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.
AQMesh has been used in a project at the Port of Kiel, Germany, to measure emissions of nitrous oxides (NOx) and fine particulate matter (PM) around its cruise ship terminal.
This year the port attracted 166 visits by 33 different cruise ships, bringing a record breaking 600,000 visitors into the city. Emissions from the cruise ship terminal and its impact on the local air quality has been in discussion for some time, as the city’s references stations indicate that nitrogen dioxide (NO2) levels regularly exceed the World Health Organisation’s annual mean limit of 40μg/m3.
The joint project with Eurofins and Olfasense, who combined AQMesh air quality monitors with the Ortelium dynamic atlas system, measured and studied levels of NO2 and PM at the cruise ship terminal over several months.
AQMesh pods, supplied by its German distributor Envilyse, measured NO, NO2, O3 alongside PM1, PM2.5 and PM10, as well as relative humidity, temperature and atmospheric pressure. After being co-located with passive samplers at the installation site to provide the greatest degree of accuracy, real time sensor data from the AQMesh pods was fed into Ortelium.
The Ortelium atlas allowed measurements from the AQMesh pod to be visualised in real time and, combined with meteorological data feeds, showed how the emission levels changed during arrival, berthing and departure of the cruise ships.
Data analysis from this study concluded the cruise ships could not be attributed to high levels of NO2. This is similar outcome to a study carried out at a UK airport, which concluded that local traffic was in fact more of an issue than the airport activity.
Plumes from shipping are notoriously difficult to detect and analyse from land, but AQMesh now has a carbon dioxide (CO2) sensor which allows a combustion plume to be detected from elevated CO2 levels. Pollutants can then be evaluated in this context.
AQMesh is in use at a variety of harbours and ports around the world including the UK, Italy, Norway, Netherlands, Germany and Vietnam. The pods can now monitor up to 6 gases using the latest generation of sensors, as well as PM1, PM2.5, PM10 and total particle count (TPC) with a light-scattering optical particle counter.
Recent co-location comparison trials against certified reference equipment continue to prove AQMesh performance and reliability for localised air quality monitoring.
Trials in the USA, UK and Western Europe this year have delivered high correlation coefficients (R2 values) for key pollutants such as nitrogen dioxide (NO2), ozone (O3) and fine particulate matter (PM2.5). An R2 value of 0.92 against reference for O3 was achieved in Southern USA over the Summer, as well as an R2 value of 0.94 against reference for NO2 in Northern USA during the cold season.
Co-location trials for AQMesh and field equivalent methods have been taking place globally for several years, with the results published on the AQMesh website, demonstrating how performance and accuracy continues to improve with each new version of the product. A number of independent studies have also been carried out, verifying the AQMesh system’s capability.
AQMesh is a small sensor air quality monitoring system for measuring pollutant gases and particles in ambient air. It is a flexible, quick to install and easy to use air quality monitor that can deliver localised, real-time readings, aiming to improve the spatial resolution, scope and accuracy of gathering air quality data.
Its range of wireless power options includes a recently improved smart solar panel, which is now larger than the previous and has a more efficient charge, allowing for year-round operation for standard gas and particulate AQMesh pods across Western Europe and regions on a similar latitude.
AQMesh pods can now monitor up to 6 gases out of NO, NO2, NOx, O3, CO, SO2, CO2 and H2S using the latest generation of sensors, as well as PM1, PM2.5, PM10 and total particle count (TPC) with a light-scattering optical particle counter. In addition to pollutants, AQMesh can measure noise, relative humidity, pod temperature and atmospheric pressure, all within a single compact unit. Data is completely secure on the AQMesh cloud server, only accessible by a secure login, which allows the user to manage their pods, view customisable graphical data, and download the data for further analysis.
AQMesh is currently in use throughout the world in a variety of air quality monitoring applications and projects, including smart city networks, indoor-outdoor air quality management, employee health and safety, traffic pollution mitigation studies and air quality modelling. Recent case studies show it forming part of a major ‘hyperlocal’ street-by-street monitoring system throughout London (UK), as well as being used in a similar project across 50 zip code areas in Minnesota (USA).
AQMesh has been measuring ozone (O3) using small sensors since 2011 and the readings from the latest generation electrochemical sensor, using AQMesh v4.2.3 processing, as compared to co-located certified reference readings, consistently show an R2 of over 0.9 with an accuracy ±10ppb (20µg/m3).
AQMesh pods have been measuring ozone levels around the world and co-location comparison studies show very good performance against reference equipment from the latest sensor and processing version. Ozone levels have been particularly high across Western Europe over this summer but are a regular concern in many parts of the world, including the USA. However, there are huge gaps between O3 monitoring points, to different degrees across the world, depending on monitoring equipment budgets. A lower cost small-sensor monitoring solution can provide valuable data within the areas currently lacking in this air quality information. Data validity is typically demonstrated by comparison with a local reference station, although AQMesh is also widely used where no reference data is available.
