千岛湖国家森林公园大气能见度变化特征及其影响因素

Patterns of Variation in Atmospheric Visibility and Impacting Factors in Qiandao Lake National Forest Park,China

【目的】研究千岛湖国家森林公园大气能见度变化特征及其影响因素,为提升森林景观及游览质量提供数据支撑。【方法】利用2015-12-01—2016-11-30监测数据,分析大气能见度变化特征,探究大气污染物(PM_(10)、PM_(2.5)、SO_2、NO_2、CO和O_3)和气象因子(风速、气温、露点温度、海平面气压和空气相对湿度)对大气能见度的影响。【结果】千岛湖国家森林公园年均大气能见度为12.84 km,除PM_(2.5)年均浓度略超出环境质量一级标准外,其他大气污染物年均浓度皆处于一级标准内,表明千岛湖国家森林公园空气质量较高;大气能见度呈夏秋季高、春冬季低的变化特征,最大值出现在8月,最低值出现在1月;从日变化规律看,最大值出现在傍晚(17:00),最低值出现在清晨(5:00);将大气能见度分为极差(<4 km)、差(4~10 km)、好(10~20 km)和极好(≥20 km)4个级别进行分析,发现不同级别大气能见度出现的频率有明显季节性,春冬季极差和差的频率高,好和极好的频率低,夏秋季好和极好的频率较高,差和极差基本未出现;年内数据相关性分析显示,大气能见度与大气污染物PM_(10)、PM_(2.5)、CO、SO_2和NO_2浓度及空气相对湿度和海平面气压负相关(相关系数分别为-0.29,-0.33,-0.26,-0.16,-0.35,-0.42和-0.11),而与气温、风速和露点温度正相关(相关系数分别为0.39,0.20和0.19);K均值聚类分析表明,千岛湖大气能见度较高时,气象条件为高温、高风速、低湿和低海平面气压,是夏秋季午后典型的气象特征,而大气能见度出现低值时,气象特征为低温、高湿、高海平面气压和低风速,为春冬季夜晚及凌晨典型的气象特征;以消光系数、干消光系数与AQI和大气污染物PM_(10)、PM_(2.5)、SO_2、CO、NO_2浓度构建回归模型,显示回归(P<0.001),且相对于其他污染物浓度指标,AQI和PM_(10)、PM_(2.5)浓度对大气能见度贡献率(R2)较高,表明其对大气能见度变化影响较大。【结论】千岛湖国家森林公园大气能见度高,空气环境质量较好,大气能见度呈现出明显的季节和日变化特征;大气能见度与大气污染物浓度和气象因子相关,气温、风速、空气相对湿度对大气能见度影响较高,AQI和PM_(10)、PM_(2.5)浓度对大气能见度影响较大;除去雨、雾等特殊天气影响后的大气能见度可有效反映大气环境质量。

【Objective】The primary objective is to investigate the patterns of variation in atmospheric visibility and its affecting factors over Qiandao Lake National Forest Park,in order to obtain data for improving forest tourism and recreation.【Method 】Based on monitoring data collected from December 1,2015 to November 30,2016,variation of atmospheric visibility and its correlations with the affecting factors（AQI,concentrations of PM_（10）,PM_（2.5）,SO_2,NO_2,CO,O_3,wind speed,temperature,dew point temperature,sea level pressure,relative air humidity） over Qiandao Lake National Forest Park were investigated. 【Result 】The annual average value of atmospheric visibility in Qiandao Lake National Forest Park was 12. 84 km; other than PM_（2.5）,which exceeded the grade Ⅰ standards slightly,annual average concentrations of the remained air pollutants met the Chinese Ambient Air Quality Standards Grade Ⅰ,indicating a good air quality of Qiandao Lake National Forest Park. Atmospheric visibilities were better in summer and autumn,but worse in spring and winter; for diurnal variation,the visibility peaked at dusk（17： 00） and showed the lowest value in the early morning（5： 00）. The ratings of atmospheric visibility were categorized by very bad（ 4 km）,bad（4-10 km）,good（10-20 km） and very good（≥20 km）,and its monthly statistics showed a distinct seasonal pattern; in spring and winter,the frequencies of very bad and bad ratings were high while those of good and very good were low. In summer and autumn,the frequencies of good and very good were high while those of very bad and bad ratings were almost none.Negative correlations between atmospheric visibility and the concentrations of PM_（10）,PM_（2.5）,SO_2,CO,NO_2,humidity as well as air pressure were found with correlation coefficients of-0. 29,-0. 33,-0. 26,-0. 16,-0. 35,-0. 42,-0. 11,respectively,while positive correlations were detected between atmospheric visibility and temperature,wind speed and dew point temperature,the correlation coefficient were 0. 39,0. 20,0. 19,respectively. K-means clustering showed the higher visibility in summer was consistent with higher temperature and wind speed as well as lower humidity and air pressure,the lower visibility in winter and spring was associated with low temperature,high humidity and high sea level pressure. The regression equation constructed by the（dry extinction coefficient） extinction coefficient and the AQI（air quality index） and the concentration of PM_（10）,PM_（2.5）,SO_2,CO,NO_2 were established（P 0. 001）. The result showed the contribution rates（R2） of AQI and the concentrations of PM_（10） and PM_（2.5） to atmospheric visibility were higher than the concentrations of other air pollutants,indicating higher impacts of AQI and the concentrations of PM_（10） and PM_（2.5） on visibility.【Conclusion】The atmospheric visibility in Qiandao Lake National Forest Park was high,indicating a good air quality of Qiandao Lake National Forest Park. The atmospheric visibility showed obvious seasonal and diurnal variation.High correlations between atmospheric visibility and AQI,concentrations of PM_（10） and PM_（2.5）,temperature,wind speed and relative air humidity was found. The study of atmospheric visibility and its affecting factors in Qiandao Lake National Forest Park showed a fundamental influence of air quality on atmospheric visibility,and atmospheric visibility can be an effective indicator of air quality,except rain,fog and other special weathers.