The UK’s first Urban Observatory, led by Newcastle University, has been designed to provide a digital view of how cities work. AQMesh air quality monitoring equipment is being deployed across Newcastle and Gateshead in conjunction with other instruments for monitoring parameters such as air and water quality, noise, weather, energy use, traffic and even tweets.
Forming part of a network of over 600 sensors, the Urban Observatory has already collected over half a billion data points and the information is now starting to shed light on the way different systems interact across the city and provide a baseline against which future cities can be developed and managed.
To date Air Monitors, UK AQMesh distributor, has supplied 55 AQMesh pods and 6 conventional air quality monitoring stations. The conventional stations employ standard reference method instruments to measure key air quality parameters such as Nitrogen Dioxide, Ozone, Carbon Monoxide and Particulates. The AQMesh pods monitor similar parameters, but are smaller, solar-powered, wireless, web-enabled devices that can be quickly and easily located in almost any location.
Commenting on Air Monitors’ involvement in the Urban Observatory project, Managing Director Jim Mills says: “The conventional stations are delivering precise, accurate data, and the AQMesh pods are providing the portability and flexibility to monitor air quality accurately and reliably in the locations of greatest interest.”
“Perhaps the most interesting aspect of this project is its ability to engage with the community, providing detailed local air quality data so that both authorities and citizens can make informed decisions on how to reduce exposure to air pollution. Looking forward, it is clear that work in Newcastle will serve as a model for other cities around the world to follow.”
The National Observatories facility was established in 2017 with the Newcastle Urban Observatory as the founding member, supported by £8.5 million investment from EPSRC (Engineering and Physical Sciences Research Council). The guiding principles are to be technology agnostic and vendor non-exclusive, open by default and transparent by design whilst developing a valued, long-term, sustainable platform. In order for the data to be useful to better understand cities and to facilitate evidence based decision-making across a range of scales and sectors, the data needs to be robust and reliable with known data quality that can be validated.
The AQMesh pods are also being used as part of the ‘Sense My Street’ tool box which enables local communities to deploy sensors and locate them on the streets, collecting evidence to inform or even change their communities.
Phil James, who co-leads the Urban Observatory research, explains: “Cities are complex environments and if we want to develop them sustainably we have to understand how everything interacts.
“By compiling observations and comparing the data, for the first time we are now able to make more informed decisions about designing our cities to work better for people and the environment. Through the Sense my Street project, we are able to give communities the power to gather data relevant to issues that are important to them at a very local scale.”
All of the data is freely available at Newcastle University’s website: www.urbanobservatory.ac.uk, and is being used by researchers, local authorities, regulators, developers, town planners, businesses and members of the public.
On Sunday 13th May 2018, Cardiff Council organised a car-free day in the city’s central area. As a result of this event air quality monitoring data showed an average 69% drop in nitrogen dioxide (NO2) – one of the pollutants of greatest public health concern. Seeking a better understanding of the relationship between air quality and traffic, Cardiff Council hired three AQMesh air quality monitoring pods from Air Monitors Ltd. The instruments were located on streets impacted by the day’s event, and within two of the Councils Air Quality Management Areas (AQMAs); City Centre & Stephenson Court, Newport Road. The instruments continuously recorded air quality at these locations for 20 days before, during and after the event.
“In comparing the results obtained during the Car Free Day Event with results from the following Sunday (20th May) , the monitor on Duke Street showed an 87% reduction in nitrogen dioxide, the monitor in Westgate Street showed an 84% reduction and the third monitor, which was located less centrally from the main road closures, in Stephenson Court, showed a 36% reduction,” commented a Specialist Services Officer, working for Shared Regulatory Services (SRS) on behalf of Cardiff Council . “Comparing the car-free datasets with those of the following Sunday (20th May); the daily average nitrogen dioxide levels recorded by two of the monitors situated within the City Centre AQMA exceeded the EU yearly average limit (40 µg/m3), but on the car-free day, these two monitors measured daily average figures of just 5 and 8µg/m3 of nitrogen dioxide, providing clear evidence that air pollution in Cardiff city centre is generated by traffic.”
