Observations and model calculations of trace gas scavenging in a dense Saharan dust plume during MINATROC M. de Reus1, H. Fischer1, R. Sander1, V. Gros1,3, R. Kormann1, G. Salisbury1, R. Van Dingenen2, J. Williams1, M. Zöllner1, and J. Lelieveld1 1Max Planck Institute for Chemistry, PO Box 3060, 55020 Mainz, Germany 2Joint Research Centre, Ispra, Italy 3now at: Laboratoire des Sciences du Climat et de l’Environnement (LSCE), Gif sur Yvette, France
Abstract. An intensive field measurement campaign was performed in July/August 2002 at
the Global Atmospheric Watch station Izaña on Tenerife to study the
interaction of mineral dust aerosol and tropospheric chemistry (MINATROC). A
dense Saharan dust plume, with aerosol masses exceeding 500 µg m-3,
persisted for three days. During this dust event strongly reduced
mixing ratios of ROx (HO2, CH3O2 and higher organic peroxy
radicals), H2O2, NOx (NO and NO2) and O3 were observed.
A chemistry boxmodel, constrained by the measurements, has been used to
study gas phase and heterogeneous chemistry. It appeared to be difficult to
reproduce the observed HCHO mixing ratios with the model, possibly related
to the representation of precursor gas concentrations or the absence of dry
deposition. The model calculations indicate that the reduced H2O2
mixing ratios in the dust plume can be explained by including the
heterogeneous removal reaction of HO2 with an uptake coefficient of
0.2, or by assuming heterogeneous removal of H2O2 with an
accommodation coefficient of 5x10-4. However, these heterogeneous
reactions cannot explain the low ROx mixing ratios observed during the dust
event. Whereas a mean daytime net ozone production rate (NOP) of 1.06 ppbv/hr
occurred throughout the campaign, the reduced ROx and NOx
mixing ratios in the Saharan dust plume contributed to a reduced NOP of
0.14-0.33 ppbv/hr, which likely explains the relatively low ozone
mixing ratios observed during this event.
Citation: de Reus, M., Fischer, H., Sander, R., Gros, V., Kormann, R., Salisbury, G., Van Dingenen, R., Williams, J., Zöllner, M., and Lelieveld, J.: Observations and model calculations of trace gas scavenging in a dense Saharan dust plume during MINATROC, Atmos. Chem. Phys., 5, 1787-1803, doi:10.5194/acp-5-1787-2005, 2005.