What Controls Springtime Fine Dust Variability in the Western United States? Investigating the 2002-2015 Increase in Fine Dust in the US 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 covariability 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 (0.060.04gm(-3)a(-1), p<0.05). Multiple linear regression analysis suggests that these increases are associated with the following: (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. Plain Language Summary Soil-derived particulate matter, also known as mineral dust, contributes to air quality degradation, visibility reduction, and public health risks in the western United States, where abundant arid lands serve as dust sources. Dust is also transported here from Asian deserts across the Pacific Ocean. Improved understanding of how meteorology influences airborne dust levels in the present day can help us assess future changes due to human-caused climate change. Using statistical methods, we identify the key drivers of year-to-year changes in springtime dust across the West to be regional precipitation, temperature, and soil moisture. These drivers are in turn influenced by the El Nino-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO). Trans-Pacific transport of Asian dust also contributes to the observed dust variations. We find that dust levels have been increasing in southwestern regions between 2002 and 2015. This increase is associated with (1) regionally drier and warmer conditions associated with ENSO and PDO, (2) declines in soil moisture across North American deserts, and (3) stronger transport of Asian dust. With the U.S. Southwest projected to experience severe and persistent droughts in coming decades due to climate change, our results suggest that this region could also become increasingly dustier.