中国科技网12月10日报道（张微 编译）在过去十年里，美国航空航天局的科学家们一直在利用最新的，高分辨率的空气质量指标的全球卫星地图，来跟踪全球不同地区和195个城市的空气污染趋势。这项研究成果提交在本周一旧金山召开的美国的地球物理联盟会议上，并发表在《地球物理研究》期刊上。

“空气质量的变化模式不是随机的，” 这项研究的领导者邓肯布莱恩说，他是马里兰州，格林贝尔特美国宇航局戈达德航天飞行中心的大气科学家。“当政府介入并表示我们想要有所建树，或我们想要控制污染，你就看到了这些数据的影响。”

邓肯和他的团队研究了2005到2014年NASA Aura卫星上的臭氧检测仪器的监测数据。设备检测出的大气气体之一是二氧化氮，一种黄褐色的气体，是常见的排放气体主要来自汽车、发电厂和工业活动。二氧化氮能迅速转化成地面臭氧，这是城市雾霾中的主要可吸入污染物。二氧化氮热点，用作衡量大气质量综合指数的一项指标，在发达国家和发展中国家的大多数主要城市中都有踪迹可寻。

科研团队分析了世界各地历年二氧化氮水平的发展趋势。为了寻找发展趋势的可能解释，研究人员将卫星记录与排放控制条例、国内生产总值和城市增长的信息进行了对比。

邓肯说：“随着最新高分辨率数据的发展，我们能够将污染变化的研究目标缩小到一个城市的范围内，包括个体污染源，，比如大型发电厂。”

之前的工作利用较低分辨率的卫星照片，会错过一些邻近地区发生的变化。这个新的空间视图为一个城市或国家的污染情况提供一致性的信息，而地面空气监测站有一定的局限性。产生的趋势图让我们了解到每个区域不同的污染信息。

美国和欧洲是二氧化氮最大的排放国。但是这两个地区在2005到2014年间的排放量急剧减少。在美国二氧化氮排放从20%降低到50%，在西欧排放量降低了50%。研究人员得出的结论是，排放量的降低主要是受环境法规的影响，法规要求进行技术改进以减少汽车和发电厂的污染排放量。

中国，世界日益增长的制造业中心，二氧化氮水平从20%增长到了50%，这主要发生在华北平原。中国三个主要的大都市群——北京，上海，和珠江三角洲，二氧化氮水平降低了40%。

南非地区包括约翰内斯堡和比勒陀利亚的二氧化氮水平在南半球是最高的，但高分辨率趋势图显示，这两个城市和邻近电厂与工业区域之间的情况有点复杂。

“我们在过去的研究中看到南非这个工业区域中看似矛盾的趋势，”汤普森 安妮说，她是这项研究论文的合著者也是戈达德中心的大气化学首席科学家。直到我们有了这个新的空间视图，它仍旧是个谜。”

比勒陀利亚——约翰内斯堡城市群在2008年要求更换新汽车之后，二氧化氮水平下降，排放得到了很好的控制。而在重工业地区，如城市群的东部地区，二氧化氮水平既有增加也有减少。排放水平降低可能与城市东部八个大型发电厂降低排放量有关，因为图像显示在发电厂区域二氧化氮水平降低。而排放量的增加发生在南部和再往东的地区，主要由于采矿和工业活动。

在中东，伊拉克、科威特和伊朗这三个国家自2005年开始二氧化氮排放水平增加，可能与这些国家的经济增长相对应。在叙利亚，自2011年开始二氧化氮水平开始下降，最大的原因是内战，这场战争使经济活动中断，数百万人流离失所。

New NASA satellite maps show human fingerprint on global air quality

Using new, high-resolution global satellite maps of air quality indicators, NASA scientists tracked air pollution trends over the last decade in various regions and 195 cities around the globe. The findings were presented Monday at the American Geophysical Union meeting in San Francisco and published in the Journal of Geophysical Research.

"These changes in air quality patterns aren't random," said Bryan Duncan, an atmospheric scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, who led the research. "When governments step in and say we're going to build something here or we're going to regulate this pollutant, you see the impact in the data."

Duncan and his team examined observations made from 2005 to 2014 by the Dutch-Finnish Ozone Monitoring Instrument aboard NASA's Aura satellite. One of the atmospheric gases the instrument detects is nitrogen dioxide, a yellow-brown gas that is a common emission from cars, power plants and industrial activity. Nitrogen dioxide can quickly transform into ground-level ozone, a major respiratory pollutant in urban smog. Nitrogen dioxide hotspots, used as an indicator of general air quality, occur over most major cities in developed and developing nations.

The science team analyzed year-to-year trends in nitrogen dioxide levels around the world. To look for possible explanations for the trends, the researchers compared the satellite record to information about emission controls regulations, national gross domestic product and urban growth.

"With the new high-resolution data, we are now able to zoom down to study pollution changes within cities, including from some individual sources, like large power plants," said Duncan.

Previous work using satellites at lower resolution missed variations over short distances. This new space-based view offers consistent information on pollution for cities or countries that may have limited ground-based air monitoring stations. The resulting trend maps tell a unique story for each region.

The United States and Europe are among the largest emitters of nitrogen dioxide. Both regions also showed the most dramatic reductions between 2005 and 2014. Nitrogen dioxide has decreased from 20 to 50 percent in the United States, and by as much as 50 percent in Western Europe. Researchers concluded that the reductions are largely due to the effects of environmental regulations that require technological improvements to reduce pollution emissions from cars and power plants.

China, the world's growing manufacturing hub, saw an increase of 20 to 50 percent in nitrogen dioxide, much of it occurring over the North China Plain. Three major Chinese metropolitan areas—Beijing, Shanghai, and the Pearl River Delta—saw nitrogen dioxide reductions of as much as 40 percent.

The South African region encompassing Johannesburg and Pretoria has the highest nitrogen dioxide levels in the Southern Hemisphere, but the high-resolution trend map shows a complex situation playing out between the two cities and neighboring power plants and industrial areas.

"We had seen seemingly contradictory trends over this area of industrial South Africa in previous studies," said Anne Thompson, co-author and chief scientist for atmospheric chemistry at Goddard. "Until we had this new space view, it was a mystery."

The Johannesburg-Pretoria metro area saw decreases after new cars were required in 2008 to have better emissions controls. The heavily industrialized area just east of the cities, however, shows both decreases and increases. The decreases may be associated with fewer emissions from eight large power plants east of the cities since the decrease occurs over their locations. However, emissions increases occur from various other mining and industrial activities to the south and further east.

In the Middle East, increased nitrogen dioxide levels since 2005 in Iraq, Kuwait and Iran likely correspond to economic growth in those countries. However, in Syria, nitrogen dioxide levels decreased since 2011, most likely because of the civil war, which has interrupted economic activity and displaced millions of people.