Research On Concentration Characteristics And Sources Of Reactive Gases At Akedala Background Station

Akedala regional atmospheric background station is one of World Meteorological Organization Global Atmosphere Watch regional background stations,which is located in the northernmost part of China and the most upstream region of the westerlies in Central Asia,bordering Mongolia,Kazakhstan and Russia,and has important geographical and environmental characteristics.There is no strong emission source around Akedala,which is a relatively clean background region in Xinjiang and even the whole Central Asia.Long-distance atmospheric transport is the main transport path of reactive gases in this region.The observation and study of the main reactive gases SO₂,NO₂,CO and O₃in the atmosphere in this region is conducive to mastering the concentration change characteristics of regional reactive gases,providing a valuable reference for monitoring and controlling of the air pollution prevention.Based on the observation data of reactive gases and meteorological elements at Akedala regional atmospheric background station from September 2017 to August 2018,this study systematically analyzed the multi-time scale variation characteristics of reactive gases,and discussed the importance of meteorological elements to reactive gases.Backward trajectory analysis,cluster analysis,potential source contribution function（PSCF）,concentration weight trajectory（CWT）and other methods were used to reveal the main airflow trajectories and potential source areas that affected the concentration of reactive gases in Akedala in different seasons.The research results were as follows:（1）The concentration of the four reactive gases at the Akedala station was lower than the Grade 1 and Grade 2 Standard specified in the Ambient Air Quality Standards（GB3095—2012）.During the observation period,the background station of Akedala was relatively clean.The average concentrations of O₃,CO,NO₂and SO₂in the whole observation period were 29.65±11.44 ppb,123.78±73.35 ppb,3.79±0.98 ppb,and4.59±0.88 ppb,respectively;The overall average concentrations of O₃,CO,and NO₂in Altay were 37.51±13.02 ppb,303.12±156.81 ppb,and 8.46±7.18 ppb,respectively,which were 1.27 times,2.45 times,and 2.25 times higher than those in Akedala.The average concentrations of O₃,CO,and NO₂in Shangdianzi were 36.93±17.29 ppb,496.44±295.16 ppb,and 8.86±4.89 ppb,which were 1.21 times,4.63 times,and 2.46times higher than those in Akdala.The average SO₂values in Altay and Shangdianzi was lower than that in Akedala,because Akdala was affected by transportation from neighboring countries or regions.（2）By summarizing the characteristics of basic meteorological elements and analyzing their correlation with reactive gases,it was found that the prevailing winds on the surface of Akedala during the observation period were northwest wind and easterly wind,accounting for 18.62%and 13.68%respectively.Visibility was the main meteorological influence factor for SO₂and CO,and the importance accounted for24.87%and 27.44%respectively.Wind speed and relative humidity were the dominant meteorological factors for NO₂and SO₂,respectively.These two meteorological factors accounted for 21.54%and 19.06%respectively.Through the analysis of CO/SO₂ratio,it was found that the correlation coefficient between them was the highest,showing certain homology.Through the analysis of pollutant wind rose map,CO was highly influenced by wind direction in the winter.Winds from the southwest（SW）,south—southwest（SSW）,south（S）,and south—southeast（SSE）corresponded to higher CO mixing ratios,which were above 400 ppb.The high O₃mixing ratio mainly appeared in the southern area of the background station in winter,with O₃mixing ratio of more than 40 ppb.In the northwest（NW）,southwest（SW）,and northeast（NE）directions,the mixing ratios of O₃had a significant increase in summer,which was above 50 ppb.The south（S）,southwest（SW）,and west（W）wind directions corresponded to a higher mixing ratio of NO₂（5—7 ppb）in winter.The high value areas of SO₂appeared in the north（NW）and south（S）of the background station in winter.These two wind directions had high SO₂mixing ratios,concentrated at 7—13 ppb.（3）Through backward trajectory analysis,it was found that Akedala was mainly affected by northwest airflow in the four seasons.Cluster analysis showed that there were 6 main paths affecting the Akedala atmosphere.Through pressure profile and 3D trajectory analysis,it was found that the Akedala airflow was mainly affected by the pressure above 700 h Pa,and the maximum vertical height was generally below 2100 m.The airflow trajectory blocked by tall terrain was affected by uplift,and the trajectory was arc.The results of PSCF and CWT analysis showed that the Akedala reaction gas was affected by two sources at home and abroad.High PSCF values were found in eastern Kazakhstan,northern Xinjiang,western Mongolia and southern Russia.The WCWT values of CO and SO₂were the highest in winter,ranging from 180—240ppb and 5—5.5 ppb,respectively.The WCWT value of O₃in spring and summer was higher than that in autumn and winter.In spring and summer,the main source region of O₃was about 32—36ppb,while the main source region of NO₂in summer had a lower WCWT value of 3—3.5 ppb,and the WCWT value of NO₂in other seasons was concentrated in4—4.5 ppb.