We are often asked by customers whether AQMesh air quality monitors can operate in cold conditions. Long-term use at temperatures well below freezing, with ice and snowfall, is indeed challenging.

Cold weather operation has been key to AQMesh – improved upon and proven in the field – for over 10 years. The main features, described below, have been most recently been put to the test in Iceland.

Ölfus, a municipality in Iceland, installed a number of AQMesh pods during December to measure local air quality across the town in relation to the region’s volcanic activity. The pods – supported by Vista, AQMesh distributor for Iceland – will monitor NO, NO2, CO, H2S, SO2 and particulate matter and report the data to the local Environment Agency.

A monitoring network has also been recently installed on a construction site in Reykjavík, measuring dust (PM), NO, NO2, NOx and wind speed and direction, powered by the smart solar pack. AQMesh was chosen because of successful performance in previous deployments in Iceland, as well as ease of installation and minimal maintenance requirements.

The successful operation of AQMesh pods in extremely cold temperatures can be attributed two main factors: power management and weatherproof design.

Power management

Many small sensor air quality monitoring systems use lithium batteries, which carry a recommendation for use only down to 15°C. Lithium ion batteries should not be charged below 0°C – there are risks in trying to do so – and performance is also significantly poorer at low temperatures. This is because lithium ions can plate the anode surface in freezing conditions, reducing battery capacity and increasing resistance.

The AQMesh solar pack uses the heavier but more practical 22Ah lead acid battery, which performs reliably in such temperatures. The AQMesh battery has 264Wh capacity, compared to lithium-based systems which store less than 100Wh solar power. With the battery built into the smart solar pack, capable of powering the pod for 1.5 to 2 weeks without sunlight, the pod can be powered at full capacity over the whole year at surprisingly high and low latitudes. This is particularly significant for relatively power-hungry sampling of PM: AQMesh will continue to sample at the optimal rate and not reduce sampling, which would deviate from MCERTS test conditions, voiding certification. Lead acid batteries are also easier to ship than lithium: a major consideration if you are moving pods around the UK or internationally.

Weatherproof design

Simple design considerations can be vital. Right from the first deployments across North America and Scandinavia, AQMesh design has shown that equipment cannot just survive but provide full functionality through a harsh winter, without maintenance visits. The shape of the pods prevents water, ice and snow building up on the surface, and there are no moving parts that can be affected by freezing temperatures. The AQMesh wind speed and direction sensor option is an ultrasonic anemometer, with no moving parts to wear or recalibrate, making it reliable and low maintenance.

AQMesh pods use a pump for drawing in particles, as opposed to a fan. Fans are more likely to be affected by snow and ice, potentially recirculating the same air if even partially blocked, whereas a pump will still actively draw an air sample.

Data processing on the secure AQMeshData.net server uses correction algorithms based on over 10 years of real-world testing which can compensate for extreme environmental conditions and flag affected data points if necessary.

A network of 50 AQMesh pods in Minnesota, USA, continues to operate smoothly in temperatures as low as -25°C, despite the area being under several feet of snow for long periods of the year. Other deployments include Alaska, Mongolia and Scandinavian regions, all of which experience harsh winter conditions.

For more information and to discuss your potential air quality network deployment contact our experienced team today.

A UK local authority installed nine AQMesh air quality monitoring systems at different points across a busy town, measuring nitrogen dioxide (NO2) at 15 minute intervals, monitoring 24/7.

These locations were established monitoring points, where measurements had been taken previously using diffusion tubes, limited to one average reading every few weeks.

AQMesh – in common with all lower cost air quality systems – can provide near real-time air quality information, with high frequency measurements that allow daily and weekly patterns to be seen. However such systems are not certified, as are reference stations or diffusion tubes. As a result, AQMesh readings need to be ‘calibrated’ against certified readings, at some point in the network, to provide confidence in data accuracy and traceability to an approved standard.

