Measuring particulate matter (PM) accurately comes with a number of challenges, including effects from humidity and differing particle sizes. Technological considerations are also a factor, such as variable sample flow rates and the physical size and diameter of the sample path, which could affect the number of particles able to be measured.

AQMesh has been able to overcome many of these challenges through its proprietary OPC development, making it a robust, reliable and accurate solution for PM monitoring. From sample inlet to final data output, each design requirement for precise measurement of particles in ambient air has been carefully thought out to result in a truly bespoke and fit-for-purpose optical particle counter (OPC) – a solution that only AQMesh can offer. There are a few key aspects:-

Active sampling using a pump

By using a pump instead of a fan, the AQMesh OPC samples at a steady flow rate from the inlet to sensor, which provides a more consistent air sample than other methods used. Systems which use fans run the risk of creating vacuums, which can interrupt the flow rate and affect the sample measurement.

Laser-focused

A funnelled inlet helps the OPC taper the particle samples to a focal point, and then a straight line sample path from this focal point to the laser bench means larger particles are not ‘stuck’ in a bend and ensures all particles within the sample pass through the laser path, allowing for complete capture of particles, categorised by diameter from 0.3 – 30um. This means the laser OPC in AQMesh gives a true PM10 measurement, which many systems – including nephelometers – cannot offer.

Heating the sample to reduce deliquescence

The optional heated inlet allows AQMesh to reduce the effects of humidity on particle sizes. Known as deliquescence, this effect can make particles larger in diameter due to the absorption of moisture. The heated inlet overcomes this by drying the sample as it is drawn in, bringing the particles back down to their true size and therefore resulting in more accurate measurement. Additionally, AQMesh can detect when deliquescence is likely to have happened during data processing and can ‘flag’ the data point – including with non-heated samples – allowing it to be easily identified and redacted. Use of the heated inlet results in less than 1% of data points being flagged in this way.

Autonomous power for uninterrupted sampling

Using AQMesh’s bespoke smart solar pack for autonomous power allows for uninterrupted PM monitoring, with no need to change the sampling regime to take fewer readings – a process which could potentially void an instrument’s MCERTS certification. The AQMesh solar pack provides consistent, smooth power all year round for AQMesh pods.

Minimal maintenance

Other benefits of the AQMesh OPC include reduced maintenance – there is no need to change any filters, and there is no need to replace the whole OPC unit when it requires servicing. We simply advise the pump and laser is replaced every two years, which can be carried out by the user without returning the instrument to factory. Exceedance alerts can also be set for PM fractions, alongside any other pollutants being measured, which enable users to receive immediate information if levels breach a user-defined level over a user-defined period.

MCERTS indicative

AQMesh has been accurately measuring PM for over 10 years, and offers the added reassurance of MCERTS Indicative measurements for PM2.5 and PM10.

For more information on how AQMesh can support your PM monitoring requirements, contact our experienced team today.

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.

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.