Development of a Statistical Model to Identify Spatial and Meteorological Drivers of Elevated O3 in Rural Nevada and Its Application to Other Rural, Mountainous Regions

Abstract:

Baseline ozone (O₃) has been defined as the mixing ratio of O₃ measured at sites not influenced by recent, local emissions. Measurements of O₃ at relatively remote monitoring sites, particularly in the western US, are useful for quantifying baseline O₃ and subsequently the magnitude of O₃ not controllable by local regulations. As the National Ambient Air Quality Standard (NAAQS) for O₃ becomes more stringent, there is an increased need to quantify baseline O₃ particularly in the western US where regional and global sources can significantly enhance O₃ measured at surface sites yielding baseline mixing ratios approaching or exceeding the NAAQS threshold. With the pending reduction in O₃ NAAQS, there is a growing need to develop tools to quantify baseline O₃ that are readily comprehensible to a wide range of stakeholders. Past work has indicated that meteorological conditions as well as site specific spatial characteristics (e.g. elevation, basin size, gradient) were significantly correlated with O₃ intercepted at rural monitoring sites. Here, we used 2 years of data measured at sites throughout rural Nevada to develop a readily comprehensible Categorical And Regression Tree (CART) model to identify spatial and meteorological characteristics that lead to elevated baseline O₃. A third year of data from rural Nevada sites was used to test the model and its applicability to the state of Nevada. Data from other sites in the intermountain west were used to test the representativeness of the model for sites throughout the region.