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NML Established the Performance Verification on PM2.5 Analyzers and Sensors

Due to increasing air pollution, arising from industrialization and urbanization, our living environment suffers from multiple stationary and mobile pollutant sources.  Even though the government has set up air pollutant monitoring stations, the covered dimension and distribution areas are not sufficient to provide adequate information for the general public, for real-time monitoring and conduct timely preventive measures.  In recent years, community awareness and citizen engagement have prompt the utilization of “Low-Cost” air quality analyzers, equipped with multi-function sensors for particulate matter (PM) measurement and wireless communication, to be deployed in campuses and urban communities.  This trend has also boosted varies open-data platforms, “MAKERS” for data analysis and geospatial visualization in Taiwan.  One example is “LASS(Location Aware Sensing System)”; LASS(Location Aware Sensing System).  However, many problems remain to be dealt with, when coming to measurement accuracy and if the data are to be used for surveillance or control matters.  There are more than 5 000 units of “Low-Cost” air quality sensors distributed along west-coast cities and 39 countries in Taiwan.

Considering public needs and potential commercial development, Taiwan Environmental Protection Agency (EPA), with cooperation from Minister of Science and Technology (MOST), has entrusted NML as the certified body for “Testing and Verification Center for Air Quality Sensors”.  A four-year project has been awarded since 2017 for design and development of ‘out-door’ and ‘in-door’ test platforms.  The aim is to perform various testing protocols systematically of commercially available analyzers/sensors for their accuracy, data-validity, linearity, etc.

Two environmental conditions are provided for the evaluation platform, one is conducted in an outdoor atmosphere (field test), and the other is under well-controlled conditions (wind speed, temperature, relative humidity and PM2.5 concentration) in the laboratory.  The traceability concerning mass concentration for data collected by PM2.5 analyzers/sensors is achieved by comparison with USEPA Federal Reference Method (FRM).  A description of an in-door test chamber, in the form of a circulating wind-tunnel, is shown in Fig. 1 with its controlled parameters.

Two test setup are operational since early 2018, and the result initial observation is: at 25 °C 80 RH% in the laboratory test, a condition similar to common weather in Taiwan, the slope of linear regression of some analyzers/sensors could be higher than 2 while the slope is around 1 in field test, indicating potential bias in sensors setting due to different PM concentrations.  Furthermore, using KCl (Potassium chloride) as PM2.5 source, the accuracy could be varied while humidity increases.  It indicates that the chemical compositions of PM2.5 and humidity interference are the major causes of the performance of analyzers/sensors.  With this platform, NML anticipates that not only the performance/data validity of individual PM2.5 analyzers/sensor could be improved, but also the R&D output is beneficial to the entire air quality monitoring/control IoT network in Taiwan, and the general public.

Schematic diagram of an “in-door” air sensor test chamber 

Fig.1 Schematic diagram of an “in-door” air sensor test chamber.


  • Last Updated:2020/07/01
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