Early onset of the spring fine dust season in the southwestern United States

Jenny Hand1, W. H. White2, K. A. Gebhart3, N. P. Hyslop4, T. E. Gill5 and B. A. Schichtel6

The highest fine dust concentrations (mineral particles with aerodynamic diameters less than 2.5 µm) in the United States typically occur in spring in the Southwest. Contributions of fine dust to total PM2.5 mass reaches 50% or higher at rural and remote Interagency Monitoring of Protected Visual Environments (IMPROVE) sites during spring months. Trend analyses indicate that springtime regional mean fine dust concentrations have increased from 1995 through 2014, especially in March (5.4 % yr-1, p < 0.01). This increase reflects an earlier onset of the spring dust season across the Southwest by one to two weeks over the 20-year time period. March dust concentrations were strongly correlated with the Pacific Decadal Oscillation (PDO) index (r = -0.65, p<0.01), which was mostly in its negative phase from 2007 through 2014, during which the region was drier, windier, and less vegetated. The positive spring trend and its association with large-scale climate variability have several important implications for visibility, particulate matter, health effects, and the hydrologic cycle in the region.


1Colorado State University, jlhand@colostate.edu
2University of California-Davis, whwhite@ucdavis.edu
3National Park Service, Kristi.Gebhart@colostate.edu
4University of California-Davis, nmhyslop@ucdavis.edu
5University of Texas-El Paso, tegill@utep.edu
6National Park Service, Bret.Schichtel@colostate.edu