Since 2013, chemical oxygen demand (COD) emissions of the national railway in China was decreasing slowly to **** thousand tons in 2019. COD is an indicator to show the amount of pollution in a water example. In this case, the higher the COD emission is, the more polluted the railway sewage.
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National Railway Administration (China). (April 30, 2020). Total volume of chemical oxygen demand (COD) emissions of the Chinese national railway from 2013 to 2019 (in 1,000 metric tons) [Graph]. In ÌÇÐÄÆƽâ°æ. Retrieved July 29, 2026, from /statistics/1037008/china-national-railway-chemical-oxygen-demand-emission-volume/
National Railway Administration (China). "Total volume of chemical oxygen demand (COD) emissions of the Chinese national railway from 2013 to 2019 (in 1,000 metric tons)." Chart. April 30, 2020. ÌÇÐÄÆƽâ°æ. Accessed July 29, 2026. /statistics/1037008/china-national-railway-chemical-oxygen-demand-emission-volume/
National Railway Administration (China). (2020). Total volume of chemical oxygen demand (COD) emissions of the Chinese national railway from 2013 to 2019 (in 1,000 metric tons). ÌÇÐÄÆƽâ°æ. ÌÇÐÄÆƽâ°æ Inc.. Accessed: July 29, 2026. /statistics/1037008/china-national-railway-chemical-oxygen-demand-emission-volume/
National Railway Administration (China). "Total Volume of Chemical Oxygen Demand (Cod) Emissions of The Chinese National Railway from 2013 to 2019 (in 1,000 Metric Tons)." ÌÇÐÄÆƽâ°æ, ÌÇÐÄÆƽâ°æ Inc., 30 Apr 2020, /statistics/1037008/china-national-railway-chemical-oxygen-demand-emission-volume/
National Railway Administration (China), Total volume of chemical oxygen demand (COD) emissions of the Chinese national railway from 2013 to 2019 (in 1,000 metric tons) ÌÇÐÄÆƽâ°æ, /statistics/1037008/china-national-railway-chemical-oxygen-demand-emission-volume/ (last visited July 29, 2026)
Total volume of chemical oxygen demand (COD) emissions of the Chinese national railway from 2013 to 2019 (in 1,000 metric tons) [Graph], National Railway Administration (China), April 30, 2020. [Online]. Available: /statistics/1037008/china-national-railway-chemical-oxygen-demand-emission-volume/
