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Absorbing aerosol layers in a changing climate: aging, lifetime and dynamics

Periodic Reporting for period 3 - A-LIFE (Absorbing aerosol layers in a changing climate: aging, lifetime and dynamics)

Reporting period: 2017-09-01 to 2019-02-28

Aerosols (i.e. tiny particles suspended in the air) are regularly transported in huge amounts over long distances impacting air quality, health, weather and climate thousands of kilometers downwind of the source. Aerosols affect the atmospheric radiation budget through scattering and absorption of solar radiation and through their role as cloud/ice nuclei.

In particular, light absorption by aerosol particles such as mineral dust and black carbon (BC; thought to be the second strongest contribution to current global warming after CO2) is of fundamental importance from a climate perspective because the presence of absorbing particles (1) contributes to solar radiative forcing, (2) heats absorbing aerosol layers, (3) can evaporate clouds and (4) change atmospheric dynamics.

The overall aim of A-LIFE (https://a-life.at) is to investigate the properties of absorbing aerosols (in particular mineral dust – black carbon mixtures) to (1) characterize the aging and mixing of light-absorbing aerosol layers during their lifetime, to (2) assess the contribution of individual aerosol components, in particular mineral dust and BC to the radiative forcing (RF) of mixed absorbing aerosol layers, to (3) implement complex particle morphologies in RF estimates, and (4) to investigate potential links between the presence of absorbing particles, aerosol layer lifetime and removal.

To achieve the aims of A-LIFE, an innovative aircraft field experiment has been conducted successfully in the Central and Eastern Mediterranean in April 2017 (aircraft base: Cyprus). In 22 research flights (~80 flight hours) several outbreaks of Saharan, Arabian and Middle East dust, as well as pollution, biomass burning, and dust-impacted clouds were investigated. The airborne measurements were complemented by laboratory experiments and numerical modelling.

Now, a unique data set on key properties of absorbing aerosols and aerosol mixtures is available. In addition, several novel methodologies, algorithms, and an online calculation tool for the modelling of aerosol optical properties (https://mopsmap.net) have been developed. The analysis of the extensive A-LIFE data set is ongoing.
This report covers the first part of the project until month 43. During this period ground-breaking developments of a number of unique and novel measurement and calibration techniques, data processing algorithms, and an online simulation tool for the assessment of optical properties of aerosol mixtures were developed enabling the next level of accuracy in airborne aerosol research and for the understanding of aerosol processes.

An unprecedented vertically-resolved data set on key properties of absorbing aerosols and aerosol mixtures was collected during the A-LIFE field experiment in April 2017. Furthermore, existing measurements of pure black carbon and pure mineral dust layers from various airborne campaigns in the past decade were revisited, analyzed in a consistent way, and a homogenized composite data set was compiled. Data of absorbing aerosols are available for a region of high pollution with frequent aerosol mixtures (A-LIFE field experiment), for pure mineral dust and black carbon in source regions and after long-range transport (several field experiments, e.g. SALTRACE), and for background conditions with global coverage (ATom field experiment).

The A-LIFE work is regularly presented at international conferences and so far documented in 23 peer-reviewed articles including several highly-cited and high-impact publications (Weinzierl et al. (2017), Bull. Am. Met. Soc.; Moore et al. (2017), Nature; Lund et al. (2018), Nature Partner Journal Climate and Atmospheric Science).