O3 at ground level is formed by reactions with nitrogen oxides (NOx) and volatile organic compounds (VOCs) from traffic and industrial emissions in the presence of sunlight. As such, hotter, sunnier weather can dramatically increase O3 pollution.
The World Health Organisation (WHO) currently states the daily limit of O3 levels to be 100μg/m3 over an 8-hour mean and advise that prolonged exposure to high levels of O3 can have severe effects on human health, including causing asthma, inflammation of the airways, reduced lung functionality and lung disease. Measuring O3 as a part of an air quality monitoring routine is therefore becoming increasingly important, especially in hotter climates and areas of increased VOC emissions.
O3 can be complicated to measure due to its high sensitivity to environmental conditions and cross-gas effects. Most small sensors for measuring O3 are either electrochemical or metal oxide, but electrochemical sensors (such as those used in AQMesh) have the advantage of low power requirements and can therefore be installed more flexibly. AQMesh pods are compact, wireless units and are available with a variety of power options, including solar panels, which allow them to be installed exactly where monitoring needs to take place.
During summer 2018 AQMesh has been measuring ozone at hundreds of locations across five continents and co-location comparisons show consistently high levels of accuracy. To quote two of many such studies, in an industrial region of the USA, AQMesh O3 measurements compared to FEM gave an R2 of 0.97, and in a similar comparison study in Western Europe the R2 value for O3 was 0.95. AQMesh pods measuring gases can run continuously for over two years using a battery but other power options are available, including solar. Particulate matter (TPC, PM1, PM2.5, PM10) can also monitored with an AQMesh pod, alongside gases including NO, NO2, O3, CO, SO2, CO2 and H2S, as well as pod temperature, RH% and pressure.
The accuracy of AQMesh readings has been proven through an extensive series of global co-location comparison trials and is the proven, commercially available low-cost air quality monitoring system for both pollutant gases and particulate matter, as well as simultaneously monitoring a range of environmental conditions.
AQMesh is now able to offer CO2 and H2S within its range of gas options for local air pollution monitoring.
The NDIR CO2 sensor, which can be offered within a single AQMesh pod alongside five other gases out of NO, NO2, O3, CO, SO2 or H2S, as well as PM1, PM2.5, PM10, temperature, pressure and humidity, has been developed to deliver a higher performance than those typically used for indoor air quality monitoring. It has been rigorously tested against Picarro reference equipment, resulting in an R2 value of 0.93. Pod-to-pod correlation of over 20 AQMesh pods has shown R2 values of 0.98 and 0.99, and the sensor has a MAE (mean absolute error) of less than 20ppm.
In addition to monitoring deviations from ambient levels of CO2, elevated CO2 levels can indicate that monitoring is taking place in a combustion plume and levels of other gases can be interpreted accordingly. For example, the ratio of CO2 to the other pollutant gases present can indicate whether those gases were emitted by a local or distant source.
An additional electrochemical sensor has been introduced to offer H2S measurements. After integrating the sensor, measurements have been compared to readings from a Honeywell SPM Flex installed at a sewage treatment site with an R2 value of 0.87 over a measurement range of 0-150ppb. Particularly of interest to the oil and gas industry, in association with the SO2 monitoring already available on AQMesh, it can be used to measure emissions from sour gas and residual emissions from flaring operations.
AQMesh can measure up to 6 pollutant gases in various combinations, as well as particulate matter, humidity, atmospheric pressure and noise in one small, compact easy-to-install unit. There is a range of wireless power options, including lithium battery packs and solar panels, with information sent in near real-time to a secure server via cellular GPRS. Data can be accessed by a secure login or can be streamed via an API connection.
AQMesh pods are in use across the globe in a variety of indoor and outdoor air pollution monitoring applications, and are becoming increasingly popular in smart cities and networks. Pod performance has been proven through extensive testing in worldwide co-location comparison trials with reference equipment, which have delivered impressive and reliable correlation results.
A new paper published by the American Chemical Society (ACS Sensors) reviews the use of amperometric electrochemical gas sensors for monitoring inorganic gases that affect urban air quality. Written by John Saffell and Ronan Baron of Alphasense, the paper gives a full explanation of how the sensors work, how they have developed and a review of how they have been used. Key relevant studies are summarised as well as major studies using the sensors.
