Concentrations Of Negative Air Ions Research Articles

Impact of Pulse Electric Field Stimulation on Negative Air Ion Release Capacity of Snake Plants

To investigate the effects of pulse electric field stimulation on the photosynthetic electron transport chain and negative air ion (NAI) release capacity of snake plants, the chlorophyll content, fluorescence induction kinetics curve (OJIP curve), chlorophyll fluorescence parameters, and NAI release concentration of snake plants kept under identical greenhouse conditions under different pulse electric field stimulations were compared and analyzed. The experimental results show that (1) after pulse electric field stimulation, the chlorophyll content in treatment group T1 (5 kv) and T2 (7 kv) of snake plants increased by 6.30% and 6.70%, respectively, with significant differences observed between the two treatment groups and the control group (CK). (2) In both treatment groups, the OJIP curve exhibited higher values for the inflection point (I) and peak (P) compared to the origin (O) and inflection point (J) values, with the rising trend in the I–P segment being more gentle than that of the O–J segment. Additionally, the J band was above 0, with the peak value in the T2 group being higher than that in the T1 group. (3) The chlorophyll fluorescence parameters showed fluctuating variations. Specifically, Fm, TRo/CSo, ETo/CSo, and DIo/CSo showed ascending trends in the treatment groups. Fv/Fo, Sm, and ABS/RC exhibited descending trends; Fv/Fm, Vj, ETo/RC, and φEo showed relatively minor changes. The PIabs displayed a decreasing trend. The PItotal in the CK was greater than that in the T1 and T2 groups. (4) After 4 h of pulse electric field stimulation, the NAI concentration increased by 87.60% in the T1 group and by 62.09% in the T2 group, compared to the same measurement taken at 3 h. Pulse electric field impacts the photosynthetic electron transport chain of snake plants, thereby influencing their NAI release capacity. This study aims to elucidate the physiological responses of the chloroplasts in snake plants to pulsed electric field stimulation and to lay the foundation for enhancing the plant’s release of negative air ion concentrations through physical and technological means.

The Combined Effects of the Thermal Environment and Air Quality at Recreation Places on the Physiology and Psychology of People in Urban Parks

Urban forests, crucial to urban ecosystems, are increasingly threatened by the challenges of urbanization, such as deteriorating thermal environments and declining air quality. Despite their recognized benefits to city dwellers’ quality of life, a systematic understanding of the impact of these environmental factors on public psychophysiological well-being in recreational sites is a notable gap in the literature. The objective of this research was to bridge this gap by examining the effects of the thermal environment and air quality in urban forests on the public’s perception, offering scientific evidence to inform environmental optimization and health management strategies for urban parks, essential for sustainable urban development and public health. Three urban parks in Fuzhou, Fujian Province, namely Fuzhou National Forest Park, Xihu Park, and Jinniushan Sports Park, were selected as research sites. Environmental monitoring and questionnaire surveys were conducted at 24 recreation places from October to December 2020, collecting temperature, humidity, and wind speed; the atmospheric composition includes PM2.5, PM10, negative oxygen ion, and psychophysiological data from the public. Multivariate statistical methods were employed to assess the environmental characteristics of different recreation places types and their impact on public health. The findings reveal that environmental factors explained 1.9% to 11.8% of the variation in physiological and psychological responses, mainly influenced by temperature, wind speed, and negative oxygen ions. Forests and waterfront recreation places significantly outperform canopy and open recreation places in promoting mental invigoration, stress relief, emotional tranquility, and attention restoration. Environmental monitoring results indicate that favorable meteorological conditions and good air quality are crucial for enhancing the service functions of recreation places. Notably, the positive correlation between a negative air ion concentration and psychological well-being provides a novel perspective on understanding the health benefits of urban forests. The thermal environment and air quality of urban recreation places exert a significant influence on the psychophysiological status of the public. Increasing green coverage, improving water body environments, and rationally planning recreation places layout are of great theoretical and practical significance for enhancing the environmental quality and service functions of urban forests.

