| 边界层低空急流导致北京PM2.5迅速下降及其形成机制的个例分析 |
| 摘要点击 3175 全文点击 1849 投稿时间：2015-06-30 修订日期：2015-08-13 |
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| 中文关键词 PM2.5污染 快速清除 边界层急流 惯性振荡 大气斜压性 |
| 英文关键词 PM2.5 pollution rapid clean away boundary layer jet inertial oscillation atmospheric baroclinicity |
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| 中文摘要 |
| 2015年3月17日18:00~23:00北京地区的PM2.5质量浓度快速下降,在此期间并未出现与冷空气活动相伴的强偏北风.本研究分析了导致空气质量迅速改善的原因,结果表明边界层急流起着关键的作用. 随着边界层内偏南风速增大,大气的通风量增大,污染物浓度降低. 急流发展也加大了边界层内水平风的垂直切变,从而导致湍流增强和混合层增厚. 此外,3月17日20:00在混合层顶附近出现气旋性地转涡度,Ekman抽吸的方向为垂直向上,于是底层的污染物就被带到高空并随强劲的西南风输送到下游. 边界层急流的发展与惯性振荡和大气的斜压性有关. |
| 英文摘要 |
| The concentration of PM2.5 decreased very rapidly from 18:00 to 23:00 on 17th Mar. 2015 in Beijing area. No cold air bringing strong north wind influenced Beijing. The reason leading to the clean away of PM2.5 was discussed. The results showed that a boundary layer jet played a key role. The ventilation in the boundary layer went up with the enhancement of southwesterly wind speed, which was favorable to the dilution of pollution. Besides, the development of jet also caused the increase of vertical wind shear. As a result, the turbulence in the boundary layer became more obvious and the mixing layer height rose. Furthermore, the geostrophic vorticity at the top of mixing layer was positive at 20:00 on 17th Mar. It means that the direction of Ekman-Pumping was upward. So, the pollution near the surface was brought to upper levels and transported downstream by the jet. The development of boundary layer jet attributed to inertial oscillation and atmospheric baroclinicity. |
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