Typically such ‘calibration’ is carried out by mounting at least one AQMesh ‘pod’ very close to a reference station, so pod and reference are sampling the same air and readings can be compared. However this approach does require staff to move pods from position to position, which can be time-consuming and therefore costly. An alternative approach was used for this network, similar to the one developed by the University of Cambridge and used in a major project in London (Breathe London pilot). One of the authority’s reference stations (location in red on map) was used to ‘calibrate’ the network of pods and the other (location in green on map) was used to cross-check network accuracy.

AQMesh network deployment (BELOW): AQMesh locations marked in blue, reference station used for calibration in red, reference station used for control co-location in green

The four-month project demonstrated that the AQMesh network showed that stakeholders could have the same high confidence in readings when the network was calibrated remotely as when pods were co-located for calibration (the gold standard for this technology), but with significant savings in field support and reduced data loss.

2023 is set to be a big year for AQMesh’s monitoring of particulate matter, with developments in both hardware and data processing offering improved accuracy across key PM fractions. AQMesh is also on the road towards MCERTS indicative certification, submitting data well above the required standard for indicative monitoring, and following on from achieving ISO9001:2015 certification in 2022.

The AQMesh optical particle counter already delivers high accuracy across PM2.5 and PM10, thanks to its proprietary design. The system also has the option to include a heated inlet – which has had a significant uptake during 2022 – to dry the sample prior to measurement and reduce the effects of moisture, leading to even more accurate readings.

AQMesh prides itself on its high levels of accuracy and reliability, and has already repeatedly demonstrated its performance well below the 50% measurement uncertainty required for indicative MCERTS for both PM2.5 and PM10 through extensive co-location comparisons across the globe, in real-world conditions.

The plot below shows AQMesh vs reference for PM2.5 at hourly averages during a one month time period.

Similar high performance can be seen for the more coarse PM10 particles, also at hourly averages over a one month time period, showing how AQMesh can provide more accurate results than nephelometers, which derive PM10, rather than measure it directly, as AQMesh does.

John Downie, Technical Business Development Manager for AQMesh, says “2022 has been successful for AQMesh, despite the turbulent times. We are pleased to have supplied pods to new regions this year, including Saudi Arabia, Angola, Latvia & Uzbekistan, further growing our already expansive global customer base. I’m looking forward to extending our reach even further still next year, especially as we look to achieve MCERTS & CEN certification. We have also seen huge interest in our bespoke smart solar pack – in fact, over 60% of our pod sales this year included the solar option.”

The AQMesh smart solar pack offers autonomous continuous power all year round for an AQMesh pod. More than ‘just a panel’, it features smart connectivity with a mobile app for checking power output, viewing historical data and running diagnostics.

The system continues to prove itself as fit-for-purpose flexible air quality monitor for a range of applications, including mining, construction, government agencies and transport operators. Pods can measure up to five gases out of NO, NO2, O3, CO, SO2, H2S and TVOC, as well as an additional CO2 sensor, and PM1, PM2.5, PM4, & PM10. These are all fitted in one compact unit, with various autonomous power options and seamless data delivery Wind speed & direction and noise monitoring are also available, with humidity, pressure and pod temperature included as standard.

2022 marked 10 years of innovation and leadership from AQMesh. To highlight the team’s experience, ongoing forward-thinking and its commitment to pushing the capabilities of small sensor systems, here are the top 10 things AQMesh developed first and refined since it commercially launched in 2012.

1. IoT connectivity using the mobile phone network: remote data for small sensor air quality monitoring

AQMesh was the first small sensor manufacturer to adopt an IoT approach, using the mobile phone network to connect with the cloud, allowing remote access of data from individual measurement points. Until then, conventional equipment used loggers and other early small sensor air quality equipment offered direct download or radio communication, often across a group of sensor nodes.

2. Integration of gas and PM monitoring in a single small sensor instrument

Since 2013, AQMesh pods have been able to monitor gases and particles in one instrument. The compact pods have continued to lead in terms of the wide range of measurements offered on a single unit: up to six gases out of NO, NO2, O3, CO, SO2, H2S, TVOC and CO2 as well as PM monitoring and options for noise and wind speed/direction. Pressure, relative humidity and pod temperature are all measured as standard. In the 2019 AIRLAB International Microsensors Challenge, AQMesh was recognised as the most accurate multi-parameter outdoor air quality monitor, and was evaluated for the highest number of pollutant measurements offered within a single system.

