Seasonal and diurnal behaviour of size segregated particles fluxes in a suburban area

Abstract

There are very few studies with direct emission/deposition measurements in suburban areas. In this perspective, multi-seasonal flux datasets of size segregated particles fluxes covering a suburban landscape are very important. The main goal of this work is to study the seasonal and diurnal behaviour of particle number concentration and fluxes in three different size ranges in a suburban area in a typical Mediterranean region (south of Italy). The observational campaign was carried out from April 2016 to August 2018. The observational site has been characterized from a meteorological and micrometeorological point of view, studying seasonal and diurnal behaviour of wind velocity and direction, friction velocity, turbulent kinetic energy, sensible heat flux. Annual variation of the total number concentration, as well as in the accumulation mode (0.25 < dp < 0.58 μm) and coarse mode (0.65 < dp < 3 μm) was analysed for the measurement period. The monthly observed total particle number flux shows highest positive values in the autumn/winter months, representing an emission of particles for the measuring site. In general, the accumulation mode particles do not contribute significantly (1–6%) to the total concentration in different months, suggesting the prevalence of strong sources of ultrafine aerosols. The annual behaviour of the size segregated number concentrations illustrated the combined influence of seasonally varying source strengths. Particles number concentrations and fluxes diurnal pattern have been shaped, essentially, by the two most important sources in the area: light vehicular traffic and wood burning in domestic heating. The number concentrations of particles in different modes were all higher on workdays than on weekends, in each season, with a mean increased ratio on workdays of about 9%. The weak decrease in Ntot concentration and scarce trend of N1 with temperature indicates that the source vehicular traffic doesn't change significantly during the year in the measurement site. On the other hand, the increasing of N2 with the temperature, probably, is due to the greater emission in dry periods in the higher size ranges.