Abstract
Abstract. In many urban areas the population is exposed to elevated levels of air pollution. However, real-time air quality is usually only measured at few locations. These measurements provide a general picture of the state of the air, but they are unable to monitor local differences. New low-cost sensor technology is available for several years now, and has the potential to extend official monitoring networks significantly even though the current generation of sensors suffer from various technical issues. Citizen science experiments based on these sensors must be designed carefully to avoid generation of data which is of poor or even useless quality. This study explores the added value of the 2016 Urban AirQ campaign, which focused on measuring nitrogen dioxide (NO2) in Amsterdam, the Netherlands. Sixteen low-cost air quality sensor devices were built and distributed among volunteers living close to roads with high traffic volume for a 2-month measurement period. Each electrochemical sensor was calibrated in-field next to an air monitoring station during an 8-day period, resulting in R2 ranging from 0.3 to 0.7. When temperature and relative humidity are included in a multilinear regression approach, the NO2 accuracy is improved significantly, with R2 ranging from 0.6 to 0.9. Recalibration after the campaign is crucial, as all sensors show a significant signal drift in the 2-month measurement period. The measurement series between the calibration periods can be corrected for after the measurement period by taking a weighted average of the calibration coefficients. Validation against an independent air monitoring station shows good agreement. Using our approach, the standard deviation of a typical sensor device for NO2 measurements was found to be 7 µg m−3, provided that temperatures are below 30 ∘C. Stronger ozone titration on street sides causes an underestimation of NO2 concentrations, which 75 % of the time is less than 2.3 µg m−3. Our findings show that citizen science campaigns using low-cost sensors based on the current generations of electrochemical NO2 sensors may provide useful complementary data on local air quality in an urban setting, provided that experiments are properly set up and the data are carefully analysed.
Highlights
Because air pollution is difficult to measure, instrumental and operational costs of official measurement stations are usually high
As local ozone measurements were only available during the calibration periods, we used model D for the Urban AirQ campaign, i.e. generating an NO2 value based on a linear combination of SWE, SAE, T, and relative humidity (RH)
We examined low-cost electrochemical air quality sensors for citizen urban air quality monitoring
Summary
Because air pollution is difficult to measure, instrumental and operational costs of official measurement stations are usually high. Emerging low-cost sensor technology has the potential to extend the official monitoring network significantly, and improve our understanding of local urban air pollution. Suffer from various technical issues which limit their applicability Despite their limitations many experiments are done with air quality devices containing these sensors, often by motivated but not necessarily scientifically trained people. Coping with sensor degradation remains a serious issue Some studies, such as Jiao et al (2016), include an additional temporal term in their linear regression which improves the predicted NO2 slightly. We will demonstrate that citizen air quality monitoring using the current generation of electrochemical NO2 sensors may provide useful data of urban air quality, by using a practical method for field calibration and correcting for sensor degradation in retrospect
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