On the composition of airborne particles influenced by emissions of the volcano popocatépetl in Mexico

A 17-day field campaign was carried out in April-May 1999 to determine thecontribution that gaseous volcanic emissions make to the compositionof solid particles,particularly to the presence and quantity of sulfates. Theexperimental site was located inTonantzintla (in the State of Puebla), only 30 km E from the volcanoPopocatépetl, whichhas been in an active phase since the end of 1993. An analysis ofthe carbon monoxide(CO) and sulfur dioxide (SO^sub 2^) in the ambient air identifiedvolcanic influence in 6 out ofthe 17 days sampled. Particles collected in an 8-stage cascadeimpactor were analyzed for inorganic ions (by liquid chromatography).A non-parametric test indicates asignificant difference on the total particle mass and thesulfate fraction between days withand without volcanic influence. This difference was predominantlyobserved in the stages that collect the smaller particles. Windsat 500 mb (roughly corresponding to thesummit of the volcano) indicate a westerly transport from thevolcano to the experimentalsite, even though surface winds do not show a clear signal ofsuch a transport. Back trajectories from the experimental site werecalculated and clearly indicated that air parcels on the daysindependently identified as with volcanic influence had indeed passed over the volcano.[PUBLICATION ABSTRACT]