华北平原固城站NO2对流层柱浓度变化特征

Characteristics of NO2 Tropospheric Column Density over a Rural Area in the North China Plain

  • 摘要: 基于2008年9月—2010年9月河北固城生态与农业气象试验站多轴差分吸收光谱仪 (multi-axis differential optical absorption spectroscopy, MAX-DOAS) 获得的太阳散射光谱观测,反演计算该地区NO2对流层柱浓度,分析其季节、日变化特征以及不同来源输送的影响,并与同期NO2地面观测资料和卫星产品进行对比分析。发现固城站NO2对流层柱浓度冬高 (5.14×1016 cm-2) 夏低 (1.28×1016 cm-2);日变化形态在四季均呈现中午低、傍晚高的特征,且冬季最明显。与北京城市区域同期的观测相比,冬季固城站观测值略低,而在春、夏季则偏低较显著。地面风玫瑰图分析显示,来自SW, SSW, NE方向及ENE方向的污染输送对其贡献最大。与地面、卫星NO2观测的对比表明,MAX-DOAS反演的NO2柱浓度与地面观测浓度具有一致的季节和日变化特征,卫星反演的NO2对流层柱浓度产品在华北平原农村地区存在系统性低估。

     

    Abstract: NO2 tropospheric vertical column densities (VCD) at Gucheng Eco-meteorological Observation Experiment Station (GCH) in Hebei Province from September 2008 to September 2010 are retrieved from the scattered sunlight spectra, measured by a multi-axis differential optical absorption spectroscopy (MAX-DOAS), and its characteristics are analyzed then.It shows that the mean seasonal NO2 tropospheric VCDs are high in winter (5.14×1016 cm-2) and low in summer (1.28×1016 cm-2). The mean value in winter is a little lower than that in urban Beijing and much lower than that in spring and summer. Averaged diurnal variations are always low at noon and high towards evening for the whole year. The varying amplitude in winter is the biggest among all seasons and the concentration shows a rising up trend in the late afternoon. Less variation can be seen during the day in spring and autumn, and they decrease slowly in summer, reaching a minimum value after noon. The phenomena can be explained by seasonal differences of sources and sinks of tropospheric NO2.The tropospheric NO2 over GCH site is mainly affected by the transport from sectors of SW, SSW, NE and ENE, where the major NO2 emission sources in North China are located. It's interesting to note that the NO2 tropospheric VCDs over GCH site is higher than that over Xianghe site (another rural site in North China) in winter. Backward trajectories analyses show that in winter two sites have a distinct difference of pollutant sources, which are causes of their discrepancy.Patterns of seasonal variations are quite the same for NO2 tropospheric VCDs retrieved from MAX-DOAS and satellite observation product OMNO2d, as well as the mixing ratios of in situ NO2 measurements. Compared with results from MAX-DOAS, a systematic underestimation of OMI satellite observation for NO2 is found in the rural North China area, as those found in urban Beijing and Shanghai megacities. The individual NO2 VCDs retrieved from MAX-DOAS and the surface NO2 mixing ratios are highly correlated, with an apparently higher correlation coefficient (R=0.738) than that between OMNO2d and surface mixing ratios (R=0.639).It's evident that column density levels of tropospheric NO2 can be much better captured by MAX-DOAS observations than other measurements. As a result, much more emphasis should be given on the development of MAX-DOAS observation network. Furthermore, the application of MAX-DOAS measurements on validation and correction of satellite data should be strengthened.

     

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