Case Study of Particle Number Fluxes and Size Distributions during Nucleation Events in Southeastern Italy in the Summer

Marianna Conte,Franco Belosi,Adelaide Dinoi,Antonio Donateo,Daniele Contini

doi:10.3390/atmos6070942

Marianna Conte, Franco Belosi + Show 3 more

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https://doi.org/10.3390/atmos6070942

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Abstract

Concentrations, size distributions and particle number vertical turbulent fluxes were measured by the eddy-covariance method at an urban background site in southeastern Italy during the summer. CO2/H2O concentrations and fluxes were also determined together with meteorological parameters. Time series show that particles could be divided into two size classes with negatively-correlated temporal trends in diurnal hours: nanoparticles (diameter Dp < 50 nm) and larger particles (Dp > 50 nm). Larger particles include part of the Aitken mode and the accumulation mode. Nanoparticles peaked in diurnal hours due to the presence of several days with nucleation events when particles Dp > 50 nm were at minimum concentrations. Nucleation increased diurnal total particle concentration by a factor of 2.5, reducing mean and median diameters from Dmean = 62.3 ± 1.2 nm and Dmedian = 29.1 ± 1.3 nm on non-event days to Dmean = 35.4 ± 0.6 nm and Dmedian = 15.5 ± 0.3 nm on event days. During nucleation events, particle deposition increased markedly (i.e., downward fluxes), but no significant changes in CO2 concentrations and fluxes were observed. This is compatible with new particle formation above the measurement height and a consequent net transport towards the surface. Correlation with meteorology shows that the formation of new particles is correlated with solar radiation and favored at high wind velocity.

Highlights

The high concentration of particles in the atmosphere could be due to nucleation events and subsequent growth phenomena [1]
New particle formation events have frequently been observed in remote sites in clean air conditions, for example in boreal forests [2] and polar regions [3]
The aim of this work was to investigate the effects of nucleation events on particle number turbulent vertical fluxes, characterizing the surface-atmosphere exchange of aerosol, and the effects on size distributions at an urban background area in summer conditions

Summary

Introduction

The high concentration of particles in the atmosphere could be due to nucleation events and subsequent growth phenomena [1]. New particle formation events have frequently been observed in remote sites in clean air conditions, for example in boreal forests [2] and polar regions [3]. Recent studies showed a ubiquitous distribution of these events in sites with significantly different characteristics. Nucleation events have been observed in different environments: in urban and rural sites [4,5,6], forest sites [7], urban background sites [8] and coastal sites [9,10]. The widespread occurrence of nucleation and growth events suggests that this phenomenon could play an important role in cloud condensation nuclei concentrations, potentially influencing climate

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