High number concentrations of particles in atmosphere could be due to nucleation events and successive growth phenomena (Kulmala et al., 2004). These events have been recorded in different environments including remote areas, forests, coastal and urban sites (Hamed et al., 2007). The aim of this work is to investigate the effects of nucleation events on particle number turbulent vertical fluxes, characterising surface-atmosphere exchange of aerosol, and on size distributions in an urban background area in summer conditions. The influence of meteorological and micrometeorological parameters as well as CO2/H2O concentrations and fluxes on nucleation events will be investigated. Site description, set-up and data post-processing The measurement campaign was performed between 13th and 31st July 2010 using the mobile laboratory of the Lecce Section of ISAC-CNR placed at the University Campus (40°20'10.8''N, 18°07'21.0''E) at about 3.5 km SW of the town of Lecce. Equipment includes an eddy-correlation (EC) station using a condensation particle counter (CPC, Grimm 5.403), an ultrasonic anemometer (Gill R3), and a IR gas analyser (Li-7500, LICOR Environmental) for CO2 and H2O vapour concentrations and fluxes measurements. A scanner mobility particle sizer (SMPS, Grimm 5.500) was used to measure size distributions in the size range between 11 nm and 1083 nm. Measured time series were post-processed to evaluate the fluxes of particles (FN), CO2 (FC), sensible and latent heat, and the corresponding scalar concentrations over 30 minutes averaging periods using the methodology and corrections described in Contini et al. (2012). Results Two classes of particles could be put in evidence: nanoparticles (NP, diameter Dp<50 nm) and coarse particles (NC, Dp>50 nm, including Aitken and accumulation mode) that have a completely uncorrelated dynamics. Nanoparticles show maximum concentrations, on averages, in diurnal hours around midday when coarse particles present minimum average concentrations. This behaviour is due to the presence of days with nucleation events, like that shown in Fig. 1. During event days, on average, it has been observed an increase of downward fluxes (i.e. deposition) compatible with the hypothesis of aerosol formation above the measurement height (10 m). The measurement period has been divided in two categories: event (E) and nonevent (NE) days. Measured parameters have been averaged separately for the two categories in the time period between 9:00 and 16:00. Results are reported in Table 1 with their standard errors. Event days are characterised by concentrations about 3 times larger than non-event days, an average diameter reduced to about 1/2 and significantly larger deposition. Instead, CO2 concentrations and fluxes are similar for E and NE days, whereas E days are characterised by higher temperature and wind speed.
Influence of nucleation events on number particles fluxes and size distributions in an urban background area during summer season
M Conte;A Donateo;A Dinoi;F Belosi;D Contini
2015
Abstract
High number concentrations of particles in atmosphere could be due to nucleation events and successive growth phenomena (Kulmala et al., 2004). These events have been recorded in different environments including remote areas, forests, coastal and urban sites (Hamed et al., 2007). The aim of this work is to investigate the effects of nucleation events on particle number turbulent vertical fluxes, characterising surface-atmosphere exchange of aerosol, and on size distributions in an urban background area in summer conditions. The influence of meteorological and micrometeorological parameters as well as CO2/H2O concentrations and fluxes on nucleation events will be investigated. Site description, set-up and data post-processing The measurement campaign was performed between 13th and 31st July 2010 using the mobile laboratory of the Lecce Section of ISAC-CNR placed at the University Campus (40°20'10.8''N, 18°07'21.0''E) at about 3.5 km SW of the town of Lecce. Equipment includes an eddy-correlation (EC) station using a condensation particle counter (CPC, Grimm 5.403), an ultrasonic anemometer (Gill R3), and a IR gas analyser (Li-7500, LICOR Environmental) for CO2 and H2O vapour concentrations and fluxes measurements. A scanner mobility particle sizer (SMPS, Grimm 5.500) was used to measure size distributions in the size range between 11 nm and 1083 nm. Measured time series were post-processed to evaluate the fluxes of particles (FN), CO2 (FC), sensible and latent heat, and the corresponding scalar concentrations over 30 minutes averaging periods using the methodology and corrections described in Contini et al. (2012). Results Two classes of particles could be put in evidence: nanoparticles (NP, diameter Dp<50 nm) and coarse particles (NC, Dp>50 nm, including Aitken and accumulation mode) that have a completely uncorrelated dynamics. Nanoparticles show maximum concentrations, on averages, in diurnal hours around midday when coarse particles present minimum average concentrations. This behaviour is due to the presence of days with nucleation events, like that shown in Fig. 1. During event days, on average, it has been observed an increase of downward fluxes (i.e. deposition) compatible with the hypothesis of aerosol formation above the measurement height (10 m). The measurement period has been divided in two categories: event (E) and nonevent (NE) days. Measured parameters have been averaged separately for the two categories in the time period between 9:00 and 16:00. Results are reported in Table 1 with their standard errors. Event days are characterised by concentrations about 3 times larger than non-event days, an average diameter reduced to about 1/2 and significantly larger deposition. Instead, CO2 concentrations and fluxes are similar for E and NE days, whereas E days are characterised by higher temperature and wind speed.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
