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National air pollution action plans devised by China have seen significant reductions in pollution levels and associated health risks.

China has lifted millions out of poverty like no other country on the planet. The price of that economic progress is demonstrated in the air pollution that has caused a public health crisis, killing more than 1.1 million people every year. It has also proved costly for the nation as the economy suffers an annual loss of $37 billion due to pollution-induced crop failure. 

China Air Pollution Solutions

After Beijing’s ‘airpocalypse’ sparked a mass outpouring of anger and frustration among citizens, China set out to clean up the air quality of its cities. The government prohibited new coal-fired power plants and shut down a number of old plants in the most polluted regions including city clusters of Beijing-Tianjin-Hebei and the Pearl and Yangtze Deltas. Large cities like Shanghai, Shenzhen, and Guangzhou restricted the number of cars on the road and started introducing all-electric bus fleets. The country reduced its iron-and steel-making capacity and shut down coal mines.  

The government also introduced aggressive afforestation and reforestation programmes like the Great Green Wall and planted more than 35 billion trees across 12 provinces. With investments of over $100 billion in such programmes, China’s forestry expenditure per hectare exceeded that of the US and Europe and became three times higher than the global average.

The Air Pollution Action Plan released in September 2013 became China’s most influential environmental policy. It helped the nation to make significant improvements in its air quality between 2013 and 2017, reducing PM2.5 levels (atmospheric particulate matter) by 33% in Beijing and 15% in the Pearl River Delta. In Beijing, this meant reducing PM2.5 levels from 89.5µg/m³ (micrograms per cubic metre) down to 60. The city achieved an annual average PM2.5 level of 58µg/m³– a drop of 35%.

But even so, no cities reached the World Health Organization’s recommended annual average PM2.5 level of 10µg/m³. And as of the end of 2017, only 107 of China’s 338 cities of prefectural level or higher had reached the WHO’s interim standard of 35µg/m³.

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China air pollution
China declared war on smog and launched a five-year national air quality action plan in 2013.

As part of the second phase of its battle against air pollution, in 2018, China introduced its Three-year Action Plan for Winning the Blue Sky War.

While the 2013 Action Plan only set PM2.5 level targets for the city clusters of Beijing-Tianjin-Hebei and the Pearl and Yangtze Deltas, the new three-year Action Plan applies to all the cities in China. It mandates at least an 18% reduction in PM2.5 levels on a 2015 baseline in as many as 231 cities that have not yet reached the government standard- an average of 35µg/m³.

The previous plan had not addressed a primary pollutant that made the air deadly in many cities: ground-level ozone- highly irritating gas created by volatile organic compounds (VOCs) reacting with nitrogen oxides released from vehicles. Although ozone in the upper atmosphere protects the Earth by blocking solar radiation, it is extremely toxic in the troposphere and could cause asthma and respiratory tract infections among residents. The new action plan focuses more on ozone pollution as it adds targets for both VOCs and nitrogen oxides: emissions reductions of 10% and 15%, respectively, by 2020. 

The air quality over major Chinese cities has improved as of the beginning of 2020, a byproduct of the Covid-19 pandemic that originated in Wuhan in the Hubei Province that saw the nation embark on the largest lockdown measures in the world. A drop in industrial and economic activities resulted in reduced greenhouse gas emissions and improved air quality in Wuhan over the Chinese New Year, as well as Beijing, Shanghai and the Yangtze River Delta region. However, emissions will no doubt rise again once the pandemic subsides.

Air pollution levels in major cities in China at the turn of this century were almost exactly at the level of London at the height of the Industrial Revolution in 1890. But China cleaned up its air twice as fast as the United Kingdom did after the Great Smog of postwar London killed 8 000 people.

Recent research suggests that China’s fight against air pollution has laid the foundations for extraordinary gains in the country’s life expectancy. The average citizen can now expect to live 2.4 years longer on average if the declines in air pollution persist.

When we talk about ozone, the image that most often springs to mind is the ozone layer in the stratosphere that protects us from harmful ultraviolet (UV) rays from the sun. The depletion of this ozone layer increases surface UV levels, making its protection vital. However, ozone pollution can also be detrimental to the health of plants. How does it do this and what does it mean for a warming planet?

How does ozone form?

The ozone layer depletion- called the ‘ozone hole’- over the North and South Polar regions has been a pervasive problem throughout the 20th century. Caused by pollutants such as chlorofluorocarbons (CFCs) and other anthropogenic pollutants such as halons- gases found in aerosols and refrigerants- more UV rays are able to reach the Earth’s surface and can increase rates of skin cancer. The Montreal Protocol signed in 1987 has greatly reduced the emission of CFCs; studies show that the global climate would be at least 25% hotter today without the Protocol and new satellite images show that the largest hole ever observed in the ozone layer over the Arctic has closed.