Application of DBD air plasma for indoor particulate matter removal

The use of non thermal plasma (NTP) to improve indoor air quality (IAQ) has grown considerably in recent years. This paper demonstrates the advantage of NTP for IAQ improvement in terms of particulate matter (PM) removal. The PM removal mechanism using active air ions and radicals has been investigated. From the developed dielectric barreir discharge (DBD) air plasma reactor, the total PM removal efficiency of 61.72% has been achieved at an optimised concentration of negative and positive air ions in 2 hours of continuous operation. Due to the utilised sensor's limit of quantification (LOQ), PM 2.5 and PM 10 have been reduced to a certain value. The findings revealed that DBD air plasma can be effectively used for PM removal in an enclosed environment.

Study of air deionization factors

The object of research is the dynamics in the concentration of air ions and suspended particles in atmospheric air and in supply-exhaust ventilation systems. An urgent task is to determine the factors and obtain quantitative data on the deionization of the atmospheric air that enters the environment where people live. Quantitative data on changes in the concentration of air ions depending on the time of day, temperature, and relative air humidity have been established. It was shown that even in the absence of significant man-made influence on the concentration of suspended particles, this indicator is at least 7000 cm-3. In the presence of wind, this indicator reaches 30000 cm-3 and higher. Measurement of the spectrum of suspended particles in the range of 0,3–6,0 μm showed that the predominant fraction is particles with sizes of about 3 μm. Studies have been conducted on changes in the concentrations of air ions in supply-exhaust ventilation systems. It was established that in the air duct made of galvanized iron, which has a length of 16 m, the concentration of negative air ions is reduced by 67 %, and positive by 78 %. Laboratory studies of air deionization in air ducts made of different materials were carried out. There is significant air deionization in metal and cardboard ducts while it is absent in wooden ducts. This indicates the electrical nature of deionization. A calculation method for forecasting the aero-ionic mode of premises, taking into account the factors of air deionization, is proposed. For rooms with supply-exhaust ventilation, a calculation apparatus is proposed taking into account the air exchange rate (the number of complete air changes per unit of time). The results make it possible to choose the required performance of artificial air ionization devices for normalizing the aero-ionic regimes in the premises

Factors Influencing the Concentration of Negative Air Ions in Urban Forests of the Zhuyu Bay Scenic Area in Yangzhou, China

Factors Influencing the Concentration of Negative Air Ions in Urban Forests of the Zhuyu Bay Scenic Area in Yangzhou, China

Temporal Dynamics and Influencing Mechanism of Air Oxygen Content in Different Vegetation Types

Air oxygen content, an essential index for measuring air quality, is affected by vegetation and the environment in the forest. However, the scientific understanding of the influential mechanism of air oxygen content in different vegetation types is still not clear. Focusing on four different vegetation types: broad-leaved forest, coniferous forest, coniferous and broad-leaved mixed forest, and non-forest land within Shimen National Forest Park, China, the temporal dynamics of air oxygen content and its relationship with four environmental factors (temperature, relative humidity, wind speed, and negative air ion concentration) in different vegetation types were explored based on path analysis and decision analysis. The results showed that there was a noteworthy impact of vegetation types on air oxygen content, with coniferous and broad-leaved mixed forest (21.33 ± 0.42%) presenting the highest levels. The air oxygen content indicated a fundamentally consistent temporal pattern across different vegetation types, with the highest diurnal variation occurring at noon. It reached its peak in August and hit its nadir in December, with summer > spring > autumn > winter. In broad-leaved forest, the air oxygen content was determined by temperature, wind speed, negative air ion concentration, and relative humidity; in both coniferous forest and coniferous and broad-leaved mixed forest, the air oxygen content was affected by temperature, wind speed, and relative humidity; in non-forest land, the air oxygen content was influenced by temperature and wind speed. Generally, temperature was the dominant factor affecting air oxygen content in different vegetation types, and its positive impact tremendously exceeded other environmental factors. Wind speed had a positive impact on air oxygen content in three forest communities but a negative effect on non-forest land. Relative humidity acted as a limiting factor for air oxygen content within three forest communities. Negative air ion concentration showed a significant positive correlation on air oxygen content in broad-leaved forest. Therefore, when planning urban forests to improve air quality and construct forest oxygen bars, it is recommended that the tree species composition should be given priority to the coniferous and broad-leaved mixed pattern. Meanwhile, make sure the understory space is properly laid out so that the forest microclimates are conducive to the release of oxygen by plants through photosynthesis.

