A UK train operator is carrying out an air quality baselining project at various points around some of the stations it manages.

Monitoring using diffusion tubes or passive sampling has been used around rail infrastructure but the aim here is to use near real-time hyperlocal monitoring to show how pollution levels vary minute-by-minute and across spaces accessible by rail passengers. The company has invested in AQMesh small sensor air quality monitoring pods, which are designed to be easily installed on a post or barrier. This follows a similar project with 10 pods which another UK train operator has been running since the beginning of 2020.

The six AQMesh pods measure particulate matter (PM1, PM2.5, PM4, PM10, total particle count) and six gases (NO, NO2, O3, CO, SO2, CO2) as well as temperature and humidity, and were installed in early 2023. Measurements are made every one to 15 minutes, depending on settings, and sent wirelessly to a secure cloud server, where they can be accessed by staff logging into an online application.

The monitoring positions have been chosen according to known risk factors, including topography, which affects air circulation and how air pollution can become trapped and concentrated or dispersed and diluted. Selection of locations for installation of monitoring equipment also considers the extent to which spaces are visited by diesel-powered locomotives, the degree to which the space is enclosed and whether the platform is end-of-line, where idling could occur.

The various air pollutant levels vary across locations and by time of day, influenced by rail activity as well as other factors, such as wind speed and direction and other local air pollution sources, such as road traffic near stations. Techniques can be used to understand sources and indicate pollution levels from different sources, but recent rail strikes, which have reduced rail activity to zero at times, have provided further clarification.

This project is not intended to provide comprehensive monitoring around all stations. The goal is to get a better understanding of how – and why – air quality varies across the spaces managed by the train operator, informing future strategy.

The intended EfW site will process around 300,000 tonnes of residual waste per year in order to generate electricity and heat, which will be exported for use at local properties. The operation of such a facility may result in atmospheric emissions from the combustion of waste and subsequently contribute to an increase in pollution. As such, it is important to determine the existing air quality in the local area prior to the site being established.

An AQMesh air quality monitoring system was used during the first stage of testing, which involved a programme of continuous sampling to measure concentration levels of nitrogen dioxide (NO2) in ambient air, as well as particulate matter.

The AQMesh pod was configured to undertake monitoring of NO2 concentrations at 1-minute averages and measurement of PM10 and PM2.5 at 15-minute averages. This was then placed on site and remained at its location for the course of one year.

The outcome of Redmore Environmental’s campaign was a complete data set of existing air quality conditions within the vicinity of the proposed EfW site. The results for individual pollutants were reviewed, compared with relevant Air Quality Standards set for the protection of human and ecological health and analysed in an overarching technical report.

A full range of Redmore Environmental’s testing capabilities can be found on their Air Quality Monitoring Services page.

Oxford City Council has been managing two AQMesh pods, supplied by Air Monitors Ltd, in order to monitor the impact the new Westgate centre is having on local air quality.

Westgate Oxford is a brand new £440m shopping centre comprising of retail outlets, restaurants and a cinema, and was developed as a replacement to the old shopping centre that was demolished in 2016. Having recently opened in October 2017, it estimates it will attract 15m visitors every year.

The AQMesh pods were purchased by the Westgate developer under a Section 106 agreement to monitor levels of NO, NO2 and O3. Oxford City Council’s Air Quality officer, Pedro Abreu, has been using them to supplement information available from other sources. Because the pods are battery-powered they can be mounted at exactly the point in centre where monitoring is required, and easily moved to a new monitoring location when necessary. Pedro Abreu carried out co-location comparisons with a reference station and is very satisfied with the correlations he has seen with the AQMesh pods he is using.

His comments echo those of Professor Rod Jones from the University of Cambridge, who led a project using AQMesh pods across Cambridge to demonstrate how air quality varies across the city. “Because we know that all the pods read the same and because we have a comparison between one pod and a reference instrument, we can say that all pods are working equivalently across the city. What we are seeing is correspondences in excess of 0.7, 0.8, against reference – and that is very good for something straight out of the box”, commented Professor Jones.