Tropospheric NO2 vertical column densities over Beijing: results of the first three years of ground-based MAX-DOAS measurements (2008-2011) and satellite validation
Tropospheric NO2 vertical column densities over Beijing: results of the first three years of ground-based MAX-DOAS measurements (2008-2011) and satellite validation
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DOI：
10.5194/acp-13-1547-2013
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发表时间：
2013-01-01
影响因子：
6.3
通讯作者：
Wagner, T.
中科院分区：
文献类型：
--
作者：
Ma, J. Z.;Beirle, S.;Wagner, T.
自2008年8月6日起，利用多轴差分光学吸收光谱仪（MAX-DOAS）对北京市区（39.95 ° N，116.32 ° E）的散射太阳光进行了地面测量。利用2008年8月至2011年9月的MAX-DOAS观测资料反演了北京地区对流层NO2垂直柱密度。在此期间，白天（北京时间08：00-17：00，相当于UTC + 8）对流层NO2 VCD的平均值在夏季为0.5 - 13.3，平均值为3.6，冬季为0.2 - 16.8，平均值为5.8，单位均为10（16）分子cm（-2）。北京地区对流层NO2浓度的日变化在不同季节有很大的差异，反映了不同季节的排放强度和大气寿命的差异。与以往的研究相比，我们发现北京对流层NO2 VCD存在一个小的周周期。下午晚些时候的NO2 VCD是周六最大，周日最低，周三上午达到明显的最大值。我们还发现后奥运会的影响，与2008年8月的北京对流层NO2 VCD估计减少39-54%，与随后的几年相比。由地面MAX-DOAS观测得到的对流层NO2 VCD与SCIAMACHY和OMI卫星观测资料有较好的相关性。然而，与MAX-DOAS观测结果相比，SCIAMACHY和OMI（DOMINO v2.0和DOMINO v1.02）卫星观测结果系统性地低估了北京地区对流层NO2的VCD，分别低估了43%和26-38%。基于辐射传输模拟，我们表明，气溶胶屏蔽效应可以解释这种低估，而梯度平滑效应所造成的粗空间分辨率的卫星观测可以发挥额外的作用。
Ground-based measurements of scattered sunlight by the Multi Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) have been carried out at an urban site (39.95 degrees N, 116.32 degrees E) in Beijing megacity since 6 August 2008. In this study, we retrieved the tropospheric NO2 vertical column densities (VCDs) over Beijing from these MAX-DOAS observations from August 2008 to September 2011. Over this period, the daytime (08:00-17:00 Beijing Time (BJT, which equals UTC + 8)) mean tropospheric NO2 VCDs varied from 0.5 to 13.3 with an average of 3.6 during summertime, and from 0.2 to 16.8 with an average of 5.8 during wintertime, all in units of 10(16) molecules cm(-2). The average diurnal variation patterns of tropospheric NO2 over Beijing appeared to be rather different from one season to another, indicating differences in the emission strength and atmospheric lifetime. In contrast to previous studies, we find a small weekly cycle of the tropospheric NO2 VCD over Beijing. The NO2 VCD in the late afternoon was the largest on Saturday and the lowest on Sunday, and in the morning it reached a clear maximum on Wednesday. We also find a post-Olympic Games effect, with 39-54% decrease in the tropospheric NO2 VCD over Beijing estimated for August of 2008, compared to the following years. The tropospheric NO2 VCDs derived by our ground MAX-DOAS measurements show a good correlation with SCIAMACHY and OMI satellite data. However, compared with the MAX-DOAS measurements, the satellite observations underestimate the tropospheric NO2 VCDs over Beijing systematically, by 43% for SCIAMACHY and 26-38% for OMI (DOMINO v2.0 and DOMINO v1.02). Based on radiative transfer simulations, we show that the aerosol shielding effect can explain this underestimation, while the gradient smoothing effect caused by the coarse spatial resolution of the satellite observations could play an additional role.