While these events provide a sense of hope that efforts to reduce aspects of the climate crisis are working, there is another threat associated with ozone that affects human health and particularly plants that has recently come to light- surface ozone pollution. 

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What is ozone?

Discovered by a Dutch chemist named Van Marum in 1840, ozone gas is a colourless gas that is used as a disinfectant and water treatment option because of its strong oxidative property that kills microorganisms. The gas is also used in ozone therapy, which is when ozone is injected into a patient’s body to disinfect the area around the bacteria, improving the body’s intake and use of oxygen and activating the immune system. Some have claimed that ozone therapy can be used as a treatment for the COVID-19 virus, however the Food and Drug Administration in the US has asserted that ozone is a toxic gas and ‘has no known useful medical application’. Scientists and medical professionals have asserted that ozone therapy can cause respiratory irritation, heart problems, poor circulation, strokes and other afflictions. 

Among various air pollutants, surface ozone- mostly produced photochemically from anthropogenic precursor gases such as nitrous oxide from vehicles and volatile organic compounds (VOCs) from solvents- is of particular concern due to the significant harm it can pose to both human and ecosystem health. The phytotoxicity of ozone has been shown to impair photosynthesis, reduce gas exchange, induce early leaf senescence (ageing) and hamper growth in both natural vegetation and crops. 

Ozone-Sensitive Plants

As plants play a vital role in regulating the ambient environment, ozone-induced damage in plants may further accelerate environmental degradation, with severe consequences for human health. The increasing ozone trend could be the result of increased temperature and reduction of humidity in subtropical climates, which induce stress in plants and in return reduce the ozone absorption ability of plants, increasing ozone concentration in the atmosphere.

Ozone is one of the most difficult pollutants to control because it is not directly emitted. Instead, dangerous compounds and nitrous oxides released from vehicles, power plants, landfills and other biomass and fossil fuel burning facilities react with sunlight to form this secondary pollutant. According to Hong Kong’s Environmental Protection Department’s 2019 air quality monitoring results, the average ozone level has been increasing over the past 20 years, despite government efforts to clean the air and overall air quality and other major pollutants’ level improving steadily. 

To investigate the impact of ozone on plants, Dr. Felix Leung from the Chinese University of Hong Kong established a free-air experimental garden to monitor, quantify and understand the mechanisms of ozone damage on plants. In this experimental field, dubbed the ‘ozone garden’, the team grew cultivars of beans with different ozone sensitivities as a bioindicator of the local air pollution impacts on ecosystems. 

The beans showed a distinctive red mottled pattern on the leaves according to the level of ozone in the atmosphere. There are two genotypes of beans that show different sensitivity to ozone. Dr. Felix Leung and his team found that the ozone-sensitive genotype bean suffered higher ozone-induced foliar damage, with more red mottles and a higher death rate. This shows that ozone level in Hong Kong is high enough to cause significant damage to plants even in the countryside.

Professor Amos Tai from the Faculty of Science says, “the data obtained from this garden is essential to not only demonstrate the impacts of air pollution on plants under locally specific environmental conditions, but can also be used to derive important parameters of ecophysiology and biometeorology that can be used to build a regionally relevant earth system model for predictive purposes. Such an ozone garden has also been shown to provide great opportunities for public education. The differences in visual damage on ozone-sensitive, normal and ozone-tolerant plants are often striking, and can be used in publicity and educational events to raise awareness of pollution impacts on life and to galvanize corresponding technical and policy solutions to protect regional ecosystems and agriculture against pollution threats.”

To specifically tackle ozone pollution, the governments of Hong Kong, Guangdong and Macau have committed to a 3-year joint study from 2020-2023 to better understand the origins of ozone precursors, its formation and its transportation. Hong Kong and Guangdong are also adding real-time VOCs monitoring in the regional air quality monitoring network and wind profiles at higher altitudes to track the transportation of pollutants over Hong Kong, with a view to tackle ozone pollution. 

The Hong Kong government should add more incentives to encourage the use of electric cars and convert existing public transport modes to electric. Additionally, more ozone-tolerant trees should be planted along the roadside to improve air quality. It is only through these proactive measures that ozone pollution can be tackled and mitigated; it is therefore imperative that more studies such as the one conducted at CUHK are undertaken to better understand the problem.

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