title: Frequency and Character of Extreme Aerosol Events in the Southwestern United States: A Case Study Analysis in Arizona.
abstract: This study uses more than a decade's worth of data across Arizona to characterize the spatiotemporal distribution, frequency, and source of extreme aerosol events, defined as when the concentration of a species on a particular day exceeds that of the average plus two standard deviations for that given month. Depending on which of eight sites studied, between 5% and 7% of the total days exhibited an extreme aerosol event due to either extreme levels of PM10, PM2.5, and/or fine soil. Grand Canyon exhibited the most extreme event days (120,i.e., 7% of its total days). Fine soil is the pollutant type that most frequently impacted multiple sites at once at an extreme level. PM10, PM2.5, fine soil, non-Asian dust, and Elemental Carbon extreme events occurred most frequently in August. Nearly all Asian dust extreme events occurred between March and June. Extreme Elemental Carbon events have decreased as a function of time with statistical significance, while other pollutant categories did not show any significant change. Extreme events were most frequent for the various pollutant categories on either Wednesday or Thursday, but there was no statistically significant difference in the number of events on any particular day or on weekendsversusweekdays.
authors.affiliation: Department of Chemical and Environmental Engineering, University of Arizona, Tucson, AZ 85721, USA.
authors.forename: David H
authors.initials: DH
authors.lastname: Lopez
authors.affiliation: Department of Chemical and Environmental Engineering, University of Arizona, Tucson, AZ 85721, USA.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Rabbani
authors.affiliation: National Aeronautics and Space Administration Langley Research Center, Chemistry and Dynamics Branch, Hampton, VA 23681, USA; Oak Ridge Associated Universities, Oak Ridge, TN 37831, USA.
authors.forename: Ewan
authors.initials: E
authors.lastname: Crosbie
authors.affiliation: Department of Hydrology and Atmospheric Sciences, University of Arizona, Tucson, AZ 85721, USA.
authors.forename: Aishwarya
authors.initials: A
authors.lastname: Raman
authors.affiliation: Department of Hydrology and Atmospheric Sciences, University of Arizona, Tucson, AZ 85721, USA.
authors.forename: Avelino F
authors.initials: AF
authors.lastname: Arellano
authors.affiliation: Department of Chemical and Environmental Engineering, University of Arizona, Tucson, AZ 85721, USA; Department of Hydrology and Atmospheric Sciences, University of Arizona, Tucson, AZ 85721, USA.
authors.forename: Armin
authors.initials: A
authors.lastname: Sorooshian
keywords: Arizona; Asian dust; IMPROVE; aerosol; air quality; dust; extreme events