Increase of the aerosol hygroscopicity by cloud processing in a mesoscale convective system: a case study from the AMMA campaign

Abstract

Abstract. Aerosol properties were measured during an airborne campaign experiment that took place in July 2006 in West Africa within the framework of the African Monsoon Multidisciplinary Analyses (AMMA). The goal of the present study was to determine the main microphysical processes that affect the aerosols during the passage of a mesoscale convective system (MCS) over the region of Niamey in Niger. A significant change in the aerosol profiles measured before and after the passage of the MCS was found in a layer located between 1300 and 3000 m, where the aerosol concentration drastically decreased after the passage of the MCS. Concurrently, a significant increase in the cloud condensation nuclei (CCN) fraction was also observed during the post-MCS period in the same layer. Moreover, the results of the elemental composition analyses of individual particles collected in this layer after the MCS passage have shown higher contributions of sulfate, nitrate and chloride to the total aerosol mass. A mesoscale atmospheric model with on-line dust parameterization and Lagrangian backtrajectories was used to interpret the impact of the MCS on the aerosol properties. The results of the simulation show that the MCS 1) generates dust particles at the surface in the gust front of the system and washout of particles during the system precipitation, 2) modifies the aerosol mixing state (intensive aerosol property) through cloud processing, and 3) enhances CCN activity of particles through coating by soluble material.

Ocean–Atmosphere Interactions of Particles

“…The heterogeneous processes responsible for sulphate mixing with dust may be season-dependent with predominance of coagulation process in summer and SO 2 uptake in spring (Suzuki et al 2010). Recent observations of strong internal mixing of dust with nitrate or sulphate in mesoscale convective clouds during the AMMA campaign (Crumeyrolle et al 2008;Matsuki et al 2010a) suggest in-cloud processing involving aqueous phase oxidation of NOx/SO 2 , as previously assumed by Levin and Ganor (1996) and Liu et al (2005 (Krueger et al 2004) and then observed in recent field studies (Laskin et al 2005;Matsuki et al 2005Matsuki et al , 2010bShi et al 2008;Huang et al 2010;Suzuki et al 2010). …”

Online coupled regional meteorology chemistry models in Europe: current status and prospects

“…It was extended with the sectional aerosol model ORISAM (Cousin et al, 2004) as well as with the three-moments aerosol scheme ORILAM for the simulation of aerosol dynamics and secondary inorganic and organic aerosols (Tulet et al, 2005), which laid the foundation for studies of chemistrymeteorology feedbacks. MesoNH-C was subsequently employed for a wide range of applications to study the effect of biogenic emissions on regional O 3 levels (Solmon et al, 2004), the impact of convection on aerosol hygroscopicity (Crumeyrolle et al, 2008), for regional scale CO 2 source inversion (Lauvaux et al, 2009), sulfur transport and chemical conversion in a volcanic plume (Tulet and Villeneuve, 2011), or to investigate Saharan dust transport (Bou Karam et al, 2010) to name but a few.…”

Observational study of influence of aerosol hygroscopic growth on scattering coefficient over rural area near Beijing mega-city

“…Tang (tangj@cams.cma.gov.cn) metry factor, etc. ), which could enhance the cooling effect of aerosols in the atmosphere by directly scattering more light radiation (Carrico et al, 1998(Carrico et al, , 2000Kotchenruther et al, 1998;Randles et al, 2004), or change cloud microphysical properties (Crumeyrolle et al, 2008) by serving as cloud condensation nuclei (CCN) (Houghton et al, 2001). To precisely evaluate the direct radiative forcing, light scattering coefficient (σ sp ) of aerosol particles and its dependency on relative humidity (RH), defined as f (RH)=σ sp (scanning RH)/σ sp (dry), have been investigated for decades through Integrating Nephelometers equipped with humidity control devices in clean background regions, marine boundary layers, rural and urban areas (Kotchenruther et al, 1999;Malm et al, 2001Carrico et al, 2003;Magi et al, 2003;Kim et al, 2006).…”