Measuring air pollution with low-cost sensors

Low-cost air quality sensors are attracting more and more attention. They offer air pollution monitoring at a lower cost than conventional methods, making air quality monitoring possible in many more locations. Too good to be true? At the current stage of development, unfortunately yes. Measurements by low-cost sensors are often of minor and questionable data quality than the results from official monitoring stations as carried out by EU Member States in accordance with European legislation and International standards. Sensors may become a game changer in monitoring air pollution, traffic-management, personal exposure and health assessment, citizen science and air quality assessment in developing countries. This brochure explains our current understanding of the advantages and disadvantages of sensors. Technological progress will hopefully change the picture of this summary of sensor performance in the next few years. It is also a plea to evaluate and validate sensors with field and laboratory tests in order to understand the meaning of and uncertainties in their signals.JRC.C.5-Air and Climat

Protocol of evaluation and calibration of low-cost gas sensors for the monitoring of air pollution

Metrology for Chemical Pollutants in Air (MACPoll) is a joint research project of the European Metrology Research Programme of EURAMET that among other activities deals with low-cost gas sensors for air quality monitoring. Gas sensors are identified as emerging measuring devices for “indicative measurements” regulated in the Air Quality Directive. Compared to reference measurements, gas sensors would allow air pollution monitoring at a lower cost. The Directive allows using indicative measurements without restriction in the zones where the upper assessment threshold (UAT) is not exceeded while they permit a reduction of 50 % of the minimum reference measurements where the UAT is exceeded. The Directive does not specify any indicative method but it requires to demonstrate that they can meet a data quality objective (DQO) that is about twice less stringent than the one of reference methods. The DQO is defined as a relative expanded uncertainty. Since the Directive does not give any guidance for this demonstration, within MACPoll it has been decided to draft a protocol for the evaluation of gas sensors.JRC.H.2-Air and Climat

Evaluation of low-cost sensors for air pollution monitoring: Effect of gaseous interfering compounds and meteorological conditions

In this report the performances of low-cost sensors for air pollution monitoring are evaluated in order to give guidance to users on which parameters to take into account when performing field calibration of these sensors prior to monitor air pollution with those. In particular, the effect of gaseous interfering compounds and meteorological conditions on four low cost sensors selected to be mounted on the AirSensEUR platform is characterised. The selected sensors are of the electrochemical type, as they are less power consuming and they have been shown, in previous studies, to lead to fastest response time and to suffer less from gaseous interferences than metal-oxide sensors. Ten set of four sensors for ozone (Membrapor O3/M-5), nitrogen dioxide (Alphasense NO2-B43F), carbon monoxide (Membrapor CO/MF-200) and nitrogen monoxide (Alphasense NO-B4) were evaluated under controlled conditions in a laboratory exposure chamber. The tests allow the evaluation of the interference of the gaseous compounds together with the effect of relative humidity, temperature and pressure variations. In general, each sensor was found to be highly linear when measuring its target gaseous species. Concerning the gaseous interferences, it appears that only the ozone sensors showed a high interference (> 75%) to nitrogen dioxide. The ozone filter of the NO2-B43F appears to be effective. The sensitivity of the CO and NO sensors was sufficient to be able to detect concentration levels expected at ambient gaseous concentrations. However, the interference of NO on the CO/MF-200 was found relevant at high NO and low CO values. The cross sensitivity (CO and NO on O3 and NO2 sensors and vice-versa) was found low or not significant for each type of sensor. The meteorological evaluation showed that the four types of sensor behave similarly concerning the temperature interference. In fact both sensors showed a quadratic response with the increase of the temperature. Relative humidity was only found relevant for the two Alphasense sensors (NO2-B43F and NO-B4) with a linear type of sensitivity associated with a clear hysteresis effect. Ambient pressure, however, was found relevant only for the two Membrapor sensors (O3/M-5 and CO/MF-200). Finally, the good reproducibility between sensors for the majority of effects including sensitivity to gas concentration and to meteorological variables with relative standard deviation within less than 10 % suggests that satisfactory calibration of sensors could be achieved without the need of a full characterisation of each sensor. By using calibration coefficient equal to the averages of the effects given in this report, reasonable calibration function could be established. This result is promising, allowing for future increase of the use of sensors for low cost for air pollution monitoring both by expert institutes and citizen science projects.JRC.C.5-Air and Climat

