Particulate Matter and Number Concentrations of Particles Larger than 0.25 µm in the Urban Atmosphere of Jeddah, Saudi Arabia

ABSTRACT

We investigated the temporal variation of PM and aerosol particle number concentration (TC, D_p 0.25–32 µm) during year 2012 in Jeddah city. We focused on the daily patterns, wind sector analysis, and the effect of ambient conditions. The daily median values of the PM₁₀ rarely exceeded 200 µg/m³. The PM_2.5 and PM₁ concentrations showed similar temporal variation with fraction of 39.5% and 19.3% of the PM₁₀, respectively. The daily median values of the TC were generally below 500 cm^–3 but showed three distinguished peaks (as high as 950 cm^–3) occurred during late September–early November, which was during the time of the Hajj season. These peaks were also observable in the PM_2.5 and PM₁. The PM₁₀ daily pattern on workdays and Thursdays were similar with a pronounced peak as high as 90 µg/m³ during the morning time. The PM_2.5 and PM₁ daily patterns were also similar to those of the PM₁₀, especially on Thursdays and workdays, but with lower concentrations. The TC daily pattern was almost the same on all days showing high concentrations (between 150 and 200 cm^–3) during the first half of the day. The daily patterns of the TC were similar to those of the PM₁, especially on Workdays and Fridays. The emissions from the industrial city (located in the south of Jeddah) are the main source of PM in Jeddah. During the sea breeze that occurred in the afternoon accompanied low concentrations of PM and TC concentrations. The PM concentrations showed the famous U-shape with respect to the wind speed, whereas the TC was around 150 cm^–3 when the wind speed was over 3 m/s. In general, the TC had a different behaviour with respect to the other ambient conditions than that of the PM concentrations, especially PM₁₀.