Analysis of particles and carbon dioxide concentrations and fluxes in an urban area: Correlation with traffic rate and local micrometeorology

Number particle concentrations and fluxes were measured, synchronously with CO 2 concentrations and fluxes, in an urban area. Measurements were taken with an eddy-correlation station located near the busiest road of the town of Lecce (Italy). Upward fluxes dominate completely over deposition and the area behaved as a source of aerosol and CO 2 with an average particle flux F N = 71,100 #/cm 2 s (median 64,000 #/cm 2 s) and an average CO 2 flux F C = 0.76 mg/m 2 s (median 0.46 mg/m 2 s). Pronounced diurnal and weekly cycles of F N and F C were observed, well correlated with measured traffic rate, T R , indicating that traffic is the main source of CO 2 and particles in the area. Biogenic cycle on CO 2 fluxes and concentrations was also distinguishable, decreasing the correlation between F N and F C . The relationships between particle and CO 2 fluxes with T R , friction velocity and atmospheric stability were analysed. Measured F N / T R increased when friction velocity increased and, correspondingly, number concentration decreased. Particle fluxes showed a dependence on the atmospheric stability. These dependencies were used to derive an empirical parameterisation of aerosol concentration and fluxes, based on T R and micrometeorological parameters, that could be used to estimate traffic emissions, in real operating conditions, for applications in dispersion and climate modelling. Measured F C / T R showed a limited correlation with friction velocity and stability, because of the influence of the biogenic cycle, thereby micrometeorological parameters were not used in the parameterisation of F C . ► Particle number and CO 2 concentrations and fluxes were measured in an urban area. ► The urban area is a net source of traffic related particles and CO 2. ► Daily cycles of concentrations and fluxes are correlated to vehicular traffic rate. ► The influence of micrometeorological parameters on fluxes was parameterised. ► CO 2 and particle average emissions of vehicles fleet were estimated.