OZONE COULD TURN CITIES INTO NO-GO ZONES
The invisible pollutant is rapidly becoming a main cause for concern in many areas of China, as
After the heavy, prolonged smog that often shrouds China during winter, the return of blue skies in spring and summer is always welcome.
However, sunny summer days may not be as beneficial as one might imagine: instead, people may become unwell as a result of rising concentrations of ground-level ozone, an invisible airborne pollutant.
At street level, ozone, a type of oxygen formed with an extra molecule, is created when vehicles, power plants, industrial boilers, refineries and chemical factories emit pollutants that react chemically in strong sunlight.
When Li Hui was affected by ozone pollution after working outside for long hours on sunny summer days, she had no idea what was causing her sore throat and dry eyes. “I didn’t have a cold, but I coughed a lot,” she said. “Sometimes, my mother had similar problems.”
The 31-year-old from the northern port city of Tianjin only realized the cause of her mysterious cough when she received a health alert from a smartphone app that measures air quality. The alert said the pollution level was medium and the main pollutant was ground-level ozone.
“A friend, a physician who specializes in pulmonary conditions, told me the problem had probably been triggered by breathing ozone when the level was excessive, usually on hot summer days,” Li said.
The doctor’s assumption was supported by Lyu Mengyao, an environmental engineer with the China Meteorological Administration, who said ground-level, or “bad”, ozone is different to stratospheric, or “good”, ozone, which is found in a band that stretches from about 15 kilometers above the surface of the Earth to roughly 35 km.
According to Lyu, breathing high concentrations of ozone can result in a range of health problems, including chest pain, coughing and irritation of the airways. It can also harm lung tissue and worsen the effects of bronchitis, emphysema and asthma, leading to increased need for medical attention.
Many provinces have noticed the growing risk from ozone pollution. In response, they have issued early warnings, similar to the practice adopted to tackle PM2.5, hazardous fine particulate matter with a diameter of less than 2.5 microns, which has been the main target in the battle against pollution for several years.
For example, the Shanghai Meteorological Service has set up a two-tier warning system — with yellow and orange alerts — for ozone pollution. It also recommends the suspension of outdoor activities and a reduction in the use of vehicles during periods of severe saturation.
Hazardous levels
Unlike heavy air pollution in winter, mainly caused by PM2.5 and PM10 which bring thick haze and reduce visibility, ground-level ozone pollution occurs when the skies are blue and the sun’s rays are strong. That means few people notice the ozone concentration rising to hazardous levels.
The rise in ground-level ozone has become a big issue for governments fighting to improve the air quality in their cities and regions.
A growing number of cities have seen rises in ground-level ozone. In 2015, of the 74 major cities in which air pollution was monitored regularly, only 62.2 percent recorded ozone levels below the national standard of 160 micrograms per cubic meter over an average of eight hours.
The figure surprised observers because many cities nationwide had previously witnessed reductions in ozone levels. In 2013, 76 percent of monitored cities reported levels below the national standard, while in 2014 the figure was 67.6 percent, China regularly monitors six “criteria” airborne pollutants — PM2.5, PM10, sulfur dioxide, nitrogen dioxide, ozone, and carbon monoxide — which define pollution levels. Below are the 10 provincial regions with the highest number of State-controlled monitoring stations by March. according to data from the Ministry of Environmental Protection.
Scientists use six “criteria” airborne contaminants to define pollution levels: PM2.5; PM10; sulfur dioxide; nitrogen dioxide; ozone; and carbon monoxide.
Generally, people regard PM2.5 as the prime constituent of China’s airborne pollution, and it has been targeted as the biggest enemy of the national campaign against air pollution.
Now, ground-level ozone has replaced PM2.5 as the biggest airborne pollutant in China’s southern regions.
For example, in South China’s Pearl River Delta, 56.5 percent of polluted days in 2015 were the result of excessivelevelsofozone,arisefrom 31.9 percent in 2013, according to the ministry’s data.
Even the smog-prone northern regions, including the Beijing-Tianjin-Hebei cluster, have seen rises in the number of summer days with excessive ozone.
In 2015, more than 17 percent of polluted days in the cluster were the result of excessive ozone, a rise from 7.6 percent in 2013, the ministry’s data said.
“In June last year, groundlevel ozone pollution saw Beijing listed in the top 10 cities (among the 74 monitored cities) for air pollution,” Zhang Dawei, director of the Beijing Environmental Monitoring Center, said.
Lyu, from the meteorological administration, noted that China’s vast northern and central regions, including the provinces of Hebei, Henan and Gansu, reported rises in ozone levels during the first half of last year.
Control measures
reports. during the period of the 12th Five-Year Plan (2011-15), emissions of nitrogen oxides fell by 18.6 percent. The ministry has also issued a regulation that will see emissions of volatile organic compounds in industrial centers reduced by 15 percent by 2020, Zhao said.
Complex mechanism
However, it will take more than just emissions reductions to control the rise of ozone.
“The major challenge for the controls is the complicated chemical mechanism by which ozone is formed. Also, it’s difficult to control emissions of dangerous compounds because many companies are sited in isolated areas, which makes it hard to monitor their activities,” Zhao said.
He added that effective control of ozone pollution lies in thorough research into the levels of nitrogen oxides and volatile organic compounds present during the process of ozone formation. “The conditions (for forming ozone) are different across the country because different regions have different economic and industrial structures and pollution levels, so they need targeted measures,” he said.
The existing controls on emissions of nitrogen oxides and volatile organic compounds are not as stringent as required, he said.
Lyu, the environmental engineerwiththemeteorological administration, suggested that more research should be conducted and data collection expanded to provide forecasts for ozone pollution.
She said that in addition to the growing level of emissions from heavy industry and vehicle exhausts, the problem may be closely connected with global warming and rising terrestrial radiation: “In truth, the root of the problem lies in excessive emissions caused by human activity.”