WRF-Chem Based Coastal Area Study On The Migration And Diffusion Law Of Airborne Pollutants

With the rapid development of China’s offshore economy and the acceleration of modernization and industrialization,air pollution has become one of the most important environmental problems in offshore areas.The report of the 20th National Congress of the Communist Party of China proposed to further promote environmental pollution control,strengthen coordinated control of pollutants,and continue to fight the blue sky defense war.During the 14th Five-Year Plan period,China’s industrial green development aims to achieve the coordinated management of fine particulate matter(PM2.5)and ozone(O3).The terrain and climate environment in the offshore area are complex,and the industry is developing rapidly.It is vulnerable to the pollution of airborne pollutants such as PM2.5 and O3.Sea-land breeze circulation is closely related to air pollution.Both sea breeze and land breeze have a certain impact on the diffusion of air pollutants in the air,thus affecting air quality.In order to improve the air quality in coastal areas and pay attention to air pollution,the influence of climatic conditions on the concentration distribution of airborne pollutants has become a hot topic for scholars in recent years.Therefore,this paper selects a city in the offshore area as the research area,and uses the WRF-Chem air quality model to study the migration and diffusion of airborne pollutants in this area,and uses the HYSPLIT backward trajectory model to further analyze the sources of airborne pollutants.The main results are as follows:(1)The four boundary layer schemes of YSU,MYJ,MYNN2 and BL in the WRF-Chem air quality model were used to simulate the wind speed at different heights in the near surface layer of the study area.Based on the physical scheme,RADM2 gas phase chemical mechanism and MADE/SORGAM aerosol scheme are added to simulate.The results show that the WRF-Chem air quality model can better restore the concentration distribution of PM2.5,PM10 and O3,which verifies the feasibility of WRF-Chem air quality model for the simulation of the selected research area.(2)The wind field in the study area is analyzed,and the period of typical sea-land breeze days is selected.The results show that due to the enhancement of solar radiation during the day,the land temperature rises faster than the sea level,and the thermal properties of land and sea are obviously different.With the disappearance of solar radiation at night,the sea level temperature is higher than that of land,and the land wind gradually forms,resulting in the land wind blowing from land to sea in the northeast direction.(3)For the influence of sea-land breeze on the concentration distribution of airborne pollutants,the influence of sea-land breeze on the distribution of PM2.5 and PM 10 is roughly the same.Sea breeze will lead to the accumulation of pollutants in offshore areas,resulting in high value areas of airborne pollutant concentration and reducing air quality.The land breeze has a dilution and diffusion effect on these two types of airborne pollutants,reducing the accumulation of pollutants,thereby improving air quality.However,as far as O3 is concerned,due to the special nature of O3 itself,O3 is a secondary pollutant that is not directly generated.It is formed by photochemical reaction of nitrogen oxides and hydrocarbons in the atmosphere irradiated by the sun.Therefore,both sea breeze and land breeze will cause the accumulation of O3 concentration in inland areas,resulting in pollution.(4)The HYSPLIT backward trajectory model is used to analyze the source of airborne pollutants in the study area.The results show that the pollutant air mass in a city in the offshore area mainly comes from the northeast and southwest directions above the sea level.The air mass trajectories in these two directions together cause the pollutant accumulation in the study area.The innovation of this paper is to study the influence of sea-land breeze on the concentration distribution of airborne pollutants in offshore areas by using a new generation of air quality model coupled with WRF model and Chem chemical model.