Non-exhaust emissions come from wearing down

motor vehicle A motor vehicle, also known as a motorized vehicle, automotive vehicle, automobile, or road vehicle, is a self-propelled land vehicle, commonly wheeled, that does not operate on railway track, rails (such as trains or trams), does not fly (such ...

brake pads, tires, roads themselves, and unsettling of particles on the road. This

particulate matter Particulate matter (PM) or particulates are microscopic particles of solid or liquid matter suspended in the air. An ''aerosol'' is a mixture of particulates and air, as opposed to the particulate matter alone, though it is sometimes defin ...

is made up of

micrometre The micrometre (English in the Commonwealth of Nations, Commonwealth English as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American English), also commonly known by the non-SI term micron, is a uni ...

-sized particles and causes negative health effects, including

respiratory disease Respiratory diseases, or lung diseases, are pathological conditions affecting the organs and tissues that make gas exchange difficult in air-breathing animals. They include conditions of the respiratory tract including the trachea, bronchi, ...

and

cancer Cancer is a group of diseases involving Cell growth#Disorders, abnormal cell growth with the potential to Invasion (cancer), invade or Metastasis, spread to other parts of the body. These contrast with benign tumors, which do not spread. Po ...

. Very fine particulate matter has been linked to cardiovascular disease. Multiple epidemiological studies have demonstrated that particulate matter exposure is associated with acute respiratory infections, lung cancer, and chronic respiratory and cardiovascular disease. Researchers have also found correlations between exposure to fine particulate matter and fatality rates in previous coronavirus epidemics. Studies have shown that non-exhaust emissions of particles from vehicles can be greater than particles due to exhaust. The

European Commission The European Commission (EC) is the primary Executive (government), executive arm of the European Union (EU). It operates as a cabinet government, with a number of European Commissioner, members of the Commission (directorial system, informall ...

expects that "by 2050 non-exhaust emissions will constitute up to 90% of all particles emitted by road transport".

Types of emissions

Brakes

Brake wear gets released into the air as particulate matter. When applying pressure to the braking system forces the two together, Standard frictional brakes on a vehicle function under the friction between a brake pad and a rotating disc or drum. The frictional process causes abrasion of the brake pad and the surface of the disc or drum, leading to the release of particles, a substantial fraction of which become airborne.

Tyres

Rubber pollution Rubber pollution, similar to plastic pollution, occurs in various environments, and originates from a variety of sources, ranging from the food industry processing chain to tire wear. Synthetic and natural rubber dust and fragments now occur in f ...

gets released into the air. When in contact with the road, the surface of a tire is steadily abraded by contact with the road surface. This leads to the release of large quantities of small rubber particles which cover a wide range of sizes.

Road surface

The road itself wears and releases particulate matter into the air. The friction between the tire surface and the road surface, which leads to tire abrasion, is also liable to abrade the road surface, especially where this is already fragmenting. Hence, road surface wear particles are also released into the atmosphere.

Road dust

Particles on the road get thrown or blown into the air. Emissions from road dust suspension depend on a vehicle's speed, size, shape, porosity, amount of dust on road surfaces, and weather conditions. Considerable uncertainty remains regarding the amount of PM emitted by non-exhaust sources in real-world driving conditions and how this amount varies with the abovementioned factors.

Ways of reducing emissions

Multiple scientists and regulators in the field have proposed more comprehensive regulation of tires. Lighter vehicles pollute less and reducing vehicle kilometers traveled is another method of mitigating non-exhaust emissions. Reducing demand for private vehicle travel can be accomplished by various measures that increase the relative attractiveness of public transport and non-motorized modes relative to private vehicles. These measures can consist of disincentives for private vehicle ownership and use, i.e., measures that raise their costs and inconvenience, as well as incentives for alternative modes (e.g., public transit, walking, and biking).

Electric and hybrid vehicles

Electric vehicle An electric vehicle (EV) is a motor vehicle whose propulsion is powered fully or mostly by electricity. EVs encompass a wide range of transportation modes, including road vehicle, road and rail vehicles, electric boats and Submersible, submer ...

s and

hybrid vehicle A hybrid vehicle is one that uses two or more distinct types of power, such as submarines that use diesel when surfaced and batteries when submerged. Other means to store energy include pressurized fluid in hydraulic hybrids. Hybrid powertrai ...

s with

regenerative braking Regenerative braking is an energy recovery mechanism that slows down a moving vehicle or object by converting its kinetic energy or potential energy into a form that can be either used immediately or stored until needed. Typically, regenerativ ...

do not emit the same level of brake wear, but as of 2022 were heavier than ICE vehicles so still give off more coarse (PM10) particles from re-suspended road particles, road wear, and tire wear.

Regulatory agencies and policies that target exhaust emissions

Very few agencies are charged with implementing exhaust

emission standard Emission standards are the legal requirements governing air pollutants released into the atmosphere. Emission standards set quantitative limits on the permissible amount of specific air pollutants that may be released from specific sources ov ...

s for non-exhaust emissions. Most policies target exhaust emissions and do not regulate non-exhaust particulate matter emissions. As of 2023 Euro 7 standards are still being argued about.

References

{{Pollution , state=collapsed Air pollution Pollution Transport and the environment