The large-scale burning of crop residues in the North China Plain, one of the most densely populated regions in the world, causes severe air pollution and harmful health effects. Until now there was no reliable quantification of the magnitude of these fires that take place after the wheat harvest in the month of June. An international team of researchers used satellite measurements to map the extent of the problem by estimating the emissions of volatile organic compounds in this region. Amongst these were measurements of Folkert Boersma (Meteorology and Air Quality group) on NOx emissions.
The North China Plain covers an area of approximately 400,000 km2, extending over the provinces of Hebei, Shandong, Henan, Anhui, and Jiangsu. Thanks to its fertile soil, this region is one of the largest agricultural plains, and among the most densely populated areas of the world, home to over 300 million people. Wheat and maize are the two main crops in this area. Large-scale agricultural burning of crop residues after the harvest is a well-established practice, which repeats itself every year. It helps field clearing and preparation for the next crop. But the smouldering fires also cause extremely poor air quality and raise concerns about adverse effects on human health. Straw burning limitations are actively debated in China but their implementation often faces the reluctance of farmers who use ash as a natural fertiliser.
“Quantifying the magnitude of the associated emissions and their impact on regional air quality was therefore urgently needed,” Folkert Boersma says. “With satellite measurements we can do this.” The researchers calculated crop burning to cause important increases in surface ozone (+7%) and fine aerosol concentrations (+18%) in the North China Plain in June. The impact of crop fires is also found in satellite observations of other species, glyoxal, nitrogen dioxide and methanol.
Folkert Boersma: “Our study indicates that the crop burning emissions of volatile organic compounds in June have a severe impact on the air quality in the region. Our measurements show that the crop burning emissions of volatile organic compounds in June exceed by almost a factor of 2 the combined emissions from other anthropogenic activities in this region. This underscores the need for targeted actions towards changes in agricultural management practices, such as outlawing the practice of burning agricultural waste, as is the standard in the EU.”