The Mediterranean region is an important area for air pollution as it is the crossroads between three continents; therefore, the concentrations of atmospheric aerosol particles are influenced by emissions from Africa, Asia, and Europe. Here we concentrate on an eleven-month time series of the ambient concentration of organic carbon (OC) and elemental carbon (EC) between May 2018–March 2019 in Amman, Jordan. Such a dataset is unique in Jordan. The results show that the OC and EC annual mean concentrations in PM2.5 samples were 5.9 ± 2.8 µg m–3 and 1.7 ± 1.1 µg m–3, respectively. It was found that the majority of OC and EC concentrations were within the fine particle fraction (PM2.5). During sand and dust storm (SDS) episodes OC and EC concentrations were higher than the annual means; the mean values during these periods were about 9.6 ± 3.5 µg m–3 and 2.5 ± 1.2 µg m–3 in the PM2.5 samples. Based on this, the SDS episodes were identified to be responsible for an increased carbonaceous aerosol content as well as PM2.5 and PM10 content, which may have direct implications on human health. This study encourages us to perform more extensive measurements during a longer time period and to include an advanced chemical and physical characterization for urban aerosols in the urban atmosphere of Amman, which can be representative of other urban areas in the region.
Optimization of dry deposition velocity calculation has been of great interest. Every time, determining the value of the concentration boundary layer (CBL) thickness led to a waste of numerical calculation time, which appears as a huge time in large-scale climate models. The goal of this study is to optimize the numerical calculation time in the three-layer deposition model for smooth surfaces through the development of a MATLAB code that can parameterize the appropriate concentration boundary layer height (y+cbl) and internal integral calculation intervals for each particle diameter Dp (0.01–100 µm) and friction velocity u* (0.01–100 m/s). The particle concentration, as a solution to the particle flux equation, is obtained and modeled numerically by performing the left Riemann sum using MATLAB software. On the other hand, the number of subdivisions N of the Riemann sum was also parameterized for each Dp and u* in order to lessen the numerical calculation time. From a numerical point of view, the new parameterizations were tested by several computers; about 78% on the average of the computation time was saved when compared with the original algorithm. In other words, on average, about 1.2 s/calculation was gained, which is valuable in climate models simulations when millions of dry deposition calculations are needed.
Objective: Dry deposition velocity towards a surface is commonly investigated by modelling. However, there is still a lack of understanding about the nature of the concentration boundary layer (CBL). Methods: We aimed at acquiring in-depth description of the particle concentration profile within the CBL by investigating the layer height and the concentration profile. The particle concentration, as a solution to the particle flux equation, is obtained and modeled numerically by performing left Riemann sum using MATLAB software. The friction velocity u^* and the particle diameter D_p are the major parameters taken into consideration when characterizing the concentration boundary layer above a surface. The particle concentration profile depends on the friction velocity; the concentration gradient starts from zero at the surface and reaches its maximum in the middle of the layer and then reaches zero again at the top of the boundary layer Results: The concentration profile is slightly altered with a sudden increase in the concentration gradient at the surface when considering large particles or when the friction velocity is has extreme values. Conclusion: The boundary layer height (y+cbl) varied with the particle diameter, and a proper value is 100 to ensure accurate calculations for the dry deposition velocity (diameter 0.01 – 100 µm) above a smooth surface. From a numerical point of view, the numerical setup of the calculation required y+ divisions to be more than 1000 for all particle diameters included in the investigation. In addition, y+max = 104 is important for ultrafine particles (diameter smaller than 0.1 µm). Nevertheless, y+max does not need to be investigated beyond 100 when the friction velocity is below 10 cm/s.
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