EMISSIONS OF ALKALINE ELEMENTS CALCIUM, MAGNESIUM, POTASSIUM, AND SODIUM FROM OPEN SOURCES IN THE CONTIGUOUS UNITED STATES

Models of dust emissions by wind erosion (including winds associated with regional activity as well as dust devils) and vehicular disturbances of unpaved roads were developed, calibrated,and used to estimate alkaline dust emissions from elemental soil and road composition data. Emissions from tillage of soils were estimated from the work of previous researchers. The area of maximum dust production by all of those sources is the area of the old Dust Bowl of the 1930s (the panhandles of Texas and Oklahoma, eastern New Mexico and Colorado, and western Kansas). The areas of maximum alkaline dust production are the arid southwest, the Dust Bowl, and the midwestern-mideastern states from Iowa to Pennsylvania. Our calculations show that calcium is the dominant alkaline element produced by open sources (sources too great in extent to be controlled by enclosure or ducting). Although the largest dust mass source is wind erosion (by winds associated with regional activity and convective activity), the largest producer of the alkaline component is road dust because the abundance of alkaline materials in road coverings (which include crushed limestone) is significantly higher than for soils. Comparing the above estimated sources of alkaline material with inventories of SO2 and NOx emissions by previous investigators gives the rough approximation that alkaline emission rates are of the order of the SO2 + NOx emissions in the western United States and that they are much smaller than SO2 + NOx in the eastern United States. This approximation is substantiated by data on Ca/(SO4 + NO3) for wet deposition for National Atmospheric Deposition Program sites.