Stand structure and environment jointly determine negative air ion concentrations in forests: Evidence from concurrent on-site monitoring in four typical subtropical forests during the growing season

Negative air ions (NAIs) have been extensively studied by scientists and administrators due to their crucial role in assessing the benefits of forest health to humans and improving air quality. This paper presents the results of a study conducted in four typical subtropical forests, where 24-hour on-site monitoring of NAIs, air temperature, relative humidity, wind speed, direct radiation, and particulate matter was conducted during the growing season. The vegetation characteristics of these forests were also investigated. Correlation and random forest analyses were employed to jointly evidence the effects of stand structure and environmental factors on NAI concentrations using mean data for the monitoring period. Additionally, regression analyses were employed to discuss the response of NAIs to continuous changes in meteorological factors using screened nighttime data. Our analysis revealed that NAI diurnal dynamics followed a unimodal pattern, with peaks observed in the afternoon (13:30–16:30) and troughs in the early morning (4:00–7:00). Significant variations in NAI concentrations were observed among the forest types, with mixed broadleaved forest showing the highest concentrations, followed by phoebe forest, Moso bamboo plantation, and Chinese fir plantation. The differences in NAI concentrations among forest types were primarily influenced by plant density at monitor heights, plant diversity, leaf area index, and tree height diversity. Overall, NAI concentrations were positively influenced by temperature and relative humidity and negatively influenced by particulate matter, while the influence of wind speed varied with forest type. Furthermore, our findings indicate that changes in particulate matter had a greater contribution to NAI concentrations compared to meteorological factors. By quantifying the spatial and temporal characteristics of NAIs in typical subtropical forests and their relationships with influencing factors from the perspectives of both stand structure and environment, our study provides new insights into scheduling human forest therapy activities and managing therapeutic forests.

Relative Humidity Dominances in Negative Air Ion Concentration: Insights from One–Year Measurements of Urban Forests and Natural Forests

Forests are one of the most important sources of negative oxygen ions (NAIs). NAIs have been recognized as beneficial for both physical and mental well–being, and higher concentrations of NAIs have been associated with improved health. However, the environmental factors that predominantly influence NAI concentration and their relationship with NAIs remain uncertain. This study aims to investigate the dominant factors and their impact on NAI concentration by observing NAIs and various environmental factors in two different environments (natural forest and urban forest) in the Beijing region over a one–year period. Through our investigation, we aimed to identify the key factor as well as other influential variables affecting NAI concentration. Our analysis encompassed the examination of dynamic concentration changes over multiple time scales, revealing uniform trends in both forest types. Notably, natural forests consistently demonstrated higher NAI concentration across these time scales, attributable to greater vegetation density and the stability of the forest microenvironment. By utilizing regression, correlation analysis, and structural equation analysis, we determined that relative humidity (RH) has the most significant effect on NAI concentration. Notably, both NAI concentration and RH displayed similar patterns across multiple time scales. When considering hourly average daily variation, the lowest values for both NAI concentration and RH were observed at noon, followed by an increase that persisted throughout the night. Seasonal average variation showed that both NAI concentration and RH peaked in the summer, followed by autumn. In terms of daily average annual variation, summer exhibited more days with high NAI concentration and high RH, which can be attributed to the increased rainfall during that season. Rainy weather was found to contribute to higher NAI concentration and RH levels. Furthermore, our findings revealed that on a daily scale, high RH and high NAI concentration occurred more frequently under conditions of high air temperature and low wind speed. However, the air quality index demonstrated only a minor effect in urban forest, while net radiation exhibited no significant influence on NAI concentration and RH. The fitted equations and trends of the aforementioned environmental factors with NAI concentration and RH were found to be comparable. The path analysis further corroborates these conclusions. The findings of this study indicate that RH is the primary factor driving the fluctuations in NAI concentration across various time scales, including hourly, daily, and seasonal variations. The study revealed that wind speed indirectly impacts NAI concentration by modulating RH. In contrast, air temperature influences NAI concentration both indirectly through RH and directly. The environmental factors affecting NAI concentration in the two types of forests are similar, but the degrees vary; in urban forests, wind speed, air quality index, and RH are slightly higher, while in natural forests, air temperature is slightly higher. This discovery further enhances our understanding of the underlying mechanisms and dynamic changes in NAI concentration within urban forests and natural forests. Moreover, it confirms the reliability and effectiveness of using RH as an indicator to monitor changes in NAI concentration over time.

