Study On Negative Air Ion Concentration Estimation Combining Chlorophyll Fluoresce And Environmental Meteorological Factors

Recently,the rapid industrialization and urbanization in our country has brought about a series of air pollution problems（smog,dust,acid rain,etc.）,which indirectly led to the emergence of a large number of sub-healthy people.Negative air ion（NAI）has the functions of purifying the air and releasing the sub-health of the human body.Thus it is gradually becoming an important indicator evaluating national ecological development.Analyzing the temporal and spatial distribution of NAI concentration can provide scientific guidance for the environment improvement in our country.At present,most related studies relied only on site monitoring,which only obtained discontinuous NAI distribution.Some scholars had used these data to simulate the spatial distribution of NAI,with spatial interpolation,while spatio-temporal heterogeneity of environmental factors and the limitations of data collection had led to low accuracy and universality of the simulation results.The model inversion can effectively solve these problems.However,since current estimation model inversions had only considered few of the numerous factors,especially the vegetation had not been considered,these models were lack of universality.The development of computer and remote sensing technology has enabled efficient and extensive remote sensing inversion of resource and environmental elements,and the rapid development of vegetation remote sensing technology has also made it possible to estimate NAI at the regional scale.This paper modeled the NAI concentration based on the continuous measurement of a large number of stations NAI and remote sensing products such as meteorology,topography,Sun-induced Chlorophyll Fluorescence（SIF）,and air quality site data in Zhejiang Province.The spatio-temporal distribution of NAI concentration in Zhejiang Province were realized,and the ecological value of NAI concentration were evaluated.The main results and conclusions are presented below:1.Five categories of environmental factors including weather,vegetation,terrain,air quality,and human activity intensity,were extracted from Moderate-resolution Imaging Spectroradiometer（MODIS）,Shuttle Radar Topography Mission（SRTM）,Agrometeorological Indicators From 1979 To Present Derived From Reanalysis（Ag ERA5）,Global Solar-induced Chlorophyll Fluorescence Derived From OCO-2（GOSIF）,Visible Infrared Imaging Radiometer Suite（NPP/VIIRS）and site measured datasets,with a total of23 modeling factors.Then,contribution of each factor on the NAI dynamics was evaluated.Results showed that the top 10 factors that mostly contribute to the NAI variable are Digital Elevation Model（DEM）,ASPECT,SLOPE,Air Temperature（T）,SIF,Relative Humidity（RH）,Carbon Monoxide（CO）,Nitrogen Dioxide（NO₂）,Vapor Pressure（VP）and Sulfur Dioxide（SO₂）,which represented weather,vegetation,topography and air quality factors.These results showed that the NAI dynamics are determined by a variety of factors.Among them,the contribution of SIF only followed terrain factors and T,which fully demonstrates that plant photosynthesis was of great significance to build the NAI inversion model.2.This paper used the random forest method to construct a NAI inversion model based on remote sensing technology to depict the spatial-temporal distribution of air negative ion concentration in Zhejiang Province in 2020.According to the accuracy verification of the model R²=0.878,RMSE=258.617,Bias=14.973,and regional applicability verification results were R²=0.732,RMSE=538.067,Bias=-381.990,which indicated that the model can well depict the spatial dynamics of NAI concentration.Spatially,the NAI concentration in Zhejiang Province was step wisely decreased from southwest to northeast,and temporally,was lower in winter and higher in summer.In general,the annual average NAI concentration in more than 80%of the areas can be classified as II level(1000 Ions cm^-3<NAI concentration≤2000 Ions cm^-3).The NAI concentration in cities and towns can be graded as III level(500 Ions cm^-3<NAI concentration≤1000 Ions cm^-3).3.Based on the remote sensing inversion of NAI in Zhejiang Province,this paper analyzed NAI dynamics under different land cover types from January to December 2020using land cover data.Results showed that the intra-year variations under different land use types are"single peak"type with the highest value in August.The NAI concentration rank was forest land＞wetlands＞bare land＞grassland＞bared land＞construction land.NAI concentration in forest land(1789 Ions cm^-3)was significantly higher than that of other types（p＜0.05）,and the NAI concentration of bared land(1063 Ions cm^-3)and construction land(1042 Ions cm^-3)was significantly lower than the other types,indicating that vegetation significantly increased the level of NAI,while stronger human activity reduced NAI levels.4.This paper evaluated the NAI concentration of 89 scenic spots above 4A level in Zhejiang Province and found that the annual average NAI of scenic spots was level II,and the average NAI concentration of natural scenic spots was higher than that of human scenic spots.Among the natural scenic spots,only one scenic spot was graded as levelⅢ,and there were 8 NAI concentration was graded as levelⅠ.Among the human scenic spots,10 scenic spots were graded as levelⅢ;only 3 of them was graded as levelⅠ(NAI>2000 Ions cm^-3).5.According to spatial-temporal and distribution of NAI concentrations in Zhejiang Province in 2020,the alternative engineering method was adopted to evaluate the maximum potential of NAI ecological value.Results showed that the total ecological value of NAI in Zhejiang Province in 2020 is as high as 1.80×10¹¹ yuan yr^-1.Among them,total NAI ecological value in Lishui(5.05×10¹¹ yuan yr^-1),land area based NAI value(2.93×10² yuan m^-2 yr^-1)and per capita based NAI value(1.86×10⁶ yuan yr^-1)were significantly higher than other cities,while Jiaxing(1.40×10¹¹ yuan yr^-1,30.37 yuan m^-2 yr^-1,3.80×10⁴ yr^-1)was always the lowest.The total ecological value of NAI in Hangzhou(2.74×10¹² yuan yr^-1)and Wenzhou(2.32×10¹² yuan yr^-1)were much higher,but the ecological value of NAI per capita(3.37×10⁵ yuan yr^-1,2.84×10⁵ yr^-1)were not the highest.Spatially,NAI ecological value in Zhejiang were consistent with the spatial change of NAI concentration.The southwest of Zhejiang regions had the greatest potential of NAI ecological value.