Application of a new method to measure particulate matter concentrations and chemistry to better understand sources of atmospheric pollution to Nevada and the Western United States

Abstract

The Nevada Rural Ozone Initiative (NVROI) was a project undertaken to understand the spatial and temporal trends of atmospheric ozone (O3) concentrations and to identify sources of O3 to rural Nevada. Concentrations at multiple NVROI locations were observed to approach or exceed the current National Ambient Air Quality Standard (NAAQS) for O3 of 70 ppbv. A need for additional measurements, such as lead isotopes, to aid in identifying the sources of regional and global air masses intercepted in rural Nevada, was identified by the initial findings of the NVROI. To address this need, a method was developed using a Teledyne Advanced Pollution Instrumentation model 602 BetaPlus particulate monitor, to quantify particulate matter < 2.5 µm in aerodynamic diameter (PM2.5), on two filter materials that allowed for post-processing of the filter samples for reactive mercury concentrations and lead isotopic ratios. A suite of measurements, including criteria air pollutants, meteorological data, aerosol optical properties, data collected from monitoring agencies, and statistical and back trajectory analyses were also used.Measurements of reactive mercury indicated that the filters were useful for understanding trends in atmospheric concentrations, but that more research on surface chemistry is needed. Analysis of the lead isotopic data and the results of the statistical and back trajectory analyses indicated that trans-Pacific input of atmospheric pollutants occurred spring through fall of both sample years (2014 and 2015) and was a major source of atmospheric pollutants to Nevada. Reactive mercury was likely removed from air masses due to deposition or conversion to elemental mercury before reaching the sample sites and formation was facilitated by regional sources of oxidants. Other sources of atmospheric pollutants to Nevada included local and regional urban centers, regional and global wildfires, and subsidence of pollutants aloft. Anomalous particles observed at one high elevation sample site were attributed to corrosion of the sample line tubing during prolonged, high wind events. This research developed a novel method for tracing sources of pollution to aid in understanding the sources, source regions, and physical processes affecting air pollution in the complex terrain of Nevada, USA.