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Non-linear probabilistic calibration of low-cost environmental air pollution sensor networks for neighborhood level spatiotemporal exposure assessment

Abstract

Background

Low-cost sensor networks for monitoring air pollution are an effective tool for expanding spatial resolution beyond the capabilities of existing state and federal reference monitoring stations. However, low-cost sensor data commonly exhibit non-linear biases with respect to environmental conditions that cannot be captured by linear models, therefore requiring extensive lab calibration. Further, these calibration models traditionally produce point estimates or uniform variance predictions which limits their downstream in exposure assessment.

Objective

Build direct field-calibration models using probabilistic gradient boosted decision trees (GBDT) that eliminate the need for resource-intensive lab calibration and that can be used to conduct probabilistic exposure assessments on the neighborhood level.

Methods

Using data from Plantower A003 particulate matter (PM) sensors deployed in Baltimore, MD from November 2018 through November 2019, a fully probabilistic NGBoost GBDT was trained on raw data from sensors co-located with a federal reference monitoring station and compared against linear regression trained on lab calibrated sensor data. The NGBoost predictions were then used in a Monte Carlo interpolation process to generate high spatial resolution probabilistic exposure gradients across Baltimore.

Results

We demonstrate that direct field-calibration of the raw PM2.5 sensor data using a probabilistic GBDT has improved point and distribution accuracies compared to the linear model, particularly at reference measurements exceeding 25 μg/m3, and also on monitors not included in the training set.

Significance

We provide a framework for utilizing the GBDT to conduct probabilistic spatial assessments of human exposure with inverse distance weighting that predicts the probability of a given location exceeding an exposure threshold and provides percentiles of exposure. These probabilistic spatial exposure assessments can be scaled by time and space with minimal modifications. Here, we used the probabilistic exposure assessment methodology to create high quality spatial-temporal PM2.5 maps on the neighborhood-scale in Baltimore, MD.

Impact statement

  • We demonstrate how the use of open-source probabilistic machine learning models for in-place sensor calibration outperforms traditional linear models and does not require an initial laboratory calibration step. Further, these probabilistic models can create uniquely probabilistic spatial exposure assessments following a Monte Carlo interpolation process.

Graphical abstract

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Data availability

The datasets generated during and/or analyzed during the current study are not publicly available due to them being a part of continuous ongoing research but are available from the corresponding author on reasonable request.

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Acknowledgements

This manuscript has not been formally reviewed by the Environmental Protection Agency (EPA). The views expressed in this document are solely those of the authors and do not necessarily reflect those of the Agency. The EPA does not endorse any products or commercial services mentioned in this publication. Further, any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

Funding

This publication was developed under Assistance Agreement no. RD835871 awarded by the U.S. Environmental Protection Agency to Yale University. AP was supported by a grant from the U.S. Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health to the Johns Hopkins Education and Research Center for Occupational Safety and Health (award number T42 OH0008428). AD was supported by the National Science Foundation DMS-1915803 and the National Institute of Environmental Health Sciences (NIEHS) grant R01ES033739. CB was supported by the National Science Foundation Graduate Research Fellowship Program under Grant No. DGE1752134. DG and FX would also like to acknowledge support from HKF Technology and Ken Hu. MLZ was supported by the National Institute of Environmental Health Sciences of the National Institutes of Health under award numbers K99ES029116 and R00ES029116.

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Authors and Affiliations

Authors

Contributions

AP: conceptualization, methodology, software, formal analysis, data curation, writing—original draft, writing—review & editing, visualization. AD: Methodology, software, formal analysis, data curation, writing—original draft, writing—review & editing. MLZ: Data curation, writing—review & editing, investigation. CB: writing—review & editing, investigation. FX: writing—review & editing, investigation. DG: writing—review & editing, investigation, funding acquisition. KK: conceptualization, methodology, data curation, writing—original draft, writing—review & editing, supervision, funding acquisition.

Corresponding author

Correspondence to Andrew Patton.

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Patton, A., Datta, A., Zamora, M.L. et al. Non-linear probabilistic calibration of low-cost environmental air pollution sensor networks for neighborhood level spatiotemporal exposure assessment. J Expo Sci Environ Epidemiol 32, 908–916 (2022). https://doi.org/10.1038/s41370-022-00493-y

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Keywords

  • Exposure modeling
  • Air pollution
  • Sensors
  • Geospatial analyses

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