Study on the Comprehensive Health Effects of Coastal Green Areas in Qingdao City, China

The recuperation factors (negative air ion concentration, airborne particulate matter, human comfort index, and acoustic environment index) of coastal green spaces have significant health effects. Most current studies focus on the distribution pattern of single recuperation factors in the forest environment; however, the comprehensive health effects of coastal green spaces are still unknown. To address this, we analyzed the distribution patterns of single and comprehensive health factors in different landscape configurations, landscape compositions, and coastal distances by principal component analysis and systematic clustering. The results show that: (1) coniferous and broadleaf mixed forests exhibit higher integrated health benefits than other landscape compositions; (2) closed and partially closed landscape configurations exhibit enhanced potential for promoting health benefits as opposed to partially open and open spaces; (3) a coastal distance of 150–300 m offers the strongest comprehensive health benefits. These findings collectively suggest that the increased cultivation of closed and partially closed mixed coniferous and broadleaf forest species at a distance of 150–300 m could effectively provide higher comprehensive health effects. Our study complements the ecosystem service of coastal green areas, especially in coastal health ecological services, providing support for coastal rehabilitation landscape planning; and can help to guide tourists in scheduling coastal health activities scientifically.

The Ecological Healthcare Benefits and Influences of Plant Communities in Urban Wetland Parks

Plant communities in urban wetland parks (UWP) have significant eco-healthcare benefits in terms of regulating the climate and improving the human living environment. However, factors influencing the regulation of eco-healthcare benefits are unclear. Taking Huaxi Ten Mile Beach National Urban Wetland Park as an example, the urban wetland park comprehensive healthcare index (UPCHI) was constructed based on an outdoor survey and indoor analysis to evaluate the UWP’s eco-healthcare benefits. Pathway analysis was used to investigate how climatic, geographic, and plant factors interact to affect the UPCHI. The results show that, over the whole year, tree–shrub–herb showed the best performance in terms of reducing PM2.5, PM10, and noise, as well as raising negative air ion concentrations; however, human comfort performed the worst. The UPCHI was generally beyond level Ⅲ (0.49–0.58) in the spring and summer, indicating that there are eco-healthcare benefits. Overall, the deciduous tree–shrub–herb community had the highest annual mean UPCHI, and more than half of the plant communities’ eco-healthcare benefits were class Ⅱ, which is very beneficial for eco-healthcare. The main direct factors on UPCHI were illumination intensity (0.68) and tree height (0.90), while canopy height (0.64–0.59) and tree crown radius/canopy height (0.72–0.14) directly or indirectly influenced UPCHI. The distance from the edge of the mountain (−0.39–−0.322) had a direct negative, but minor, effect on UPCHI. This study will assist residents with selecting suitable times and places for wetland recreation and healthcare activities, and it offers a valuable reference for the future planning and design of UWP plant communities.

