SAMPLING ARTIFACTS IN THE DETERMINATION OF PARTICULATE SULFATE AND SO2(G) IN THE DESERT SOUTHWEST USING FILTER PACK SAMPLERS

Particles collected in the desert Southwest on Teflon filters using an annular denuder sampling system absorb SO2(g) in a subsequential expo sure to SO2(g) in the laboratory if the concentration of fine particul ate sulfate measured with a filter pack sampling system is greater tha n the concentration of sulfate measured with the annular denuder sampl ing system. If the concentrations of sulfate determined using the two sampling systems agreed, no absorption of SO2(g) by the denuder-collec ted particles occurs. These results show that SO2(g) may be collected by Southwest desert fine particles during sampling, resulting in measu red concentrations of fine particulate sulfate that are higher than th e correct concentrations. The magnitude of this filter pack sampling a rtifact, 0.1-0.4 mu g SO42-/m(3), is small. However, the artifact is i mportant relative to the concentration of particulate sulfate present in the desert Southwest, typically 0.5-2 mu g SO42-/m(3). The magnitud e of the filter pack sulfate sampling artifact is not related to eithe r the atmospheric particulate sulfate or SO2(g) concentrations.