Observations and model calculations of trace gas scavenging in a dense Saharan dust plume during MINATROC

Abstract

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.

Photoenhanced uptake of NO2 on mineral dust: Laboratory experiments and model simulations

“…[19] Runs with the LMDz-INCA model shown in Figure 4 demonstrate the effect of photochemical conversion of NO 2 on dust into HONO and nitrates on the NO 2 concentrations during a dust episode that occurred during summer 2002 over the western Saharan, documented during the second phase of MINATROC 2 [de Reus et al, 2005;Umann et al, 2005]. For the simulations, a G phot value of 1.48 10 À5 mW cm À2 , determined for low NO 2 concentration on SiO 2 /TiO 2 surfaces, was considered.…”

Observation of atmospheric peroxides during Wangdu Campaign 2014 at a rural site in the North China Plain

“…This raises an interesting question of whether HO 2 uptake or peroxide uptake is responsible for the imbalance between observation and modeling. It has been inferred by formerly published literature that aerosol uptake of HO 2 radicals is the major reason for the overprediction of the levels of atmospheric peroxides in the model (de Reus et al, 2005;Mao et al, 2013;Guo et al, 2014). Nevertheless, it is apparent that the extent of HO 2 heterogeneous degradation depends on the atmospheric environment, especially the concentration and property of aerosol particles that vary under different conditions.…”

Generation of Internally Mixed Insoluble and Soluble Aerosol Particles to Investigate the Impact of Atmospheric Aging and Heterogeneous Processing on the CCN Activity of Mineral Dust Aerosol

“…As aerosols are transported in the atmosphere, they can undergo heterogeneous reactions that lead to changes in the chem-ical composition of the particle surface (Bauer et al 2004;Bian and Zender 2003;de Reus et al 2005;Liao et al 2004;Martin et al 2003;Song and Carmichael 2001;Tang et al 2004;Underwood et al 2001). Often, tropospheric aerosols become internal mixtures of both water-soluble and insoluble components as a result of processing or coagulation (Korhonen et al 2003).…”