Temporal And Spatial Distribution Of Biogenic Pollen Particles In The Air Of Xi’an City

The quality of atmospheric environment directly affects people’s life and health,in which particulate matter is an important factor.Atmospheric particles include not only various organic and inorganic particles,but also living particles such as pollen.In this paper,the concentration distribution and composition characteristics of pollen particles in the air were studied,and the diffusion ability of seed pollen and the factors affecting the concentration change of pollen particles were analyzed.The main conclusions are as follows:(1)The results of gravity method and volume method are consistent.The gravity method can collect pollen grains in the plane area,which is convenient and simple,and can be used for long-time periodic research;Volume method can reflect the concentration and species of pollen particles in the air.Due to the need of equipment,it can be used for high-precision observation of individual points.(2)The annual variation of the concentration of biogenic pollen particles in the air showed a bimodal distribution.The peak of pollen concentration appeared in spring in May and early June.The second peak of pollen concentration appeared in autumn from August to October,and the concentration of pollen in the air was low in the rest of the time;In the vertical spatial distribution,with the increase of sampling height,the pollen concentration increased correspondingly,and the pollen particles collected at 30 m altitude were twice as high as that at 1.5 m altitude.(3)In spring,the peak of biogenic pollens was mainly woody pollens such as Platycladus and Cupressaceae,while in autumn,the main pollens were herbaceous pollens such as Compositae,Gramineae and Chenopodiaceae;Chenopodiaceae,Compositae,Cupressaceae,Populus,Campanulaceae and Oleaceae accounted for 53.88%of the total pollen,which were the main dominant pollen species in Xi’an.(4)The diffusion rate of dandelion seeds with villi ranged from 0.24 m/s to 1.09 m/s,and villi could delay the seed sedimentation;There is a significant negative correlation between the horizontal propagation distance and the landing rate,that is,the longer the landing time is,the farther the horizontal diffusion distance is.(5)The number of pollen decreased with the increase of rainfall,but the pollen concentration increased on the day of rainfall.The pollen concentration in the air continued to decrease in the next 3-4 years,and then gradually increased;There was a significant negative correlation between relative humidity and pollen concentration,and the pollen concentration reached the maximum when the relative humidity was between60% and 65%;When the wind speed is 1～3 m/s,the pollen concentration in the air increases with the increase of wind speed,but when the wind speed is more than 3 m/s,the collected pollen particles decrease,and the average wind speed of about 2.5 m/s is most conducive to the pollen dispersion;When the temperature fluctuates,the number of pollen also fluctuates obviously.The change is more obvious in April to May and August to October when the pollen concentration is higher.At about 25℃,the number of pollen in the air reaches the highest.When the temperature reaches 30℃,the pollen concentration does not increase.The change of temperature on the same day affects the pollen concentration after 1 to 2 days.