Ambient Air Quality Measurement with Low-Cost Optical and Electrochemical Sensors: An Evaluation of Continuous Year-Long Operation

Abstract

Sensor technology is attractive to the public due to its availability and ease of use. However, its usage raises numerous questions. The general trustworthiness of sensor data is widely discussed, especially with regard to accuracy, precision, and long-term signal stability. The VSB-Technical University of Ostrava has operated an air quality sensor network for more than two years, and its large sets of valid results can help in understanding the limitations of sensory measurement. Monitoring is focused on the concentrations of dust particles, NO2, and ozone to verify the impact of newly planted greenery on the reduction in air pollution. The sensor network currently covers an open field on the outskirts of Ostrava, between Liberty Ironworks and the nearby ISKO1650 monitoring station, where some of the worst air pollution levels in the Czech Republic are regularly measured. In the future, trees should be allowed to grow over the sensors, enabling assessment of the green barrier effect on air pollution. As expected, the service life of the sensors varies from 1 to 3 years; therefore, checks are necessary both prior to the measurement and regularly during operation, verifying output stability and overall performance. Results of the PMx sensory measurements correlated well with the reference method. Concentration values measured by NO2 sensors correlated poorly with the reference method, although timeline plots of concentration changes were in accordance. We suggest that a comparison of timelines should be used for air quality evaluations, rather than particular values. The results showed that the sensor measurements are not yet suitable to replace the reference methods, and dense sensor networks proved useful and robust tools for indicative air quality measurements (AQM).

Determination of Hygroscopic Aerosol Growth Based on the OPC-N3 Counter

“…As stated in [16], previous studies report that Alphasense OPCs demonstrate strong correlations (R2 = 0.93-0.99) with PM10 in controlled laboratory investigations [17][18][19][20]. However, field-based studies have indicated relatively lower correlations (R2: 0.53-0.8) [21][22][23], primarily due to the variability in ambient meteorological conditions and fluctuations in PM compositions. More information on Alphasense OPC-N3 can be found in [24].…”

Can Air Quality Gas Sensors Be Used for Emission Monitoring of Small-Scale Local Air Pollution Sources? Pilot Test Evaluation

“…Field tests focused on sensor response and cross-sensitivity have been conducted with respect to intended use [7][8][9], but recently, questions arose as to whether such field-calibrated sensors can be relocated [10,11]. Taking into account the behavior of the used sensors from long-term AQM [12,13], we checked the sensors for changes in behavior, and differences in measured concentrations of larger than 20% detected during routine checking compared to the previous measurement periods were considered as a sign of excessive wear and end of service lifetime; thus, such sensors discarded and replaced with new ones.…”

Optimizing Urban Air Pollution Detection Systems

“…Data quality is influenced by atmospheric conditions, the concentration of the pollutants, and the time of day when measurements are taken. The factors influencing sensor measurements are described elsewhere [37,38].…”