Heavy air pollution has spread across central and eastern China, causing at least 87 cities to activate emergency-response plans, according to China Environment News.
Nitrates account for about 40% of the recent pollution’s fine particulate matter (PM2.5) content, explained Professor Zhang Qiang of Tsinghua University. These are formed by atmospheric conversion of nitrogen oxides (NOx) emitted from coal-fired heating, industrial furnaces and diesel vehicles under stagnant weather.
Emissions have remained high as demand for heating surged during low temperatures since mid January. “Non-interruptible industries like steel and coking plants continued operating, while heavy truck traffic rebounded quickly once precipitation ended,” Zhang added.
Low wind speeds have prevented pollutants from dispersing, while high humidity has caused “temperature inversions”. These occur when a layer of warmer air sits over a layer of cooler air near the Earth’s surface, reversing the norm of temperature decreasing with height. This can act like a “lid” over a city, trapping pollution.
The 87 cities that had activated emergency-response plans as of 25 January were in the regions of Beijing-Tianjin-Hebei, the Yangtze River delta, and the Yangtze’s middle reaches, China Environment News reported. Anyang and Xinxiang in Henan and Xingtai in Hebei issued red alerts. Tianjin and several other cities in Hebei issued orange alerts, while parts of Jiangsu and Zhejiang issued yellow ones.
This means local governments must apply graded emission-reduction measures, including curbs on industrial activity, traffic restrictions, construction halts and bans on straw burning.
Industry research suggests inspections linked to the pollution have already affected aluminium producers. As of 16 January, capacity utilisation at aluminium plants in Sichuan and Chongqing had fallen to 41.8%, with production cuts expected to last a further five to seven days.
Pollution levels will gradually ease from 29 January, as cold air moves in from the northeast alongside rain and snow, forecasts China National Environmental Monitoring Center.
Read Dialogue Earth’s report from last year on the westward shift of China’s air pollution.