Direct radiative effect of dust-pollution interactions

Abstract. The chemical ageing of aeolian dust, through interactions with air pollution, affects the optical and hygroscopic properties of the mineral particles and hence their atmospheric residence time and climate forcing. Conversely, the chemical composition of the dust particles and their role as coagulation partners impact the abundance of particulate air pollution. This results in an anthropogenic radiative forcing associated with mineral dust notwithstanding the natural origin of most aeolian dust. Using the atmospheric chemistry climate model EMAC with a detailed parametrisation of ageing processes and an emission scheme accounting for the chemical composition of desert soils, we study the direct radiative forcing globally and regionally. Our results indicate large positive and negative forcings, depending on the region. The predominantly negative forcing at the top of the atmosphere over large parts of the dust belt, from West Africa to East Asia, attains a maximum of about −2 W/m2 south of the Sahel, in contrast to a positive forcing over India. Globally averaged, these forcings partially counterbalance, resulting in a net negative forcing of −0.05 W/m2, which nevertheless represents a considerable fraction of the total dust forcing.