Review of low-cost sensors for the ambient air monitoring of benzene and other volatile organic compounds

This report presents a literature review of the state of the art of sensor based monitoring of air quality of benzene and other volatile organic compounds. Combined with information provided by stakeholders, manufacturers and literature, the review considered commercially available sensors, including, PID based sensors, semiconductor (resistive gas sensor) and portable on-line measuring devices (sensor arrays). The bibliographic collection includes the following topics: sensor description, field of application in fixed, mobile, indoor and ambient air monitoring, range of concentration levels and limit of detection in air, model descriptions of the phenomena involved in the sensor detection process, gaseous interference selectivity of sensors in complex VOC matrix, validation data in lab experiments and under field conditions.JRC.C.5-Air and Climat

Performance Evaluation of Low-Cost BTEX Sensors and Devices within the EURAMET Key-VOCs Project

The KEY-VOCs project is a EURAMET joint research project focused on key Volatile Organic Compounds (VOCs) in air. One of its activities is the evaluation of sensors-based measurement systems. In Europe, the monitoring of benzene in ambient air is mandatory as set by the European Directive for air quality (AQD) [1]. This Directive states that the reference method of measurement shall consist of active or on-line sampling followed by gas chromatography [2]. These methods are time consuming, expensive to implement and not easily portable prohibiting more local estimation of the population exposure. However, the AQD allows using indicative measurements with higher uncertainty than those of the reference methods. Sensor systems are good candidates for indicative methods with the additional ability of near-to real-time measurements

Review of Portable and Low-Cost Sensors for the Ambient Air Monitoring of Benzene and Other Volatile Organic Compounds

This article presents a literature review of sensors for the monitoring of benzene in ambient air and other volatile organic compounds. Combined with information provided by stakeholders, manufacturers and literature, the review considers commercially available sensors, including PID-based sensors, semiconductor (resistive gas sensors) and portable on-line measuring devices as for example sensor arrays. The bibliographic collection includes the following topics: sensor description, field of application at fixed sites, indoor and ambient air monitoring, range of concentration levels and limit of detection in air, model descriptions of the phenomena involved in the sensor detection process, gaseous interference selectivity of sensors in complex VOC matrix, validation data in lab experiments and under field conditions

Next Generation Air Quality Platform: Openness and Interoperability for the Internet of Things

The widespread diffusion of sensors, mobile devices, social media, and open data are reconfiguring the way data underpinning policy and science are being produced and consumed. This in turn is creating both opportunities and challenges for policy-making and science. There can be major benefits from the deployment of the IoT in smart cities and environmental monitoring, but to realize such benefits, and reduce potential risks, there is an urgent need to address current limitations including the interoperability of sensors, data quality, security of access, and new methods for spatio-temporal analysis. Within this context, the manuscript provides an overview of the AirSensEUR project, which establishes an affordable open software/hardware multi-sensor platform, which is nonetheless able to monitor air pollution at low concentration levels. AirSensEUR is described from the perspective of interoperable data management with emphasis on possible use case scenarios, where reliable and timely air quality data would be essential.JRC.H.6-Digital Earth and Reference Dat

Review of Portable and Low-Cost Sensors for the Ambient Air Monitoring of Benzene and Other Volatile Organic Compounds

This article presents a literature review of sensors for the monitoring of benzene in ambient air and other volatile organic compounds. Combined with information provided by stakeholders, manufacturers and literature, the review considers commercially available sensors, including PID-based sensors, semiconductor (resistive gas sensors) and portable on-line measuring devices as for example sensor arrays. The bibliographic collection includes the following topics: sensor description, field of application at fixed sites, indoor and ambient air monitoring, range of concentration levels and limit of detection in air, model descriptions of the phenomena involved in the sensor detection process, gaseous interference selectivity of sensors in complex VOC matrix, validation data in lab experiments and under field conditions

