The Aarhus University Research on Aerosol atmospheric simulation chamber consists of a cubic ∼5 m3 Teflon bag. The chamber is suspended from a metal frame inside a temperature regulated room, where the temperature is adjustable from -16 to 26 °C. Sunlight is simulated by 24 UV lamps which are installed below and above the chamber. It is possible to connect various instruments to AURA through either stainless steel tubings or Teflon tubings. In AURA, the temperature, relative humidity and the concentration of ozone and nitrogen oxides (NOx) are always monitored. A more detailed description of AURA is presented in Kristensen et al. (2017).
AURA is used for simulations of aerosol formation from various sources, e.g. biogenic volatile organic compounds (BVOCs) like oxidation of α-pinene and dimethylsulfide. When AURA is used for studies of formation of secondary organic aerosols, the chamber is filled with a certain amount of oxidant (either ozone or hydroxyl radicals), whereafter a small amount of a volatile organic compound is added. The subsequent new particle formation and growth of the particles, formed from the oxidation processes, are monitored with different instruments. Typically, a scanning mobility particle sizer, SMPS, which measures particle size distributions; an aerosol mass spectrometer, AMS, which measures the elementary chemical composition; and a method for particle sampling for detailed offline analysis are most often applied. The particle sampling is done either with a filter collection or by using a sequential spot sampler. It is also possible to connect other instruments, which can measure cloud formation properties, for example.
AURA is also used for experiments with sea spray, where the sea spray particles are produced outside the chamber either by coupling the AURA chamber with a sea spray tank or a particle generator, e.g. an atomizer. After the injection of the sea spray particles, it is possible to age them by exposing them to processes which might change their composition. As for the studies of secondary organic aerosol, a suite of instruments may be applied to investigate the development in the particles. For sea spray experiments, often an optical particle sizer (OPS) or a nephelometer, which measures optical properties, are applied.
Sea spray particles are formed over the oceans when air bubbles are entrained by waves breaking. The air seeks to the surface of the ocean and by the surface they burst, which results in droplets containing sea salt and other components. These droplets are brought into the atmosphere and contribute to aerosols.
To simulate similar processes in the laboratory, sea spray tanks are used. A sea spray tank is a large container which can contain up to 20 L of water. We have two sea spray tanks: CALYPSO, which is a 15 L sea spray tank that can carry about 10 L of water; and AEGOR, which is a 34 L sea spray tank that can carry about 20 L of water. Sea spray particles are formed through various processes, and to simulate different processes, the sea spray tanks are both fitted with a jet, which shoots a water stream onto the surface of the water in the tank, and a diffuser, which bubbles air from the bottom of the tank through the water. Additionally, CALYPSO has a 'shower head' which replaces the jet and lets water fall from above onto the surface of the water. CALYPSO operates at room temperature and AEGOR is equipped with temperature control and is able to operate from -25 to 85 °C. Normally, it operates from about -2 to 35 °C.
The sea spray tanks are operated in combination with other instruments. Often a scanning mobility particle sizer (SMPS) which measures the particle size distribution from about 10 nm to 400 nm is used in combination with an optical particle sizer (OPS) which measures the particle size distribution from 300 nm to 10 µm. Typically, particles will also be collected onto filters for chemical characterisation, and water samples are often collected as well.
