Since pre-industrial times aerosol concentrations have increased substantially. Aerosols impact climate both directly by scattering and absorbing radiation, and indirectly by acting as cloud condensation nuclei, thereby changing cloud lifetimes and cloud optical properties. This has been identified as one of the major sources of uncertainty in climate models. Our research aims at a better understanding of the interactions between aerosol and clouds and radiation to reduce these model uncertainties.
Satellite observations of aerosols, data assimilation, and inverse modelling
Evaluation of aerosol distributions in the atmosphere, especially for climate modelling purposes, requires spatially uniform, long-term data sets. Also, air quality forecasting systems require near real-time observations to constrain the model. Both requirements are met by polar-orbiting satellites. However, satellites do not provide us with direct information about aerosol concentrations; rather, they deliver aerosol optical properties. To extract aerosol concentrations from optical observables, one needs to solve an ill-posed inverse problem. We use data assimilation techniques for solving the inverse problem.
Data assimilation techniques require an optics (forward) model for mapping aerosol concentrations to aerosol optical properties. Also, scattering and absorption by aerosols perturbs the radiative balance, thus influencing the climate. To address these issues we develop aerosol optics models for different types of particles, such as black carbon, mineral dust, and volcanic ash.
Wind-blown dust, volcanic ash, and wildfires
Episodic natural emissions of particles such as wind-blown dust, volcanic aerosols, and smoke from wildfires can have a strong impact on regional and hemispheric air quality and on climate; volcanic ash can also compromise air traffic safety. We employ both modelling approaches and satellite-derived emissions to describe such episodic events in our models.
Aerosol particles can have sizes ranging from a few nanometres to several micrometres. The particles can grow by condensation and coagulation processes, as well as shrink by evaporation. Also, new particles can form from the gas phase by nucleation processes. Knowledge of the size and composition of the particles is important for assessing their health effects, their optical and radiative properties, and their interaction with cloud droplets, which, in turn, is essential for climate and remote sensing applications. We work with a state-of-the-art aerosol dynamics model that takes into account these processes. It also includes a cloud-activation model, which we have coupled to a regional climate model developed at SMHI.