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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union

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© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
07 Aug 2017
Review status
This discussion paper is a preprint. A revision of the manuscript was accepted for the journal Atmospheric Measurement Techniques (AMT).
Intra-urban spatial variability of surface ozone and carbon dioxide in Riverside, CA: viability and validation of low-cost sensors
Kira Sadighi1, Evan Coffey1, Andrea Polidori2, Brandon Feenstra2, Qin Lv3, Daven K. Henze1, and Michael Hannigan1 1University of Colorado Boulder, Department of Mechanical Engineering, 427 UCB, 1111 Engineering Drive, Boulder, CO 80309, USA
2South Coast Air Quality Management District, Air Quality Sensor Performance Evaluation Center, 21865 Copley Drive, Diamond Bar, CA 91765-4178, USA
3University of Colorado Boulder Department of Computer Science, 430 UCB, 1111 Engineering Drive, Boulder, CO 80309, USA
Abstract. Abstract. Sensor networks are being more widely used to characterize and understand compounds in the atmosphere such as ozone and carbon dioxide. This study employs a measurement tool, called the U-Pod, constructed at the University of Colorado Boulder, to investigate spatial and temporal variability of O3 and CO2 in a 314 km2 area of Riverside County near Los Angeles, California. This tool provides low-cost sensors to collect ambient data at non-permanent locations. The U-Pods were calibrated using a pre-deployment field calibration technique; all the U-Pods were collocated with regulatory monitors. After collocation, the U-Pods were deployed in the area mentioned. A subset of pods was deployed at two local regulatory air quality monitoring stations providing validation for the collocation calibration method. Field validation of sensor O3 and CO2 measurements to minute resolution reference observations resulted in R-squared and root mean squared errors (RMSE) of 0.95–0.97 and 4.4–7.2 ppbv for O3 and 0.79 and 15 ppmv CO2, respectively. Using the deployment data, ozone and carbon dioxide concentrations were observed to vary on this small spatial scale. In the analysis based on hourly binned data, the median R-squared values between all possible U-Pod pairs varied from 0.52 to 0.86 for ozone during the deployment. The medians of absolute differences were calculated between all possible pod pairs, 21 pairs total. The median values of those median absolute differences for each hour of the day varied between 2.2 and 9.3 ppb for the ozone deployment. For carbon dioxide, distributions of all measurements vary from 413–425 ppm during the calibration (collocation) and 406–472 during the deployment. Since median differences between U-Pod concentrations during deployment are larger than the respective root mean square error values for ozone and carbon dioxide, we can conclude that there is spatial variability in these pollutants across the study area. This is important because it means that citizens may be exposed to more ozone than they would assume based on current regulatory monitoring.

Citation: Sadighi, K., Coffey, E., Polidori, A., Feenstra, B., Lv, Q., Henze, D. K., and Hannigan, M.: Intra-urban spatial variability of surface ozone and carbon dioxide in Riverside, CA: viability and validation of low-cost sensors, Atmos. Meas. Tech. Discuss.,, in review, 2017.
Kira Sadighi et al.
Kira Sadighi et al.

Data sets

Ozone and carbon dioxide low-cost mobile sensor data from Riverside, CA 2015 K. Sadighi
Kira Sadighi et al.


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Short summary
Ground-level ozone has negative human health impacts, and CO2 has connections to climate change. In the summer of 2015, we took 13 of our low-cost sensor monitors to Riverside California, and spread them out over a 314 km2 area. Both ozone and carbon dioxide had significant spatial differences between monitors. This is important because it means that ozone and CO2 in certain places may be higher than what EPA monitors report for an area, which is important for people who live there.
Ground-level ozone has negative human health impacts, and CO2 has connections to climate change....