“The relationship between Covid-19 and air pollution has shed new light on the latter, especially as many sites have clearly observed cleaner air – revealing the potential for improving air quality through urgent collective action,” the report said.
Researchers from IQAir – a global information technology and air quality company – analyzed pollution data from 106 countries, specifically measuring PM 2.5, a microscopic pollutant that can pose serious health risks.
Singapore, Beijing and Bangkok – which all imposed circuit breaker and widespread business shutdowns – saw the biggest cuts in PM 2.5. But this effect will not last: levels of air pollution are likely to rise as Covid-19 containment measures end and business resumes, the report said.
In general, the sites of South Asia and East Asia still top the list of the most polluted places in the world, according to the report. Bangladesh, China, India and Pakistan share 49 of the world’s 50 most polluted cities.
Hotan, an oasis in the Xinjiang region of western China, was ranked the most polluted city in the world in 2020. Its average annual levels of PM 2.5 were 110.2 micrograms per cubic meter – 11 times higher than the WHO target for annual exposure. At the height of Hotan, those levels rose to 264.4 in March – deep in the “dangerous” zone.
The report said Xinjiang has seen rapid increases in coal and fossil fuel emissions. Land degradation caused by human activity and climate change has also increased the severity of droughts, leading to more frequent sand and dust storms that contribute to severe pollution.
The report said that China is also still the world’s largest coal producer and consumer, and a major contributor to PM 2.5 pollution. The country is making great strides in renewable energies – but these sources account for only 23% of energy consumption in China, while coal accounts for 58%.
After Hotan, the next 13 most polluted cities are in India, with the main sources of pollution including transportation, construction and waste incineration.
In the northern provinces of Punjab and Haryana, farmers also practice hay burning – deliberately setting fires to cultivated fields to prepare the land for its next crop. Straw-burning incidents in Punjab reached record levels in 2020, an increase of 46.5% from 2019. According to the report, up to 40% of air pollution in the capital, Delhi, stems from Punjab farm fires.
The global decrease in human-related emissions in 2020 was also partially offset by “severe air pollution events” such as forest fires and dust storms, which are linked to the worsening climate crisis and unpredictable weather around the world.
Wildfires have devastated parts of the United States, Australia, South America, Indonesia and more – causing spikes in air pollution and massive amounts of greenhouse gas emissions. Sao Paulo, Los Angeles and Melbourne – all affected by severe bushfires – saw the largest rise in PM 2.5 levels compared to 2019.
But there are bright spots, too. The 25 most polluted cities in South Asia either experienced a decrease in PM 2.5. Since 2019, or show a general downward trend in the past four years. East Asian countries have also made efforts to improve air quality, and PM 2.5 levels in the region generally tend to be lower. In South Korea, all cities saw an improvement in air quality in 2020, after new measures were introduced to control the seasonal effect of coal on air pollution.