A Study On The Purification Effect Of Nitrogen Oxides In An Urban Area By Plants Based On A Stable Isotope Method

As a consequence of rapid urbanization,industrial activity and transportation,the deterioration of the atmospheric environment in urban area is more serious than other areas.Long-term exposure to the primary air pollutants induced by anthropogenic activities,such as particulate matter(PM),sulfur dioxide(SO2),nitrogen oxides(NOX),and ground-level ozone(O3)may increase the risk of vascular and respiratory disease.In Beijing,although air pollution has been mitigated in recent years due to the implementation of several 'capital clean air' policies.The concentration of NOx still didn't reach the standard of clean air.Public concern about mitigating the NOx concentration has become a pressing issue.It is widely accepted that urban vegetation can capture and absorb air pollutants.Trees can capture the PM due to their large leaf area and dense canopy structure.Gaseous pollutants,such as NO,and O3 can enter leaves through leaf deposition and stomatal absorption.However,the effectiveness of vegetation in absorbing NOx in large urban areas remains unclear.To quantify the ability of urban trees to absorb NO.,we selected four commonly roadside trees(Sophora japonica,Populus tomentosa,Fraxinus chinensis,Sabina chinensis)in Beijing as the research object.The research questions of our study were:1)How to quantify the amount of NOx absorbed by the urban trees.2)Are there significant differences in the absorption amount of NOx between different tree species?3)How to estimate the monetary value of air pollutants purification ecosystem service provided by urban trees?Combining with in-situ sampling,laboratory measurement,and model estimation,the main conclusions of our study were as follows:1)The capacity of NOX removal by the urban trees in the central part of Beijing was estimated using the stable isotope method.The annual NOX uptake by these trees was estimated to be 1.57?4.17 mg N/gDw.2)By combing the data acquired from the field survey,we also estimated the annual NOx uptake by trees in a typical urban park(Shi liu zhuang park)and in the urban core area of Beijing.The annual uptake of NOx by trees in Shi liu zhuang park was to be 0.59?2.08 g/m2.The annual uptake of NOx by trees in urban core area was to be 0.69?1.41 g/m2.3)The monetary value of air purification services provided by urban trees in urban district of Beijing was 792032.3 yuan year-1.The monetary value of air purification services provided by urban green spaces was 1646745.4 yuan year-1.The results of our study will be useful for environmental managers to develope ecological management practices that use trees with high NOx uptake capacity to mitigate the atmospheric nitrogen pollution in urban areas.