Measuring CO2 to optimise bulk storage of food.


Meeting the food requirements of a growing global population is becoming increasingly difficult. Despite the need for additional food, it is estimated that 50-60% of grain is lost after harvesting, at a cost of about $1 trillion per year. (See note 1 below)

One of the major reasons for lost grain is spoilage due to mould or insect infestation during storage.2 To provide a constant supply of grain year-round, after grains are harvested they are often kept in long term storage. Maintaining the quality of stored grain is crucial, both to ensure the quality of the final food products, and to prevent economic losses for farmers.

Edinburgh Sensors GascardNG Sensor

Insects and moulds can grow in stored grain, and their ability to flourish depends on the temperature and moisture of the stored grain. Moulds are the most common cause of grain spoilage and can cause changes in the appearance and quality of stored grains. Some moulds can release toxic chemicals called mycotoxins which can suppress the immune system, reduce nutrient absorption, cause cancer, and even be lethal in high doses. It is therefore crucially important to prevent the presence of mycotoxins in food products.2

Monitoring Stored Grain
Farmers are advised to check their stored grain weekly for signs of spoilage.3 Traditionally, grains are checked visually and by odour. Grain sampling can allow earlier detection of insects and moulds, but these methods can be tedious and time-consuming. Rapid, simple methods are needed for early detection of spoilage and to prevent grain losses.2

When moulds and insects grow, and respire, they produce CO2, moisture and heat. Temperature sensors detect increases in temperature caused by mould growth or insect infestation, therefore indicating the presence of grain spoilage. However, they are not able to detect temperature increases caused by infestation unless the infestation is within a few meters of the sensors. CO2 sensors can detect the CO2 produced by moulds and insects during respiration. As the CO2 gas moves with air currents, CO2 sensors can detect infestations that are located further away from the sensor than temperature sensors. CO2 measurements are therefore an important part of the toolkit needed to monitor stored grain quality.2

Using CO2 Measurements to Detect Spoilage
CO2 monitoring can be used for early detection of spoilage in stored grains, and to monitor the quality of stored grains. Safe grain storage usually results in CO2 concentrations below 600 ppm, while concentrations of 600-1500 ppm indicate the onset of mould growth. CO2 concentrations above 1500 ppm indicate severe infestations and could represent the presence of mycotoxins.4

CO2 measurements can be taken easily, quickly and can detect infestations 3-5 weeks earlier than temperature monitoring. Once spoilage is detected, the manager of the storage facility can address the problem by aerating, turning, or selling the grain. Furthermore, CO2 measurements can aid in deciding which storage structure should be unloaded first.2

Research published by Purdue University and Kansas State University have confirmed that high CO2 levels detected by stationary and portable devices are associated with high levels of spoilage and the presence of mycotoxins.4,5 Furthermore, they compared the ability of temperature sensors and CO2 sensors in a storage unit filled with grain to detect the presence of a simulated ‘hot spot’ created using a water drip to encourage mould growth.

The CO2 concentration in the headspace of the storage unit showed a strong correlation with the temperature at the core of the hot spot, and the CO2 sensors were, therefore, able to detect biological activity. The temperature sensors were not able to detect the mould growth, despite being placed within 0.3-1 m of the hotspot.6

To enable efficient monitoring of grain spoilage accurate, reliable and simple to use CO2 detectors are required. Gascard NG Gas Detector from Edinburgh Sensors provide accurate CO2 measurements along with atmospheric data, enabling grain storage managers to make decisions with confidence.

The Gascard NG Gas Detector uses a proprietary dual wavelength infrared sensor to enable the long term, reliable measurement of CO2 over a wide range of concentrations and in temperatures ranging from 0-45 °C. Measurements are unaffected by humidity (0-95% relative humidity) and the onboard pressure and temperature sensors provide real-time environmental compensation, resulting in the most accurate CO2 concentration readings.

Easy, fast, and accurate CO2 concentration monitoring during grain storage can provide early detection of grain spoilage, resulting in reduced grain losses, higher quality stored grain, and lower mycotoxin levels. CO2 monitoring could save millions of dollars annually in the grain production industry.4


  1. Kumar D, Kalita P, Reducing Postharvest Losses during Storage of Grain Crops to Strengthen Food Security in Developing Countries. Foods 6(1):8, 2017.
  2. Accessed May 25th, 2017.
  3. HGCA Grain storage guide for cereals and oilseeds, third edition, available from: Accessed May 25th, 2017.
  4. Maier DE, Channaiah LH, Martinez-Kawas, A, Lawrence JS, Chaves EV, Coradi PC, Fromme GA, Monitoring carbon dioxide concentration for early detection of spoilage in stored grain. Proceedings of the 10th International Working Conference on Stored Product Protection, 425, 2010.
  5. Maier DE, Hulasare R, Qian B, Armstrong P, Monitoring carbon dioxide levels for early detection of spoilage and pests in stored grain. Proceedings of the 9th International Working Conference on Stored Product Protection PS10-6160, 2006.
  6. Ileleji KE, Maier DE, Bhat C, Woloshuk CP, Detection of a Developing Hot Spot in Stored Corn with a CO2 Sensor. Applied Engineering in Agriculture 22(2):275-289, 2006.



