Is there new particle formation in the marine boundary layer of the North Sea?

Abstract: The effect of aerosol particles on climate and the human health emphasizes the necessity to focus on the research about aerosol particles. Aerosol particles emitted due to anthropogenic activities increase the scattering and absorption of solar radiation in the atmosphere which leads to an increased cooling of the climate (direct effect). In addition, they take part in cloud formation, and thereby they affect the radiative properties of clouds, and an increase in the emission of aerosol particles in general leads to an increasing solar radiation scattering and an alteration of precipitation (indirect effect). Aerosol particles emitted directly to the atmosphere through natural or anthropogenic processes are called primary aerosol particles. Secondary aerosol particles are formed after gas to particle conversion. New particle formation (NPF) mechanism is one of the important secondary aerosol particle sources. The newly formed particles have the ability to grow to cloud activation sizes after processing in the atmosphere, and hence are important for the indirect climate effect. There are still many discussions about the theories describing nucleation process and conditions favorable for NPF, but not a single theory can be regarded as correct yet. However it is known that such components as SO2, NOx, Biogenic volatile organic compounds (BVOC), other organic compounds, and NH3 are important gaseous precursors in the NPF process. NPF events have been detected at many sites at different environments but there is no information about NPF events detected over the North Sea or over other polluted marine atmospheres. The aim of the study is to investigate whether there are NPF events over the North Sea, how frequent they are, and to identify geographical positions of the NPF events over the North Sea using the newly developed NanoMap method. The Nano Map method requires only the aerosol particle size distribution data, and air mass back trajectories from Hysplit model. For this investigation a size distributions of nano-particles were measured with the Air ion spectrometer (AIS) instrument for particles 2 – 40 nm diameter, and with the scanning mobility particle sizer (SMPS) instrument for particles 10 - 300 nm diameter during March – May 2012 at the Danish North Sea coast field station Høvsøre. This data was combined with data measured 2010-2011 at the Cabauw field site in the Netherlands and data measured 2009-2010 at the Birkenes field site in Norway. The NanoMap analysis showed that there are NPF during 27% of the days at Høvsøre and that the aerosol particles are formed close to or along major shipping lanes. Hence, SO2 from ship emissions is a possible source of NPF over the North Sea. However, also continental air pollution, continental BVOC emissions, and volatile organic carbon (VOC) emissions from oil stations at the North Sea can be contribution to NPF.