Abstract
Particle size distribution measurements from 7 nm to 850 nm are being conducted in Western Saudi Arabia utilizing a Differential Mobility Particle Sizer (DMPS). The early results show that the particle size distribution is highly variable, with signatures from the nucleation, Aitken, and accumulation mode. The accumulation mode dominates from midnight to early morning, after which an elevated Aitken mode appears, denoting to local morning activities. New particle formation begins regularly around 10 am, elevating first the nucleation mode concentrations and then the Aitken mode. During evening hours, the nucleation-and Aitken mode concentrations decrease, and the accumulation mode becomes dominant again. The average particle number concentration from December 2012 was 1640 #/cm(3). The maximum particle concentration in the region is originated from new particle formation, with a maximum 1h-average of 11400 #/cm(3).