Photochemically, Traffic-, and Boundary Layer-Influenced New Particle Formation in the Urban Atmosphere of Ljubljana, Slovenia
KUMAR SARANG, Kristijan Vidovic, Petra Dolšak Lavrič, Samo B. Hočevar, National Institute of Chemistry, Ljubljana, Slovenia
Abstract Number: 325
Working Group: Aerosol Processes and Properties in Changing Environments in the Anthropocene
Abstract
New particle formation (NPF) is recognized as a major source of atmospheric aerosol particles and a key contributor to the burden of ultrafine particles (UFPs, <100 nm) and cloud condensation nuclei concentrations globally, thereby influencing radiative forcing and climate and pose significant health risks through respiratory exposure. Despite its importance, NPF remains poorly understood, particularly in polluted urban environments, due to challenges in detecting early molecular clusters, complex precursor chemistry, high condensation sinks, regional transport, and the non-linear interaction of local meteorology and emissions. Globally, NPF exhibits diverse seasonal patterns and intensities across various environments, underscoring the persistent need to study this process under a wide range of atmospheric and geographical conditions.
This study presents, for the first time, a 190-day dataset from an urban background site in Ljubljana, Slovenia, comprising particle number size distribution (PNSD) measurements alongside meteorological and air pollution data. The data enabled a comprehensive analysis of the atmospheric urban NPF events. Results highlight the roles of meteorological parameters (temperature, RH, wind speed, wind directions, and solar intensity), atmospheric oxidants (OH, O3), and pollutants (BTX compounds, NOx, SO2 and PM2.5 ) in shaping the diurnal behavior of NPF in Ljubljana. Inter-quantile overlap analysis effectively distinguishes the parameters that best separate NPF from non-NPF days, while principal component analysis identifies three distinct source regimes: i) traffic-related, ii) photochemically driven, and iii) boundary layer-influenced, corresponding to morning, noon, and evening NPF events, respectively. Moreover, the local NPF events in Ljubljana contribute approximately 45% to the city’s annual UFP formation, underscoring their significance in urban air quality and regulatory contexts.
The present research received funding from the Slovenian Research Agency (Contract P1-0034).