Aix-en-Provence (Bouches-du-Rhône) is one of two European cities, alongside Florence in Italy, to be selected for a project called Airfresh (Air pollution removal by urban forests for a better human well-being) which will see 400 trees planted on the boulevard du Général Paul Angenot – located in a suburb to the south west of the city.
The aim is to find out if the newly planted trees will have an impact on the city’s air quality. The project, led by Pierre Sicard, a scientist who specialises in pollution and climate change in forests, aims to reduce ozone by three tonnes per year.
The species selected include plane trees, lime trees, maples, oaks and Japanese sophoras – all adapted to local climatic conditions and an urban environment as well as being resistant to disease. They also absorb harmful volatile compounds while emitting few allergenic pollens.
Sensors installed 1m80 up the trees measure what pollutants humans breathe in (fine particles, CO2, ozone, and nitrogen dioxide) while others higher up the trees record meteorological data.
Aix-en-Provence in Southeastern France (143,000 inhabitants) has a Mediterranean climate and is the third most polluted city in France. By 2100, the annual mean temperature will increase by + 1.9-4.6°C, and up to 5.7°C in summer. By way of comparison, in Aix-en-Provence, during the 2019 heat wave, the deviation was + 3.5°C compared to the nearby cities. In 2019, the EU target values for the protection of human health were exceeded for NO2 and O3. The main species of street trees are are Platanus spp., Populus spp., Quercus ilex, Pinus halepensis, Ulmus spp. and Cupressus sempervirens.
Southeastern France and Italy are the highest O3 risk areas in European Union with increasing O3 levels in cities. In 2019, about 95% of the population of the city was exposed to PM2.5, PM10, NO2 and O3 levels exceeding the WHO target values for health protection.
In 2019, a total of 55 deaths for non-accidental causes were attributed to O3, NO2 and PM10 in Aix-en-Provence . A total of 163 hospital admissions for cardiovascular and respiratory diseases was also reported . For O3, we observed a high number of hospital admissions for cardiovascular endpoints, i.e. about 67 per 100,000 people at risk in Aix-en-Provence .
The new planted trees will enhance the abatement of air pollution and urban heat island. The tree will also contribute to carbon sequestration and improve the infiltration of runoff water.
Tree charter in Aix-en-Provence
In 2019, the city of Aix accounts 180-ha of green spaces including 20,400 public trees (managed by the municipality).
The City of Aix made a plan to develop and protect its public tree heritage. The Tree Charter consists in preservation of the existing tree heritage. From now, the City wants to determine whether trees can be planted in certain quarters, which tree species, which planting and management strategy, and how to increase the pace of new plantations.
The charter aims to:
1) make people aware of the role of trees in the city;
2) evolve and adapt best practices;
3) prepare the renewal (e.g. methods of planting, places of plantation);
4) make the tree one of the vectors of nature and biodiversity in city; and
5) set up communication tools towards public.