Qualité de l’air à Wuhan

What is the air quality index of Wuhan?

Wuhan is the capital of the Chinese province of Hubei and is the most populous city in central China with an estimated population of over 11 million people. It is located at the confluence of the Yangtze and its largest tributary, the Han River.

At the beginning of 2021, the air quality in Wuhan was classified as “Unhealthy” with a US AQI reading of 184. Concentrations of the pollutants suspended in the air were as follows: PM2.5 - 119.5 µg/m³, PM10 - 154.5 µg/m³, ozone (O₃) - 39 µg/m³, nitrogen dioxide (NO₂) - 76.5 µg/m³, sulphur dioxide (SO₂) - 21 µg/m³ and carbon monoxide (CO) - 1800 µg/m³. With levels as unhealthy as these, it is advisable to wear a good quality mask when venturing outside and to close doors and windows to prevent the ingress of dirty air. Running an air purifier is also advisable if one is accessible and outdoor exercise should be avoided where possible until the quality improves.

In 2019, Wuhan experienced “Moderate” air quality for 5 months of the year with pm2.5 reading between 12.1 and 35.4 µg/m³. During the winter months of December, January and February it was classified as being “Unhealthy” with levels of 55.5 to 150.4 µg/m³. The remaining 4 months saw levels of “Unhealthy for sensitive groups” with levels of 35.5 to 55.4 µg/m³. These figures are based on the target levels recommended by the World Health Organisation (WHO). Looking back at the previous years of 2017 and 2018 the air quality is not getting much better. 2017 was 51 µg/m³, 2018 was 46.9 µg/m³ and 2019 was 44.4 µg/m³ all of which fall into the “Unhealthy for sensitive groups” category.

Why is Wuhan so polluted?

In mid-2019, Wuhan was among China’s most polluted cities being ranked at 146 globally. Plans were released for the building of a new garbage incineration plant which was not welcomed by the local residents. In an almost unprecedented manner, the locals protested openly waving banners which read "we don't want to be poisoned, we just need a breath of fresh air". This continued for almost two weeks by way of protest and in hope that the plans would be suspended. They were concerned over the proximity of the proposed development to residential areas and were concerned that the emissions would contribute to the already poor quality air.

The protest was classed as successful because the local government has suspended plans for its opening. However, there remains a large police presence in the area as though they are expecting some trouble in the future.

Is air pollution in Wuhan getting worse?

The outbreak of the epidemic in Wuhan and the measures being taken have stopped economic activities in most parts of the province, including factories, construction sites, transportation, and catering. However, the smog in the northern region is still very serious. The analysis of experts from the National Centre for Air Pollution Prevention and Control is that “ fireworks and firecrackers have caused a large increase in pollutants ” and that “ highly polluting steel, coking, glass, refractory materials, chemical, pharmaceutical and other heavy chemical industries have a large number of uninterruptible processes. Some companies are also undertaking the task of coordinated heating, and continuous production is still required during the Spring Festival. At the same time, coal-fired power plants, heating boilers, etc. continue as usual, to ensure the normal operation of society and the heating needs of residents.

The firecrackers and fireworks are traditionally set off around the Chinese New Year festivities which take place at the end of January or the beginning of February, each year. The exact time is based on the lunar calendar.

What can be done to improve the air quality in Wuhan?

At present, there are three main control indicators for flue gas emissions from power plants and heating boilers: sulphur dioxide (SO₂), nitrogen oxides (NO_x) and particulate matter PM2.5 and PM10 (originally called soot, but actually filterable particulate matter). The main technical measure to control sulphur dioxide emissions is wet desulphurisation, that is, desulphurisation by spraying flue gas with lime slurry.

Subsequently, the power plants began to implement ultra-low emissions, that is, to further control the white smoke emitted by wet desulphurisation, and use wet electric dust removal technology to further reduce the emission of sulphur dioxide and (filterable) particulate matter.

The technology to reduce nitrogen oxide (NO) emissions is mainly the selective catalytic reduction method, which uses ammonia to convert nitric oxide to nitrogen and water that have little effect on the atmosphere. However, during the treatment process, the ammonia gas that has not been used in the conversion reaction is carried out of the flue through fly ash, desulphurisation wastewater, fog droplets and discharged into the atmosphere.

The control of particulate matter emissions is mainly to use bag dust removal or electrostatic dust removal. In order to achieve ultra-low emissions, most power plants have added wet electrostatic precipitators to their flues. This should be one of the best flue gas purification facilities in the world at present, but the cost is also high. However, wet electric dust removal equipment cannot solve the problem of flue gas humidity, and the reduction of condensable particulate matter (aerosol) is not monitored, because the current particulate matter standard does not include condensable particulate matter.

What are the effects on health through breathing in Wuhan’s polluted air?

Carbon monoxide will reduce the oxygen-carrying capacity of red blood cells, and its impact on health depends on the length of time the body is exposed to it and the concentration inhaled. The average person feels headache, dizziness and fatigue when inhaling low levels of carbon monoxide. When inhaling high concentrations, it can cause blurred vision, loss of coordination, and even death.

Nitrogen dioxide can irritate the mucous membranes of the eyes, nose, throat, and respiratory tract. Exposure to low concentrations of nitrogen dioxide can cause bronchial allergies and aggravate asthma patients' reactions to allergens. In addition, nitrogen dioxide will also worsen the condition of patients with chronic respiratory diseases. Prolonged exposure to nitrogen dioxide may weaken lung function and reduce the ability of the respiratory system to fight disease.

Suspended particles can be defined according to their diameters, such as PM10 (particles with a diameter less than 10 microns) or PM2.5 (diameter less than 2.5 microns). The latter are more dangerous because when inhaled, they can penetrate deeper into the lungs. According to many studies, there is an important relationship between the number of people admitted to hospital and premature deaths due to respiratory and cardiovascular diseases and the concentration of suspended particles. Patients with cardiovascular diseases and chronic respiratory diseases are more susceptible.