RESUMEN
PM10 and PM2.5 samples were collected using the particulates E-Sampler from congested roads in three major cities of Oman. The average PM10 concentration varied from 35.87 µg/m3 in Salalah during the monsoon season to 18.95 µg/m3 in Sohar. PM2.5 concentration ranged from 20.74 µg/m3 in Muscat to 7.20 µg/m3 in Sohar. Average concentrations of PM10 and PM2.5 in all cities were below NAAQS and WHO standards. Scanning Electron Microscopy coupled with energy dispersive spectrometer (SEM-EDS) of PM2.5 particles from all cities showed spherical like fly ash and chain like soot aggregates. These might have originated from fuel burning and vehicle emissions. Fe, O and Si are the major components present in the PM2.5 and PM10 particles while other elements are present in lower percentages. PM10 particles collected from Muscat and Salalah were irregular and chain like soot aggregates that are referred to originate from natural and anthropogenic emissions. However, PM10 collected from Sohar showed irregular shape containing aluminosilicate particles that might have initiated from natural sources.