Under the European Ambient Air Quality Directive, Welsh Ministers have a duty to ensure that compliance with air quality objectives defined within the directive is achieved. As outlined in Defra’s UK Action Plan for tackling roadside nitrogen dioxide concentrations, July 2017, modelling has indicated that certain road networks in Cardiff fail to meet EU air quality requirements. Cardiff Council has been directed by Welsh Government to undertake a feasibility study, in order to demonstrate how compliance with the directive and its specified limits will be achieved in the shortest time possible. In order to implement air quality interventions, the Council therefore needs to evaluate the sources of pollution so that appropriate interventions can be assessed to ensure that effective mitigation measures can be implemented. At the same time, it will be necessary to engage with citizens to ensure that they appreciate the importance of tackling air pollution.
Nitrogen dioxide and particulates are the main cause of failures to meet EU air quality limits in cities around the world, and it is well known that traffic, and diesel vehicles in particular, are a major source of these pollutants. The AQMesh pods measure a range of gases including nitrogen dioxide, so by monitoring the effect of removing traffic, the Council will be in a better position to implement improvement measures.
Two automatic air quality monitoring stations are located in Cardiff, and the Council supplements the data from these monitors with a network of non-automatic passive diffusion tubes. However, the Specialist Services Officer from SRS says: “The fixed stations can’t provide street-level monitoring at the most sensitive locations, and the use of diffusion tubes does not provide a detailed understanding of daily trends as they only provide a monthly average figure. However, SRS are aware of the capabilities of the AQMesh pods and are familiar with the accuracy and flexibility that they are able to deliver, which is why they were chosen for the car-free day project.”
In order to assure the quality of the monitoring data, the AQMesh pods that were employed during the project were checked against a reference station and were found to have performed very well. “The pods are small, lightweight and battery-powered which makes them quick and easy to deploy,” the Specialist Services Officer adds. “This is crucial to our work because it gives us the ability to site them on lamp posts so that they measure the air that people are breathing. In addition, they are web-enabled which means that we can monitor air quality in almost real-time; providing a unique insight into the specific events that impact air quality.”
It has been estimated that around 40,000 people in the UK die prematurely as a result of air pollution, mainly in the larger towns and cities. In Wales, the urban areas exceeding EU limits include Cardiff, Swansea, Port Talbot, Newport, Chepstow and Wrexham.
Following completion of the monitoring work in Cardiff, SRS has had requests for the data from a number of organisations, and are keen for the work to be publicised as widely as possible. Highlighting the importance of citizen engagement, the SRS Specialist Services Officer says: “A wide variety of potential measures are available to combat air pollution in Cardiff, but many involve inconvenience for members of the public and cost to the public purse, so we need those affected to be on-board with the measures being taken. We are also hoping that the public will be keen to help, by participating in car-share schemes for example.”
London Mayor Sadiq Khan has launched a new, street-by-street monitoring system that will help to improve that capital’s air quality. From July 2018, and operating for a year, London will benefit from what is being described as the world’s most sophisticated air quality monitoring system. A consortium involving academia, an environmental charity, and commercial partners will install a network of 100 multiparameter AQMesh air quality monitors, whilst also operating two Google Street View cars that will map air pollution at an unprecedented level of detail.
Air Monitors Ltd will supply the AQMesh pods and manage data from all the sensor systems, so that air quality can be visualised and mapped in almost real-time. Working closely with the Greater London Authority, the project will be run by a team of air quality experts led by the charity Environmental Defense Fund Europe, in partnership with Air Monitors Ltd., Google Earth Outreach, Cambridge Environmental Research Consultants, University of Cambridge, National Physical Laboratory, King’s College London and the Environmental Defense Fund team in the United States.
Air Monitors Managing Director Jim Mills says: “It is difficult to underestimate the importance of this project – traditional monitoring networks provide essential information to check compliance against air quality standards, but this network will be ‘hyperlocal’ by which we mean that it will deliver street-level air quality data, which will be of tremendous interest to the public and also enable the effective assessment of air quality interventions.
“The Google Street View cars will take readings every 30 meters, helping us to find pollution hot-spots, so that AQMesh pods can be positioned in these locations. However, the pods are wireless and independently powered, so they can also be quickly and easily fixed to lamp posts in other sensitive locations such as schools.”
