Long-term changes of tropospheric NO2 over megacities derived from multiple satellite instruments
Long-term changes of tropospheric NO2 over megacities derived from multiple satellite instruments
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DOI：
10.5194/acp-13-4145-2013
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发表时间：
2013-01-01
影响因子：
6.3
通讯作者：
Burrows, J. P.
中科院分区：
文献类型：
--
作者：
Hilboll, A.;Richter, A.;Burrows, J. P.
对流层NO2是一种主要污染物，特别是在城市中，自20世纪90年代中期以来，GOME、SCIAMACHY、OMI和GOME-2仪器一直在从空间测量。这些数据提供了一个独特的全球对流层污染长期数据集。然而，这些观测在空间分辨率、测量的当地时间、观测几何和其他细节方面有所不同。在这项研究中，我们提出了三种方法来解释卫星测量的NO2柱的趋势分析中的仪器差异，同时保留各个仪器的空间分辨率。为了将来自国美和SCIAMACHY的测量组合成一个一致的时间序列，我们开发了一种方法来明确地解释仪器在地面像素大小上的差异（40 x 320 km（2）与30 x 60 km（2））。这在分析小的局部来源的NO2变化时尤其重要，例如，G.特大城市。该方法是基于测量的地照光谱的空间平均和提取的分辨率效应的空间图案。此外，两个经验的校正，其中总结了所有工具的差异，包括工具相关的偏移量在一个拟合的趋势函数，开发。这些方法分别应用于GOME和SCIAMACHY的数据，合并的时间序列，并扩展数据集，包括GOME-2和OMI measurement.All的方法显示一致的趋势对流层NO2的区域和城市尺度上的选择区域，第一次允许一致的趋势分析的完整的时间序列在高空间分辨率。与以前的研究相比，较长的研究周期导致显着降低的不确定性。我们表明，测量对流层NO2柱一直在中国，中东和印度，与中国中东部地区的值增加了两倍，从1996年到2011年。发达国家的所有地区，包括西欧、美国和日本，在同一时期都显示出NO2含量的显著下降。在特大城市水平上，达卡和巴格达的个体趋势分别高达+27.2 +/- 3.9%（-1）和+20.7 +/- 1.9%（-1），而洛杉矶显示出非常强劲的下降，为-6.00 +/- 0.72%（-1）。中国、印度和中东的大多数特大城市的NO2柱呈+5至10%的年（-1）增长，导致研究期间的两倍至三倍。
Tropospheric NO2, a key pollutant in particular in cities, has been measured from space since the mid-1990s by the GOME, SCIAMACHY, OMI, and GOME-2 instruments. These data provide a unique global long-term dataset of tropospheric pollution. However, the observations differ in spatial resolution, local time of measurement, viewing geometry, and other details. All these factors can severely impact the retrieved NO2 columns.In this study, we present three ways to account for instrumental differences in trend analyses of the NO2 columns derived from satellite measurements, while preserving the individual instruments' spatial resolutions. For combining measurements from GOME and SCIAMACHY into one consistent time series, we develop a method to explicitly account for the instruments' difference in ground pixel size (40 x 320 km(2) vs. 30 x 60 km(2)). This is especially important when analysing NO2 changes over small, localised sources like, e. g. megacities. The method is based on spatial averaging of the measured earthshine spectra and extraction of a spatial pattern of the resolution effect. Furthermore, two empirical corrections, which summarise all instrumental differences by including instrument-dependent offsets in a fitted trend function, are developed. These methods are applied to data from GOME and SCIAMACHY separately, to the combined time series, and to an extended dataset comprising also GOME-2 and OMI measurements.All approaches show consistent trends of tropospheric NO2 for a selection of areas on both regional and city scales, for the first time allowing consistent trend analysis of the full time series at high spatial resolution. Compared to previous studies, the longer study period leads to significantly reduced uncertainties.We show that measured tropospheric NO2 columns have been strongly increasing over China, the Middle East, and India, with values over east-central China tripling from 1996 to 2011. All parts of the developed world, including Western Europe, the United States, and Japan, show significantly decreasing NO2 amounts in the same time period. On a megacity level, individual trends can be as large as +27.2 +/- 3.9% yr(-1) and +20.7 +/- 1.9% yr(-1) in Dhaka and Baghdad, respectively, while Los Angeles shows a very strong decrease of -6.00 +/- 0.72% yr(-1). Most megacities in China, India, and the Middle East show increasing NO2 columns of +5 to 10% yr(-1), leading to a doubling to tripling within the study period.