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General overview about non-exhaust emissions

In general, all automotive emissions can be classified roughly into the exhaust and non-exhaust emissions. Before the introduction of air quality and emission standards, the exhaust emissions, especially from diesel vehicles, were a major source of particulate matter (PM). Since then, the passenger cars are fitted with diesel particulate filter (DPF), which has been effective in lowering the emitted mass of PM by almost 99.3% [1]. The current upcoming standards (Bharat VI in India, Euro6 in EU) would dictate that the new automobiles should need to emit less than 5 mg/km of PM. The latest generation of petrol-driven automobiles are emitting on average about 3.1 mg/km (PM10) and 3.0 mg/km (PM2.5); and diesel-driven automobiles about 2.4 mg/km (PM10) and 2.4 mg/km (PM2.5) [2 – 6].

Shifting gears, in the recent past, there have been many studies concerning non-exhaust emissions. The non-exhaust emissions are primarily from tire wear, brake wear, and road wear. While road wear is beyond the control of automotive manufacturers, the quality of tire and brake products are areas where stringent standards need to be introduced to reduce non-exhaust emissions. Unlike exhaust emissions, these are much more difficult and trickier to measure, estimate and control. While a DPF helped reduce emissions from diesel engines, the same idea cannot be applied here. The estimates of non-exhaust emissions are generally based on laboratory measurements, roadside & tunnel measurements, mobile on-board measurements using trailers. Today, the average estimated non-exhaust emissions from petrol and diesel automobiles are about 22.9 mg/km (PM10) and 8.2 mg/km (PM2.5); while for electric vehicles about 18.1 mg/km (PM10) and 7.5mg/km (PM2.5) [2 – 6]. While these data are from EU and other developed countries, the data from developing countries like India (particularly the National Capital Region) is no different [7]. Recent studies show that since 2002 the PM10 emissions from exhaust are about 14 – 34% while that from non-exhaust are about 66 – 86%.

One of the strategies adopted in many countries to improve air quality is to incentivize the electrification of passenger vehicles. While EV’s promise a zero-emission and pollution-free environment, the truth is far from it. EV’s would involve a significant increase in the overall weight of the passenger cars. A Ford Focus weighing about 1500 kg would weigh 1719 kg, leading to nearly a 15% increase in weight, or a Chevrolet spark weighing about 1104 Kg would weigh about 1431 kg, leading to about 30% weight increase. The alarming aspect is that the non-exhaust emissions directly scale with the vehicle weight. The 30% increase in the Chevrolet spark would lead to about 50% increase in the non-exhaust emissions. However, this area of research needs significantly more systematic study to understand the effects of increased vehicular weight on the non-exhaust emissions [8 – 10].

While EV’s have been touted to make transport zero-emission, today, non-exhaust emissions account for 90% of PM10 and 85% of PM2.5. While EV’s will indeed reduce the reliance on fossil fuels, they will only reduce emitting by 1 – 3% of IC engines, on average. These differences are likely going to disappear as exhaust emission standards become even stricter or with optimization of frictional dissipation in the IC engine.

As evident from the number, it is about time that the world starts thinking about particulate content produced from tire and brake wear. Today, there are no standards in any country worldwide, with relation to control of non-exhaust emissions. If measures cannot be imposed on manufacturing industries, concerning quality of products produced, it would be nearly impossible to reduce non-exhaust emissions.

References

[1] A.Thorpe and R. M.Harrison, "Sources and properties of non-exhaust particulate matter from road traffic: A review," Science of The Total Environment, vol. 400, pp. 270 - 282 (2008)

[2] European Commission Brussels, “EU Thematic Strategy on Air Pollution.” Available from: http://eur-lex.europa.eu/legal-content/EN/TXT/?uri¼CELEX:52005DC0446.

[3] H. Cai, A. Burnham, M. Wang, “Updated emission factors of air pollutants from vehicle operations in GREET using MOVES,” Argonne National Laboratory. Available from https://greet.es.anl.gov/files/vehicles-13.

[4] L. Ntziachristos and Z. Samaras, “EMEP/EEA Emission Inventory Guidebook 2013: Exhaust emissions from road transport,” Copenhagen: EEA; updated 2014. Available from: http://www.eea.europa.eu/publications/emep-eea-guidebook-2013/part-b-sectoral-guidance-chapters/1-energy/1-a-combustion/1-a-3-b-road-transport.

[5] J. Klein, G. Geilenkirchen, J. Hulskotte, N. Ligterink, P. Fortuin, “Molnar-in 'tVeld H. Methods for calculating the emissions of transport in The Netherlands,” Dutch Emission Inventory (2014). Available from: http://www.emissieregistratie.nl/erpubliek/misc/documenten.aspx.

[6] P. Brown and Y. Pang, “PM Speed-related Emission Functions (COPERT 4v10),” National Atmospheric Emissions Inventory, London (2014). Available from: http://naei.defra.gov.uk/data/ef-transport.

[7] A. Nagpure, B. R. Gurjar, V. Kumar and P. Kumar, “Estimation of exhaust and non-exhaust gaseous, particulate matter and air toxics emissions from on-road vehicles in Delhi,” Atmospheric Environment, vol. 127, pp. 118 – 124 (2016)

[8] A. Simons, “Road transport: New life cycle inventories for fossil-fuelled passenger cars and non-exhaust emissions in ecoinvent,” International Journal of Life Cycle Assessment, vol. 3, pp. 1 – 14 (2013)

[9] B. Gard, S. Cadle, P. Mulawa, P. Groblicki, C. Laroo and G. Parr, “Brake wear particulate matter emissions,” Environmental Science and Technology, vol. 34, pp. 4463 – 4469 (2000)

[10] T. Barlow, "Briefing Paper on Non-exhaust Particulate Emissions from Road Transport," Transport Research Laboratory, Wokingham, UK (2014). Available from: http://www.lowemissionstrategies.org/downloads/Jan15/Non_Exhaust_Particles11.pdf.
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