In addition to nitrogen dioxide and particulates, which are the pollutants of greatest concern, the pods will also measure ozone, nitric oxide, carbon dioxide, temperature, humidity and pressure. Data will sent, near real-time, to Air Monitors’ cloud-based data management system, which can be accessed by PC, tablet or smartphone by authorised partners, using an assigned login.
The monitoring data will provide baseline air quality data that will be essential in the assessment of mitigation measures, particularly in London’s expanding ultra-low emission zone. For example, on 20th June 2018, Sadiq Khan, announced the creation of the largest double-decker electric bus fleet in Europe, and the new monitoring network will enable the assessment of this initiative’s impact on air quality.
“This project will provide a step change in data collection and analysis that will enable London to evaluate the impact of both air quality and climate change policies and develop responsive interventions,” said Executive Director for Environmental Defense Fund Europe, Baroness Bryony Worthington. “A clear output of the project will be a revolutionary air monitoring model and intervention approach that can be replicated cost-effectively across other UK cities and globally, with a focus on C40 cities.”
Mark Watts, C40, Executive Director said: “Almost every major city in the world is dealing with the threat of toxic air pollution, which is taking an incredible toll on the health of citizens, public finances, quality of life and contributing to climate change. London is already a world leader in responding to this global threat and with this initiative it will set a new global standard for how street level air quality monitoring can inform strategic policy making. Cities across the C40 network and around the world will be watching closely to understand how this monitoring can deliver cleaner air for their citizens.”
About Environmental Defense Fund
Environmental Defense Fund Europe is a registered charity (1164661) in England and Wales. A recently established affiliate of leading international non-profit Environmental Defense Fund (EDF), the organisation links science, economics, law, and innovative private-sector partnerships to create transformational solutions to the most serious environmental problems. Connect with us at edf.org/europe, on Twitter and on our EDF Voices, EDF+Business and Energy Exchange blogs.
About Air Monitors Limited
Air Monitors is the UK’s leading air quality monitoring company, supplying and supporting instrumentation to central government, local authorities, research and industry. Air Monitors supplies and supports AQMesh in the UK and will also provide and maintain the equipment within the Google Street View cars in the project.
AQMesh is a fully developed and independently evaluated small sensor outdoor air quality monitoring system, manufactured in the UK by Environmental Instruments Ltd. and in use worldwide since 2012.
About Cambridge Environmental Research Consultants
Cambridge Environmental Research Consultants (CERC) are world leading developers of air quality modelling software. Their renowned ADMS-Urban model will be used together with the sensor data to generate hyper-local air quality mapping both for nowcasts and forecasts, and for policy studies.
About Google Earth Outreach
Google Earth Outreach is a program from Google designed specifically to help non-profit and public benefit organisations around the world leverage the power of Google Maps and Cloud technology to help address the world’s most pressing social and environmental problems.
About the National Physical Laboratory (NPL)
NPL is the UK’s National Measurement Institute, providing the measurement capability that underpins the UK’s prosperity and quality of life. Every day our science, engineering and technology makes a difference to some of the biggest national and international challenges, including addressing air quality issues. http://www.npl.co.uk/about/what-is-npl/
About University of Cambridge Department of Chemistry
The University of Cambridge Department of Chemistry is a world leading research and teaching institution. At Cambridge, the Centre for Atmospheric Science has played a primary role in the development of low-cost sensors for air quality monitoring and in the development of techniques for analysing and interpreting measurements from sensor networks.
About the C40 Cities Climate Leadership Group
Around the world, C40 Cities connects 96 of the world’s greatest cities to take bold climate action, leading the way towards a healthier and more sustainable future. Representing 700+ million citizens and one quarter of the global economy, mayors of the C40 cities are committed to delivering on the most ambitious goals of the Paris Agreement at the local level, as well as to cleaning the air we breathe. The current chair of C40 is Mayor of Paris Anne Hidalgo; and three-term Mayor of New York City Michael R. Bloomberg serves as President of the Board. C40’s work is made possible by our three strategic funders: Bloomberg Philanthropies, Children’s Investment Fund Foundation (CIFF), and Realdania.
