When driving, cars send back a lot of airborne particles

Globally, the deterioration of air quality is a major concern because its impact on our wider quality of life is significant. According to the World Health Organization (WHO) and the Organization for Economic Co-operation and Development (OECD), in 2010, the cost of air pollution in the European Union countries for health and mortality is 1.575 billion dollars.

Air pollution causes more or less serious pathologies such as allergies, asthma, lung infections and cardiovascular diseases. In addition, in the context of the current health crisis, researchers have shown the impact of air pollution (mainly PM10 (particles smaller than 10 µm), PM2.5 (particles smaller than 2.5 µm), ozone, nitrogen dioxide). ) is not only a comorbidity factor of SARS-COV-2, but also a factor of its transmission in closed environments.

Finally, it is also recognized that air pollution has major environmental impacts on visibility (haze), biodiversity and buildings (especially building pollution).

Road emission sources

The contribution of road transport to atmospheric pollutants is significant for many substances in gaseous or particulate form. Emissions related to road transport are generally divided into two categories: exhaust emissions (EE), which are mainly caused by the incomplete combustion of fuel, and non-exhaustive emissions (EHE), which are caused only by the wear of pavements (road, tires, tires, cars). brake pads), but also particles that accumulate on roads and can be resuspended by turbulence caused by vehicle traffic and wind.

Over the past decades, research and development efforts, mainly EE-oriented policy measures and increasingly strict regulations (AVRO standards) imposed on car manufacturers have led to a decrease in the share of particulate matter in the total concentrations of particulate matter in the environment. However, it has been shown that even with zero EE, traffic will continue to contribute to the emission of fine and very fine particles due to EHE.

Contribution of resuspension

In recent years, increasingly significant efforts have been made by research organizations to improve the scientific knowledge of EHEs, and particularly of resuspension-induced particles. Various studies conducted to study this phenomenon have shown that it depends on the type of vehicle (mainly its weight), its speed and the characteristics of the road surface. Regarding the contribution of resuspension, these emissions have been shown to exceed 50% of global emissions under certain conditions.

Considering these elements, we better understand the need to deepen the state of knowledge about the phenomenon of particle resuspension associated with the passage of vehicles. In particular, it is important to pay attention to the mechanisms that affect the detachment of particles from the surface and their subsequent distribution in the environment close to the vehicle.

To effectively characterize resuspension, it is important to first understand its emission mechanisms. This goal poses a real problem with the many parameters that influence the phenomenon and may interact with each other. Physically, the resuspension of particles caused by the passage of a vehicle is the result of tire/ground and tire/air interactions. These interactions create two main disturbances: mechanical (earth vibration, electrostatic forces due to friction between surfaces) and aerodynamic (turbulent flows due to wheel rotation).

These disturbances interact with particles initially deposited on the pavement under the influence of adhesion forces. Under the combined effect of various parameters, these particles can be re-introduced directly (the particle is detached from the ground surface) or indirectly (the particle first adheres to the tire surface and then centrifugally separates from the latter). .

After re-entry, particles can be redeposited on the road, on the vehicle structure, or transported into the environment by air currents (aerodynamic disturbance caused by tires, cars and wind). . Once resuspended, these PHEs also have the potential to disperse onto pavements and/or seep into vehicles below, thereby exposing pedestrians and passengers to high levels of particulate matter, respectively.

CEPARER project

In this context, a project called Characterization of Resuspended Particulate Emissions by Road Vehicles (CEPARER) is being carried out by a group of researchers from the École supérieure des technique aeronautiques et de construction automobile (ESTACA) in collaboration with Airparif and the Technical Union. for cars, motorcycles and bicycles (UTAC). This project is supported by the Agency for Environment and Energy Management (ADEME) as part of the AQACIA2020 (Improving Air Quality: Understand, Innovate, Act) program launched in 2020.

The aim of the CEPARER project is to study in detail the mechanisms promoting particulate resuspension, the characterization of emission regimes and the main factors influencing resuspension (speed, vehicle category and weight, and pneumatic type). The project, which will span three years (2022-2025), will consist of two parts: laboratory research on a test bench at ESTACA and outdoor research on one of the UTAC tracks at the Linas-Montlhéry autodrome. These two phases of the project should provide important information on resuspended particle concentrations and particle sizes depending on vehicle type, speed and tire type. Factors contributing to this phenomenon will also be studied.