Urban Aerosol Particle Size Characterization in Eastern Mediterranean Conditions

Characterization of urban particle number size distribution (PNSD) has been rarely reported/performed in the Middle East. Therefore, we aimed at characterizing the PNSD (0.01–10 µm) in Amman as an example for an urban Middle Eastern environment. The daily mean submicron particle number concentration (PNSub) was 6.5 × 103–7.7 × 104 cm−3 and the monthly mean coarse mode particle number concentration (PNCoarse) was 0.9–3.8 cm−3 and both had distinguished seasonal variation. The PNSub also had a clear diurnal and weekly cycle with higher concentrations on workdays (Sunday–Thursday; over 3.3 × 104 cm−3) than on weekends (below 2.7 × 104 cm−3). The PNSub constitute of 93% ultrafine fraction (diameter < 100 nm). The mean particle number size distributions was characterized with four well-separated submicron modes (Dpg,I, Ni): nucleation (22 nm, 9.4 × 103 cm−3), Aitken (62 nm, 3.9 × 103 cm−3), accumulation (225 nm, 158 cm−3), and coarse (2.23 µm, 1.2 cm−3) in addition to a mode with small geometric mean diameter (GMD) that represented the early stage of new particle formation (NPF) events. The wind speed and temperature had major impacts on the concentrations. The PNCoarse had a U-shape with respect to wind speed and PNSub decreased with wind speed. The effect of temperature and relative humidity was complex and require further investigations