Morphology And Components Of Atmospheric Particulate Matters From Motor Vehicles In Typical Regions

With the rapid growth of automobile volume,particulate matters exhausted from motor vehicles have been one of the main sources of PM_2.5.However,the source appointment of atmospheric particulate matters has been always a serious problem.In this paper,a thorough investigation on the characteristics of external morphology and internal component for both the raw diesel/gasoline particles and the diluted particles from motor vehicles in atmosphere was carried out,which helps to identify the source of atmospheric particulate matters.Particulate matter samples from different sources were collected by the Micro-orifice uniform deposition impactors（MOUDI）.A variety of theory and measures including fractal theory,Field emission scanning microscope（FESEM）,Energy dispersive X-ray spectroscopy（EDX）and organic carbon/elemental carbon analyzer were employed to investigate the size distribution,external morphology and internal component of atmospheric particulate matters from motor vehicles in typical regions,which assists to present a valuable reference for the source appointment of atmospheric particulate matters from motor vehicles.The main researches and conclusions are as follows:（1）The size distribution of particulate matters collected respectively from the diesel/gasoline engine,near the chimney of an engine laboratory and in the basement garage with MOUDI was investigated.It was revealed that with the increase in particle size,the mass concentration of raw diesel/gasoline decreased.For the diffused particles in atmosphere,the most mass concentration of particles collected near the chimney of an engine laboratory was located at the size of 0.32⁰.56μm,while particles with the size of 1.0¹.8μm gathered in the basement garage took the most mass fractions.（2）Surface morphology of atmospheric particulate matters from motor vehicles in typical regions was detected by FESEM.Most of the raw diesel particles were spherical,and particles with small sizes were more agglomerative.While for those atmospheric particulate matters collected from typical regions,particles with large size were prismatic,and particles with small size were spherical.（3）The fractal characteristics of atmospheric particulate matters was interpreted with the assistance of Matlab.It was revealed that the box dimensions of raw diesel particles at each one given size were greater than others.With the decrease in particle size,the box dimensions of each particle from different sources increased.（4）The element contents of particles collected from different sources were detected by EDX.It was revealed that raw diesel particles contained a great number of carbon and oxygen.While atmospheric particulate matters from motor vehicles had many kinds of elements.With the increase in particle size,atmospheric particulate matters from motor vehicles had more calcium and silicon contents,which indicates there were many mineral and dust in big particles.（5）The carbon component of particulate matters as well as the ratio of OC/EC was determined by the organic carbon/elemental carbon analyzer.Results showed that OC1,OC2 and OC3 were the major part of OC contents in raw diesel particles,while the OC4 content was few.EC2 took the main part of EC.There were more OC3 and OC4 contents in the atmospheric particles collected in typical regions,while the most volatile content of OC1 was few.EC1 was the main part of EC in particles collected in the basement garage.The ratios of OC/EC ranged from 0.92 to2.50 in raw diesel particles.With the increase in particle size,the ratios of OC/EC increased.The ratios of OC/EC ranged from 1.40 to 2.53 for particles collected near the chimney of an engine laboratory,and they ranged from 2.36 to 4.82 for particles collected in the basement garage.With the increase in particle size,the ratios of OC/EC decreased at first and then increased.Moreover,the ratios of OC/EC in particles collected in the basement garage normally exceeded 2.0（largest 4.82）,which hints that there were a large number of secondary particles generated in the basement garage.