Investigating the amount of pollutants emitted from the exhaust of diesel cars in the city of Mashhad using statistical analysis

Air pollution is one of the important environmental problems in the modern world. Sources of air pollution are various and variable. the share of air pollution resulted from vehicles traffic finds importance increasingly and has become an important environmental and health issue. It has been announced that around 80 percent of air pollution is related to the mobile sources, and to control and reduce air pollution, the priority should be assigned to vehicles, particularly heavy and public vehicles. Despite the many advantages that made diesel engines used in the past for various purposes and in various types of vehicles, their use for passenger car propulsion has faced problems that have prevented their large production in this field. The most important of these problems are: more noise and vibration than gasoline cars, bad smell of diesel when refueling, emission of gas and visible smoke from the exhaust, higher price than gasoline cars, low acceleration and speed, and bad starting in cold weather. Despite these problems, these cars are still very popular due to their economical fuel economy.Researchers have identified a significant relationship between the amount of air pollution, respiratory diseases and cardiovascular diseases, which have a special importance in the admission rate of hospitals in metropolitan cities. Therefore, according to the small number of studies conducted in the field of the effect of emissions caused by diesel cars in the field of air pollution, the purpose of the current study is investigating the amount of exhaust emissions of diesel vehicles and the relationship between such amounts and the life of the vehicle, in the city of Mashhad.

In the current study, in order to investigate the amount of exhaust emissions of diesel vehicles among all vehicles of this type throughout Mashhad, which were 5861 vehicles, 425 vehicles were selected randomly. The diesel vehicles used in the present study included garbage trucks, buses, minibuses, garbage Nissan Junior, Isuzu garbage truck, Dongfeng irritation truck, HOWO irritation truck, garbage Hyundai truck, irritation Benz truck, sweeper vehicles, irritation Volvo truck, garbage Amico truck, Fh12 irritation truck, Kavian garbage truck.The sampling of the study was carried out continuously from December 6, 2017 through April 29, 2018 (except for 1st to 4th of Farvardin Iranian Month), from 9 a.m. to 12 p.m. and 15 p.m. to 20 p.m.Sampling was conducted by the five-gas detector (NDIR OPTIM7), the model of which was MRU, and it was made in Germany. Sampling was conducted when the engine was idling. Before the experiments, the device was tested and calibrated by the maker. The gases measured by the five-gas detector included HC, CO2, CO, O2 and NOx. The device is connected to the compute by Bluetooth and it includes a software program by which it is possible to run and test the device and observe and record the amount of pollution. The device used in the current study was calibrated by the relevant manufacturing company, before the experiments.Finally, after collecting data, they were analyzed by SPSS (version 20) statistical software. Considering that the variables were not normalized, the Kruskal-Wallis Test was used. Given the significance of Kruskal-Wallis Test, the post hoc test relevant to the Kruskal-Wallis Test, meaning the Dunn's Multiple Comparisons Test, was used, which is calculated by the Prism software. Moreover, In order to draw diagrams, the Excel software was used.

A comparison of the average CO emissions among different groups of vehicles:The highest amount of CO pollutant emissions is related to the sweeper vehicles. The minibuses are in the second place, heavy vehicles in the third place, semi-heavy vehicles in the fourth place and the lowest amount of CO emissions is related to the buses. Considering the post hoc test conducted, there is a difference between semi-heavy vehicles and sweeper vehicles, in terms of CO. considering the obtained results, it might be concluded that the fuel combustion in sweeper vehicles occurs in a more incomplete way compared to the semi-heavy vehicles. A comparison of the average HC emissions among different groups of vehicles:The highest amount of HC pollutant emissions is related to the minibuses. The heavy vehicles are in the second place, sweeper vehicles in the third place, buses in the fourth place and the lowest amount of HC emissions is related to the semi-heavy vehicles. The highest amount of HC pollutant is related to the minibuses, which is probably due to the low density or improper spraying of injectors; however, by modifying the geometric shape of the combustion chamber and the piston head at the time of combustion and density, the ratio of the mixture of air and fuel or turbulence increases, the result of which is complete combustion with minimum amount of CO and HC polluting gases. A comparison of the average CO2 emissions among different groups of vehicles:The highest amount of CO2 pollutant emissions is related to the buses. The minibuses are in the second place, sweeper vehicles in the third place, heavy vehicles in the fourth place and the lowest amount of CO2 emissions is related to the semi-heavy vehicles. As seen in the current study, buses, compared to other vehicles, produce the highest amount of CO2 and the lowest amount of CO, which indicates complete combustion in them. A comparison of the average NOX emissions among different groups of vehicles The highest amount of NOX pollutant emissions is related to the minibuses. The buses are in the second place, heavy vehicles in the third place, semi-heavy vehicles in the fourth place and the lowest amount of NOX emissions is related to the sweeper vehicles. by using the system of exhaust gas recirculation on the engines with the TIER3 emission standard, the temperature of gases exiting the exhaust becomes normal and as a result, the amount of NOX emissions from the exhaust decreases. However, when the engine runs at a high speed and under high load, the temperature rises at the time of combustion, and as a result, the temperature of the gases exiting the exhaust rises, too, and consequently, the amount of NOX increases.