Extensive research has shown that indoor air quality is often worse than outdoors. Closed system buildings trap harmful particles inside, and external air intakes can bring in more polluted air from outside.
Whilst many heating, ventilation and air conditioning systems (HVAC) use particle filtering, managed through air exchanges, they can often worsen levels of polluting gases, such as NO2 – now classified by the World Health Organisation as a Class 1 carcinogen. Natural ventilation systems have no particulate filtration at all, and buildings are also frequently completely shut up all night with no ventilation running, trapping the pollution that has built up over the day.
Unlike outdoor air quality (which the government is responsible for), indoor air quality is the responsibility of the building owner or manager, and with research proving that poor air quality has a significant impact on human health, air pollution should be a key factor of employee health & safety.
Future Decisions has teamed up with AQMesh and UK distributor, Air Monitors Ltd, to supply pollution mitigation to improve indoor air quality. Future Decisions has developed patented smart management strategies that aim to reduce internal air pollution by 30% – this is usually enough to bring the air quality within UK & EU regulatory levels, and often within the World Health Organisation levels.
AQMesh measures NO, NO2, O3, NOx, CO, CO2, SO2, PM1, PM2.5, PM10, temperature, pressure and relative humidity in a small pod which can be mounted both indoors and outdoors on a wall or post. Batteries, solar power and DC power options give flexibility of mounting anywhere. AQMesh was designed to offer an easy-to-use air quality monitoring system that can deliver localised real-time readings, improving the accuracy and scope of gathering air quality data in order to support initiatives to reduce air pollution and its risk to human health.
Minnesota Pollution Control Agency (MPCA) has purchased fifty AQMesh pods to measure key air pollution gases and particulate matter across fifty different zip code areas. These small sensor air quality monitoring systems measure NO, NO2, O3, CO, SO2, PM1, PM2.5, PM10, temperature, pressure and relative humidity and will be installed – one per zip code – around the twin cities of Minneapolis and Saint Paul. The two-year project, funded by a legislative grant*, is to supplement the air quality information available to the public.
Deployment across the 50 zip codes has been mapped out after several public meetings involving the local community to determine where residents felt monitoring was needed. The small yellow triangles represent the points which local residents asked for sensors to be installed, and the green dots indicate the planned installation site based on the infrastructure available for mounting the AQMesh pods.
“This project is about understanding small-scale differences in air pollution in urban areas in order to minimise exposure to harmful air pollutants, particularly for vulnerable communities. The Assessing Urban Air Quality project will use new air monitoring sensors to broaden our knowledge about air quality in Minneapolis and St. Paul”, commented Monika Vadali, Ph.D, who is leading the project.
The pods are currently installed at the Blaine airport Federal Equivalent Method (FEM) station so that AQMesh readings can be compared to and validated against air quality readings taken using this US approved methodology, with scaling then applied if necessary. The MPCA team intends to install the pods in each zip code during the next month or two. The pods will be powered using a bespoke solar power pack: 30W panels have been specified for such a northern location, compared to the 15W normally required to supply the low-power AQMesh platform. The pods can be battery powered but 12V DC supply was specified, given the 2-year project timescale.
The pods were installed in November 2017 and have achieved 100% uptime to date, including during severe weather conditions, with temperatures below -25°C / -15°F and heavy snow. Initial comparisons against co-located pods show a high level of pod-to-pod precision, with an average R2 of 0.94 for NO2, 0.92 for O3 and 0.93 for PM2.5.
The 50 pods have been compared to the FEM station in two batches of 25, and the first batch of comparisons show an average co-location comparison correlation R2 of 0.74 for O3 and NO2, 0.86 for PM2.5, 0.93 for PM10 and 0.82 for NO. The reference CO showed a baseline shift part way through the comparison period, so that comparison is being reviewed. The SO2 R2 was depressed by a max FEM reading of 2.5ppb, with low FEM resolution, but AQMesh readings were within +/- 2ppb of reference.
The MPCA team is setting up an API connection to the AQMesh server, allowing air quality data to be streamed, near real-time, to the MPCA server, from which it can be published.