3. Mini optical particle counter, counting and sorting particles by size, for accuracy across all PM fractions

AQMesh’s in-house designed optical particle counter measures particulates PM1, PM2.5, PM10, TPC and TSP (up to 30 microns). Its bespoke design uses a straight line between the sample inlet and bench, meaning larger particles do not settle in a bent sample path, allowing for complete capture of pollutants. Additionally, the OPC uses a pump instead of a fan, which produces a steady flow from inlet to sample measurement, and subsequently provides consistency for the sample calculations – fans can cause vacuums which could interfere with the flow rate and affect the sample measurement. The AQMesh OPC therefore allows more coarse particles (PM10) in the sample to be accurately measured.

4. Pioneers of city-wide small sensor networks from Citi-Sense to the Breathe London Pilot

Initiated in 2012, AQMesh was part of the EU-funded consortium which set up a ground-breaking project to advise citizens about air quality, across eight cities, using hundreds of measurement devices. The Breathe London pilot, which ran from 2018 to 2020, and in which 100 AQMesh pods were used, was the world’s first hyperlocal monitoring network. The two year pilot project proved & validated small sensors for city-wide monitoring, and also led to the Environmental Defense Fund (EDF) publishing a ‘blueprint’ for other cities.

5. Real-time out-of-the-box accuracy with correction for environmental conditions and cross-gas effects without the need for machine learning

AQMesh’s high accuracy and performance has been achieved through years of extensive global co-location comparison trials against certified reference equipment, in all seasons, meaning AQMesh can accurately operate in the widest possible range of environments and conditions. No other manufacturer has access to the wealth of data that AQMesh has gathered. With these datasets AQMesh has been able to develop meaningful correction of cross-gas effects and interference from environmental conditions through its fully traceable data processing algorithms.

6. ‘Gold pod’ approach

The ‘gold pod’ approach, as originally described by the AQMesh team, involves one unit being co-located with and scaled against a maintained reference station and then moved around a network of nodes to calibrate each of the other units. This method has now been widely adopted and offers an effective way to improve accuracy and achieve traceability. It was back in 2017 when Professor Rod Jones from the University of Cambridge presented the results of the ‘gold pod’ approach in which 20 AQMesh pods were deployed across Cambridge after co-locating one with reference, and he commented at the time “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.”

7. White reflective sunshield and insulation for temperature management

The sunshield was first added to AQMesh pods in 2013 to minimise the impact of direct sunlight on pod sensors. Various solutions were tested – for active or passive cooling – and AQMesh’s reflective shield, insulation and air flow gap was found to be most effective at minimising the challenge to temperature stability from strong, direct sunshine.

8. Promote rigorous QA/QC and offer feasible methods to achieve it

Since 2015, the AQMesh onsite reference station means each sensor has been tested through a rigorous quality control process before it leaves the UK factory. The custom-built enclosure uses climate-controlled reference/equivalence analysers sampling air from an ambient cage which can hold up to 100 AQMesh pods at a time. This ambient characterisation during manufacture is part of a stringent AQMesh quality assurance process, which also includes strict criteria for PM, so every AQMesh pod out in the field to date has been through specific quality control measures to ensure the efficiency and reliability of each sensor in real-world conditions. QA/QC doesn’t end at the factory either; the AQMesh team regularly offer remote QA/QC of data once pods are out in the field.

9. CO2 emissions profiling

AQMesh can offer incredibly high out-of-the-box accuracy (typically less than 15% uncertainty) for CO2 monitoring. Using this reliable data, AQMesh can be used for CO2 source apportionment, and measuring alongside NO and NO2 can allow for emissions profiles for different locations to be determined. This means the combustion contributing to the pollution can be specifically identified; such as whether there is either gas or diesel traffic, which is only possible with such accurate data.

