Component Characteristic Of Water-soluble Ions In Pm_2.5 And Its Influencing Factors In A Coastal City From Zhejiang Province,China

With the social and economic development.the acceleration of the urbanization,problem of regional environmental pollution is raised.In recent years,haze weather appears frequently in coastal cities in Zhejiang Province,seriously affected the local public health.Since PM_2.5 is widely known as the main factor for the dust haze in the cities and the water-soluble ions are the main component of PM_2.5,the water-soluble ions in the particles are urgently needed to be studied.The present thesis studied the content,distribution charactristic,seasonal variation of the water-soluble ions in PM_2.5,analyszed the relationships among the water-soluble ions as well as the correlation of the weather factor and the water-soluble ions,and furtherly proposed corresponding policies and suggestions,based on the test data from an auto-monitoring station for the ambient air quality in a coastal city in Zhejiang Province,China.The following conclusions are thus made:1.The concentration of the water-soluble ions took up above 50%of the mass concentration of PM_2.5 and there was a significant correlationship between the two.The seasonal variation tendency of both was also quite similar:the concentration in the summer was relatively lower,that in spring and autumn followed while the concentration in winter was the highest,for in summer they were greatly affected by the air mass from the ocean which was slightly polluted.Meanwhile,the sun exposure was stronger and the temperature was higher in summer so that the air pollutants were more easily to be dispersed,while in winter,under the influence of the polluted air mass from the inland as well as the pollution of the local area,the pollutants were harder to be dispersed due to the lower temperature and mixed layer height.2.In all the water-soluble ions of PM_2.5,SO₄^2-,NO₃^-and NH₄⁺/took up over 80%of the total ions content as the major water-soluble ions.The ratio of NO₃^-/SO₄^2-indicated that the stationary pollution source of the area was the root reason for the air pollution.However,with the increasing improvement of the people’s life,the car ownership of the coastal regions in Zhejiang increased annually and the exhaust emission of the motor vehicles thus exerted greater impacts on the atmosphere.In spring,the ratio of NO₃^-/SO₄^2-was higher,even beyond 1 in some of the monitored days.It meant that the exhaust pollution played a more important role in the atmospheric pollution and the traffic pollution became even more serious.3.According to the analysis on the seasonal variation of the dominant ions,the contents of NO₃^-and NH₄⁺ changed more distinctly throughout the four seasons.The concentration in winter was highest and that in summer was the lowest since in summer the temperature was higher and the oxidization rate of NOx,the precursor gaseous substance was also higher so that the concentration of NO₃^-in the particle phase since the nitrate ion could not exist in the phase of particle.By contrast,in the low-temperature winter,the nitric acid was easy to transfer to the ammonium nitrate in the phase of particle,which led to the higher concentration of NO₃^-in the water-soluble ions.Besides,the concentration of SO₄^2-was also lower in summer and higher in winter but the rangeability was not large due to the fact that in summer when the temperature was high and the sun exposure was strong the transformation rate from the gaseous SO2 to the particle-phase sulfate was higher,while in winter the transformation process last longer.4.The concentration of Na⁺ was not obvious due to the bigger influence of the air mass from the ocean in summer.Na⁺ mainly came from the sol of the sea salt.The ion content of Cl-changed obviously with seasons:highest in winter and relatively lower in summer mainly due to the chlorine consumption in summer and chlorine enrichment in winter.The average content of K+ changed slightly with seasons,indicating that the biomass burning in the area was characterized by the regional pollution that had some influence on the atmospheric quality but not as the main source of the air pollution.Ca2+ took up only a small proportion in the water-soluble ions and was lower in concentration.It mainly came from the human-induced reasons such as the ground dust and construction dust.5.The correlation analysis of the major water-soluble ions showed that there was a significant correlation among NH₄,SO₄^2-and NO₃^-,which indicated that the main forms of SO₄^2-and NO3 in the water-soluble ions of PM_2.5 were（NH₄）2SO4 and NH₄NO3.There was a significant correlation between K+ and Cl-,SO₄^2-and NO₃^-in the anion,indicating that in the water-soluble ions of PM_2.5 kalium could exist in all the three forms of KCl,K2SO4 and KNO3.6.There was no significant correlation between the air temperature and the concentration of the ions,which meant that temperature was not the main factor that influenced the total content of the water-soluble ions.Furthermore,the relative humidity exerted distinct influence on the concentration of the water-soluble ions in PM_2.5:when the relative humidity was greater,the amount of the particles in the atmosphere would increase,which might lead to the increase of the concentration of the main water-soluble ions.Precipitation seemed to have obvious scavenging effect on the water-soluble ions and there was significant negative correlationship between the wind speed and the concentration of the dominant ions of the aerosol,indicating that the water-soluble ions were more easily to disperse and dilute in the atmosphere at the higher wind speed.7.Based on the source identifying of the water-soluble ions in the fine particles,some counter-measures were proposed.