RENNES AND THE IMPACT OF URBAN ENVIRONMENT

A City Shaped by Human Activity
Since the 19th century, Rennes has experienced significant growth, transitioning from an administrative and commercial city to a metropolitan area integrated into modern economic dynamics. While industrialization has been less pronounced than in other parts of France, rapid urbanization and the expansion of road infrastructures have profoundly transformed its environment. Today, Rennes is a city where challenges related to air pollution, urban sprawl, and transportation emissions are central concerns.

Environmental Pressures and Their Impacts
Human activities have had notable effects on the environment in Rennes. Road traffic, which remains a major source of commuting in the metropolitan area, contributes significantly to air pollution, particularly nitrogen dioxide and fine particle emissions. These pollutants affect residents' health, increasing the risk of respiratory and cardiovascular diseases. Rennes is not spared from pollution episodes, which are worsened by weather phenomena such as intense heatwaves.

Moreover, urban sprawl, characteristic of recent decades, has led to increased consumption of agricultural and natural land, reducing spaces available for ecosystems and contributing to the fragmentation of habitats. This phenomenon exacerbates challenges related to stormwater management, increasing flood risks in certain peripheral areas.

Local Responses to Environmental Challenges
In response to these issues, Rennes and its metropolitan area have launched initiatives to mitigate their environmental impacts. The development of sustainable mobility, with the addition of a second metro line and the expansion of the bike lane network, directly addresses traffic congestion and car pollution. Additionally, urban greening campaigns and reforestation efforts aim to improve air quality and reduce the effects of urban heat islands. However, challenges remain, particularly with residual industrial emissions and diffuse pollution sources from agricultural activities surrounding the city.

Evolving Environmental Awareness
The residents of Rennes are actively involved in this transition. Citizen collectives and environmental organizations play a key role in raising awareness of local issues and implementing community-driven initiatives. These movements, sometimes in tension with economic and social imperatives, reflect a growing commitment to balancing quality of life with environmental sustainability.

Air quality is a public health and climatic issue, which is particularly affected in urban areas with a high density of inhabitants and activities. In Rennes, air quality is considered to be low in relation to the objectives set by European regulations. Episodes of fine particle air pollution regularly affect the city, due to its geographical location, climate and activities. The metropolis of Rennes is the largest agglomeration in the Brittany region (France). Due to its population (450,000 inhabitants) and population density within the ring road (road traffic), a reinforced monitoring system has been set up on this territory: 4 fixed measurement stations + 1 indicative measurement site placed in various environments.

The sensors of this urban station analyse in particular nitrogen oxides and fine particles (emitted by road traffic but also by wood heating or industrial activities) and now pesticides, which unsurprisingly are present in the ambient air, which is systematically monitored since the beginning of 2022 and for a period of five years. To mobilise residents on this subject, the City of Rennes, the "House of Consumption and Environment" and "Air Breizh" have set up the "Ambassad'Air" citizen air measurement operation with the provision of open source micro-sensors of fine particles "Sensor Community", deployed since 2018 in Rennes.

The city of Rennes drew up an Atmosphere Protection Plan in 2005, a second one was adopted in 2015 and a third one is being drawn up for 2022. A limited traffic zone will be experimented in Rennes from February 2023, in the historic city centre with a double objective: to reduce air pollution and to make the city centre more pleasant.