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[16–18]. 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 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 PM2.5 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, exposure to PM2.5 showed association with decreased lung function. Our study did not find the relationship between PM2.5 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 PM2.5 and childhood lung function insignificant.
However, it seems too hasty to conclude that PM2.5 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. McMichaelalso have founded that cold temperatures did not have much effect on respiratory. To explain this conclusion, the following factors may take into consideration. Firstly, Air could be warmed or cooled to 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 PM2.5 on lung function. We found that three air pollutants (PM2.5, SO2 and NO2) 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 (NO2) 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. 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.
There are two major strengths in this study. This is the first article to study the effect of PM2.5 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.