The ‘ins and outs’ of air quality monitoring!

The British National Institute for Health and Care Excellence (NICE) recently issued draft guidance on ‘Air pollution – outdoor air quality and health.’ 

Here, Jim Mills, Managing Director of Air Monitors Ltd, explains why there will need to be more funding for monitoring if the mitigation measures mentioned in the guidance are to be implemented effectively. Jim also highlights the close relationship between outdoor air quality and the (often ignored) problems with indoor air quality.

The NICE guidelines are being developed for Local Authority staff working in: transport, planning, air quality management and public health. The guidance is also relevant for staff in healthcare, employers, education professionals and the general public.

Covering road-traffic-related air pollution and its links to ill health, the guidelines aim to improve air quality and so prevent a range of health conditions and deaths. Unfortunately, on the day that the draft guideline was published, most of the national media focused on one relatively minor recommendation relating to speed bumps. ‘Where physical measures are needed to reduce speed, such as humps and bumps, ensure they are designed to minimise sharp decelerations and consequent accelerations.’ Measures to encourage ‘smooth driving’ are outlined; however, the guidelines also address a wide range of other issues, which, in combination, would help tackle urban air pollution.

Public sector transport services should implement measures to reduce emissions, but this is an area that could involve the greatest financial cost.

Many local authorities would doubtless comment that they are already implementing many of the guideline recommendations, but refer to budgetary constraints on issues that involve upfront costs. This issue was raised on BBC Radio 4 when the issue was discussed on 1st December.

AQMesh Pod

AQMesh Pod

The NICE guidelines recommend the inclusion of air quality issues in new developments to ensure that facilities such as schools, nurseries and retirement homes are located in areas where pollution levels will be low. LAs are also urged to consider ways to mitigate road-traffic-related air pollution and consider using the Community Infrastructure Levy for air quality monitoring. There are also calls for information on air quality to be made more readily available.

LAs are also being urged to consider introducing clean air zones including progressive targets to reduce pollutant levels below the EU limits, and where traffic congestion contributes to poor air quality, consideration should be given to a congestion charging zone. The guidelines also highlight the importance of monitoring to measure the effects of these initiatives.

As part of the consultation process, NICE is looking for evidence of successful measures and specifically rules out “studies which rely exclusively on modelling.”

In summary, all of the initiatives referred to in the NICE report necessitate monitoring in order to be able to measure their effectiveness. However, most LAs do not currently possess the monitoring capability to do so. This is because localised monitoring would be necessary before and after the implementation of any initiative. Such monitoring would need to be continuous, accurate and web-enabled so that air pollution can be monitored in real-time. AQMesh is therefore the ideal solution; small, lightweight, quick and easy to install, these air quality monitors are able to monitor all the main pollutants, including particulates, simultaneously, delivering accurate data wirelessly via the internet.

Whilst AQMesh ‘pods’ are very significantly lower in cost both to buy and to run than traditional reference stations, they still represent a ‘new’ cost. However any additional costs are trivial in comparison with the costs associated with the adverse health effects caused by poor air quality, as evidenced in the recent report from the Royal College of Physicians.

Inside Out or Outside In?

Fidas® Frog

Fidas® Frog

The effects of air pollution are finally becoming better known, but almost all of the publicity focuses on outdoor air pollution. In contrast, indoor air quality is rarely in the media, except following occasional cases of Carbon Monoxide poisoning or when ‘worker lethargy’ or ‘sick building syndrome’ are addressed. However, it is important to understand the relationship between outdoor air quality and indoor air quality. Air Monitors is currently involved in a number of projects in which air quality monitoring is being undertaken both outside and inside large buildings, and the results have been extremely interesting.

