“How many air quality monitors do I need?” is a question we regularly hear, and the easy responses – “it depends”, “how big is your budget?” – are not very helpful.

To give a better idea, it will depend on all these factors:-

Which pollutants you want to measure

Some pollutants are mixed better / are more homogeneous / more background in ambient air, such as PM2.5 and O3. Others are less so, and can be affected by a local source, like NO. Background pollutants can be measured with fewer measurement points than those which will vary greatly over short distances. For example, O3 may range between 50ppb and 60ppb across a city, but NO could vary from 0ppb to 1,000ppb within just 100m.

Your analysis capability

If you have the resources or skills to carry out detailed analysis, you will get more information out of fewer measurement points. For example, if using wind speed and direction data alongside air quality readings, you can look at an area in terms of pollution sources and areas potentially affected by air quality. The resulting plots and mapping allow reading levels to be visualised across space. Taking it further, measurement points can be linked to emissions inventories and modelling can fill the gaps to give an estimated reading for every geographical point. The more measurement points, the more accurate the estimates are likely to be. Additionally, some analysis techniques – such as long distance scaling or network calibration – require a minimum number of measurement points in order to work, which will therefore determine how many pods you might need. As an example, the long distance scaling method offered by AQMesh requires a minimum of 6 different locations.

The area you’re monitoring in

Multiple pollution sources (think busy city vs. a factory in open countryside) create a more complex air quality situation, as do canyons (naturally confined air corridors or streets between high buildings). A single source within an open environment could achieve a lot with just one pod upwind and one downwind, but a city environment means that NO or NO2 readings could be massively different just other sides of a road junction.

Local conditions

If your air quality monitoring location is generally windy you will have to work harder (install more measurement points to pick up plumes) to capture pollutant bursts before they are swept away.

Environmental justice

We have seen customers distribute pods based on one per ZIP code, to achieve fairness to local communities. This is a good idea in itself, but a ZIP code can include a wide range of pollution levels so all the factors about choosing a precise monitoring point still apply.

And, of course, budget!

Seriously, small sensor systems are described as monitoring ‘hyperlocal’ air quality for a reason and even the densest networks will be leaving some gaps where air quality variation is not recorded. So, measurement points can be added infinitely – air quality mapping of an area will improve in accuracy, but there are obviously diminishing returns.

Because, even after all this, “it depends”, just talk to us about your air quality monitoring requirements and we will be more than happy to share our recommendations and give you a more helpful answer to “how many air quality monitors will I need?”

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.

Two AQMesh pods measuring airborne particulate matter have been loaned to the University of Cambridge, ahead of the COP26 meeting in Glasgow, to support research into measurement of particulate matter. The pods have been monitoring PM1, PM2.5, PM4, PM10 mass estimates and Total Particle Count, since April 2021. The team from the University of Cambridge, led by Professor Rod Jones, are using data from these units, which have the heated inlet option to minimise the effect of air moisture on readings, to support their work on understanding differences in chemical composition between particles.

The compact small sensor air quality monitoring system, designed to measure levels of pollutant gases in ambient air, also offers a non-dispersive infrared (NDIR) carbon dioxide (CO2) sensor, providing accurate outdoor CO2 measurements. As well as monitoring deviations in background levels of CO2, analysis of data from the system can also identify combustion plumes and provide an indication of whether the gases are being produced by a local or distant source, and from which direction.

Professor Jones has previously used CO2 data from AQMesh pods during the Breathe London pilot project, in conjunction with other AQMesh gas measurements. AQMesh offers a range of ambient air measurements relevant to climate change studies, including NOx, SO2, CO, CO2, Black Carbon, TVOC and methane. The Ecotec group – which owns AQMesh – specialises in methane leak detection and gas stream methane monitoring. Applications include pipeline methane measurement for energy-from-waste on landfill, biogas, waste water treatment and agricultural sites. Methane leaks are also detected using a range of laser-based sensors, providing a critical resource for methane-generating operations, including the oil and gas industry.

COP26 is the upcoming 26^th United Nations Climate Change Conference, taking place in Glasgow, Scotland between 31^st October and 12^th November 2021. The aim of the conference is to progress global efforts towards the goals the UN Framework on Climate Change and the Paris Agreement – the legally binding international commitment to reduce carbon emissions, agreed at the COP21 conference in 2015.

