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A study of trends for Mexico City ozone extremes

ABSTRACT The goal of this article is to analyze trends of high values of tropospheric ozone over Mexico City based on the Generalized Extreme Value (GEV) distribution and modeling from a Bayesian perspective. Our study of trends is based on data corresponding to three consecutive months: April, May, and June and for the years 2007–2013 for which we computed the maximum ozone concentrations per 72 h for 16 monitoring stations. First, we perform a station-by-station analysis of the data in which the location parameter of the GEV distribution includes a time-trend regression component. Additionally, we consider a Bayesian hierarchical model to study jointly the data from all the stations. For this model, the trend and intercept parameters for each station are assumed to have a spatial behavior centered on a common trend and intercept. Our analyses show that for a few stations there is some evidence of decaying levels, however, the global trend estimate confirms that there is no significant change during the period of study.