Poorly ventilated offices tend to suffer from increased Carbon Dioxide as the working day progresses, leading to worker lethargy. In many cases HVAC systems bring in ‘fresh’ air to address this issue, but if that fresh air is in a town or city, it is likely to be polluted – possibly from particulates if it is not sufficiently filtered and most likely from Nitrogen Dioxide. Ventilating with outdoor air from street level is most likely to bring air pollution into the office, so many inlets are located at roof level. However, data from recent studies indicate that the height of the best air quality can vary according to the weather conditions, so it is necessary to utilise a ‘smart’ system that monitors air quality at different levels outside the building, whilst also monitoring at a variety of locations inside the building. Real-time data from a smart monitoring network then informs the HVAC control system, which should have the ability to draw air from different inlets if available and to decide on ventilation rates depending on the prevailing air quality at the inlets. This allows the optimisation of the internal CO2, temperature and humidity whilst minimising the amount of external pollutants brought into the indoor space. In circumstances where the outside air may be too polluted to be used to ventilate, it can be pre-cleaned by scrubbing the pollutant gases in the air handling system before being introduced inside the building.

Fidas200The implementation of smart monitoring and control systems for buildings is now possible thanks to advances in communications and monitoring technology. AQMesh pods can be quickly and easily installed at various heights outside buildings and further units can be deployed internally; all feeding near-live data to a central control system.

Another example of indoor air quality monitoring instrumentation developing from outdoor technology is the ‘Fidas Frog,’ a new fine dust aerosol spectrometer developed by the German company Palas. The Frog is an indoor, wireless, battery-powered version of the hugely popular, TÜV and MCERTS certified Fidas 200. Both instruments provide simultaneous determination of PM fractions, particle number and particle size distribution, including the particle size ranges PM1, PM2.5, PM4, PM10 and TSP.

Evidence of outdoor air pollution contaminating indoor air can be obtained with the latest Black Carbon monitors that can distinguish between the different optical signatures of combustion sources such as diesel, biomass, and tobacco. The new microAeth® MA200 for example, is a compact, real-time, wearable (400g) Black Carbon monitor with built-in pump, flow control, data storage, and battery with onboard GPS and satellite time synchronisation. Samples are collected on an internal filter tape and wireless communications are provided for network or smartphone app integration and connection to other wireless sensors. The MA200 is able to monitor continuously for 2-3 weeks. Alternatively, with a greater battery capacity, the MA300 is able to provide 3-12 months of continuous measurements.

In summary, a complete picture of indoor air quality can be delivered by a combination of AQMesh for gases, the Palas Frog for particulates and the microAeth instruments for Black Carbon. All of these instruments are compact, battery-powered, and operate wirelessly, but most importantly, they provide both air quality data AND information on the likely source of any contamination, so that the indoor effects of outdoor pollution can be attributed correctly.

@airmonitors #Environment #PAuto @_Enviro_News

Analyzer underpins growth of container inspection company.


After a career as a customs officer in the Netherlands, Wim van Tienen was well aware of the toxic gas hazards presented by some freight containers, so in 2009 he started a company, Van Tienen Milieuadvies B.V., offering gas analysis and safety advice. The company grew quickly and now employs 23 staff. Wim attributes a large part of this success to the advanced FTIR gas detection and analysis technology upon which the company’s services depend.


Wim van Tienen

Wim van Tienen

It has been estimated that there are more than 17 million shipping containers in the world, and at any time about one third of them are on ships, trucks, and trains. Over a single year, the total number of container trips has been estimated to be around 200 million.

The air quality inside containers varies enormously, depending on the goods, the packing materials, transit time, temperature, humidity and the possible presence of fumigants. Consequently, many containers contain dangerous levels of toxic gases and represent a major threat to port and transport workers, customs officials, warehousemen, store employees and consumers. It is therefore essential that risks are assessed effectively before entry is permitted.

Solvent vapours and most fumigants, whilst harmful, can be detected by the human nose, but Wim says: “Some gases are odourless and some have a high odour detection threshold, which means that you can only smell the substance in high concentrations; ethylene oxide for example, is commonly used as a sterilant in relation to medical devices. It is extremely toxic and has a low TLV limit of 0,5 ppm. However the odour threshold limit of ethylene oxide is 500 ppm, so detection with instrumentation is essential.”

The wide variety of potential contaminants represents a technological challenge to those responsible for testing, because if testers seek to detect specific gases, they risk failing to detect other compounds. It is also not practical to test every single container, so logical procedures must be established in order to minimise risks.

Gas Detection and Measurement
In 2009, when Wim first established the company, container gas detection was carried out with traditional field measurement techniques (gas detection sensors and tubes). “This approach was complicated, costly and time-consuming, and it was impossible to cover all risks,” he says. “With sensors and tubes, only a limited number of compounds can be measured specifically. Furthermore, the accuracy of detection tubes is poor and they can suffer from cross-sensitive reactions by interfering substances.

