Million Tons

Ref: https://www.epa.gov/airmarkets/power-plant-emission-trends

·        Electricity generation in US : 4171 Billion kWh

Ref : https://www.eia.gov/tools/faqs/faq.php?id=427&t=21

·        Electricity consumption of Tesla 3 : 24 kWh/100 mi

Ref: https://www.fueleconomy.gov/

Based on above, NOx emissions from power generation = 222 mg/kWh

NOx emissions for a BEV = 33 mg/km

Note that this is much smaller than the number cited above, and is probably a conservative estimate (that is likely NOx emissions are probably higher given the higher electricity consumption in winter and after battery degradation, etc.)

The limit for combined NOx and HC emissions for passenger cars in the US is 18.7 mg/km (so that NOx emissions alone are a fraction of this limit). China 6b starting 2023 and Euro 7 regulations (~ 2025) tighten Diesel NOx limit to 35 mg/km.

The above clearly shows that when it comes to NOx emissions, ICE vehicles are as clean, if not cleaner than BEVs today. An important point is that ICE emissions are mostly in urban areas, and an emphasis on reducing them even further is therefore justified. Another concern is whether we are past Dieselgate, that is whether real world emissions are as low as obtained in lab conditions during certification. The plot shows the reductions in NOx since the introduction of the real-world driving emission testing, for the same model of Diesel vehicles. Data taken from the same Aachen reference mentioned above, plot is mine.

Clearly, huge reductions in NOx are happening and more to come. The race to near-zero emissions is on.