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Nonseparable covariance models on circles cross time: A study of Mexico City ozone

Lookup NU author(s): Professor Emilio Porcu

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This is the authors' accepted manuscript of an article that has been published in its final definitive form by Wiley-Blackwell Publishing Ltd., 2019.

For re-use rights please refer to the publisher's terms and conditions.


Abstract

© 2019 John Wiley & Sons, Ltd. We propose a continuous spatiotemporal model for Mexico City ozone levels that account for distinct daily seasonality, as well as variation across the city and over the peak ozone season (April and May) of 2017. To account for these patterns, we use covariance models over space, circles, and time. We review relevant existing covariance models and develop new classes of nonseparable covariance models appropriate for seasonal data collected at many locations. We compare the predictive performance of a variety of models that utilize various nonseparable covariance functions. We use the best model to predict hourly ozone levels at unmonitored locations in April and May to infer compliance with Mexican air quality standards and to estimate the respiratory health risk associated with ozone exposure. We find that predicted compliance with air quality standards and estimated respiratory health risk vary greatly over space and time. In some regions, we predict exceedance of national standards for more than a third of the hours in April and May, and on many days, we predict that nearly all of Mexico City exceeds nationally legislated ozone thresholds at least once. In southern Mexico City, we estimate the respiratory risk for ozone to be 55% higher, on average, than the annual average risk and as much at 170% higher on some days.


Publication metadata

Author(s): White P, Porcu E

Publication type: Article

Publication status: Published

Journal: Environmetrics

Year: 2019

Volume: 30

Issue: 5

Print publication date: 01/08/2019

Online publication date: 21/01/2019

Acceptance date: 02/01/2019

Date deposited: 09/04/2019

ISSN (print): 1180-4009

ISSN (electronic): 1099-095X

Publisher: Wiley-Blackwell Publishing Ltd.

URL: https://doi.org/10.1002/env.2558

DOI: 10.1002/env.2558


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