Original Research Article
Study on the change of negative air ion concentration and its influencing factors at different spatio-temporal scales

https://doi.org/10.1016/j.gecco.2020.e01008Get rights and content
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Abstract

Many studies have shown that negative air ions (NAIs) are beneficial for human health. Therefore, the spatial and temporal variations of NAIs and their influencing factors have attracted much attention. The Wudalianchi Scenic Area was selected as the research area in which to determine the differences of environmental factors that influence NAIs at different time and space scales. The sampling frequency of the field observation data was 1 h. NAI, meteorological factors, gas pollutants, and particulate matter were monitored simultaneously. Pearson correlation analysis, linear regression analysis, principal component analysis, and the Random Forest algorithm were used to quantify the relationship between NAIs and the influencing factors. The results revealed the following: (1) The NAI concentration from least to greatest appeared in the following order: open space (blank) (843 ions cm−3) ≈ lake (892 ions cm−3) < forest (2871 ions cm−3); (2) The diurnal variation of NAIs generally presented a U-shaped distribution, and was high in the early morning, decreased at noon, and gradually increased in the evening, with a peak time from 7:00 to 11:00; (3) There may be seasonal variations in the correlation between NAI concentration and single environmental factors, and the correlation between NAI concentration and air temperature was found to be positive in the spring and negative in the summer and autumn, and the effect of wind speed was in contrast to that of temperature; thus, there were seasonal differences in the synergistic relationship between NAI concentration and some environmental factors. NAI concentration was susceptible to various environmental factors, such as gas pollutants and particulate matter, in the spring and autumn; (4) The sensitivity of the NAI concentration to different factors in order from greatest to least was found to be as follows: inside the forest, ozone > PM10 > temperature > radiation; outside the forest, humidity > ozone > NO. In general, the relationships between the NAI concentration and the influencing factors were greatly affected by the observed spatio-temporal scale. The research results are of great significance to the construction of forest healthcare.

Keywords

Negative air ions (NAIs)
Spatial and temporal variations
Seasonal differences
Random forest algorithm

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