Modeling the growth and regional extent of new particle formation events

Abstract: As aerosol particles are important for global climate effects, their sources and influence on global aerosol particle concentrations need to be quantified. One of the major aerosol sources in the atmosphere is new particle formation (NPF) of new nanometer sized particles in the atmosphere. The influence on the global aerosol concentration due to NPF events is however not well quantified. The goals of this study is to examine how new particle formation (NPF) events influence the regional particle number size distribution in the air and how this affect the time dependent number size distribution measured at different field sites around the world. The method we used to approach this was to create a one dimensional box model including various aerosol dynamic processes that simulates NPF events during long range transport in the atmosphere. The factors, which influence NPF events and the resulting size distributions that can be studied in this model are: 1. Particle formation rates during NPF events. 2. Wind speed, and 3. Growth of the newly formed particles. In the examination of the effects of the aerosol dynamic processes, coagulation and dry deposition, the analysis showed us the effectiveness of coagulation in removing small particles (< 10 nm diameter) and that dry deposition was also effective in removing the largest particles below 1 µm diameter. During the examination of the effect of formation rates, we could clearly see that the concentration of particles is dependent on the magnitude of the NPF event. If the formation takes place over a smaller geographical area the NPF events, as registered at a downwind site, were consisting of particles of approximately the same size. During the simulations with varying time and place where particles experienced growth during NPF events, the size distribution measured downwind of where the particles were formed showed relatively varying sizes and concentrations, which is difficult to interpret in real situations at a field site where the size distribution is measured. With this model, these situations can be understood and simulated. We have, however, not tried the model against measured data at field sites. In future research one should include quantifying the effects at field sites and continue to investigate in detail the other effects of varying different factors like the wind speed, formation rate and growth rate during NPF events.