The Effect of Air Pollution and Temperature on Pulmonary Function in Healthy People in Xi’an, China

Temperature and air pollution has been reported to be associated with respiratory diseases. However, little is known about these effects on healthy people, and the potential interaction between the two factors is still uncertain. This study aims to estimate the effects of air pollution combined with temperature on lung function in healthy people. Methods The lung function of 132 healthy people was measured in Xi’an, Shaanxi province of Northwest China in summer and winter. Meanwhile, the daily concentrations of air pollution and temperature were obtained from monitoring stations. Statistical analyses were assessed by generalized estimating equations (GEEs). Results Every FEV1/FVC (95% L/min). Lag effects showed that Lag0 of FEV1, FEV1/FVC and FEF25-75% were more strongly associated with PM2.5. There was no significant interaction between PM 2.5 and temperature.


Introduction
The pulmonary function test (PFT) is an effective tool to evaluate the respiratory system including airway resistance, lung compliance and diffusing capacity [1][2][3]. Clinically, it is a golden standard for physicians to diagnose some lung diseases, such as chronic obstructive pulmonary disease (COPD), asthma [4,5].However, lung function is affected by many inner and extrinsic factors. Especially, extrinsic factors may damage the lung function.
Many studies have founded that climate change is related to respiratory health. TORCH (Towards a Revolution in COPD Health) studies showed that COPD exacerbations and hospitalization were more frequent in winter [6].Studies have also reported the acute effects of air pollution in patients with respiratory diseases [7][8][9].Epidemiological studies have reported associations between particulate matter or temperature and human health [10].However, the results are inconsistent even conflicted. Zhang and collages [11]showed that PM 2.5 had an acute adverse effect on lung function in healthy people and had an antagonistic effect on temperature. Zheng [12]also performed a study on temperature and air pollution on lung function, but come to the opposite conclusion.They founded synergistic effects of PM and high temperatures on cardiopulmonary mortality. Therefore, it is necessary to clarify the relationship between air pollution, temperature and lung function. Besides, few studies have investigated the effects in healthy adults, and even fewer have examined the effects of air pollution combined with climate on lung function simultaneously.
This study therefore aimed to investigate the effects of temperature and air pollution on lung function among healthy people in Xi'an.

Study participants and design
The study was conducted in 11 communities of Xi'an city (34°15′44″N,108°56′16″E) with the adult residents by multistage cluster sampling in summer (from July 23th to August 23th) and in winter (November 26th to December 27th). Participation in the survey was voluntary. Participants of 428 from 11 communities were recruited in summer, among these, 296 adults could not be traced in winter, Finally, the remaining 132 were participant in this study. The inclusion criteria for eligible residents were as follows: Adult, and residence>3 years in Xi'an city. Non history of pulmonary, and other chronic disease.
The exclusion criterion was history of asthma with. A flowchart is presented in Fig.1 Air pollution exposure The concentrations of air pollutants and the meterological date were derived from the

Statistical analysis
All the statistical date was analysis by SPSS17.0 software (SPSS Inc., Chicago, IL, USA).
Pearson correlation was used to analyze the correlation between pollutants concentrations and temperature. The lung function data of these volunteers were self-control in summer and winter. Since there is autocorrelation between the individual lung function data measured repeatedly in this study, the generalized estimating equations (GEES) were 5 using to evaluate the multivariable correlation. This method is a statistical model for fitting the dependent variables of various distributions such as normal distribution and binomial distribution, which can better solve the problems related to the dependent variables in the longitudinal data [13]. The estimated value of parameters was calculated, and the difference was statistically significant when P < 0.05).
For parameter estimation, the daily measured pulmonary function of each subject was taken as the dependent variable. Single-pollutant and two pollutant models were used to estimate the effects of PM 2.5 and temperature on summer and winter, the covariates included (gender, height, season, BMI, 24h average temperature and age). SO 2 or NO 2 was also adjusted for in the two-pollutant models. The effect of increase of pollution concentration per 10ug/m 3 on PEF, FEV1, FVC, FEF25-75 and FEV1/FVC of participants was studied. β value is used as the index to measure the change of lung function index for every 10 ug/m 3 increase of particle concentration. Considering the lag effect of air pollution on health, the impact of pollution level with a lag of 3 days is also analyzed.

Descriptive statistics of exposure and health data
During the year 2018, the basic information of subjects was shown in Table1 Analysis of the effects of PM2.5 and Temperature on lung function Table 4 and Table 5 shows the relationship between air pollutants (PM 2.5 , SO 2 and NO 2 ), temperature and pulmonary function indexes (PEF, FEV1, FVC, FEF25-75 and FEV1/FVC) in summer and winter, respectively. As shown in Table 4 In addition, the cumulative lags of temperature (Lag0) were more corelated with both PFE and FEV1/FVC. The temperature of Lag 1 was related to FEV1 and FEF25-75.

