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中国西部荒漠城市高背景臭氧浓度受局地弱人为影响特征研究

Characteristics of weak anthropogenic influences on high background ozone concentrations in the desert cities of western China

  • 摘要: 国内外针对沙漠地区臭氧浓度演变特征研究存在较大空白。阿拉善左旗属于我国西部典型的荒漠城市,在人为活动强度较低的基础下,具有较高的臭氧(O3)背景浓度。其中2015年-2022年日最大臭氧8小时滑动平均值(MDA8 O3)年增长约为2μg·m-3,春夏秋冬季节平均MDA8 O3分别为111.3 μg·m-3、132.3 μg·m-3、101.8 μg·m-3和82.9 μg·m-3。由于高温强辐射的有利条件促进O3的大气光化学反应,增强O3的二次生成,因此O3污染主要出现于夏季。夏季夜间在NO滴定效应影响下,阿拉善左旗各监测站O3浓度仍然可以达到93-106μg·m-3,且观测站点距地面越高O3浓度越高,表明西部沙漠地区受到高O3背景浓度控制。观测发现近地面人为排放对三个距离地面不同高度站点的O3浓度产生不同的影响。以距地面22m的环保局新楼站O3浓度为参考,距地面15m的蒙二幼站夜间O3浓度低5-25μg·m-3,日间O3浓度高5μg·m-3;距地面12m西花园站站点夜间O3浓度低10-25μg·m-3,日间O3浓度高5μg·m-3。对于城区夜晚越靠近地面NO滴定效应越强,白天随着对流扩散和近地面快速的O3光化学反应影响,越靠近地面O3浓度越高。说明弱人为活动对O3浓度的影响,反映沙漠城市O3垂直分布特征。

     

    Abstract: There are large gaps in domestic and international research on the characteristics of ozone(O3) concentration evolution in desert areas. Alxa Left Banner belongs to a typical desert city in the western China, which has high background concentrations of O3 on the basis of low intensity of anthropogenic activities. From 2015 to 2022, the annual growth of the 8-hour moving average of daily maximum ozone (MDA8 O3) was about 2 μg·m-3. And the average MDA8 O3 in spring, summer, autumn and winter was 111.3 μg·m-3, 132.3 μg·m-3, 101.8 μg·m-3 and 82.9 μg·m-3. Due to the favourable conditions of high temperature and strong radiation, the atmospheric photochemical reaction of O3 will be promoted and the secondary production of O3 will be enhanced, thus the O3 pollution incidents mainly appear in the summer. The O3 concentrations in Alashan Left Banner were 93-106 μg·m-3 in the summer night under the influence of NO titration effect, indicating that the Alashan region was controlled by high background O3 level. The higher the distance from the observation site to the ground, the higher the O3 concentration. The observations show that the near-surface anthropogenic emissions has direct and significant influence on the vertical O3 concentrations at three stations with different heights over the ground surface. Setting the O3 concentration at the Huanbaojuxinlou Station (22 m above the ground) as a criteria. The O3 concentration at the Mengeryou Station, which is 15 m above the ground, is lower by 5-25 μg·m-3 during the night, and it is higher by 5 μg·m-3 during the noon; the O3 concentration at the Xihuayuan Station, which is 12 m above ground, is lower by 10-25μg·m-3 during the night, and it is higher by 5 μg·m-3 during the noon. The stronger NO titration effect was found in the near ground atmosphere in the urban area at night. However, the higher O3 was found in the near ground atmosphere due to the convective diffusion and rapid photochemical reaction. The effect of weak human activities on O3 concentration was illustrated, and the vertical distribution characteristics of O3 in desert cities were reflected.

     

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