Temporal Variation Characteristics of Negative Air ion Concentration and Air Quality Evaluation in Songshan National Nature Reserve, Beijing

Temporal Variation Characteristics of Negative Air ion Concentration and Air Quality Evaluation in Songshan National Nature Reserve, Beijing

Effect of light intensity on negative air ion under phytotron control.

Negative air ion (NAI) is an important index for measuring air quality and has been widely recognized to be influenced by photosynthesis processes. However, vegetation type and light intensity are also known to impact NAI, contributing to significant uncertainties in the relationship between light and NAI. In this paper, we selected Pinus bungeana, Platycladus orientalis and Buxus sinica as research subjects and obtained their NAI, light intensity, and meteorological data through synchronous observation under the relatively stable condition of the phytotron. We analyzed the change characteristics of NAI and the difference of NAI production ability in needle and broadleaf vegetation under different light intensities. Finally, we determined the relationship and underlying mechanism governing light intensity and NAI using diverse tree species. The results showed that the influence of light on NAI was significant. In the environment without vegetation, the influence of different light intensities on NAI was not significant, and the mean NAI concentration was 310 ions·cm-3. Conversely, in the presence of vegetation, NAI showed a "single-peak" trend with increasing light intensity. The NAI concentration of the three tree species was significantly higher than under different light intensities when vegetation was not present. The NAI promoting ability of P. bungeana was the highest (675 ions·cm-3), followed by P. orientalis (478 ions·cm-3) and B. sinica (430 ions·cm-3), which increased by 117.5%, 53.9% and 38.6% compared to the environment without vegetation. The NAI growth rate was significantly different between needle and broadleaf vegetation based on the specific tridimensional green biomass. Additionally, the NAI growth rates of P. bungeana and P. orientalis were 647 and 295 ions·cm-3·m-3, respectively, which were 3.06 and 1.39 times that of B. sinica (211 ions·cm-3·m-3). The piecewise equation fitting effect of NAI and light intensity was better for different tree species, the determination coefficients (R2) of P. bungeana, P. orientalis and B. sinica were 0.926, 0.916 and 0.880, and the root mean square errors (RMSE) were 7.157, 6.008 and 5.389 ion·cm-3, respectively. Altogether, our study provides a theoretical basis as well as technical support for the construction of healthy vegetation stands, the selection of preferred tree species, and the optimization of vegetation models, and promotes air quality and the provision of ecosystem functions and services.

The effect of air velocity and indoor ambient properties on the effective operating range of an air ionizer device

Air ionizers are devices that purify the indoor air by artificially generating negative air ions (NAIs) which are proven to improve air quality and well-being of humans. Hence, more ionizers are being incorporated into heating, ventilation and air conditioning (HVAC) applications nowadays. . Every ionizer has its effective range of operation, which is the area inside a room that can potentially be covered by significant concentration of NAIs compared to the general concentration of ions naturally present in the room. This range may change depending on the indoor temperature, humidity and fan speed of the HVAC unit as preferred by the room occupants. Present research intends to design an experimental setup that could measure negative air ion (NAI) concentration at varying distances from an ionizer under different values of the aforementioned parameters. The experiment was conducted inside an indoor psychrometric test room to allow controlling of ambient temperature and humidity. Air velocity through the ionizer was varied from 1.5 m/s to 4.5 m/s, whereas the range of temperature and relative humidity were set from 25°C to 31°C and 60% to 80% respectively. To evaluate the ionizer’s operating range, NAI concentration was measured at every preset longitudinal (0 cm to 75 cm), lateral (-25 cm to 25 cm) and elevation (-15 cm to 15 cm) distance relative to the ionizer for 6 minutes using an ion counter named “Air Ion Counter Model AIC2”. The results reveal that the ionizer’s effective operating range increased with velocity, with the furthest range recorded at 4.5 m/s. Whereas a negative correlation was found between the ionizer’s effective operating range with temperature and humidity, with the furthest range recorded at 25°C and 60% respectively. The results also show that most ions were distributed in areas below and towards the right side from the ionizer’s perspective.

