Desert aerosol aging in polluted environments and impact on its optical properties

• Applicant: Professor Dr. Konrad Kandler
• Subject Area: Atmospheric Science
• Term: from 2017 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 378741973

Atmospheric aerosol absorption is one of the major effects influencing the solar energy balance in terms of direct aerosol climate effect. Absorption is mainly driven by three major compounds, soot, mineral dust, and brown carbon. The relative quantities, in which these anthropogenic and natural compounds become effective, are, however, now well known. The present proposal aims therefore at a quantification of the absorbing effects of soot, organic carbon and mineral dust based on the quantification of the chemical composition and structure of many single particles by electron microscopy. As region of interest, the Eastern Mediterranean was selected because there in spring a most complex mixture of biomass burning aerosol, anthropogenic emissions, marine aerosol, and African and Asian mineral prevails. The proposed work will be performed in connection with a third-party-funded aircraft and ground-based measurement campaign, which offers the unique opportunity to obtain samples in and over the region of interest in connection with a wealth of atmospheric, aerosol and cloud measurement from third parties. Major goals of the proposed project are: A) General characterization of aerosol composition: Aerosol particle types will be identified by chemical properties and quantified. Size distributions of chemical composition will be estimated from relative chemical composition and separate size distribution measurements for sub 2.5-µm aerosol particles, as well as from a dedicated large particle collection technique directly. B) Partitioning into volatile / refractory components: Based on electron microscopy, volatile and refractory components will be identified and quantified inside single particles. Types of refractory materials will be identified. C) Assessment of dust / soot absorption partitioning based on single particles: The absorbing fraction of aged aerosol particles will be identified by their chemical and morphological properties. The volume contribution of the absorbing components will be determined by image analysis and element mapping. The according number abundance of absorbing particles will be used to determine the contribution of dust and soot. Soot particle microstructure and chemical composition will be used to determine the contribution of major soot sources. D) Exploring potential links between dust source and dust absorption: Absorption modeled through dust chemical composition will be related to dust source, based on a year-long time series of aerosol composition to allow for capturing seasonal cycles. Summarizing, the proposed project will yield new and detailed insights in absorption partitioning, potential dust contribution to radiative forcing in a polluted / mixed environment, possible connections with dust sources and soot source apportionment.

• DFG Programme: Research Grants