Real time measurements of PM2.5 concentrations and vertical turbulent fluxes using an optical detector

In this work the possibility of measuring real-time concentrations of PM2.5 and the corresponding vertical turbulentfluxes using the optical detector Mie pDR-1200, operating synchronously with an ultrasonic anemometer, is investigated.This detector is known to be sensitive to high values of relative humidity (RH) and a new procedure to correct the effect ofRH on concentration measurements is presented. Results of optical measurements have been compared with gravimetricdetections of PM2.5 and results show a reasonable correlation between them and an improvement of the agreement whenRH-correction is used. Results presented have been collected at two measurement sites that can be representative of urbanbackground environments but in one of them was present an industrial area nearby. Post-processing of data has beenperformed with the eddy-correlation technique that allows evaluation of vertical turbulent fluxes of PM2.5 as well assensible heat and momentum fluxes. The turbulent mass fluxes, together with the analysis of real-time concentrations andtheir correlation with meteorology proved to be an useful tool to infer details about the local aerosol dynamics helping tointerpret traditional gravimetric analysis of aerosol that is usually performed on a 24 h basis. Results show that themethodology can be useful in identifying the contribution of local sources like ground level emissions or industrial plumeswith respect to the contribution of sources located far away from the measurement site.