“Technologies such as PID-detectors respond to a wide variety of organic compounds, but they are not selective and unable to detect commonly found substances with high ionisation potentials such as 1,2-dichloroethane and formaldehyde.” Wim does not, therefore, believe that traditional measurement techniques are the best approach for covering all risks. “In order to test for the most common gases, it would be necessary to utilise a large number of tubes for every container, but this would still risk failing to detect other compounds and would be very expensive.

“It is possible to speciate organic compounds when using a Gas Chromatograph, but the number of compounds that can be tested is limited, and the use of a GC necessitates frequent calibration with expensive standard gases.”

Simultaneous multigas analysis
As a result of the problems associated with traditional gas detection techniques, Wim was keen to find an alternative technology and in 2013 he became aware of portable FTIR multigas analyzers from the Finnish company Gasmet Technologies. “The Gasmet DX4040 appeared to be the answer to our prayers,” Wim says. “The instrument is able to both detect and measure hundreds of compounds simultaneously; with this technique all inventoried high risk substances, such as ethylene oxide and formaldehyde, are always measured in real-time.

“With the help of Peter Broersma from Gasmet’s distributor Reaktie, a special library of over 300 gases was developed for our container monitoring application, and 8 Gasmet DX4040 FTIR instruments are now employed by our team of gas testing specialists.”

The major advantage of the Gasmet FTIR analyzers is the simultaneous multigas analysis capability. However Wim says: “Our testing work is now much faster, efficient and cost-effective, not least because the analyzers are small, lightweight, relatively simple to run, and no calibration is required other than a quick daily zero check with Nitrogen.”

Van Tienen Milieuadvies also employs a fully trained and highly qualified chemist, Tim Gielen, who is able to conduct in-depth analysis of recorded FTIR spectra when necessary. This may involve comparing results with Nist reference spectra for over 5000 compounds.

Most of the gases that are detected and measured by FTIR analyzers are cargo related. Wim says: “Off-gassing during shipment is the greatest problem, producing VOCs such as Toluene, Xylenes, MEK, 1,2 dichloroethane, blowing agents such as isopentane, and butanes from the packing materials and products.

“Formaldehyde, which evaporates from glued pallets, is most commonly found. On the other hand, less frequently found fumigants, such as sulfuryl difluoride and hydrogen cyanide are also always monitored with our FTIR analyzers.”

Container management
The need for container gas testing is driven by employers’ duty of care for employees, which is embedded in international health and safety regulations. Companies receiving containers must investigate whether employees that open or enter containers, may be exposed to the dangers of suffocation, intoxication, poisoning, fire or explosion. In order for employers to protect staff from these hazards, a risk assessment is necessary, coupled with an effective plan to categorise and monitor container flows. “This is how we develop an effective testing strategy,” Wim explains. “If a flow of containers from the same source containing the same goods and packing materials is found to be safe, the number of containers being tested within that flow can be reduced. Similarly, if toxic gases are identified regularly in a container flow, the frequency of testing will be increased.”

Once a container has been found to contain toxic levels of a gas or gases, it is necessary for that container to be ‘de-gassed’ which is a service that Van Tienen Milieuadvies provides. The process involves fitting a powerful ventilator to the door and capturing the gases with activated carbon. Once degassing is complete, it is important that the container is unloaded promptly, because the gases involved will re-accumulate quickly in a closed container, resulting in the need for repeat testing.

With the benefit of many years of experience, Wim estimates that around 10% of containers contain toxic gases. “This means that hundreds of thousands of containers are travelling the world, representing a major risk to anyone that might enter or open them, so it is vital that effective testing strategies are in place wherever that risk exists.”

“FTIR gas analysis has benefited this work enormously. For us, the main advantages are speed and peace of mind – we are now able to test more containers per day, and by testing for such a large number of target compounds, we are able to dramatically lower the risks to staff. The speed with which we are now able to test containers, coupled with the negligible requirement for service, calibration and consumables, means that the ongoing cost of monitoring is minimal.

“Van Tienen combines the Gasmet DX4040 measurements with risk analysis, which provides the best protection for staff responsible for opening containers. We have LRQA certification for the procedures that we have developed to demonstrate compliance with occupational health and safety legislation.

“Risk analysis provides cost reduction for our clients, due to the fact that measurement frequencies in safe flows can be reduced significantly. Root cause analysis is also part of our risk analysis.”

Looking forward Wim believes that the use of Gasmet FTIR will expand rapidly around the world as the risks associated with containers become better understood, and as employers become more aware of the advantages of the technology.