Spatial and temporal variations of airborne dust fallout in Khorasan Razavi Province, Northeastern Iran

Dust deposition rates depend mainly on the rate of dust supply, climatic conditions, and topography in the source and sink areas. The objective of this study was to investigate the role of these variables in the spatial and temporal variation of airborne dust fallout in Khorasan Razavi Province, Northeast Iran. Airborne dust samples were collected monthly from May 2014 to April 2015. Dust fallout rate was modelled as a function of air temperature, precipitation, relative humidity, wind velocity and distance from source regions. The lowest and highest rates of atmospheric dust fallout occurred in December and June, with average amounts of 9.97 gm(-2) and 20.96 gm(-2), respectively. The strongest winds were observed in June immediately following a relatively humid period (i.e., March-May) with considerably higher precipitation and lower evaporation. Spatial distributions showed that the highest dust fallout rates occurred in the southern and western parts of the province-areas adjoining the vast playas. During the spring and summer season, the distance from the nearest playa was a key factor that explained more of the variation in dust flux than climatic parameters. Both runoff by fresh sediment moved onto the surface of the playa and the formation of loose sediment on the surfaces of wet playas are mechanisms that can increase dust emissions. The lowest deposition rates were observed in the mountainous region in the north of the province likely due to higher precipitation, atmospheric humidity, and soil moisture. This work represents the first baseline dust data for Khorasan Razavi Province and may be useful in evaluating the effects of future land use and climate change on aeolian land surface processes.