Following a successful evaluation phase in 2018, AQMesh small sensor air quality monitoring ‘pods’ have been selected for use in a project to control the ventilation of a road tunnel in the city of Marseille.
Supported by the AtmoSud (AirPACA) local air quality monitoring network, the CETU (Tunnel Studies Centre) and AQMesh distributor Addair, eight AQMesh pods were installed in February 2019, monitoring nitrogen oxides NO and NO2, in an innovative experiment in one of the covered sections of the L2 ring road in Marseille. Called “Boreas project”, after legendary ‘dispersing’ winds, this study aims to use pollution measurements near tunnel entrances to activate in-tunnel fans.
Urban planning is increasingly routing vehicles underground. Although this approach eases air quality and noise at some locations – and overall reduces the level of pollution the population is exposed to – there is a risk that residents living close to the tunnel heads are actually exposed to higher concentrations of pollution as air is expelled from the tunnel.
The L2 ring road in Marseille consists of a succession of covered tunnels over 12Km in dense urban areas. The phased project at the Montolivet South tunnel heads will implement a system for the conditional triggering of in-tunnel fans to evaluate its impact on air quality in the zones adjacent to the nearest residents. This approach was tested in 2018, with micro-sensor readings compared at the AirPACA Kaddouze monitoring station. A first phase analyses the pollution without activation of the ventilation system, then a second phase with ventilation.
The aim is to determine the link between ventilation and dispersion of the pollution at the end of the tunnel and to determine the most effective protocol for activation of the ventilation systems based on real-time air quality levels, inside and outside the tunnel. Automated alerts for high NO2 levels are already in place. The feasibility of this approach will also be reviewed by analysing efficiency in terms of cost and energy consumption. In theory, the use of ventilation could improve the quality of air at the head of the tunnel. However, in some weather conditions this could simply displace the pollution and this forms part of the study – analysing the pollution concentration and dispersion in different meteorological and traffic conditions.
AQMesh has been used in other tunnel monitoring projects, including several in the UK, specifically to study ventilation efficiency in road tunnels where pollution can build up if sufficient air flow is not maintained. During the UK projects, AQMesh pods were also first co-located with a nearby reference station to ensure measurements were directly comparable.
The pods were then deployed at different positions within the tunnels and in ventilation ducts, studying how the concentration of pollution changed when air flows were adjusted in varying traffic scenarios. The pods were able to run for up to six months without any maintenance or calibration, despite the very high pollution levels recorded. The results obtained in these studies enabled optimisation of the ventilation settings and helped to reduce energy consumption whilst maintaining cleaner air for tunnel users and maintenance personnel.
Suite à une phase d’évaluation et en raison de sa qualité de mesure, la solution AQMesh a été sélectionnée dans le cadre d’un projet d’asservissement de la ventilation d’un tunnel routier dans la ville de Marseille. Ce projet, porté par le réseau de surveillance de la qualité de l’air local AtmoSud et le CETU (Centre d’Etudes des Tunnels), a vu l’installation de 8 capteurs AQMesh en février 2019 pour le suivi des oxydes d’azotes NO et NO2.
Pour réduire la pollution de l’air aux sorties des tunnels et ainsi limiter l’exposition des riverains, AtmoSud et le CETU (Centre d’Etudes des Tunnels) testent un dispositif innovant basé sur l’activation de la ventilation par des micro-capteurs. Ces derniers, installés début février 2019 par AtmoSud, enregistrent les données sur le terrain pour une phase d’observation, avant de passer à la phase test de déclenchement de la ventilation.
L’implantation des 8 micro-capteurs a été décidée en concertation avec les acteurs
L’adaptation de la ventilation aux niveaux de pollution mesurés en tête de tunnel n’a jamais été mise en œuvre à ce jour et constitue donc une réelle innovation.
Comme pour tout projet innovant, les phases de concertation à chaque étape sont essentielles. Celle du choix de l’emplacement des micro-capteurs l’a été particulièrement.
AtmoSud a donc consulté et les différents acteurs : la DREAL PACA, l’association CAN L2, les services de la mairie de secteur du 11e/12e arrondissement de Marseille, le CETU (Centre d’Etudes des Tunnels), la métropole Aix-Marseille Provence et la Région Sud Provence-Alpes-Côte d’Azur.
Des micro-capteurs soigneusement étalonnés par AtmoSud
Le monoxyde d’azote (NO) et le dioxyde d’azote (NO2), marqueurs du trafic automobile sont les polluants qui vont être mesurés en 8 points. Avant de procéder à leur installation, AtmoSud s’est assuré de la fiabilité des données qui vont être recueillies, en testant les capteurs dans la station de mesure Kaddouz, à proximité de la L2. La phase d’observation va se dérouler sur une période de 3 à 6 mois.
North Americans will be well aware of the particularly harsh weather in the early months of 2019, but AQMesh has taken conditions in its stride. The AQMesh stated operating range of -20°C to + 40°C is backed up by long-term operation across a wide range of climates.
AQMesh pods used by Minnesota Pollution Control Agency (MPCA) to measure pollutant gases and particulate matter, such as NO2 and PM2.5 , installed on streetlights around Minneapolis St. Paul have seen temperatures as low as -25.4°C (-13.7°F) and continue to run smoothly.
Monika Vadali, leading the MPCA project, commented “We are quite impressed with the temperatures we have seen this winter”. However, when asked for a photo of the pods, she said “I can’t get to any of the pods as we have had so much snow and cold that there is 5-6ft of snow around some of the poles, making access difficult.” Temperatures recorded elsewhere have not been so low this year but AQMesh pods have been installed over previous winter in Sweden, Finland, Canada and central Europe, with temperatures regularly dropping below -20°C.
Despite such harsh weather conditions, the AQMesh pods have continued to monitor and communicate data to the AQMesh server, where it is securely accessed by users. The hardware design has been refined to ensure the equipment has the resilience to survive, with minimal maintenance, for years. The initial concept was for the pod to measure pollutant gases, particularly NO2, for two years on a single lithium battery. Although many users now run shorter projects or choose solar or DC power sources, the principle – and challenge – is unchanged.
In addition to its physical design, data processing on the AQMesh server includes carefully developed correction algorithms which compensate for extreme conditions. Remote diagnostics also identify unexpected patterns in sensor output, which may affect confidence in the data, which is then flagged.
At the same time as the AQMesh pods were under several feet of snow in Minnesota, pods in the southern hemisphere have been regularly operating at temperatures in excess of 30°C, hitting 44.7°C in South Africa and 46.2°C in Australia.
AQMesh pods have been deployed long-term (many pods are in their sixth year of deployment around the world) and as temperatures rise across some of the hottest locations where pods are deployed – Kurdistan, Pakistan, Myanmar, Arizona (USA), Ghana – the latest generation of sensors and processing algorithm will continue to provide reliable and traceable air quality measurements in locations where other monitoring equipment cannot readily be deployed.
In the southern regions of the USA, with very hot temperatures and varying levels of humidity, AQMesh pods maintained high precision and accuracy against co-located certified reference equipment, with a correlation R2 of 0.92 for ozone, compared to collated FEM. Many parts of the world where AQMesh operates record relative humidity (RH%) over 90%, often on a regular or sustained basis.
AQMesh also stands up to high winds and extreme rainfall and is now available with an optional wind speed and direction sensor to complement its extensive range of measurable parameters. The meteorological data gathered by this sensor can help distinguish between local and regional sources of pollution.