| Negative air ion(NAI)is an important indicator to measure the cleanliness of air in a region,with the functions of sterilization and dust removal,enhancing human immunity and assisting in the treatment of a variety of diseases,and can regulate the psychological and physiological functions of the human body,known as "air vitamins" In this study,NAI of Quercus variabilis,Platycladus orientalis,the hilltop clearing and mountain residential area in Henan Xiaolangdi Earth Critical Zone National Research Station from 2021 to 2022 were used as experimental subjects to explore the variation characteristics in different seasons in this area.The Random Forest(RF)model was used to analyze the main influencing factors of environmental factors on NAI,to explore the differences of NAI in different types of plots and the dominant factors affecting NAI in different seasons,and provides a basis for further in-depth study of the change mechanism of air negative ions of different types in this area.The results of the study showed that:(1)The NAI concentrations of different underlying surfaces in descending order were: Platycladus orientalis(692.47±70.33 ion·cm-3),> Quercus variabilis(602.97±90.42ion·cm-3),> hilltop clearing(545.65 ion·cm-3),> mountain residential area(455.28 ion·cm-3)(p<0.01).(2)In both 2021 and 2022,the NAI of Quercus variabilis reached a maximum of 893.51±84.66ion·cm-3 in July,and the NAI concentration reached a minimum of 325.00±65.37 ion·cm-3 in January.The NAI of Platycladus orientalis reached a maximum of 791.95±107.02 ion·cm-3 in July and August,and a minimum of 428.7789±46.7421 ion·cm-3 in January.The diurnal variation of NAI in coniferous and broadleaf plantations showed a unimodal trend in four seasons,and the diurnal variation of NAI in Quercus variabilis plantations were not obvious in winter.In spring and summer,Quercus variabilis NAI> Platycladus orientalis NAI,while in autumn and winter,Platycladus orientalis NAI > Quercus variabilis NAI.Visitors to the area are advised to enjoy wellness activities in the Quercus variabilis plantations in July.(3)In Quercus variabilis plantations,the vertical height of NAI the understory(Quercus variabilis1.5 m)and the middle canopy(Quercus variabilis 5m)were 883.07±57.46 ion·cm-3,1098.12±394.96 ion·cm-3,respectively.The lowest values were 325.00±65.38 ion·cm-3,398.58±95.22 ion·cm-3 in January.During the observation period,the concentration of NAI in the understory was higher than that in the middle of the canopy.The diurnal variation of understory NAI in four seasons showed a unimodal trend in spring,summer and autumn,and showed a trend of first declining and then rising in winter.The occurrence time of the NAI extremum the understory were1-3h lagging compared with that in the middle of the canopy.(4)The NAI in mountain residential area reached a high of 636.49±76.16 ion·cm-3 in July,and the lowest value were 276.96±26.93 ion·cm-3 in January;The hilltop clearing of NAI showed irregularities,with the highest NAI value in June at 632.26±114.86 ion·cm-3,and the lowest value at 485.15±100.50 ion·cm-3.In spring,autumn and winter,the hilltop clearing NAI > the mountain residential area NAI,while in the summer the mountain residential area NAI > the hilltop clearing NAI.The diurnal variation of NAI variation of hilltop clearing showed a bimodal trend in summer,and a unimodal NAI trend in spring,autumn and winter.In mountain settlements,there is a trend of single valley changes in winter,and a single peak trend in spring,summer and autumn.The intraday NAI variation of mountaintop clearing showed a bimodal trend in summer,and a unimodal NAI trend in spring,autumn and winter.In the mountain residential area,there is a trend of single valley changes in winter,and a single peak trend in spring,summer and autumn.(5)The most important environmental factors affecting NAI in and outside the forest were screened out by random forest model,the main environmental factors affecting NAI in the four-season hilltop clearing were WS,the NAI affecting mountain residential areas was mainly particulate matter,the main environmental factors affecting coniferous and broadleaf plantations were VPD in spring and summer,and particulate matter was mainly in autumn and winter. |
