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Trades transport pollutants, reveals PKU climatologist

Peking University, Jan. 21, 2014: Recently, research group of Lin Jintai, a ‘Bairen’ professor at Peking University (PKU), led a study jointly with Professors He Kebin and Zhang Qiang at Tsinghua University (THU) to analyze the impacts of China’s international trade on regional air pollution and global atmospheric transport. The research was published in the Proceedings of the National Academy of Sciences (of the United States of America). Lin Jintai, He Kebin and Zhang Qiang are the corresponding authors of the paper, and Lin Jintai and his undergraduate student Pan Da (now pursuing PhD at Princeton University) are the first authors.


Production of goods for consumption and associated economic processes (transportation, power generation, etc.) result in tremendous amounts of air pollutant emissions with a profound impact on regional air quality and global atmospheric pollution transport. Transboundary pollution transport is of serious concern for air quality globally. The United States has a particular interest in understanding the impacts of trans-Pacific transport of air pollution from China and other Asian countries, and much research has been conducted in this regard. However, previous research on air pollution transport and source attribution has been based on a so-called production-based accounting approach, where pollutant emissions related to production of goods are attributed to the country producing the products, no matter whether the products are consumed in the same country or are exported to supply foreign consumers.


International trade allows a country to import goods from other countries; therefore it alters the location of production and thus affects the spatial distribution of emissions. Also, the amount of emissions from production of a particular product differs significantly between countries, due to differences in economic structure, energy structure and emission control levels. This might greatly change the total amount of global emissions. Changes in both magnitude and spatial distribution of emissions will lead to substantial changes in regional air pollution and global transport, due to the relatively short lifetimes of air pollutants (from several hours to several months). Through these mechanisms, international trade has a profound impact on the global atmospheric environment.  However, research has rarely been done in this regard.


The research team, led by PKU and THU with collaborations from several research groups in Britain and America, analyzed the impacts of China’s international trade on the global atmospheric pollution and transport. Instead of adopting the traditional production-based pollution analysis, the team examined the trade influences from the consumption perspective. The team calculated the emissions between 2000 and 2009 related to China’s exports and imports through an economic input-output analysis and emission statistics. The study revealed that, for 2006 alone, as much as 36% of sulfur dioxide, 27% of nitrogen oxides, 22% of carbon monoxide and 17% of black carbon in Chinese anthropogenic emissions were related to production of goods for export. For each pollutant, 21% of the export-related emissions were tied to China-to-U.S. export. The total amounts of export-related Chinese emissions were larger than emissions in foreign countries related to China’s imports by a factor of 4-6. Using a global atmospheric chemical transport model called GEOS-Chem, the team further revealed that in 2006, 23-34% of sulfate particulate concentrations in the surface atmosphere of East China were caused by export-related emissions (Fig. 1a). The fractions were about 10-23% for black carbon and 12-23% for carbon monoxide (Fig. 1c, d).


 Fig. 1: Simulated percentage contribution of surface air pollution in 2006 from Chinese export-related emissions for (a) sulfate, (b) ozone, (c) black carbon, and (d) carbon monoxide.


The study further showed the impacts of China’s export-related pollution on the global atmospheric environment, with a particular focus on air quality in the United States. The study showed that in 2006, about 3-10% of sulfate and 0.5-1.5% of ozone in the surface atmosphere of the western United States were tied to China’s export-related emissions (Fig. 1a, b). The U.S. outsourcing manufacturing to China reduced emissions produced in the United States with a significant increase in emissions produced in China and thus an increase in pollution transported from China. The two factors compensated for each other, resulting in an improvement in sulfate air quality over the eastern United States with reductions in China and the western United States (Fig. 2a). The changes in U.S. air quality were overall beneficial for the United States due to the much denser population in the east. Enhancing China’s energy efficiency and emission control technologies to the U.S. level (e.g., through enhanced technology exchange) would not only reduce Chinese air pollution but also improve air quality in the United States.



Fig. 2a: Simulated percentage change in 2006 surface sulfate pollution due to Chinese export of goods to the United States versus producing the same goods in the United States.


The study concluded that analysis of the trade impacts on the global atmospheric environment with a consumption-based accounting would facilitate discussions of international collaboration in reducing global air pollution and transboundary transport.



Edited by: Arthars