AQMesh is in use at various locations in the USA, as well as 35 other countries. The pods deployed in Minnesota are the current production version (v4.2.3).
More information about the MPCA project is available at https://www.pca.state.mn.us/air/assessing-urban-air-quality-project.
* The project is funded by a legislative grant: Environment and Natural Resources Trust Fund (ENRTF) M.L. 2017, Chp.96, Sec. 2. Subd.07b
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.
Cleves School in Weybridge, Surrey (UK) has used AQMesh to measure pollution at the primary school’s entrance. The project, led by Dr. Edward Salter over the school’s summer term, aimed to understand exposure of the children (aged 7-11) to dangerous pollutant gases, with particular interest in the levels of nitrogen dioxide (NO2) and ozone (O3).
Initial findings showed that levels of O3 exceeded 100µg/m3 on several occasions during the high temperatures in June, and a daily pattern of gas peaks coinciding with school pick-up and drop-off was noticeable for nitric oxide (NO). NO2 levels increased later in the day both as a result of oxidation of school-related NO and from general traffic locally, with elevated levels of NO2 up to the end of the evening commute, probably from traffic on local and major roads nearby. The monitoring also showed 15-30 minute spikes from diesel buses or cars parked very early in the morning or late at night with their engines running constantly, as well as from local events at the weekend, when the air quality is otherwise generally seen to improve considerably.
The project set out to determine whether pollution peaked at school drop-off and pick-up times in order to encourage cleaner methods of getting to and from school, after a transport assessment for the expansion of the school highlighted that traffic peaked around 8.30am and 3.15pm for approximately 30 minutes. The school is reviewing findings and will consider a number of mitigation measures, including timing exercise sessions for periods of lower pollution.
AQMesh monitors were installed to monitor NO, NO2, NOx and O3 at each school gate during these peak traffic periods. “There is clearly an effect between pollution levels and travelling to school by car. If I were to do this again I would ask to monitor to additional gases, VOCs and particulates”, said Dr. Edward Salter. AQMesh can currently measure PM1, PM2.5, PM10, CO and SO2, as well as the three gases in this study, and options for H2S and CO2 are due to be released by the end of 2017.
“The AQMesh pods were simple enough for the school to handle, which is not true of all such equipment”, added Dr. Salter.
AQMesh was designed to offer a robust and easy-to-use air quality monitoring system that can deliver localised real-time readings, improving the accuracy and scope of gathering air quality data in order to support initiatives to reduce air pollution and its risk to human health.
AQMesh has been used in various education-related projects globally. At the simplest level AQMesh offers an accessible way for schoolchildren to engage with local air quality issues. Used in conjunction with wind speed and direction information, local real-time data from AQMesh can be used to distinguish between local sources of pollution, which can be managed, and more distant sources of pollution which require a different approach. AQMesh data can also be used to improve the accuracy of air quality models at the local level.
On 9th April The Sunday Times reported that employers have been told they are legally obliged to protect their staff from diesel fumes — and could be sued if workers develop cancer later in life. Read the full article here.
Employers who want to assess risk to employees can use AQMesh to take round-the-clock readings of a range of measurements including key pollutants NO2 and PM2.5. The small, battery-powered devices transmit data using the mobile phone network and data can be accessed using a secure online login.
The Sunday Times article is based on a reclassification of diesel fumes as a “grade 1 carcinogen” by the International Agency for Research on Cancer, part of the World Health Organisation, after it found that people exposed to diesel fumes at work were up to 40% more likely to develop cancer.
The Institute of Occupational Safety and Health (IOSH) and Health and Safety Executive (HSE) have issued the warnings and as many as 500,000 UK jobs may be affected. Clearly it is not just UK workers who are affected by diesel fumes in the workplace. Employees with jobs that could involve high exposure to diesel fumes are any who spend much of their time on or close to busy roads or railways, or near running diesel engines or generators.