Negative Air Ion (NAI) Dynamics over Zhejiang Province, China, Based on Multivariate Remote Sensing Products

Negative air ions (NAIs), which are known as the “air vitamin”, have been widely used as a measure of air cleanness. Field observation provides an alternative way to record site-level NAIs. However, these observations fail to capture the regional distribution of NAIs due to the limited number of sites. In this study, satellite-based bio-geophysical parameters from the climate, topography, air quality, vegetation, and anthropogenic intensity were used to estimate the daily NAIs with the Random Forest model (RF). In situ NAI observations over Zhejiang Province, China were incorporated into the model. Daily NAIs were averaged to capture the spatio-temporal distribution. The results showed that (1) the RF algorithm performed better than traditional regression analysis and the common BP neural network to generate regional NAIs at a spatial scale of 500 m over the larger scale, with an RMSE of 258.62, R2 of 0.878 for model training, and R2 of 0.732 for model testing; (2) in the variable importance measures (VIM) analysis, 87.96% of the NAI variance was caused by the elevation, aspect, slope, surface temperature, solar-induced chlorophyll fluorescence (SIF), relative humidity (RH), and the concentration of carbon monoxide (CO), while path analysis indicated that SIF was one of the most important factors affecting NAI concentration across the whole region; (3) NAI concentrations in 87.16% of the region were classified above grade III (>500 ions cm−3), which was able to meet the needs of human health maintenance; (4) the highest NAI concentration was distributed over the southwest of the Zhejiang Province, where forest land dominates. The lowest NAI concentration was mostly found in the northeast regions, where urban areas are well-developed; and (5) among different land types, the NAI concentrations were ranked as forest land > water bodies > barren > grassland > croplands > urban and built-up. Among different seasons, summer and winter have the highest and lowest NAIs, respectively. Our study provided a substantial reference for ecosystem services assessment in Zhejiang Province.

Exurban and suburban forests have superior healthcare benefits beyond downtown forests

Forests in urban areas provide great healthcare benefits to citizens, but it is less well known whether this benefit is related to different geographical spaces. We selected exurban forest, suburban forest, downtown forest, and urban control in Guangzhou, China to analyze the change characteristics of negative air ion concentration (NAIC), air oxygen content (AOC), and human comfort index (HCI). Based on Criteria Importance Through Intercriteria Correlation (CRITIC) method, the urban forest comprehensive healthcare index (UFCHI) was established. Finally, the evaluation criteria for UFCHI were identified by cluster analysis. The results demonstrated that (1) The NAIC in exurban forest (2,713 ± 1,573 ions/cm3) and suburban forest (2,147 ± 923 ions/cm3) was evidently better than downtown forest (1,130 ± 255 ions/cm3) and urban control (531 ± 162 ions/cm3). (2) The AOC was in the order of exurban forest (21.17 ± 0.38%) > suburban forest (21.13 ± 0.30%) > downtown forest (21.10 ± 0.16%) > urban control (20.98 ± 0.12%). (3) The HCI in urban control (5.56 ± 2.32) and downtown forest (5.15 ± 1.80) is higher than suburban forest (4.02 ± 1.53) and exurban forest (3.71 ± 1.48). (4) The UFCHI in exurban forest (1.000), suburban forest (0.790), and downtown forest (0.378) were beneficial to human health to some extent, while urban control (0.000) was at Level IV, having no healthcare benefit. Except in winter, the UFCHI in exurban forest and suburban forest were all at Level II and above; while downtown forest and urban control were all at Level III and below at all seasons. Overall, urban forests in the exurbs and suburbs have better healthcare benefits than those in the downtowns. Furthermore, it is recommended that urban residents visit exurban and suburban forests for forest therapy in spring, summer, and autumn.

