Temporal Variations of Submicron Particle Number Concentrations at an Urban Background Site in Amman-Jordan

This paper presents the temporal variation of fine particle number concentrations and their dependence on some weather parameters (T, P, and RH) during August 2016 – May 2017 at an urban background site in Amman. The measurement was conducted with a condensation particle counter with one-minute time resolution. The daily mean concentrations showed a clear annual cycle (annual average of ~8×10^3 cm^-3) with high concentrations (~2.8×10^4 cm^-3) during winter and low concentrations (~1.2×10^4 cm^-3) during summer. This annual cycle was inversely correlated with the daily mean temperature (T), but was proportional with the daily mean relative humidity (RH); however, the concentration cycle had about a twenty-two day shift with respect to T and RH cycles. Further analysis based on the hourly mean aerosol database revealed a weekly cycle and distinguished daily patterns for three types of days: (1) Sunday–Wednesday, (2) Thursday, and (3) Friday–Saturday. The workdays had the highest daily mean concentrations, and their daily pattern had the highest concentrations during morning rush hours. The weekend type daily pattern had the highest concentrations during midday and late night. Both pattern types had the lowest concentrations between the times 03:00 – 06:00. These temporal variations (annual, weekly, and daily) reflect the anthropogenic emissions, especially those emitted from combustion traffic-related activities in the city. The aerosol database was of a long-term type (about eight months in total), which encourages the researchers to perform more extensive measurements for a longer term to fill in the missing gaps and reveal more accurate temporal characteristics of the fine particle number concentrations.