Anthropogenic influence on new particle formation in the marine boundary layer atmosphere

Sammanfattning: The most important parameter for estimates of the anthropogenic induced climate change is the radiative forcing. In a comparison of the earth’s radiative budget in the year 2011 relative to 1750, the intergovernmental panel on climate change concludes that the largest uncertainty in the total radiative forcing derives from aerosol particles and their ability to modify cloud properties as cloud condensation nuclei (CCN). This uncertainty may be reduced from increased knowledge of the spatial and temporal distribution of aerosol particles with CCN properties. In this project, aerosol particles formed in coastal and marine atmospheres through so called new particle formation (NPF) were analysed spatially and temporally and an assessment of the anthropogenic impact on the marine NPF was attempted. A method known as the NanoMap method was applied to infer the frequency of NPF in marine environments in the North Sea, Baltic Sea and the Mediterranean Sea. The results of the NanoMap analysis clearly identifies NPF frequently occurring in all three marine environments. The results suggested furthermore an increased probability of NPF in areas with heavy shipping. If the particles formed by the NPF grow to sizes with diameters larger than 50 nm, these may participate in the formation of clouds as CCN. To assess the anthropogenic impact on marine NPF, aerosol properties and NPF were simulated with the ADCHEM model. The input gas phase emissions to the model were emissions from anthropogenic, biogenic and natural sources. The simulations were carried out mainly over the the North Sea and the model was evaluated against the total particle volume measured in Høvsøre, Denmark. The model results were reasonably consistent with the observations. From the ADCHEM modelling results, it was concluded that anthropogenic marine emissions do influence NPF. The modelled particle size distribution at Høvsøre showed evidence of an increase in the NPF most likely as a result of anthropogenic emissions of condensable gases. However, particulate matter from shipping emissions were in some cases found to suppress the NPF. It was therefore concluded that new marine emission control legislations of sulphur-containing compounds may result in a decrease of marine NPF. If particulate emissions were also to be reduced, the result may instead be an increase of marine NPF. The ADCHEM model results were furthermore compared to the NanoMap analysis of the same period. The comparison showed that the modelled and the inferred NPF in the marine areas coincided to a large extent. The consistency between the modelled and the inferred NPF is an encouraging result and provides a first verification of the NanoMap analysis.