Adsorption of organic compounds pertinent to urban environments onto mineral dust particles

The interaction of mineral dust particles from the Sahara with semivolatile organic compounds over an urban region in Israel's coastal plain was studied. Dust samples were collected during numerous dust storm events in 2000 and 2001, under varying meteorological conditions. Organic compounds adsorbed on collected mineral dust particles were analyzed using an integrated, multitechnique study that employed a scanning electron microscope equipped with an energy dispersion system (SEM-EDS) and bulk aerosol analysis by gas chromatography/mass spectrometry (GC/MS) and ion chromatography (IC). The SEM-EDS analysis exemplifies the coexistence of inorganic and organic species on individual mineral dust particles. Using the GC/MS and IC analysis, specific tracers for urban air pollution and photodegradation products of agriculture emissions have been identified, and their size distributions have been obtained. Redistribution of semivolatile organics such as polycyclic aromatic hydrocarbons (PAH) and pesticides from submicron to larger particle size fractions, governed by the mineral dust transport trajectory and size distributions, was observed. Nonvolatile species, such as anhydrous sugars and large PAH, do not redistribute between the phases because of their low vapor pressure. The concentrations of short chain carboxylic acids increased with higher ambient relative humidity, suggesting water-assisted uptake onto the mineral particles.