Abstract
Deposition of aeolian (windblown) dust and sand in drylands, such as the El Paso, Texas, USA / Ciudad Juarez, Chihuahua, Mexico metropolitan area within the Chihuahuan Desert, impacts soils, ecosystems, human infrastructure, and air quality. We monitored dry bulk deposition using marble dust collectors (MDCOs), a passive sampler, deployed atop a university building 21m above ground level during synoptic-scale wind events in urban El Paso, for five years (2011-2016). A nearby Texas Commission on Environmental Quality air monitor continuously measured particulate matter concentrations. MDCO sediment deposition rates over five synoptic dust event seasons (October- May) averaged 111 gm(-2)yr(-1) (range 85 - 164 gm(-2)yr(-1)), higher than almost all other North American sites but generally lower than Global Dust Belt locations. These deposition rate values, representing only synoptic-scale wind events, underestimate total annual aeolian deposition (augmented by convective dust events and inputs during non-windstorm conditions). Deposition rates were ~2x those reported for rural El Paso County, suggesting urban fugitive dust enhances total dry deposition. Mean grain size of deposited sediment in all events was >50 μm (sand), even though collected ~20 m above the height of saltation, indicating that events in El Paso can be considered "blowing sand" rather than "blowing dust." PM(10) concentrations averaged 28 μg/m(3) over all collection years but 200 μg/m(3) during hours dust was observed, were extremely variable, and were significantly higher during years of strong drought. PM(2.5)/PM(10) ratios averaged 0.13-0.14 during collection periods and dust hours. PM(2.5) concentrations were less strongly variable, showing the roles of dust and drought in PM(coarse) in El Paso. Back trajectories during synoptic events were predominantly from the southwest and west, crossing sandy, erodible desert soils and remote-sensing-identified dust hotspots. MDCO sediments were comprised primarily of predominant Chihuahuan Desert soil minerals (quartz, feldspars, and calcite). Compared to global average aeolian deposition of major and minor elements, El Paso samples were enriched in silicon but depleted in aluminum, titanium, and manganese, as well as iron, an element with important ecological, radiative, and human health impacts. El Paso, Texas appears to be one of the dustiest / sandiest cities in North America.