Spatiotemporal modelling of ozone distribution in the State of California

This paper is concerned with the spatiotemporal mapping of monthly 8-h average ozone (O-3) concentrations over California during a 15-years period. The basic methodology of our analysis is based on the spatiotemporal random field (S/TRF) theory. We use a S/TRF decomposition model with a dominant seasonal O-3 component that may change significantly from site to site. O-3 seasonal patterns are estimated and separated from stochastic fluctuations. By means of Bayesian Maximum Entropy (BME) analysis, physically meaningful and Sufficiently detailed space-time maps of the seasonal O-3 patterns are generated across space and time. During the summer and winter months the seasonal O-3 concentration maps exhibit clear and progressively changing geographical patterns over time, suggesting the existence of relationships in accordance with the typical physiographic and climatologic features of California. BME mapping accuracy can be superior to that of other techniques commonly used by EPA: its framework call rigorously assimilate useful data sources that were previously unaccounted for; the generated maps offer valuable assessments of the spatiotemporal O-3 patterns that can be helpful in the identification of physical mechanisms and their interrelations, the design of human exposure and Population health models, and in risk assessment. As they focus on the seasonal patterns, the maps are lot contingent on short-time and locally prevalent weather conditions, which are of no interest in a global and nonforecasting framework. Moreover, the maps offer valuable insight about the space-time O-3 concentration patterns and are, thus, helpful for disentangling the influence of explanatory factors or even for identifying some influential ones that Could have been otherwise overlooked. (C) 2009 Elsevier Ltd. All rights reserved.