Spatially varying parameters in observed new particle formation events

Abstract: Aerosol particles affect the global climate due to its influence on the scattering and absorption of short-wave and long-wave radiation. The extent of the influence of aerosol particles on the climate varies a lot by time and space, and needs to be quantified. One of the most important natural sources of atmospheric particles is new particle formation (NPF). However, the contribution of NPF events on the aerosol concentrations in different regions need to be better quantified before they can be realistically described in climate models. This is of great interest due to the ongoing climate debate. Atmospheric NPF events are typically studied at stationary measurement sites, at which the observed changes in particle number concentration and size can be linked to both temporal and spatial changes in the particle formation and growth parameters, even though the spatial component is often neglected. The goal of this study is to examine how common the spatial variations in particle formation and growth parameters are, and how they affect the observed NPF events. The method used to examine this was to first use an improved version of an existing model to simulate different NPF cases assuming spatially and/or temporally varying input parameters. From these simulations the “fingerprints” for the different parameter variations were identified. Thereafter we analyze 8 years of particle number size distribution data from measurement sites Pallas and Värriö, in Finnish Lapland, and compared the observations of NPF events to the fingerprints of the different variations in cases when the same air mass was observed at both sites. Our results indicate that the beginning of the event is typically time dependent which could be explained by the diurnal evolution of a turbulent boundary layer. The end of the NPF event tends to be more typically dependent on location. In our observations in Northern Scandinavia this could be connected to the air mass arriving from sea to land or over the Scandinavian mountains. These findings indicate that the spatial variations of the particle formation and growth parameters cannot be neglected when analyzing NPF events.