The Study Of Influence Of Atmospheric Iodine On Formation Of Secondary Particles

As the phenomenon of haze around our country become more and more frequent, covering area is more and more wide,fine particles caused haze weather received unprecedented attention in our country.Particles induced haze are mainly secondary particles.Secondary particles was formed through physical and chemical reaction of primary pollutants(SO2, NOx, HC, etc.) in the atmosphere,with small size, large surface area and long time in the air.And secondary particles can harm the environment and hμman health seriously.Iodine(I) takes a great part in the photochemical reactions of troposphere, which has a close connection with the loss of ozone layer, the formation of marine aerosols, and cloud condensation nuclei in marine boundary layer, even the earth’s albedo and global climate.Sulfate is the main species of secondary particle, and iodine can increase the retention rate of sulfate nucleation one hundred times.This paper studied nucleation of iodine, the effect of environmental factors(sample heating temperature, illμmination and oxalic acid) on nucleation of iodine, and the effect of iodine on the system composed of NO2, NH3, NO and SO2.In this study,we found that both in dark and light conditions, nμmber concentration and mass concentration of generated particles increase with the addition of the iodine solution increase. The experiment which only add KI solution showed that mass concentration of particles formed in illμmination conditions is greater than that in dark environment.The reason may be that there have two kinds of mechanisms:(1) the reaction among I-,O2 and H2 O is the main mechanism in light condition;(2) I- may prefer to react with O3 in dark environment.From the studies of the effect of environmental factors on iodine nucleation, we found sample heating temperature have less effect on the particle size distribution, however, light has a promoting effect on growth of particle size and particle mass concentration.Oxalic acid basically have no effects on the particle nμmber concentration, but could inhibit the growth of particulate matters,which lead to the decreases of particulate mass concentration.In the dry and dark environment, the hybrid system composed of NO2, NH3, NO and SO2 cannot be found the formation of new particle,however,when adding iodine solution, large amount of particles are generated,and nμmber concentration and mass concentration of particles were larger than which generated iodine itself. This suggested the presence of iodine can promote gas mixture to participate nucleation and growth of new particles.We estimates that in the higher relative hμmidity environment, the promoting effect of iodine can be more obvious.In the mixed system of NO2, NO, NH3 and SO2 and iodine, SO2 may be involved in the formation or growth of new particles.And the concentration of SO2 can affect the mass concentration of secondary particles. When there have iodine in the smog chamber, NO2 is involved in the photochemical reaction of the mixed system, and NO2 have inhibitory effect on nucleation of iodine and the formation of new particles, the higher the concentration, the more obvious inhibitory effect. The reasons may be : NO2 may change the related chemical mechanism of gas phase and have an effect on subsequent gas particle distribution and mass concentration of particulate matter.Even the influence mechanism has great relationship with NO2 concentration.