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Tropospheric NO2 vertical column densities over Beijing: results of the first three years of ground-based MAX-DOAS measurements (2008ndash;2011) and satellite validation

机译:北京对流层NO2垂直柱密度:基于地面的MAX-DOAS的前三年测量结果(2008-2011年)和卫星验证

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摘要

Ground-based measurements of scattered sunlight by the Multi AxisDifferential Optical Absorption Spectroscopy (MAX-DOAS) have been carried outat an urban site (39.95° N, 116.32° E) in Beijing megacitysince 6 August 2008. In this study, we retrieved the tropospheric NOvertical column densities (VCDs) over Beijing from these MAX-DOASobservations from August 2008 to September 2011. Over this period, thedaytime (08:00–17:00 Beijing Time (BJT, which equals UTC + 8)) mean tropospheric NO VCDs variedfrom 0.5 to 13.3 with an average of 3.6 during summertime, and from 0.2 to16.8 with an average of 5.8 during wintertime, all in units of 10 molecules cm.The average diurnal variation patterns of troposphericNO over Beijing appeared to be rather different from one season toanother, indicating differences in the emission strength and atmosphericlifetime. In contrast to previous studies, we find a small weekly cycle ofthe tropospheric NO VCD over Beijing. The NO VCD in the lateafternoon was the largest on Saturday and the lowest on Sunday, and in themorning it reached a clear maximum on Wednesday. We also find a post-OlympicGames effect, with 39–54% decrease in the tropospheric NO VCD overBeijing estimated for August of 2008, compared to the following years. Thetropospheric NO VCDs derived by our ground MAX-DOAS measurements show agood correlation with SCIAMACHY and OMI satellite data. However, comparedwith the MAX-DOAS measurements, the satellite observations underestimate thetropospheric NO VCDs over Beijing systematically, by 43% forSCIAMACHY and 26–38% for OMI (DOMINO v2.0 and DOMINO v1.02). Based onradiative transfer simulations, we show that the aerosol shielding effect canexplain this underestimation, while the gradient smoothing effect caused bythe coarse spatial resolution of the satellite observations could play anadditional role.
机译:自2008年8月6日以来,已经在北京特大城市的一个城市站点(北纬39.95°N,东经116.32°E)进行了多轴差分光吸收光谱法(MAX-DOAS)的地面日光测量。在本研究中,我们检索了对流层从2008年8月到2011年9月从MAX-DOAS观测到的北京非垂直列密度(VCDs)。在此期间,白天(北京时间08:00-17:00(BJT,等于UTC + 8))表示对流层NO VCDs与北京地区对流层NO的平均日变化模式与一个季节差异很大,夏季为0.5至13.3,夏季平均为3.6,冬季为0.2至16.8,冬季平均为5.8。另外,表明发射强度和大气寿命存在差异。与以前的研究相比,我们发现北京对流层NO VCD的每周周期很小。下午晚些时候的NO VCD在周六最大,在周日最低,并且在早晨它达到了明显的最大值。我们还发现了奥运会之后的效应,与接下来的几年相比,估计北京在2008年8月对流层NO VCD下降了39–54%。通过我们的地面MAX-DOAS测量得出的对流层NO VCD与SCIAMACHY和OMI卫星数据具有很好的相关性。但是,与MAX-DOAS测量相比,卫星观测系统地低估了北京对流层NO VCDs,对于SCIAMACHY来说是43%,对于OMI(DOMINO v2.0和DOMINO v1.02)是26-38%。基于辐射传输模拟,我们证明了气溶胶屏蔽效应可以解释这种低估,而由卫星观测的粗糙空间分辨率引起的梯度平滑效应可以起到另外的作用。

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