Fine Particle Number Concentrations in Amman and Zarqa during Spring 2014

We measured the fine particle number concentrations at four sites in Amman and one site in Zarqa during March 6 – May 28, 2014. These were urban except for one, which was a sub-urban site. The highest number concentrations (24-hour median as high as 5.2×10^4 cm^-3) were observed at Hai Masoum; an urban site in Zarqa influenced by traffic and industrial activities. In Amman, the highest number concentrations were observed at the urban residential sites (Umm Summaq and Al-Hashmi Al-Shamali, 24-hour median as high as 4.6×10^4 cm^-3), whereas the lowest was at the sub-urban site (Shafa Badran, 24-hour median as high as 2.3×10^4 cm^-3). The daily pattern of the fine particle number concentrations was characterized by three peaks during the daytime. The first and last peaks are probably related to the morning and afternoon traffic rush hours, which are similar to those observed in the developed countries. The third peak was around midday, which is possibly related to increased traffic activities related to school buses. The lowest concentrations (~4600 cm^-3) at Shafa Badran were observed after midnight and before the morning rush hours. Different lowest values were observed at the five sites because of different population densities and nearby anthropogenic activities.