Air pollution has greatly reduced in recent weeks, and especially in recent days in China. This observation, highlighted this week by maps of AirVisual, an index of air quality in the world produced by the Swiss company IQAir, we wanted to verify it. And above all to know the impact of the measures taken against the coronavirus.
Air pollution has collapsed in recent days in China. Experts are categorical: the cessation of industrial activity and the traffic restrictions to stem the coronavirus mechanically clean the air. @le_parisien #coronavirus # covid19 pic.twitter.com/76IEC7guj8
- Le Parisien Infog (@LeParisienInfog) February 18, 2020The data provided by the World Air Quality Index is without appeal: in Shanghai, the rate of fine particles 2.5 (diameter less than 2.5 µm) reached on average 100 μg / m3 in February 2020, against 135 μg / m3 in February 2015. Similarly, the rate of particles 10 (of diameter less than 10 µm) drops to 36 μg / m3 in February 2020, compared to 61 μg / m3 in February 2015.
Another (slightly) declining pollutant: nitrogen dioxide (NO2). Also in Shanghai, the NO2 rate drops to 9 μg / m3 for 19 μg / m3 in February 2015. Only the ozone rate, a gas formed when there is a combination in the air of volatile organic compounds, nitrogen oxide, and high heat has been relatively stable over the past five years.
Finally if we look at the scale of the country, the level of fine particles drops sharply from February 12: we go from 139 μg / m3 on the same day to 55 μg / m3 on February 15, a drop of 60%.
A slowdown in heavy industries
How to explain such a drop in pollutants? Air quality results from various factors. It then remains difficult to assess the responsibility of each of them (industrial activities, rainfall, displacement of populations) in the composition of the air.
However, these "extremely low" pollution rates are "not surprising," says Jean-François Huchet, economist and author of the book "The environmental crisis in China", on the phone.
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For the specialist, this decline is mainly explained by the "economic slowdown" of the country which has implemented restrictive measures to stem the coronavirus.
“There is a sharp drop in building and public works activity. Steel mills but also cement factories are idling, as are power plants and coal-fired power plants. These so-called heavy industries are at the origin, extremely polluting ”, specifies the sinologist. The effect is then mechanical and almost immediate: "the factories close and pollution decreases", he adds.
Transport paralysis
Another criterion to take into account is the extremely limited movement of the population. "The paralysis of transport, in particular of the car, also lowers pollution", specifies the Parisian, Jean-Paul Maréchal, lecturer in economic sciences in Rennes and specialist in China. Since January 23, the start of quarantine in Wuhan, no public transport (trains, planes, buses and metro) has been operating in the city and the highways are blocked. These containment measures have extended to almost the whole of Hubei province, of which Wuhan is the capital and where more than 57 million Chinese live.
On the outskirts of the megalopolis, the cities of Huanggang, Ezhou and Xianning have also taken quarantine measures. According to the New York Times, these travel restriction measures affect nearly 760 million people, more than half of the Chinese population ... and one tenth of humanity.
A (relative) "new year" effect
Some could put forward another hypothesis: the drop in pollution is partly explained by the holding of the Chinese New Year. This spring festival which started on January 25 and continues for two weeks usually causes a slowdown in activity in the country. “This is the longest vacation period in China. People stay with their families and most businesses and offices close, ”explains Mary-Françoise Renard, a specialist in the Chinese economy.
However, the graphics prove it: pollution continued to drop beyond February 9, the date that marks the end of these holidays. "There are two overlapping phenomena: the new year and the measures taken to stem the coronavirus," notes Jean-Paul Maréchal. “We can clearly see that the levels of particles are still very low when people have stopped celebrating the New Year. By prevention, many did not return to work. Restrictive measures are therefore responsible for this drop, ”added the specialist.
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Limited rain
Weather conditions can also affect air quality. "Usually, the high pressures that occur at the start of the year in the north of the country prevent the pollution from dissipating," says Jean-François Huchet. Conversely, the rains and the winds will disperse the particles.
However, little precipitation fell over the east of the country, which was usually very dry at this time of the year. On average, 2 mm of rain fell in January in China, according to online weather records. In the current case, the weather conditions will "play little" on the state of pollution, says the specialist who recalls the importance of the industrial slowdown.
This “clean cloud” effect could be felt even in the surrounding countries. "We will undoubtedly be able to see repercussions on South Korea or Japan", estimates Jean-François Huchet. However, it is difficult to imagine that these positive effects will reach Europe.
A temporary improvement?
If the levels of fine particles have dropped sharply in recent days, China has already experienced similar episodes. With the difference that these improvements were officially wanted. Beijing had stepped up efforts to clear the air before the 2008 Olympics, promising athletes blue skies. "All the cities located within a radius of 500 km around the capital had slowed down their industrial activities", specifies Jean-François Huchet. "The effects on pollution had been immediate".
Similar measures were also put in place to ensure cleaner air, when former US President Barack Obama came to the country in 2014.
But if the air is less polluted to date, there is no guarantee that this improvement will continue once the epidemic is over. "We could even fear a peak in pollution as during the end of the SARS epidemic in 2003," says the researcher. “At the time, the country had compensated for its losses by redoubling its activity. The pollution immediately increased. Proof that it would be wrong to declare victory too quickly ”.