Microsystèmes capteurs de gaz sélectifs au dioxyde d'azote associant structures semi-conducteurs et filtres chimiques (indigo ou/et nanomatériaux carbonés) destinés au contrôle de la qualité de l'air

This work is devoted to the study and the development of gas sensors microsystems highly selective to nitrogen dioxide, dedicated to the air quality control. The strategy developed consists in the implementation of a sensitive structure based on semiconductor materials partially selective to oxidizing gases associated to an ozone selective filter. The first objective is the development of chemical filters strictly impervious to ozone (O3) and non-reactive towards the nitrogen dioxide (NO2). We have chosen a molecular material, indigo, well-known for its reactivity towards O3, and several carbonaceous nanomaterials. For these one, the possibility to modify their textures, their morphologies and their surface chemistries by chemical, mechanical and thermic treatments, enables us to extend the range of potential materials and to identify the factors of influence on their reactivity with gaseous species. The characterization of all these materials required the use of appropriate and complementary techniques (N2 adsorption at 77 K, Raman, XPS, IR in ATR mode, EPR and NEXAFS). The more efficient filters (high filtering yield and life-time) have been selected by means of specific tests of gas exposure. Finally, the association of the best filter and the sensitive structure has led to the development of optimized gas sensors microsystems prototypes.Ce manuscrit est consacré à l’étude et au développement de microsystèmes capteurs de gaz sélectifs au dioxyde d’azote, destinés au contrôle de la qualité de l’air atmosphérique. La stratégie que nous avons développée consiste à associer une structure sensible à base de matériaux semi-conducteurs partiellement sélectifs aux gaz oxydants et des filtres sélectifs à l’ozone. L’objectif premier est la mise en oeuvre et la caractérisation de matériaux chimiques strictement imperméables à l’ozone (O3) et non-réactifs vis-à-vis du dioxyde d’azote (NO2). Notre choix s’est focalisé sur un matériau moléculaire, l’indigo, connu pour sa réactivité vis-à-vis de O3, et plusieurs nanomatériaux carbonés. Pour ces derniers, la possibilité de conformer leurs textures, leurs morphologies et leurs chimies de surface par traitements thermiques, chimiques et mécaniques, permet d’étendre le panel de matériaux potentiels et d’identifier les facteurs d’influence de leur réactivité avec les espèces gazeuses. La caractérisation de l’ensemble de ces matériaux a nécessité l’utilisation de techniques adaptées et complémentaires (adsorption de N2 à 77 K, spectroscopies Raman, XPS, IR en mode ATR, RPE et NEXAFS). Les filtres chimiques les plus efficaces (hauts rendements de filtration et grande durabilité) ont été sélectionnés d’après des tests de soumission aux gaz selon une méthodologie adaptée. Enfin, l’association de ces meilleurs filtres et de la structure capteur a conduit à l’élaboration de prototypes microsystèmes capteurs de gaz optimisés. De plus, une contribution à la compréhension des mécanismes d’interaction de l’indigo et de certains nanocarbones avec O3 et NO2 a aussi permis d’améliorer le microsystème en développant des méthodologies pertinentes et innovantes mais également en réalisant la synthèse de nouveaux filtres indigo / nanocarbone

Performance Evaluation of Low-Cost BTEX Sensors and Devices within the EURAMET Key-VOCs Project

The KEY-VOCs project is a EURAMET joint research project focused on key Volatile Organic Compounds (VOCs) in air. One of its activities is the evaluation of sensors-based measurement systems. In Europe, the monitoring of benzene in ambient air is mandatory as set by the European Directive for air quality (AQD) [1]. This Directive states that the reference method of measurement shall consist of active or on-line sampling followed by gas chromatography [2]. These methods are time consuming, expensive to implement and not easily portable prohibiting more local estimation of the population exposure. However, the AQD allows using indicative measurements with higher uncertainty than those of the reference methods. Sensor systems are good candidates for indicative methods with the additional ability of near-to real-time measurements