Studies with AQMesh have shown high exposure to NO2 and particulate matter inside vehicles such as taxis and also inside office buildings. Although buildings often have active air management to reduce CO2 levels, air intakes can be positioned such that they draw in air from a highly polluted area. Particles may be filtered out but without knowing how levels of the invisible, odourless pollutant NO2 are potentially building up, it is very difficult to manage indoor air quality. Read more…
Employers may be required to take action, including practical advice for employees to minimise exposure. However, exposure can vary dramatically depending on location – inside or outside a vehicle or building – time of day, day of the week, etc. For employers to understand the risk presented to employees and to take appropriate action, it is straightforward to assess air quality very close to the point at which employees are inhaling air.
The best quality data about air pollution comes from reference stations, using validated equipment. However, such stations are large, immobile and require power and communications infrastructure. AQMesh can be located in a fixed position to monitor a workplace on an ongoing basis, such as inside a facility, next to a professional driver or on a fence next to a construction team. AQMesh can be calibrated against reference instruments to establish reading validity. Further advice about management of AQMesh data is available from www.airmonitors.co.uk.
AQMesh showed its versatility in the BBC’s Inside Out feature on air quality (West region). The programme aired on 6th March but is available on iPlayer at www.bbc.co.uk/iplayer/episode/b08h4m30 until 5th April. AQMesh pods were used on the back of a bicycle and inside a taxi, to show the NO2 and particulate matter exposure experienced by a cyclist and a driver.
The feature, shown in the first 10 minutes of the programme, underlines the high levels of PM 2.5 that drivers in queueing traffic are exposed to and Professor Gavin Shaddick of the University of Bath provided an overview of the issues.
The fact that battery powered AQMesh pods can be used to measure air quality in such a range of locations has made it popular with broadcasters, as well as more typical users, such as local authorities, researchers or industrial customers. AQMesh has featured recently on BBC Newsnight and Channel 4 Dispatches.
It is generally accepted that whilst measurements from air quality reference stations are highly accurate, they are not sufficiently location-specific. Key pollutants – such as NO2 and PM2.5 – vary dramatically over short distances and time intervals, but the large size, maintenance requirements and relatively high cost of reference equipment limits the places it can be installed. Diffusion tubes can offer a very cheap alternative and are much easier to install in specific locations, however they only offer a single reading over a number of weeks, and air quality professionals therefore rely on modelling techniques to fill the gaps. With research continuing to prove the extent to which air pollution varies significantly over space and time, the answer would be a reliable and accurate tool for taking real-time, localised measurements.
A number of new low-cost air quality monitoring systems are available, each with benefits and shortcomings. It is fair to say that the available sensors, whether electrochemical, optical or metal oxide, are all working at or close to their limit of detection to provide the low ppb or µg/m3 level of sensitivity required for any of the common ambient air quality applications. However, several systems offered for these applications provide readings in ppm or even % level readings – which clearly makes them inappropriate for ambient air monitoring. Some are also not fit for long-term outdoor use, as they are not fully weather proof or cannot cope with the expected temperature ranges. However, at least one system – AQMesh – does operate across a wide range of conditions and territories, so having established that a viable product exists, can it deliver the accuracy required?
Performance is clearly a major consideration for any user and comparing readings from a lower cost system against a reference station is the obvious place to start. One immediate challenge is ensuring meaningful results. Particularly in roadside applications or where there is an immediate source of pollution, all sensors and intakes must be within a metre of each other and at an equal distance from the immediate source. Most sensors, not unreasonably, also require an uninterrupted air flow around them – mounting immediately above hot or wet surfaces will not give accurate readings. On the other hand, some limitations of reference equipment come to the fore when comparing with a different type of measurement. For example, single channel NOx analysers switch between measuring NO and NOx, calculating NO2 as the difference. This switching can have dramatic effects on readings for the two gases (which are measured separately and directly by other sensors) at short reading intervals, such as 1 minute. Similarly, any differences in clock synchronisation or reading averaging protocol (time beginning or time ending) can make the difference between a regression comparison R2 of 0.9 and 0.1, which can render comparisons meaningless.
