فهرست مطالب امیر باقری مصلح آبادی

Particulate pollutants in urban areas affect human health, environment clouds and climate. With rapid growth of the population and increase in the number of vehicles, in urban areas, air pollution also in large cities has increased substantially. Mobile sources of air pollution have a major contribution to the pollutant levels in urban areas. For example, motor vehicles (gasoline and diesel) play a major role in air pollution in large cities such as Tehran and in fact, they are the main sources of primary aerosols emissions. Aerosols can act as cloud condensation nuclei (CCN) and ice nuclei (IN) and impact on precipitation of different regions. Precipitation can also supply water resources and help to improve the air quality of cities. In Iran, most clouds are cold clouds and ice crystals play a major role in cold precipitation. Using field emission scanning electron microscopy and energy dispersive X-ray spectroscopy (FESEM/EDX) methods, morphology and elements composition of aerosols from the vehicle exhaust pipes were investigated. In this study, we injected such aerosols into a cold cloud chamber in laboratory to get a better understanding of microphysics processes on interaction of urban aerosols and clouds. The experimental simulations include growth of graupels through rotating rods mechanism in the presence of vehicles produced aerosols and supercooled droplets. In order to obtain size distribution of supercooled droplets we used replicas method. Also we focused on ice crystals and the impact of pollutant particles on the ice crystals in cloud microphysics. The size distribution of ice crystals was evaluated from images of fallen crystals on a lamella under a microscope. By creating an electric field inside the cloud, the effect of these particles on the electrostatic torque of the ice crystals has been tested. It can provide a better view of predicting the short term lightning. The results show that vehicles produced aerosols are mainly soot and ash and in the presence of these particles, the average diameter of supercooled droplets decreases. By decreasing diameter of supercooled droplets, the growth of the graupel also decreases. Besides, the average diameter of the ice crystals in the presence of vehicles produced aerosols was reduced. However, pollutant particles do not have much effect on the electrostatic torque of ice crystals. The shape of the observed crystals in the experiments included hexagonal, stellar and sectored plates, solid and capped columns, prisms, triangular shapes, needles and dendrites. Because of the different thickness of various parts of the ice crystal exposed to light, different wavelengths of dispersed visible light with different colors appear and then, it can be seen in different colors (like a soap bubble exposed to light). When the crystals are grown large enough, they appear white. With more sophisticated mentoring system, one may distinguish between the formed crystals in different aerosol types.

Fog formation reduces the visibility, and low visibility cause problems mainly in airports and roads. Fog modification or even clearance can reduce such problems. Here, in the laboratory the effects of some aerosols on the modification of artificial fog have been investigated. This research is carried out using the method used in the work of Vajaiac et al. (2014), for hydrophilic particles. These particles, as the fog modification factor, can be effective as condensation nuclei by increasing the effective radius of the droplets and reducing the concentrations of the fog droplets in the fog.. We used a glass chamber with a height of 41cm and diameter of 28 cm in which a red laser and a detector were placed on both sides of the chamber. We dissolved water-soluble compounds in water and by pumping the air into water of the chamber, the bubbles are formed and their breaking led to formation of particles. Then the particles are dispersed inside the chamber, while the pressure inside the chamber was increased with an air pump, and so the temperature was rised. Then suddenly or quasi-adiabaticaly, the pressure is released and hence, the air temperature was dropped creating the fog (cloud). The cloud droplets are mainly formed on these particles. With the formation of droplets, the received laser signal was decreased and after falling all of droplets, the received laser signal reached its primary level. Hence, by measuring the level of drop in the signal and its duration some properties to the cloud structure can be found. In this study, we used sodium hydroxide, urea, and salt particles that was compared with background aerosols affecting the cloud. First, the optical depth of fog was calculated and then size distribution of fog droplets was estimated. Also other parameters like the concentration of the fog droplets, liquid water content and fog lifetime were evaluated. The results show that hydrophilic particles as condensation nuclei played a significant role in fog modification. So, in the presence of these particles, the concentration of fog droplets in comparison with that of the background aerosols, was decreased and the fog was diluted significantly. The maximum of fog lifetime was observed in the presence of background aerosols as 63 s, also these particles have had the lowest effective radius of 7.77µm. In the presence of sodium hydroxide particles, the concentration of total droplets was decreased significantly. In addition, the maximum effective radius was 10.48 µm for these particles. Also, fog lifetime was reduced to 31s which suggests that this component for fog modification has a better performance. The area under the curve’s of the size distribution of droplets for salt and urea were nearly identical, that indicated the concentration of the droplets was close to each other. Parasitic structures might appear in curves of the size distribution of droplets that were smoothed. As the time passed all of the effective radius curves showed decreasing trends due to the fact that, the larger droplets can droped out of the laser beam, so gradually the effective radius should be decreased. In comparison with other compounds, when sodium hydroxide particles were used in the cloud chamber, observationally small droplets that moved up an down in the laser beam weren’t present, hence no oscillations were seen in the laser signal. Considering experimental errors, while neglecting the process of coalescence that might occur in the falling stage of the droplets, when the droplets were passing the laser beam, they appeared at larger sizes, which could lead to an overestimation. The signal noises and non-uniform distribution of condensation nuclei could also be considered as experimental errors.