Sensors for Air Quality Assessment

Dear Colleagues,

Environmental monitoring is, today, based on fixed-site measurement stations using advanced analytical equipment to achieve high data quality. However, such monitoring is associated with high costs for investment in equipment, as well as for quality control and maintenance. Therefore, only a limited number of stations are usually operated in routine monitoring programs, and often these programs only include measurements of pollutants that are directly required for testing compliance with guidelines. Many monitoring programs are supplemented by model calculations in order to better meet the requirements from the local population for obtaining information with personal relevance, i.e., about pollutant levels at their residence or in the streets where they commute. The limited number of monitoring stations means that the models may not be validated for all types of locations. For example, street stations usually include hot spots, i.e., the busiest street canyons, whereas streets with openings in the building face, substantial difference in building heights, or streets with only buildings on one side usually are not represented.

Supplementary networks based on low-cost sensors for gaseous as well as particulate pollutants have been established in many urban areas. Such networks may be fixed site, and/or include mobile measurements on individuals or on buses, trams, etc., in the urban area. Such measurements can supplement conventional measurement stations for mapping local pollution levels in the urban area, as well as for model validation. Moreover, they may also be highly valuable in data fusion or data assimilation where data are merged into model calculations to obtain better concentration surfaces, e.g., over an urban area, or to extend the pollutant spectrum.

In addition, recent developments in Sensor and Internet of Things technologies have led to the introduction of small, portable, low-cost gas and particle sensors into everyday life via smart phones (also with integrated temperature, humidity and pressure sensors), smart air conditioning and air purifying units (combined with temperature, humidity and CO₂ sensors), as well as a multiplicity of devices and applications that is growing continuously. This has led to a paradigm shift towards participatory environmental monitoring which has been fueled by citizen science initiatives.

However, in many cases, the data quality from low-cost sensor systems has not been tested before implementation and little or no calibration of the systems was performed. Thus, a lot of data of unknown quality is currently being generated and distributed, e.g., to local authorities, to the population and the media. In some cases, data is very far from describing the real world conditions, but the users cannot judge the quality from what is being reported. There is thus a considerable need for guidelines regarding test, validation and calibration of low-cost sensor based measurement devices, as well as recommendations regarding which type of sensors and systems are applicable for which pollutant, concentration range and location.

The Special Issue will cover a range of topics addressing modern sensor technologies, tests, validation and calibration as well as practical applications including multisensor integration, uses for model validation, data fusion and data assimilation, but also for supporting environmental information services and citizen science goals. The editors target high quality papers on the latest technological developments as well as examples of field studies using low-cost air pollution sensors of various types and for numerous applications in ambient, as well as indoor, environments.

Dr. Ole Hertel
Dr. Andreas Schütze
Dr. Kostas Karatzas
Guest Editors

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• Low-cost sensors
• System integration
• Data analysis
• Air pollution measurements
• Ambient air quality
• Exposure assessment
• Data fusion and data assimilation
• Air pollution mapping
• Environmental information services
• Citizen science