Comparisons of particulate measurements are also problematic due to the range of reference-equivalent methods available and the limitations, in many ways, of the reference method itself. Since the expanded uncertainty of the reference equivalent measurements for PM10 and PM2.5 allows up to 25%, this should be borne in mind when making comparisons with lower cost particulate sensors. Overall, for both gases and particulate matter, if several identical low cost systems are co-located, the user should expect a high level of repeatability (R2 > 0.9) and should expect to be able to adjust accuracy by ‘calibrating’ – adjusting slope and offset – against a co-located reference/equivalent station. Some systems, such as AQMesh, then allow this scaling adjustment to be applied automatically to all future readings, minimising the need for manual data correction. Access to a calibrated reference station and careful co-location is currently key to getting value out of any of the current generation of emerging sensor systems, although the objective of good accuracy without the need for a reference station is being actively pursued.
First questions about these systems often include ‘How do I run gas through it to calibrate it?’ and ‘Can I calibrate (or test) it in the laboratory?’ In systems such as AQMesh the air sample is not pumped, for good power-saving reasons (low power is essential for battery operation), and so it is not obvious how a conventional gas calibration would work. More importantly, although the sensors generally do give very good results in laboratory tests with known dry, single gases, these bear no relation to real ambient field measurements with a combination of damp, humid gases at potentially varying temperature and pressure. Overall, there is no proven substitute for co-location with a reference station. Even with all of these considerations, some of these small, lower cost air quality systems, such as AQMesh, can deliver very impressive comparison results and provide a new source of air quality data. Those with in-built power and communications offer genuine freedom to gather measurements from any location and research teams worldwide are using such systems to understand pollution around cities, inside and outside buildings, at different heights, in street canyons, around industrial facilities and within neighbourhoods, at different times of day, and so on. This new granularity of measurement and flexibility of location gives air quality management teams a real tool to carry out ‘before and after’ studies and evaluate a range of policy or pollution mitigation activities. Where a number of sensor systems are used, and particularly in combination with wind speed and direction information, the relative measurements and source distribution can provide very powerful insights about where to target pollution mitigation activity.
One such low cost outdoor air quality monitoring system offering this type of flexibility is AQMesh, which has proven its repeatability, accuracy and performance through a series of these careful co-location comparisons with calibrated reference stations in a variety of global locations and applications. The small size, battery power and wireless communications technology mean users can benefit from reliable and accurate real-time, localised air quality measurements in a broad range of studies.
How accurate is ‘accurate’?
One area of discussion is what level of accuracy is ‘good enough’. Although this depends on the application, it is still tempting to look for a very high level of agreement between the low cost sensor system and reference equipment. Whilst this may be the goal, the lower cost systems are considerably cheaper and have the benefit of being correctly located so perhaps it is better to have slightly less accurate readings from the right location than highly accurate readings from the wrong location? For some applications it is really only the relative readings which are required, and systems like AQMesh provide very high levels of precision between identical systems. Or it may only be appropriate to provide a ‘traffic light’ indication for communicating air quality to the public. Until more general guidance is available, users will have to take a view on accuracy relevant to their application.
Publishing air quality data
Another area of confusion is regarding data privacy vs online publication of air quality data. Most of the new air quality systems take advantage of remote data management and online access. This makes sense for a number of reasons. Hard-wired communications infrastructure is a barrier to freedom of location and new systems generally communicate either using the mobile network, radio or wi-fi. Online access to data is also very convenient and less resource hungry. Few of us who readily use mobile phones, online banking and many of the commonplace applications of modern life fully understand security of communications and the reality of data hosting. The bottom line is that air quality data from sensor systems using wireless communications can be as secure as any other online application. Confusion is caused by the systems which are focused on citizen engagement and offer automated sharing and publication of data, but these are the exception and in most cases, such as AQMesh, data is private and secure.
Current low cost air quality sensor systems are a very mixed bag. Some products may well appear to offer the same measurements and even claimed accuracy as the more thoroughly developed and tested systems and the user has little choice but to ask searching questions and ask for demonstration of performance and reference projects before purchasing. But the need for such systems is clear and performance is already good enough for many leading institutions and organisations to be actively using the technology. Sensor and sensor system manufacturers are seizing on every new shared comparison dataset and development in technology to make further improvements. The insights that these sensor systems can offer are real and relevant and there is no substitute for trying the technology in any given application to see what it can offer. Many users have found that one insight can lead to another and, working with a clear understanding of the strengths and weaknesses of the systems, the benefits of making a start with this new tool are overwhelming.