Number and Size Distribution of Airborne Nanoparticles during Summertime in Kuwait: First Observations from the Middle East

We made fast response measurements of size-resolved particle number concentrations (PNCs) and distributions (PNDs) in the 5-1000 nm range close to a busy roadside, continuously for 31 days, in Kuwait. The aims were to understand their dispersion characteristics during summertime and dust events, and association with trace pollutants (NOx, O-3, CO, SO2, and PM10) and meteorological parameters. PNCs were found up to similar to 19-times higher (5.98 x 10(5) cm(-3)) than those typically found in European roadside environments. Size distributions exhibited over 90% of PNCs in ultrafine size range (<100 nm) and a negligible fraction over 300 nm. Peak PNDs appeared at similar to 12 nm, showing an unusually large peak in nucleation mode. Diurnal variations of PNCs coincided with the cyclic variations in CO, NOx, and traffic volume during morning and evening rush hours. Despite high traffic volume, PNC peaks were missing during noon hours due to high ambient temperature (similar to 48 degrees C) that showed an inverse relationship with the PNCs. Principal Component Analysis revealed three probable sources in the area-local road traffic, fugitive dust, and refineries. Dust events, categorized by PM10 with over 1000 mu g m(-3), decreased PNCs by similar to 25% and increased their geometric mean diameters (GMDs) by similar to 66% compared with nondust periods.