2.3. Physical characterization of PMPM size distribution determination and analyses of single particles were carried out using scanning electron microscopy (SEM) coupled with energy dispersive X-ray analysis (SEM-EDX; SEM Hitachi SU3500 and EDAX Premium Octane Ametek, Germany). The automatic mode of SEM was used with the following operating conditions for determination of PM size: accelerating voltage = 10 keV;intensity = 300 nA; and magnification = 5000. A Nanophox instrument (1000 HS,Malvern Instruments Ltd., UK), based on the dynamic light scattering measurement technique, was used to analyze the size distribution of PM2.5.