CO2 emissions are a key factor in climate change and are largely caused through the burning of fossil fuels such as coal, gas and oil, which are burned to generate heat and electricity for the world’s power plants, cars, planes and industrial facilities, to name a few. Monitoring CO2 emissions is therefore vital in understanding, managing, mitigating and reducing sources of CO2 and its impact on the atmosphere and environment. Methane is an even more potent greenhouse gas and prompt identification of methane leaks is a critical part of the action plan to reduce greenhouse gas emissions.

AQMesh is an air quality monitoring ‘pod’ which can be mounted on a post, wall, fence or other position to measure ambient air pollution. Each pod measures about 20cm / 8 inches in each direction and weighs about 2Kg / 4lb. Sensor data is securely transmitted using the global mobile phone network to a cloud server, where carefully developed corrections for environmental conditions are made and data accessed by secure web login or API. Sensor options are offered on the basis that the level of sensitivity and selectivity for the target pollutant are fit for purpose, whether directed towards local air pollution or climate change pollutant monitoring.

AQMesh is currently in use in Nicaragua, monitoring air quality in communities living near Masaya volcano. The six AQMesh pods have been used to show variations in volcanogenic SO2 and PM levels at different times and at different locations across the area.

The pods, which have independent power and communications so they can be mounted where required, were installed in March 2017 as part of a research project funded by the Global Challenges Research Fund: Unseen but not unfelt: resilience to persistent volcanic emissions (UNRESP). The project is led by the University of Leeds and is a multi-partner collaboration of several universities in the UK and Nicaragua, as well as Nicaragua’s natural hazards observatory INETER and the Icelandic Met Office.

The Global Challenges Research Fund supports projects focusing on challenges faced by developing countries, aiming to build resilience to natural and anthropogenic hazards. The aim of UNRESP project is to devise an early warning system for dangerously high levels of air pollution, specifically SO2 and particulate matter. As this is a 12-month foundation phase project, the data are not currently being made public but will be put in the hands of local authorities and other stakeholders when the warning system is refined. AQMesh readings are being compared to predictions from a pollution dispersion model, CALPUFF, which requires relatively little computing power. The CALPUFF model has been successfully used for air pollution forecasting at other volcanic sites, such as a recent eruption in Iceland which did not produce ash but emitted twice as much SO2 as all European Union countries combined and caused repeated air pollution in Iceland for 6 months.

“Air pollution is a chronic and serious hazard affecting many developing countries, but there is generally very limited capability to monitor and mitigate it. AQMesh provided us with an opportunity to install the first AQ monitoring system in Nicaragua – the pods are very cost-effective which is of utmost importance for the local setting, yet they provide data that are of high quality. Real-time data on the ground is vital for quantifying and understanding the duration, peak concentration and frequency of high air pollution episodes, which are factors that directly impact human health”, commented Dr. Evgenia Ilyinskaya who is leading the project. The UNRESP team started by hiring five pods for three months via UK distributor, Air Monitors Ltd. as well as purchasing one AQMesh pod for long-term observations. The pod rental has been extended for another three months and the practicality of long-term use of this sort of equipment is being evaluated, including the use of rechargeable batteries or solar power. The team is working closely with local communities and such stakeholders taking custody of the equipment intended to protect their own community mitigates against some risks, such as theft or damage.

Although there is no reference station at the site, diffusion tubes have been used to take measurements which can be compared to the 15-minute average, real-time readings from AQMesh. Whilst EU air quality standards focus on the short-term high concentrations typical of SO2 from an industrial source the UNRESP team is trying to understand the impact of long-term elevated SO2 on the population. Having SO2 measurements with high time and spatial resolution is critical for this and the plan is to potentially create an alert for accumulated concentration of pollutants.

The draft proposal for a follow-on project at the site states the collaboration with AQMesh identified ways of improving the equipment for monitoring volcanogenic pollution, which tends to be much more corrosive than ‘typical’ urban pollution. Dr. Evgenia Ilyinskaya commented, “the AQMesh equipment is extremely cost-effective while providing data quality comparable with EU-certified monitoring. One AQMET station was purchased during the UNRESP foundation phase and it will remain in Nicaragua to form part of the permanent AQ network.”