The contribution of road transport to air pollutant emissions is significant for many gaseous or particulate substances, according to our partner The Conversation.
Emissions related to road transport are generally classified into two categories: those from the exhaust (EE) and those outside the exhaust (EHE).
This analysis was conducted by Ahmed Benabed, teacher-researcher in fluid mechanics at the Ecole Supérieure des Techniques Aeronautiques et de Construction Automobile.
Globally, the deterioration of air quality is a major concern, as its impact on our wider quality of life is considerable.
According to the World Health Organization (WHO) and the Organization for Economic Co-operation and Development (OECD), the cost of air pollution on health and mortality in European Union countries in 2010 is at $1.575 billion.
Air pollution is responsible for many more or less serious pathologies such as allergies, asthma, lung infections and cardiovascular diseases.
Moreover, in the context of the current health crisis, researchers have shown that exposure to air pollution (mainly to PM10 (particles of size less than 10 µm), PM2.5 (particles of size less than 2.5 µm), ozone, nitrogen dioxide) is not only a factor of comorbidity of SARS-COV-2, but also of its transmission in indoor environments.
Finally, it is also recognized that air pollution has a major environmental impact on visibility (fog), on biodiversity and on buildings (fouling of buildings in particular).
Road emission sources
The contribution of road transport to atmospheric pollutant emissions is significant for many substances, whether gaseous or particulate.
Emissions related to road transport are generally classified into two categories: exhaust emissions (EE) which result mainly from the imperfect combustion of the fuel and non-exhaust emissions (EHE) which result not only from the wear of the coatings (road, tires, brake pads), but also particles deposited on the roads and which can be resuspended by the turbulence generated by vehicle traffic and by the wind.
Over the past decades, research and development work, mainly EE-focused policy measures combined with increasingly stringent regulations imposed on vehicle manufacturers (EURO standards) have led to a drop in the percentage contribution of particulates. exhaust on total ambient particulate concentrations.
However, it has been shown that even with zero EE, traffic will continue to contribute to the emission of fine and ultrafine particles due to EHE.
The contribution of resuspension
In recent years, increasingly significant efforts have been made by research organizations to improve scientific knowledge of EHEs and in particular particles resulting from resuspension.
The various studies conducted with the aim of studying 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, it has been shown that these emissions can exceed 50% of global emissions under certain conditions.
Considering these elements, we better understand the need to deepen the state of knowledge on the phenomenon of resuspension of particles associated with the passage of vehicles.
In particular, it is important to focus on the mechanisms that influence the detachment of particles from a surface and then their dispersion in the environment close to the vehicle.
In order to effectively characterize resuspension, it is important to first understand its emission mechanisms.
This objective constitutes a real challenge with regard to the many parameters which influence the phenomenon and which can interact with each other.
Physically, the resuspension of particles produced by the passage of a vehicle is the result of wheel/ground and wheel/air interactions.
These interactions generate two main disturbances: mechanical (ground vibrations, electrostatic forces related to friction between the surfaces) and aerodynamic (turbulent flows related to the rotation of the wheel).
These disturbances interact with the particles initially deposited on the pavement under the effect of adhesion forces.
Under the combined action of different parameters, these particles can be re-entrained directly (the particle detaches from the surface of the ground) or indirectly (the particle initially attaches to the surface of the wheel and then detaches from the latter by centrifugal ejection).
After their re-entrainment, the particles can be redeposited on the road, on the structure of the vehicle or be transported in the surrounding atmosphere under the action of air flows (aerodynamic disturbance created by the wheel, by the car and by the wind ).
Once resuspended, these PHEs also have the ability to disperse to sidewalks and/or infiltrate following vehicles and thereby expose pedestrians and occupants, respectively, to elevated levels of particulate matter.
The CEPARER project
In this context, a project entitled Characterization of particulate emissions resuspended by road vehicles (CEPARER) is currently being carried out by a team of researchers from the École supérieure des techniques aeronautiques et de construction automobile (ESTACA) in partnership with Airparif and the Technical Union for automobiles, motorcycles and cycles (UTAC).
This project is supported by the Environment and Energy Management Agency (ADEME) as part of the AQACIA2020 program (Improvement of air quality: understand, innovate, act) launched in 2020.
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The objective of the CEPARER project is the detailed study of the mechanisms contributing to promote the resuspension of particles, the characterization of the emission modes and the main factors influencing the resuspension (speed, category and weight of the vehicle and type of pneumatic).
The project, which will span three years (2022-2025), will be carried out in two parts: a laboratory study on a test bench at ESTACA and an outdoor study on one of the tracks of the UTAC at the Linas-Montlhéry autodrome.
These two phases of the project should make it possible to obtain important information on the concentrations and particle sizes of the resuspended particles, depending on the type of vehicle, its speed and the type of tire.
The factors favoring this phenomenon will also be studied.
This analysis was written by Ahmed Benabed, teacher-researcher in fluid mechanics at the Graduate School of Aeronautical Techniques and Automotive Construction (ESTACA).
The original article was published on The Conversation website.
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