Watching China's smog from space

China's rapid industrialization over the past few decades has given rise to an economy dependent on emissions-intensive manufacturing with a serious pollution problem. In January images from a sudden onset of haze blanketing northern China quickly made the rounds of the Internet and in February MIT researchers estimated that health damages from pollution cost the Chinese economy over $112 billion in 2005. As the Chinese economy continues to grow at an unprecedented rate, how has this pollution problem changed?

Fortunately, it's possible to consider this question directly by looking at actual pollution data. The SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY, because physicists cannot resist implausible acronyms) project launched in 2002, and provides worldwide data coverage for a variety of atmospheric pollutants. Here, I'll look at nitrogen dioxide specifically - it's produced through the combustion of fuel in air to form a principal component of smog, and it's useful for looking at local trends since it decays in the atmosphere on a timescale of hours or days. The data set is helpfully provided for free through the TEMIS project.  

The graph above shows the abundance of nitrogen dioxide in four major Chinese cities: Shanghai, Beijing, Guangzhou, and Chongqing. (Values here are averaged over daily observations for the month of September.) These are four of the largest cities in the country by population and economic production, and each has experienced massive growth over the past decade. However, this growth has not been accompanied by an associated increase in pollution levels. To the contrary, there appears to be little trend in pollution over the past decade. (It is worthwhile to note that all the pollution levels observed here are generally quite high by developed-country standards; for example, density levels are around 10×10¹⁵ molecules per cm² in London and 5×10¹⁵ in Vancouver.)

Why has pollution not continued to grow with the size of the economy? A variety of effects could be contributing here. To some extent, increasingly wealthy and well-informed citizens are less enthusiastic regarding the tradeoff between rising pollution and greater incomes; the government has responded accordingly by setting more stringent policy. Also, Chinese companies may be acquiring and installing more energy-efficient technology. At any rate, it is encouraging to see no strong trend in pollution levels over a period when total economic output quadrupled. Hopefully China will be able to bring its pollution problem under control as the economy continues to grow.

(I gratefully acknowledge the free use of tropospheric NO2 column data from the SCHIAMACY sensor from TEMIS. Image source: photo of Xian from Benjamin Vander Steen's flickr photostream. Licensed via Creative Commons.)