10. Long distance scaling

The Breathe London pilot showed how pods could be traceably scaled across a city, using a novel approach pioneered by partners at the University of Cambridge. This technique, which reduces the field demands of the proven gold pod approach, requires basic measurement data of a good quality in order to be effective, and AQMesh have built on the initial Breathe London methodology with their own simplified Long Distance Scaling tool.

Many small sensor air quality monitoring systems cannot reliably measure coarse particulate matter, or PM10, because of the technology they use. AQMesh’s proprietary optical particle counter (OPC) delivers high out-of-the-box accuracy across all key particle matter (PM) fractions thanks to its bespoke, in-house design. Measuring PM1, PM2.5, PM4, PM10, PM-Total (up to 30 microns) as well as Total Particle Count, the proven OPC uses the most direct path possible between the sample inlet and measurement chamber. This allows more coarse particles in the sample to be measured compared to off-the-shelf OPCs and nephelometers, where these particles can be deposited in a maze-like pattern before being measured.

Humidity-related challenges have also been addressed by the AQMesh team. In some areas of high relative humidity, certain types of particles can absorb moisture from the surrounding environment (known as deliquescence), which can make them appear larger in diameter and result in erroneous readings. In most cases AQMesh can detect when this is happening and add a flag to the data point, allowing for it to be easily identified, reviewed and redacted as part of a robust data QA/QC process. Additionally, the OPC used in AQMesh has the option to include a heated inlet, which dries the sample prior to measurement and further reduces the effects of deliquescence. This option results in less than 1% of the data points being flagged and ensuring more consistent data accuracy.

Other benefits of the AQMesh OPC include its reduced maintenance schedule compared to other sensors – there is no need to change any filters, making it the ideal solution for industrial applications where critical processes create higher levels of particle pollution. Active sampling is performed with a pump instead of a fan, which means less turbulence in the measurement air flow and eliminates the opportunity for vacuums to affect the sampling accuracy. There is also no need to replace the whole OPC unit when it requires servicing – only the parts that need changing are replaced so the product remains sustainable whilst keeping the ongoing cost of ownership low. A silent pump will shortly be commercially available for indoor applications and already has orders to assist with clinical research for one of the UK’s leading research universities.

Customisable alerts for PM fractions, along with all other pollutants measured, are available to all AQMesh users. Email alerts can be set for exceedances on any channel and are completely customisable to individual detection limits. Where a pod is battery powered, alerts can also be set up to communicate the on-board battery voltage, triggering the battery replacement process in good time.

AQMesh prides itself on its accuracy and has always backed up its claims by publishing performance data online, making it easy for users to see real results, from real trials, in real world conditions. All AQMesh co-location comparison results can be viewed on the AQMesh website, alongside numerous independent and academic studies which verify AQMesh as a high-performing small sensor air quality monitoring system.

Data collected as part of the UKRI SPF Clean Air Program has proven that AQMesh out-of-the-box performance for PM2.5 exceeds new US EPA targets*, with excellent results for PM1 and PM10 as well.

AQMesh prides itself on its accuracy and has always backed up its claims by publishing performance data online, making it easy for users to see real results, from real trials, in real world conditions. Since the product was first commercially launched in 2012, after being developed in collaboration with the University of Cambridge, it has been out in the field continually in numerous trials. Data from these extensive global co-location comparison trials against certified reference equipment / field equivalent methods have continued to be made publicly available, as well as being used to drive product development and performance improvement.

The most recent advancement has been the launch of the latest gas processing algorithm, V5.3. Now the current production standard, and available as a free remote upgrade for existing users, the new algorithm has been developed from over 140 co-location datasets across four continents using a wide range of extreme environments and conditions over extensive time periods. Its benefits include improved out-of-the-box accuracy, particularly at the extremes of the temperature range, reducing the requirements for seasonal scaling.

