Mapping urban air quality in near real-time using observations from low-cost sensors and model information

• Published in: Environment international Vol. 106; pp. 234 - 247
• Main Authors: Schneider, Philipp, Castell, Nuria, Vogt, Matthias, Dauge, Franck R., Lahoz, William A., Bartonova, Alena
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier Ltd 01.09.2017; Elsevier
• Subjects: Air Pollutants - analysis; air pollution; Air Pollution - analysis; Air quality; Cities; Crowdsourcing; data collection; Environmental Monitoring - methods; geostatistics; instrumentation; Low-cost microsensors; Mapping; Models, Theoretical; monitoring; Nitrogen dioxide; Nitrogen Dioxide - analysis; Norway; space and time; uncertainty; Urban air quality; urban areas; Norway; Urban air quality; Crowdsourcing; Air quality; Mapping; Low-cost microsensors; Nitrogen dioxide
• DOI: 10.1016/j.envint.2017.05.005
• ISSN: 0160-4120; 1873-6750

The recent emergence of low-cost microsensors measuring various air pollutants has significant potential for carrying out high-resolution mapping of air quality in the urban environment. However, the data obtained by such sensors are generally less reliable than that from standard equipment and they are subject to significant data gaps in both space and time. In order to overcome this issue, we present here a data fusion method based on geostatistics that allows for merging observations of air quality from a network of low-cost sensors with spatial information from an urban-scale air quality model. The performance of the methodology is evaluated for nitrogen dioxide in Oslo, Norway, using both simulated datasets and real-world measurements from a low-cost sensor network for January 2016. The results indicate that the method is capable of producing realistic hourly concentration fields of urban nitrogen dioxide that inherit the spatial patterns from the model and adjust the prior values using the information from the sensor network. The accuracy of the data fusion method is dependent on various factors including the total number of observations, their spatial distribution, their uncertainty (both in terms of systematic biases and random errors), as well as the ability of the model to provide realistic spatial patterns of urban air pollution. A validation against official data from air quality monitoring stations equipped with reference instrumentation indicates that the data fusion method is capable of reproducing city-wide averaged official values with an R2 of 0.89 and a root mean squared error of 14.3 μg m−3. It is further capable of reproducing the typical daily cycles of nitrogen dioxide. Overall, the results indicate that the method provides a robust way of extracting useful information from uncertain sensor data using only a time-invariant model dataset and the knowledge contained within an entire sensor network. •A method is presented to map urban air quality in real time with low-cost sensors.•The method merges low-cost sensor data with time-invariant model output.•Resulting maps exhibit realistic spatial patterns of urban air pollution.•Comparison against station data shows good replication of temporal daily cycle.•Validation indicates an R2 value of 0.89 against reference observations.