Discussion
Air pollution has become a major threat of public health worldwide, causing up to 7 million premature deaths annually [14,15]. In recent years, the developing countries in Asia, such as India and China, have begun large-scale industrialization of urbanization process, so they have been struggling with serious air pollution [16][17][18]. Besides, Xi'an is located in the lowest part of Guanzhong Basin, which makes it difficult for pollutants to be discharged, just like a "garbage bags" [19,20]. In addition, as an important industrial center, Xi'an bears the responsibility of poor air quality in the area with serious air pollution. Therefore, the research on the relationship between air pollutants and public 8 health in Xi'an is more important and urgent. Moreover, this study is still in the development stage in Northwest China and has not been studied in Xi'an.
In this study we recruited 132 healthy people from 11 communities in Xi'an city to estimate the air pollution combined with temperature on lung function. We founded that there was a negative correlation between PM 2.5 and lung function (PEF, FEV1, FVC, FEF25-75 and FEV1/FEVC) in winter. This results is consisting with previous studies conducted in Tangerang and Makassar [21], exposure to PM 2.5 showed association with decreased lung function. Our study did not find the relationship between PM 2.5 and lung function in summer. This is more likely that the air pollution is serious in Xi'an, especially in winter, ranking the top of the China. But in summer, the concentration is relatively low. A study conducted by Chen BYin Taiwan of China also demonstrated that the improvement in air quality over time made the correlation between PM 2.5 and childhood lung function However, it seems too hasty to conclude that PM 2.5 concentration is related to lung function, because the influence of temperature is ignored, which is also an important factor on lung function. In order to make up for this defect. We also analyzed the relationship between temperature and lung function. The results demonstrated that there was no significant correlation between temperature and lung function in both summer and winter. This result contradicts many previous studies. However, a previous study conducted including 5896 residents by Mary B. Ricealso founded that these was no association between temperature and lung function in summer which may be explained by increase outdoor exposures in warm days [23]. McMichaelalso have founded that cold temperatures did not have much effect on respiratory [24]. To explain this conclusion, the following factors may take into consideration. Firstly, Air could be warmed or cooled to 9 constant temperature in nasal cavity and may not stimulate the respiratory system very much on heathy people. Secondly, the seasonal change of behavior is also obvious in Xi'an, the time of outdoor activities increases significantly in summer, which may weaken the influence of temperature on lung function. Furthermore, it is worth noting that the current research focuses on the short-term temperature effect within 30 days, resulting in insignificant temperature change. Lastly, Xi'an has a distinct climate pattern of four seasons per year, corresponding to the subhumid and temperate continental monsoon climate [25,26]. The average temperature in summer is 30.35±2.24. This is different from that of Zhengmin Qian and Zhang Y, whose studies were performed in Wuhan. Wuhan has been in a high temperature area all the year round [12,11]. The residents were exposed to high temperatures for longer periods than these in many other cities.
We also analyzed the effect of temperature combined with PM 2.5 on lung function. We found that three air pollutants (PM 2.5 , SO 2 and NO 2 ) were high positively correlated with each other and negative with temperature. In the study of temperature and air pollutants, we found that these two factors are positive correlation with FEV1/FVC in both single and two pollution model (NO 2 ) in winter. Our results are consistent with the study conducted by Yi Li in Beijing, they founded that low temperature enhanced the impacts of PM2.5 on cardiovascular mortality [27]. FEV1/FVC is the ratio of forced expiratory volume in the first second to all expiratory volume, which reflects the airway obstruction index and is more sensitive, The synergistic effect of temperature and PM2.5 was founded in winter [28].
There are two major strengths in this study. This is the first article to study the effect of PM 2.5 and temperature on lung function in healthy people in Northwest China. Second, Other articles usually refer to PEF and FEV1 as indicators of lung function. In this study, five indicators were included which are more comprehensive.
However, the limitations of this study worth noting. First, the population participated in the study are mainly yellow, middle-aged men and women living in Northwest China, which limits the universality of the population. Secondly, measurement of community temperature and pollutants ignores the potential significant differences that may affect individual residential temperature. Third, research period is relatively short, only 30 days are included in each quarter, which is not enough to represent the temperature change of the whole season. Last, our study focuses on two extreme temperature seasons, summer and winter, and ignores the seasons with mild climate conditions in spring and autumn.

Conclusions
In conclusion, our research suggests that exposure to PM 2.5 in winter has an acute adverse effect on lung function among healthy people in Xi'an of China. Further big number of subjects from different countries needed to be included to confirm these findings.

Availability of data and materials
The datasets generated and/or analyzed during the current study are not publicly available due other analyses are proceeding but are available form the corresponding 11 author on reasonable request.

Ethics approval and consent to participate
The study protocol was approved by the Institutional Ethics Committee of the First Affiliated Hospital of Xi'an Medical College (No.XYYFY2017LSK-017).All participants signed the consent form before entering the study.  The concentrations of Temperature, PM2.5, SO2 and NO2 for each subject during the study period.