Seasonal variation of size-resolved aerosol fluxes in a Peri-urban deciduous broadleaved forest

Eddy covariance measurements of aerosol fluxes were performed above an oak-hornbeam forest in the Po Plain (Northern Italy), from February to May and from September to December 2019. Measurements aimed at assessing the influence of forest phenology and leaf presence/absence on the seasonal evolution of size-segregated aerosol fluxes. The size-resolved aerosol concentration in the range 0.006-10 μm was sampled with a 14-stage impactor (ELPI+, Dekati, FI), and the filters exposed in May were subjected to chemical analysis. Over the whole sampling period, the forest removed from the atmosphere an average of 3.12 mg of aerosol m−2 d−1. The direction and the intensity of the aerosol fluxes were not constant through the year, as a strong seasonal and size-dependent variability emerged. In particular, leaf-presence drove a net deposition of the accumulation mode aerosol (100 nm< particle diameter Dp<1000 nm) and an emission of the Aitken (10 nm< Dp<100 nm) and coarse mode (Dp>1000 nm) aerosols. On the contrary, in absence of leaves all the sub-micrometer aerosol size-classes showed net daily upward fluxes, while coarse mode aerosol fluxes were prevalently downward. Monthly averages of deposition velocities of Aitken and accumulation mode aerosols correlated with the Leaf Area Index (LAI) seasonal trend, thus indicating an important role of the amount of the leaf surface area on the deposition and emission of these size-classes. Furthermore, an influence of the stomatic activity was suggested for the Aitken mode aerosol, since its deposition velocity followed the same diel course of the stomatal conductance to water. The analysis of the influence of meteorological parameters on aerosol deposition velocities highlighted that dynamic and convective turbulence (described by friction velocity, u* and Deardorff velocity, w*) enhanced the vertical aerosol exchanges, both upward and downward, while the approaching of condensing conditions reduced the flux intensities

Size-segregated aerosol fluxes, deposition velocities, and chemical composition in an Alpine valley

The paper presents eddy covariance measurements of aerosol fluxes performed above an Alpine pasture in the Camonica Valley (Italian Alps) during summer 2019 and winter 2020. Vertical fluxes and deposition velocities (vds) were computed for nine aerosol size classes, with geometric mean diameters (GMDs) ranging from 10 nm to 0.76 μm, employing a fast-response electrical low-pressure impactor (ELPI+, Dekati, FI). At the end of each campaign, the concentration of water-soluble ions was estimated from the ion chromatography chemical speciation performed on the multi-impactor filters. K+ concentrations tripled in winter, evidencing the impact of biomass burning emissions, while nitrate, nitrite, ammonium, and sulphate were ascribed to secondary inorganic aerosol (SIA) formation. During summer, classes characterized by downward net daily fluxes presented a high percentage of SIA (> 70%) deposited on the respective filters. Phenomena of growth or coagulation of particles were also detected from the steady increase in concentrations during the day in classes with GMD ≥ 20 nm. Turbulence favoured intense aerosol exchange during the day. During summer nights, low friction velocities (u∗) led to weaker fluxes, while a strong, stable stratification in winter determined aerosol trapping at ground level and non-negligible, mostly negative, fluxes during nighttime. The trends of vds versus aerosol GMDs showed prevailing deposition phenomena under stable atmospheric conditions, with relative humidity higher than or equal to 90%, friction velocity lower than 0.15 m s−1, or wind speed lower than 2 m s−1. Cluster analysis identified groups of days with or without nucleation events and highlighted a rainout effect in summer during a period characterized by intense precipitation

Site- and house-specific and meteorological factors influencing exchange of particles between outdoor and indoor domestic environments

The aim of this study was to investigate the influence of site- and house-specific as well as meteorological factors on indoor and outdoor particle concentrations. Particle number (PN) and particle mass (PM) concentrations were monitored in 62 houses in Brescia, Northern Italy, during two winter monitoring periods. Measurements were conducted in houses of non-smokers and without the activation of any internal aerosol sources from domestic activities such as cooking and cleaning. Indoor and outdoor particle concentrations were measured for 30 min in each house. A wide-range aerosol spectrometer (MINIWRAS 1371, GRIMM) was used to detect 41 classes of particles from 10 nm to 35 \u3bcm. The effects of natural ventilation on indoor particle concentrations were also considered by measuring PM and PN indoor/outdoor ratios before and after a window was opened for a period of 15 min. An ANOVA analysis was performed on a sub-dataset of 35 houses to evaluate the dependence of PN and PM concentrations on site- and house-specific as well as meteorological factors. The house energy class was significantly related to indoor particle concentrations, and window dimensions seemed to influence the concentrations both before and after the ventilation period. We found that some factors, e.g., the floor level, need further investigation