Validation of low-cost sensor measurements in urban territory for air pollution monitoring. Riga city example

Low-cost sensors, either electrochemical, optical or light scatter based and piezoelectric, due to low price and performance explainability are becoming more available for monitoring, studying and explaining urban air quality. This paper explores low-cost sensor technology applicability for air quality measurements in urban territory. At least two month long monitoring campaigns were conducted during summer 2018 in Riga (Latvia). For validation purposes different monitoring sites were selected in order to assess influence of human activities, meteorological and morphological aspects, e.g. traffic flow and structure, street cleaning, architecture, accessibility of green zones. Site validation for sensor measurements was set up by parallel measurements of sensor outputs and reference measurements by OPSIS DOAS (Differential Optical Absorption Spectroscopy) for gaseous pollutants analysis and OPSIS SM200 beta attenuation particle gravimetric analyzer for particle measurements. Sensor matrix was set-up to measure carbon monoxide (CO), nitrogen dioxide (NO₂), sulphur dioxide (SO₂), ozone (O₃), particulate matter – PM₁₀, PM_2.5 and PM₁; additionally relative humidity and air temperature were measured. Obtained results show practical applicability of low-cost sensors for air pollution spatial and temporal assessment, sensors show moderate to high correlations with reference site within averaging of 1-hour and 24-hour periods, e.g. Pearson correlation factor for PM₁₀ varies from 0.63-0.76 accordingly (p < 0.01).