Ozone in Rural Nevada: Investigating spatio-temporal patterns and source regions contributing to elevated concentrations

In 1993, an ozone (O3) monitoring site was established at Great Basin National Park (GBNP), located in rural eastern Nevada. Analyses of data from this site indicate that compliance with a revised National Ambient Air Quality Standard (NAAQS) ≤70 ppb will be challenging. With the exception of GBNP, ambient O3 monitoring has been limited to the areas in and around the 3 urban areas of Nevada. The objectives of the research presented here were to (1) characterize spatial and temporal trends in ambient O 3 across rural Nevada, and (2) identify source regions contributing to elevated O3 in rural Nevada. To pursue these objectives, a network of 13 monitoring sites was established throughout rural Nevada over a period ranging from July 2011 to June 2014. Data from 6 sites during the first 2 years of measurement indicate that maximum MDA8 O3 ranged from 68 to 80 ppb. Ambient O3 measured at GBNP was significantly higher than that measured at other rural Nevada sites. Back trajectory analyses, vertical profile measurements from aircrafts and sondes, statistical analyses, as well as results of regional and global models were employed to identify sources contributing to elevated O3. Our analyses indicate that regional and global sources contribute to O3 at surface sites throughout rural Nevada and that the high elevation and complex terrain make the State ideally situated to intercept air from the free troposphere and thus, pollution derived from complex sources included long-range transport, stratospheric intrusions, and regional emissions. Our data suggest that regional and global cooperation will be necessary to comply with a revised NAAQS in rural Nevada.