The unexplored world of aerosol surfaces and their impacts.

Project Information

SURFACE

Grant agreement ID: 717022

DOI

10.3030/717022

Project closed

EC signature date 13 December 2016

Start date 1 March 2017

End date 29 February 2024

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 499 625,99

EU contribution

€ 1 499 625,99

Coordinated by

OULUN YLIOPISTO
Finland

Periodic Reporting for period 5 - SURFACE (The unexplored world of aerosol surfaces and their impacts.)

Reporting period: 2023-03-01 to 2024-02-29

Summary of the context and overall objectives of the project

We are changing the composition of Earth’s atmosphere, with profound consequences for the environment and our wellbeing. Tiny aerosol particles are globally responsible for much of the health effects and mortality related to air pollution. Atmospheric particles also play several key roles in regulating Earth’s climate via their critical influence on the global radiation balance and formation of clouds in the atmosphere. Every cloud droplet has formed from water nucleating on the surface of an aerosol particle. Aerosols and droplets provide the media for condensed-phase chemistry and multiphase processes in the atmosphere, but large gaps remain in our understanding of their formation, transformations, and climate interactions. Our key idea was that surface properties play crucial roles in these processes, but next to nothing is known about the surfaces of atmospheric aerosols and cloud droplets and their impacts. Based on preliminary discoveries, our hypothesis was that such surfaces are significantly different from both the interior and surrounding air and their unique properties can impact aerosol processes all the way to the global scale. To demonstrate this, we used novel spectroscopic and imaging techniques, recently made possible with ultra-brilliant synchrotron radiation, to identify unique surface properties for aerosol and atmospherically relevant systems. We then developed a combination of experiments and computational methods to decouple the role of surfaces in several key aerosol processes taking place in the atmosphere. Finally, we searched for characteristic fingerprints of surface properties on aerosol effects in state-of-the-art atmospheric models used for air pollution and climate forecasting. All objectives were successfully achieved. Our results show that surfaces are highly distinct and significantly impact aerosol and droplet processes central to their atmospheric and climate effects, on all scales, for all systems, and via all mechanisms so far investigated. Surface effects can therefore contribute to closing the knowledge gap surrounding atmospheric aerosols, with wide-reaching implications for our understanding of air pollution and its human health effects, climate change, and mitigation strategies.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

We performed a large number of novel spectroscopy and imaging experiments to characterize the surfaces, internal structure, and interactions with surrounding gas-phases, for a suite of aerosol and atmospheric model systems, made possible by using ultra-brilliant synchrotron radiation. Other cutting-edge molecular-level techniques were also successfully applied. A total of 44 weeks of beamtime were carried out by the project team at synchrotron facilities world-wide. We developed new machine learning algorithms and other methods to analyze these first-of-a-kind experimental data and carried out molecular dynamics and quantum chemical simulations for new atmospheric aerosol components to support the interpretation.

We designed new aerosol experiments to determine the influence of unique surface properties on processes that are key to aerosol formation and their atmospheric and climate effects, including water uptake and cloud nucleation, condensation and evaporation, and aqueous and surface chemistry. We directly measured surface tension of microscopic aqueous surfactant droplets for the first time using a novel holographic optical tweezer setup at University of Bristol and used the state-of-the-art AIDA environmental chamber at Karlsruhe Institute for Technology with EUROCHAMP-2020 TNA. We developed a new monolayer surface model, based on the insights from surface-sensitive molecular-level experiments, together with a suite of supporting thermodynamic models, to accurately decouple the contributions from surface and interior to aerosol processes.

We implemented descriptions of surface effects in the box-model version and full ECHAM-HAM atmospheric chemistry-climate model and investigated their impacts on formation of aerosols and their climate effects on cloud, regional, and global scales.

For all systems and conditions investigated, we identified unique surface properties which are highly distinct from the interior (Objective I). In all cases, we found that these surface properties can significantly impact aerosol processes (Objective II) with atmospheric chemistry and climate effects on all scales. The fingerprints of surfaces are complex and seen by significant changes in the magnitudes, distributions, and sensitivities of aerosol effects in the atmosphere (Objective III).

Throughout the project, we have engaged a wide range of stakeholders. Team members have been invited to present results in international conferences, workshops, and research seminars in aerosol, atmospheric, and synchrotron science. We have contributed to the MAX IV 2023-2032 strategic plan and the white paper presenting the new Centre for Molecular Water Science coordinated by DESY. We have taken part in outreach initiatives to the general public, including TEDx talk “Small steps for us, a big leap for the planet”, graphic novel “Little Things”, podcast “Intronauts – Exploring brilliant science”, popular events, such as the Air Guitar World Championship and Polar Bear Pitching, and interviews in national and international media. We have also given presentations and participated in panel discussions addressing civil society and local, national, and EU policymakers.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Novel applications of cutting-edge spectroscopic and imaging methods generated unique data sets and provided entirely new molecular level information about the composition and structure of atmospherically relevant surfaces. We directly observed that equilibria of atmospheric acids and bases are systematically shifted towards the neutral species at the surface of aqueous cloud droplet model solutions. This challenges previous interpretations and could affect numerous pH-sensitive chemical reactions in the atmosphere.

We developed new experimental methods for delivering actual aerosol samples to the experiments, either deposited on a substrate or as a stream of unsupported particles. These methods enable a wealth of further exploration into properties which go entirely unnoticed in state-of-the-art aerosol experiments.

We directly measured size-dependent surface tension of microscopic aqueous surfactant droplets for the first time. Surface tension is a key parameter determining the growth of cloud droplets in the atmosphere and verification of this long-speculated phenomenon has strong implications for climate predictions. The new monolayer surface model successfully reproduced the measured micro-droplet surface tensions and size-dependence. It is fully predictive and uniquely predicts both the thickness of the surface layer and surface and interior concentrations for all chemical components in a droplet.

We introduced new descriptions of surface tension and acidity in a climate model. We showed that surface acidity can strongly affect aqueous sulfate chemistry and the formation of highly climate active secondary aerosols. Both surface tension and acidity lead to significant changes in aerosol cloud nucleation and radiative climate effects. These properties are currently not considered in any state-of-the-art atmospheric models or climate forecasts.

First atmospheric experiments at the FinEstBeAMS beamline at MAX IV, December 2018

Clouds over MAX IV synchtrotron in Lund, Sweden, aerosol cloud seeds and their climate effects