Many of the observed compounds in the atmosphere have low volatilities – i.e. they prefer to exist in the condensed phase and do not readily evaporate. Despite the low volatilities of the compounds, their relatively large abundance entails that a significant amount of the compounds are found in the gas phase in the atmosphere. Since the compounds tend not to evaporate, it is difficult to determine the thermodynamic parameters, which relates to the partitioning between the condensed phase and the gas phase. The ASVAP project is about determining these parameters, the central parameter being the saturation vapor pressure. In a collaboration with the Institute of Physics and Astronomy, Aarhus University, we are building a new instrument to measure very low vapor pressures of pure compounds. In the atmospheric simulation chamber AURA, we are working on determining the parameters based on equilibriums between a gaseous phase and a particle phase. The goal is to determine the relevant parameters with high accuracies which will contribute to a larger understanding of the atmospheric system.
Aerosols are liquid or solid particles suspended in the atmosphere. They are either emitted directly to the atmosphere, i.e. primary, or they are formed in the atmosphere and thereby secondary. Secondary organic aerosols (SOA) are formed from gases, which are emitted to the atmosphere where they are oxidised. The oxidation products are less volatile than the precursors and will therefore partition into the particle phase. One of the most common precursors to SOA is monoterpenes, which contribute substantially to SOA over pine forests. They form the well-known blue fog over large forest areas, e.g. Blue Mountains in Australia or Smokey Mountains in the United States. We study the formation of secondary organic aerosols in AURA, our atmospheric simulation chamber. By filling a certain amount of oxidant, e.g. ozone, into the chamber and thereafter adding a SOA precursor, we can study the SOA formation. We measure the physical properties of the aerosols, e.g. particle size and particle number concentrations. In collaboration with Associate Professor Marianne Glasius, we also measure the chemical composition of the particles.
Recently, the presence of microplastic particles in air has been discovered. Plastic fibres and fragments are being deposited from the sky with rain and snow even in remote areas, such as the Arctic. However, the sources of microplastic particles are currently unknown. One hypothesis is that the ocean may act as a source of airborne nanometer- and micrometer-sized plastic particles through sea spray. There are four general sea spray aerosol generation processes: bubbles bursting, jet droplets, spray from the top of large waves and large splashes leading to formation via the before-mentioned processes. In this project, we are exploring the sea surface as a key source of airborne plastic with our sea spray simulation chamber, AEGOR, and we are developing new state-of-the-art techniques for analysis of airborne plastic. Furthermore, we are investigating how plastic particles in the air are affected by atmospheric processes, influencing their environmental and climate impact.
Many different particles, both natural and anthropogenic, are emitted into the atmosphere. Some examples are organic aerosols, sea spray particles, microorganisms, combustion particles and microplastic. These particles can act as seeds on which water can condense or freeze and therefore they influence ice and cloud formation in the atmosphere and thus climate. Ice nucleation has a major influence of the hydrological cycle as 50 % of the rain that reaches the Earth originates form ice nucleation in the atmosphere. In addition, ice nucleation affects the cloud’s radiative properties and thus Earth’s total radiation budget and climate. Moreover, ice nucleation in the atmosphere impacts the chemistry that takes place in the troposphere and stratosphere. Knowledge about cloud formation is limited and it is one of the biggest uncertainties in modern climate models. That is why it is interesting to research cloud formation and the role atmospheric particles play in cloud formation. In addition, it is also interesting to investigate the connection between ice and cloud formation. The focus of the project is ice nucleation, where a cold stage instrument is used to investigate the freezing temperature of different samples.
Ice formation in clouds strongly influences their interaction with light and their precipitative properties. Here, ice nucleating bioaerosols - in particular bacteria that are capable of producing ice nucleation active proteins - may play an important role in ice formation in mixed phase clouds. However, how physical parameters such as temperature and relative humidity affect the ice nucleating activity of these organisms is still an open question. This project concerns the hygroscopicity of airborne cells of the ice nucleation active bacteria Pseudomonas syringae. Hygroscopicity is a measure of how well a particle takes up water. Water uptake might be a central parameter for the microorganisms to stay alive, active and facilitate de novo synthesis of the ice nucleation active proteins while airborne. Thus, the goal is to determine the water uptake or evaporation of the bacterial aerosol at subsaturated conditions and if the water permeates to the cell interior.
Atmospheric aerosols directly impact Earth’s radiation balance and cloud formation. The aerosol-radiation interaction is dictated by the aerosols ability to scatter and absorb sunlight, i.e. their optical properties. Aerosol particles can stay in the atmosphere for weeks, allowing for reactions to occur with surrounding gases and particles, solar radiation, and changes due to varying temperature and relative humidity. This is called ageing of the aerosols, and this ageing can impact the aerosols optical properties and their ability to act as cloud condensation nuclei. In this project, we study the optical properties of and ageing effects on sea spray aerosols – in the laboratory but also through field measurements. In the laboratory, we generate sea spray aerosols for example by using the sea spray simulation chamber, AEGOR, and we simulate different ageing processes using the atmospheric simulation chamber, AURA. This work is done by Assistant Professor Bernadette Rosati as part of OceANIC in collaboration with Professor Merete Bilde.