What Controls Springtime Fine Dust Variability in the Western United States? Investigating the 2002–2015 Increase in Fine Dust in the U.S. Southwest

We use empirical orthogonal function (EOF) analysis to investigate the role of meteorology in controlling the interannual variability of fine dust concentrations in the western United States during 2002-2015 March-May. We then develop a prediction model to explore the causes of an observed increase in fine dust concentrations during March in the Southwest. For each spring month, 54-61% of the total variance in fine dust anomalies can be explained by the first two leading EOF modes, which consist of a coherent pattern of co-variability across the West and a dipole Northwest-Southwest pattern. We identify the key meteorological controlling factors to be regional precipitation, temperature, and soil moisture, which are in turn mostly driven by large-scale changes in sea surface temperature and/or atmospheric circulation patterns, including the El Nino-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO). In addition, fluctuations in the trans-Pacific transport of Asian dust likely contribute to fine dust variability in March and April. We find that March fine dust concentrations have increased from 2002 to 2015 in the Southwest (0.06 ± 0.04 μg m-3 a-1, p < 0.05). Multiple linear regression analysis suggests that these increases are associated with: (1) regionally drier and warmer conditions driven by constructive interference between ENSO and PDO; (2) soil moisture reductions in areas spanning the North American deserts; and (3) enhanced trans-Pacific transport. Our results provide an observational basis for improving dust emission schemes and for assessing future dust activity under climate change.