Combined with improvements in small sensor technology, AQMesh processing algorithms are carefully developed from real world datasets and understanding how sensors respond in varying conditions. All AQMesh algorithms are fully traceable, fixed by version number and have been achieved with no use of machine learning or artificial intelligence. This means no training period is required and co-location with reference is not a necessity unless validation of data is required. These features, along with unique out-of-the-box accuracy, allows quick access to reliable data after installation, enables flexibility in monitoring locations without access to reference and ensures the pods can be moved between locations efficiently to make the most of the time available.

In addition to continual improvement of sensor performance, the team at AQMesh is always looking to add new hardware options to the pods to offer even more flexibility and users can now benefit from TVOC monitoring. The new electrochemical TVOC sensor is one of eight available sensors in the suite of gas options on offer. It can be specified within a single AQMesh pod alongside five other gases out of NO, NO2, O3, CO, SO2 or H2S, as well as an additional NDIR CO2 sensor, and PM1, PM2.5, PM4, & PM10 via an optical particle counter. Wind speed & direction and noise monitoring are also available, with humidity, pressure and pod temperature included as standard.

These new results for PM1, PM2.5 and PM10 are the latest example of the product’s high performance, with AQMesh previously been recognised as the most accurate multi-parameter small sensor system for outdoor air quality monitoring in the 2019 AIRLAB Microsensors Challenge. It was also the system used by the Environmental Defense Fund to develop a blueprint for hyperlocal air quality monitoring following the successful 3 year Breathe London pilot.

All AQMesh co-location comparison results can be viewed on the AQMesh website, alongside numerous independent and academic studies which verify AQMesh as a high-performing small sensor air quality monitoring system.

*As published in the Air Sensor Toolbox on the EPA website.

Refinement and development of the AQMesh small sensor air quality monitoring system over many years, and through numerous global co-location comparisons, brings a wealth of unique benefits.

As well as a range of comparison datasets across climates from the Middle East to Scandinavia, each AQMesh pod has always been subject to a comprehensive factory set-up, following best practise of co-location comparison with reference equipment.

The AQMesh onsite reference station means each sensor has been tested through a meaningful and rigorous quality control process before it leaves the UK factory. The sensitivity of each sensor to the target pollutant is measured against the reference equipment and sensors which show a response outside the defined range are rejected. Adjustments can also be applied to optimise consistency, precision and accuracy through AQMesh’s proprietary data processing algorithms.

At the AQMesh factory, a custom-built mobile enclosure houses climate-controlled reference/equivalence analysers sampling air from an ambient ‘cage’ which can hold up to 100 AQMesh pods at a time. As well as sensor characterisation, this allows pod-to-pod precision to also be evaluated at the same time. The reference equipment includes Thermo Scientific 42i for NO, NO2 and NOx, Thermo Scientific 43i for SO2, Ecotech Serinus 10 for O3, Ecotech Serinus 30 for CO as well as the industry standard FIDAS 200 for PM1, PM2.5, PM4 and PM10. The enclosure is maintained at a constant, consistent temperature of 18 +/-2 degrees centigrade all year round, and all analysers are serviced regularly and calibrated themselves before each sensor characterisation batch.

Since 2015, the electrochemical sensors used in AQMesh have gone through this ambient characterisation during manufacture as part of the stringent AQMesh quality assurance process, which also includes strict criteria for particulate matter (PM). This means every AQMesh pod out in the field to date has been through specific quality control measures to ensure the efficiency and reliability of each sensor in real-world conditions.

Access to their own reference station, and the ongoing development of AQMesh since it first commercially launched in 2012, has also enabled the team to continually review the product’s long-term performance. Baseline stability of AQMesh’s electrochemical sensors has been proven over many years of independent global co-location trials against certified reference equipment.

Another benefit that AQMesh brings to the table is its low cost of ownership, as pods require little to no ongoing maintenance – it is simply recommended that the electrochemical sensors are replaced as standard every two years. And those sensors will have, of course, undergone the same thorough characterisation and quality control as the ones each pod first came with.

This combination of long-standing factory “calibration”, extensive global co-location comparison field testing now spanning over eight years in real, ambient conditions across a range of environments and climates, and a number of other unique benefits means AQMesh is arguably the most reliable and accurate small sensor air quality monitoring system available on the market today.