I am a professor in atmospheric science and the director of the Bolin Centre for climate research at Stockholm University, Sweden. My own research focuses particularly on atmospheric aerosols and clouds, especially on their microphysics and interactions. I finished my PhD 2008 in physics at University of Helsinki, where I worked especially on atmospheric nucleation and nanoparticle formation. After this, I did a post-doc at Carnegie Mellon University in Pittsburgh, US, focusing on atmospheric organic aerosol and its evolution and impacts in the atmosphere.
I moved to Stockholm in 2011, where I have been leading various research endeavours on the interactions between aerosols, clouds, climate and air quality: including e.g. two ERC-funded projects and the Horizon 2020 project FORCeS (www.forces-project.eu) which brought together 23 European partners working on these topics. At present, I am focusing particularly on the impacts that aerosol particle size distributions and chemical composition have on the microphysics of clouds, and how these interactions are represented in atmospheric numerical models.
Aerosol particles, clouds and precipitation interact with each other and the atmospheric gas phase in multiple ways. These complex interactions need to be better understood and quantitatively described to improve the estimates on how anthropogenic aerosol emissions have impacted the Earth’s radiation budget during the industrial period. Such mechanistic understanding will also facilitate making reliable future projections on climate, the hydrological cycle and various biogeochemical cycles in the Earth system.
Perturbations in the concentrations and properties of atmospheric aerosol particles directly influence the total number and size distribution of cloud droplets formed through activation, thereby influencing the overall microphysics and radiative properties of clouds. Direct measurement of this aerosol-cloud interaction (ACI) is challenging, but novel experimental techniques and the improved statistics provided by long-term observations in selected field sites provide unprecedented opportunities for identifying the key drivers of Cloud Condensation Nuclei (CCN) and Cloud Droplet Number Concentrations (CDNC) in conditions representing various pollution levels and meteorological conditions. Identifying these drivers, in turn, will help guide the prioritization of future experiments and theory development towards better description of ACI in e.g. Earth System Models.
Clouds and precipitation, in their turn, impact the atmospheric aerosol particle concentrations and properties through various pathways. Wet removal (i.e. uptake of particulate material to hydrometeors and removal by precipitation) is the most important loss pathway for aerosol particles from the atmosphere. In fact, long-term field observations suggest that trends in precipitation can contribute significantly to overall long-term trends in atmospheric particles. Processing by cloud cycling is also widely recognized to significantly influence both the size distribution as well as the chemical composition of atmospheric aerosol populations. Clouds and precipitation also influence the sources of atmospheric aerosol: they can influence New Particle Formation (NPF) processes through 1) transporting nucleating vapors to higher, colder, altitudes; 2) cleaning up the air from accumulation mode particles which act as a sink for the newly-formed particles; 3) influencing the atmospheric chemical reactions central to NPF. Field studies suggest a direct link between precipitation and the addition of small particles into the atmosphere, but the exact mechanisms behind these observations are not fully resolved.
In my talk, I will present some of our recent studies targeting the various branches of the two-way interactions between atmospheric aerosol particles, clouds and precipitation – based on a suite of numerical models, field observations and laboratory experiments. I will focus primarily on warm-cloud microphysics, and present work relevant for various pollution conditions, with a particular focus on clean forest environments.
