Abstract
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 a change in the aerosol direct radiative effect that we interpret as an anthropogenic radiative forcing associated with mineral dust–pollution interactions. Using the ECHAM/MESSy atmospheric chemistry climate model (EMAC), which combines the Modular Earth Submodel System (MESSy) with the European Centre Hamburg (ECHAM) climate model, including 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, considering solar and terrestrial radiation. Our results indicate 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 m−2 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 m−2, which nevertheless represents a considerable fraction (40 %) of the total dust forcing.
Highlights
Atmospheric aerosols play an important role in the climate system by affecting radiative transfer and the planet’s energy budget, both directly by scattering and absorption and indirectly via its impact on cloud formation (IPCC, 2014)
Using the ECHAM/MESSy atmospheric chemistry climate model (EMAC), which combines the Modular Earth Submodel System (MESSy) with the European Centre Hamburg (ECHAM) climate model, including 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, considering solar and terrestrial radiation
We interpret the resulting effect on the radiative transfer as an anthropogenic climate forcing linked to mineral dust, even though most of the dust itself is emitted from natural sources
Summary
Atmospheric aerosols play an important role in the climate system by affecting radiative transfer and the planet’s energy budget, both directly by scattering and absorption and indirectly via its impact on cloud formation (IPCC, 2014). Fine particulate matter can be a human health hazard and is a major cause of morbidity and mortality globally (Lelieveld et al, 2015) Aerosols originate both from natural and anthropogenic sources, the former being mostly mineral dust, sea salt and emissions from naturally ignited fires. The natural sources provide an inevitable background level of atmospheric particulate matter, while studies of the human impact on climate and air pollution commonly focus on aerosol from anthropogenic sources. In the present study we analyse the impact of mineral dust interactions with anthropogenic air pollution on radiative transfer using the ECHAM/MESSy chemistry climate model (EMAC; Jöckel et al, 2005, 2010). The effects of dust–pollution interactions on the aerosol burdens and correspondingly the optical properties are analysed, and the resulting impacts on radiative transfer and atmospheric heating are analysed in Sect.
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