Effect of negative air ionization technology on microbial reduction of food-related microorganisms

Negative air ions (NAI) have been shown to have bactericidal effects on various microbial species.Different concentrations of NAI and ozone (106-7x106 NAI cm-3 s−1, 2.20 mg h-1 of ozone or 8 × 106-2x107 NAI cm−3 s−1, 0.02 mg h−1 of ozone, respectively) were studied to determine whether the effect of these treatments on six food-related microorganisms was due to NAI or also to the ozone that forms.Bacillus subtilis, Escherichia coli, and Listeria monocytogenes showed a significantly microbial reduction after the treatments of NAI with a low concentration of ozone, while Pseudomonas fluorescens, Penicillium roqueforti, and Saccharomyces cerevisiae were affected mainly by NAI and higher ozone concentration. It should be noticed that the reduction of the pathogen L. monocytogenes has been 2.17 Log after 72 h treatment to NAI and low ozone concentration.The results proved that ions (NAI) contribute to microbial killing. However, the sensitivity of microbial species is different and depends on individual parameters of the different microorganisms.NAI technology with low ozone production can be rapid, green, and low-cost and it can represent an alternative to the use of chemicals for the sanitation of air and surfaces in the food sector in order to reduce microbial contamination.

Associations of forest negative air ions exposure with cardiac autonomic nervous function and the related metabolic linkages: A repeated-measure panel study

Forest environment has many health benefits, and negative air ions (NAI) is one of the major forest environmental factors. Many studies have explored the effect of forest environment on cardiac autonomic nervous function, while forest NAI in the among function and the underlying mechanism still remain unclear. To explore the associations and molecular linkages between short-term exposure to forest NAI and heart rate variability (HRV), a repeated-measure panel study was conducted among 31 healthy adults. Participants were randomly selected to stay in a forest park for 3 days and 2 nights. Individual exposures including NAI were monitored simultaneously and HRV indices were measured repeatedly at the follow-up period. Urine samples were collected for non-targeted metabolomics analysis. Mixed-effect models were adopted to evaluate associations among NAI, HRV indices and metabolites. The median of NAI concentration was 68.11 (138.20) cm−3 during the study period. Short-term exposure to forest NAI was associated with the ameliorative HRV indices, especially the excitatory parasympathetic nerve. For instance, per interquartile range increase of 5-min moving average of NAI was associated with 9.99 % (95%CI: 8.95 %, 11.03 %) increase of power in high frequency. Eight metabolites were associated with NAI exposure. The down-regulated tyrosine metabolism was firstly observed, followed by other amino acid metabolic alterations. The NAI-related metabolic changes reflect the reduction of inflammation and oxidative stress. HRV indices were associated with 25 metabolites, mainly including arginine, proline and histidine metabolism. Short-term exposure to forest NAI is beneficial to HRV, especially to the parasympathetic nerve activity, by successively disturbing different metabolic pathways which mainly reflect the increased anti-inflammation and the reduced inflammation. The results will provide epidemiological evidences for developing forest therapy and improving cardiac autonomic nervous function.

Temporal dynamics of negative air ion concentration and its relationship with environmental factors: Results from long-term on-site monitoring

Negative air ions (NAIs) play an important role in evaluating forest health effects and promoting human physical and mental health. In this paper, long-term on-site monitoring of NAI concentration, air temperature, and relative humidity was conducted in real time over 24 h, from July 2019 to March 2021, to explore the temporal dynamic patterns of NAIs. We found that the daily dynamics of NAI concentration showed a bimodal curve. The peak concentrations usually occurred in the early morning (5:00–7:00) and afternoon (15:00–17:00), and the lowest concentrations usually occurred at noon (11:00–13:00). At the monthly scale, NAI concentrations were relatively high in February and August and low in May and December, and at the seasonal scale, NAI concentration was significantly higher in summer than in other seasons. Autumn had the second highest NAI concentration. There was no significant difference in NAI concentration between winter and spring. A comprehensive analysis shows that the AQI was the most key factor affecting NAI concentrations compared to temperature and relative humidity, especially the two indicators of particulate matter and ozone, and that NAI concentration had a negative correlation with these indicators and was significantly higher under favorable air quality conditions than under polluted air conditions. NAI concentrations and air temperature showed marked piecewise characteristics, with NAIs increasing linearly with rising temperature only if the Ta was separated into three ranges of −5 °C–10 °C, 10 °C–30 °C, and 30 °C–40 °C. With rising relative humidity, NAI concentration increased in accordance with a quadratic function. Our research provides new insights into the NAI temporal dynamics patterns and its driving factors, and will aid in scheduling outdoor recreation and forest health activities for urban people.

