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.
Highlights
The interactions between aerosols and clouds have a large influence on the role of aerosols in climate change
The CN and cloud condensation nuclei (CCN) concentrations and the aerosol size distribution were first used to characterize the evolution of the hygroscopic properties of aerosols by comparing their microphysical properties before and after the mesoscale convective systems (MCS) passage
This paper describes the increase of aerosol hygroscopicity by aqueous mixing in a mesoscale convective system observed during the African monsoon multidisciplinary analysis (AMMA) experiment by using a combination of airborne observations and simulation exercises
Summary
The interactions between aerosols and clouds have a large influence on the role of aerosols in climate change These interactions mainly depend on the particle characteristics (concentration, size, composition, hygroscopic properties, mixing state) and the type of clouds involved (continental or maritime, convective or stratiform, cold or warm). These interactions are complex because the aerosol characteristics can be modified by in-cloud processes. Wurzler et al (2000) shows that cloud processing of dust particles is a possible effective pathway to form soluble coatings on dust particles. This study shows that after one or two cycles of particles through convective clouds the contribution of gas uptake by drops and subsequent liquid phase oxidation add considerable soluble material to dust particles
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