Two-year observations of aerosol size distributions: investigating new particle formation at coastal and rural sites in the Netherlands

This study aims to analyze the dynamics of aerosol behavior, particularly focusing on particle number size distribution (PNSD) in contrasting environments — coastal and rural areas of the Netherlands. Our goal is to interpret the environmental factors and mechanisms influencing New Particle Formation (NPF) events in these distinct geographic settings, thereby enhancing our understanding of aerosol dynamics in varied environmental conditions. Our results indicate significant differences in particle number concentrations between the sites, with Cabauw showing notably higher concentrations, largely due to Ultrafine Particles (UFPs). Wind patterns strongly influence UFP levels, particularly winds from the direction of Amsterdam airport and the Rotterdam port area. However, the two sites exhibited good agreement (r²=0.62) in the concentration of accumulation mode particles, suggesting a regional rather than local source. Seasonal variations in nuclei mode particles were observed for both sites, with concentrations peaking in summer and diminishing in winter.  Our analysis extends to PNSD clusters and NPF classes. The results suggest that NPF events are typically associated with high solar radiation, lower relative humidity, higher temperature, and higher SO2 and O3, but lower NOx. The growth of these newly formed particles often relies on stable diffusion radiation conditions, while frequent cloud occurrence impedes particle growth. Additionally, particle size growth is often accompanied by increased concentrations of organics, nitrate, and ammonium. Notably, two distinct NPF episodes in the morning and at noon were observed at Cabauw. Suppressed growth of morning particles often coincides with higher NOx concentrations. In contrast, Lutjewad often experienced noon NPF events, which demonstrated sustained growth in particle size until the following day. These findings underscore the influence of local environmental conditions on aerosol dynamics.