The paper mentions AQMesh as ‘the first provider of integrated air quality networks’ using the Alphasense sensors, and also refers to AQMesh correction algorithms (the authors consider data correction necessary) and the comparison field trials published regularly on the AQMesh website. University of Cambridge, Citi-Sense and IDAD projects, which used AQMesh, are mentioned: of the range of sensor systems submitted for the 2 week field comparisons trial in Aveiro, ‘The AQMesh unit achieved the highest correlation coefficient and the lowest mean absolute errors: R2 was 0.70 for O3, 0.89 for NO2, 0.86 for CO and 0.80 for NO. Other sensor boxes were unable to provide the same degree of correlation, possibly because of the lack of data correction for temperature variations.’
Recent co-location comparison trials using the latest AQMesh processing (v4.2.3) have further proven AQMesh performance with impressive R2 values in excess of O.8 and 0.9 for NO2 in Benelux, Slovakia and Spain.
Particulate matter (PM2.5) was also monitored throughout the Slovakia trial and delivered an R2 value of 0.98.
Correlation values for NO continue to be high throughout all AQMesh co-location trials, with results exceeding 0.9 in nearly all cases.
For more information on co-location trials and performance please contact us.
Leading small sensor air quality monitor, AQMesh, has recently been shown to work alongside passive samplers and air quality models, as well as complementing reference station networks. A recent study shows AQMesh calibration against diffusion tubes and two 2017 conferences have highlighted the potential of such systems used in an air quality network.
At the Dispersion Modellers User Group Meeting (DMUG, London, April 2017), CERC showed that the model optimisation of 7-day average NO2 concentrations using AQMesh readings as well as reference data affects concentration contours, giving a general reduction, but increase in some areas. The study shows the potential to achieve a higher level of local air quality accuracy from this combined approach.
The CERC study uses near real-time NO2 data from 20 AQMesh pods and 5 reference stations across Cambridge, UK over three months. The presentation acknowledged the potential from large networks of low cost sensors installed across a city: accuracy and reliability is generally lower than reference monitors, but larger spatial coverage is possible. The study addressed how these sensor data can best be used in modelling. See the full presentation here.
It is important to distinguish between small air quality sensors and sensor systems. The best sensor systems offer optimisation of sensor output through quality control, platform design and sensor output processing and correction for cross-gas effects and environmental effects. Teams which want to invest in similar air quality studies or city-wide monitoring projects can get a head start by using AQMesh – the most developed such system. See the Cambridge case study of latest AQMesh performance.
International air quality experts meeting at RIVM in the Netherlands in February reviewed a range of studies using small sensor systems to measure air pollution, particularly NO2 and particulate matter. Whilst highlighting the need for good characterisation of sensors and the pace of development of this new technology, discussions focused on how to make the best use of ‘low cost’ sensors.
Two speakers highlighted the ways in which a small sensor system can be characterised. The best method is by regularly co-locating with a reference station and comparing readings; another method is similar but one sensor system is co-located against reference and then moved around the other units to allow comparison. Other options include comparison with passive samplers or by comparing co-located sensor systems against each other.
AQMesh NO2, PM10 and PM2.5 readings from the Citi-Sense project (2015-16, AQMesh v3.5) – a superceded version of AQMesh without standard sensor quality control or characterisation – were compared with maps of reference data using data fusion and showed encouraging results. An even earlier AQMesh project in Asia (2014, AQMesh v3.0) compared source apportionment plots generated using reference data to those from co-located AQMesh pods and the conclusions to be drawn about pollution sources were the same.
AQMesh continues to build on years of global studies and continued development, offering the most ‘project-ready’ small sensor system which can be used in an air quality network – including reference stations, passive samplers and modelling – to proven effect. See more information about AQMesh performance and versions.
The AQMesh team has carried out a test which shows that calibration (scaling) of AQMesh against one, or ideally several, diffusion tubes, is a viable option when no local reference station is available.
When three AQMesh pods and four NO2 diffusion tubes were co-located against a reference station, the diffusion tube readings were so consistent with the reference average reading for the period that the diffusion tube average could be used to apply a slope correction to AQMesh data.
By careful management of the co-location phasing it is possible to record sufficient data points to also correct any offset.
Passive samplers for key pollutants such as NO2 are widely available and are often used to reach areas not covered by more expensive and bulky reference stations. Small sensor systems or so-called ‘low cost’ sensor systems can help to fill the data gap between reference real-time readings, passive sampling single average measurements and model output. Calibration of small sensors systems, such as AQMesh, against certified and validated measurements provides a trail of data validity.
An AQMesh pod used in the recent Citi-Sense project in Norway was returned to us at the end of the project, and we were surprised at the condition. Despite the damage, this robust little pod was still working perfectly, with data still being received.
AQMesh pods are able to measure up to 6 gases, including NO2 and CO2, particulate matter, noise and atmospheric conditions within a variety of environments – and it seems they can also possibly withstand significant damage.
For more reasons to choose AQMesh, click here.