Effects of Altitude, Plant Communities, and Canopies on the Thermal Comfort, Negative Air Ions, and Airborne Particles of Mountain Forests in Summer

Forest bathing is considered an economical, feasible, and sustainable way to solve human sub-health problems caused by urban environmental degradation and to promote physical and mental health. Mountain forests are ideal for providing forest baths because of their large area and ecological environment. The regulatory mechanism of a mountain forest plant community in a microenvironment conducive to forest bathing is the theoretical basis for promoting physical and mental health through forest bathing in mountain forests. Based on field investigations and measurements, differences in the daily universal thermal climate index (UTCI), negative air ion (NAI), and airborne particulate matter (PM2.5 and PM10) levels in nine elevation gradients, six plant community types, and six plant community canopy parameter gradients were quantitatively analyzed. In addition, the correlations between these variables and various canopy parameters were further established. The results showed the following: (1) Altitude had a significant influence on the daily UTCI, NAI, PM2.5, and PM10 levels in the summer. The daily UTCI, NAI, PM2.5, and PM10 levels gradually decreased with the increase in altitude. For every 100 m increase in altitude, the daily UTCI decreased by 0.62 °C, the daily NAI concentration decreased by 108 ions/cm3, and the daily PM2.5 and PM10 concentrations decreased by 0.60 and 3.45 µg/m3, respectively. (2) There were significant differences in the daily UTCI, NAI, PM2.5, and PM10 levels among different plant communities in the summer. Among the six plant communities, the Quercus variabilis forest (QVF) had the lowest daily UTCI and the best thermal comfort evaluation. The QVF and Pinus tabuliformis forest (PTF) had a higher daily NAI concentration and lower daily PM2.5 and PM10 concentrations. (3) The characteristics of the plant community canopy, canopy density (CD), canopy porosity (CP), leaf area index (LAI), and sky view factor (SVF), had significant effects on the daily UTCI and NAI concentration, but had no significant effects on the daily PM2.5 and PM10 concentrations in the summer. The plant community with higher CD and LAI, but lower CP and SVF, showed a higher daily UTCI and a higher daily NAI concentration. In conclusion, the QVF and PTF plant communities with higher CD and LAI but lower CP and SVF at lower elevations are more suitable for forest bathing in the summer in mountainous forests at lower altitudes. The results of this study provide an economical, feasible, and sustainable guide for the location of forest bathing activities and urban greening planning to promote people’s physical and mental health.

Spatiotemporal distribution of negative air ion and PM2.5 in urban residential areas

Urban environments are characterised by high pollution levels, which adversely affect the physiology, psychology and behaviour of the urban residents. In this study, on-site measurements and air quality evaluations were performed in urban residential areas. The negative air ion (NAI) concentration, fine particulate matter (PM2.5) concentration, temperature and relative humidity were measured in different seasons. Both PM2.5 and the NAI concentrations changed significantly with seasons. The PM2.5 concentration was the highest in winter, intermediate in autumn and the lowest in summer, while the NAI concentration showed an opposite trend. The overall changes in NAI and PM2.5 concentrations showed a trend of double peaks and double valleys, and there was a substantial difference between rainy days versus sunny days. The NAI concentration was positively correlated with temperature and relative humidity, and the influence of relative humidity on NAI was greater than that of temperature. There were notable spatial differences in the intensity of impact by different pollution sources. Based on these results, suggestions were made for optimising the layout of residential buildings and the rationalisation of traffic networks, with the aim of increasing NAI concentrations and reducing PM2.5 concentrations. This would help reduce the pollution levels in urban residential areas.