Organic matter content of rural dusts in Australia

Loss on ignition (LOI) techniques have been refined to measure dust samples down to 0.0012 g. Using this method Australian rural dusts are shown to have a high organic matter content (mean 31% suspended dusts and 34% for deposited dusts). This contrasts with the low organic matter levels in soils (commonly <1%), from which the organic matter largely derives by wind erosion and possibly local mechanical disturbance. Pollen is probably the next most important source of dust organic matter. Background suspended dusts range from 2 to 90% organic matter, depending upon: the winnowing by winds, monitoring site location, and temporal variations in local vegetation and other conditions. Dusts collected during entrainment events (dust storms) are lower in organic matter (8–67%), exhibit less variability than background dusts and decrease with total dust concentration, because of the reduced winnowing capacity of strong dust storm winds and the very low soil organic matter levels in dust storm source areas. When mixed with background dusts, entrainment event dusts dilute organic matter levels, contributing to the large temporal variability of organic matter levels in dusts. Deposited dusts show similar spatial and temporal trends to suspended dusts (3–91%). These results have significance in several contexts, including: soil erosion, dust deposition in terrestrial and marine ecosystems and environmental health.