A bivariate space-time downscaler under space and time misalignment

TL;DR

This paper introduces a bivariate space-time downscaler model to improve the fusion of monitoring and numerical model data for ozone and PM2.5 pollutants, addressing spatial and temporal misalignments to enhance prediction accuracy.

Contribution

It extends previous univariate downscaling models to a bivariate framework that accounts for space-time misalignment and pollutant correlation, enabling more effective data fusion.

Findings

Modest improvement in predictive performance for ozone and PM2.5.

Addresses computational challenges for large spatial-temporal datasets.

Provides a flexible class of bivariate space-time assimilation models.

Abstract

Ozone and particulate matter PM2.5 are co-pollutants that have long been associated with increased public health risks. Information on concentration levels for both pollutants come from two sources: monitoring sites and output from complex numerical models that produce concentration surfaces over large spatial regions. In this paper, we offer a fully-model based approach for fusing these two sources of information for the pair of co-pollutants which is computationally feasible over large spatial regions and long periods of time. Due to the association between concentration levels of the two environmental contaminants, it is expected that information regarding one will help to improve prediction of the other. Misalignment is an obvious issue since the monitoring networks for the two contaminants only partly intersect and because the collection rate for PM2.5 is typically less frequent than that for ozone. Extending previous work in Berrocal et al. (2010), we introduce a bivariate downscaler that provides a flexible class of bivariate space-time assimilation models. We discuss computational issues for model fitting and analyze a dataset for ozone and PM2.5 for the ozone season during year 2002. We show a modest improvement in predictive performance, not surprising in a setting where we can anticipate only a small gain.