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A wavelet-based approach to blending observations with deterministic computer models to resolve the intraurban air pollution field

Recent interest in near-road exposure to air pollutants and related health and environmental justice issues has highlighted the importance of improving the accuracy of intraurban ambient concentration estimates. Unfortunately, except in rare cases, no single source of information can accurately estimate the concentration at the desired spatial and temporal resolution over the full time period of epidemiological interest. However, it is possible to blend information from several sources so as to exploit the strengths and offset the weaknesses of each. Specifically, we are interested in combining data from ambient monitors with output from deterministic air pollution computer models. Monitor networks are sparse in both space and time, are costly to maintain, and are usually designed expressly to avoid detecting local-scale features. We use two types of computer models to compensate for these drawbacks. The first, a grid-based regional photochemical model, Community Multiscale Air Quality (CMAQ), covers large areas at high time resolution but cannot resolve features smaller than a grid cell, usually 4, 12, or 36 km across. The second, a plume dispersion model, AMS/EPA Regulatory Model (AERMOD), can resolve these features but cannot track long-distance transport or chemical reactions. We present a new Bayesian method that combines these three sources of information to resolve the intraurban pollution field. This method represents the true latent field using a two-dimensional wavelet basis, which allows direct, efficient incorporation of data at multiple levels of resolution. It furthermore allows a priori selection of the relative importance of each data source. We test its predictive accuracy and precision in a realistic urban-scale simulation. Finally, in the context of two air pollution health studies in Atlanta, Georgia, we use our model to estimate the daily mean concentrations of oxides of nitrogen (NOx), particulate matter with an aerodynamic diameter ≤2.5 μm (PM2.5), and carbon monoxide (CO) at a mixture of census block group and zip code centroids for the years 2001–2002. Implications: This paper describes a novel method of blending regional and local model results with observations to produce accurate air pollutant concentrations at the desired spatial and temporal resolution over urban areas to support environmental epidemiological studies.