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Chinese urban residents， vexed by the persistent smog that shrouded large parts of the country in winter and spring， can finally breathe a sigh of relief in summertime as the weather begins to change and helps to dissipate the particulate matter responsible.
However， many remain unaware of the mounting threat caused by increasing ozone levels. On hot and sunny days， ozone concentration on the ground is more likely to rise to an unhealthy level.
Chai Fahe， Vice President of the Chinese Research Academy of Environmental Sciences， said that ozone pollution is seasonal， and ozone levels are highest between May and October， with daily ozone level peaks between 2 and 3 p.m.
According to a recent air-quality report released by the Ministry of Environmental Protection （MEP）， ozone and PM 2.5， which is fine particulate matter measuring 2.5 microns or less in diameter， were the primary pollutants in June for 74 cities across China and three economically developed zones， namely the Beijing-Tianjin-Hebei region， the Yangtze River Delta and the Pearl River Delta.
The report also shows the areas monitored were polluted 45.2 percent of the first six months of this year. Ozone was found to be the primary pollutant 20.1 percent of the time， while PM 2.5 was the primary pollutant 64.3 percent of the time.
Imminent threat
With rising awareness of particulate matter’s health impacts， a growing number of Chinese urban residents have begun regularly checking PM2.5 levels to see whether they need to wear a mask when going outside. But since ground ozone is not as readily visible as the smog caused by particulate matter， the pollution has not caught public attention in the same way as PM 2.5.
Although ozone high up in the strato- sphere protects life on Earth from the sun’s ultraviolet radiation， exposure to high levels of ozone at ground level can cause a wide range of health problems such as chest pain， coughing， throat irritation and permanent damage to the lungs. Increases in the risk of premature death from heart or lung disease can also be seen， according to experts.
The gas made up of three oxygen atoms is also one of the principal components of photochemical smog， which can reduce visibility.
Ground ozone and PM 2.5 were not included in China’s ambient air-quality standards until February 2012， when the State Council released new air-quality standards， which were to be put into effect in different regions at different times before the nationwide implementation scheduled for January 1， 2016. In 2012， the standards became effective in provincial capitals and municipalities that are directly under the Central Government， as well as key areas such as the BeijingTianjin-Hebei region， the Yangtze River Delta and Pearl River Delta.
This year， the standards are implemented in a further 113 cities that are either considered to be key cities for environmental protection or to be model cities for environmental protection. All prefecture-level cities are required to meet the same standards by 2015.
The new standards set the ceiling for the maximum allowable eight-hour average ozone level at 160 ppb， or parts per billion， for residential， commercial， cultural， industrial and rural areas and 100 ppb for areas such as nature reserves and scenic areas. The maximum permissible one-hour average ozone level for these two groups of areas is 200 ppb and 160 ppb， respectively.
Some cities， including Beijing， began to publish real-time PM2.5 readings to the pub- lic last year. However， most cities have not yet published real-time readings of their ozone levels.
Beijing began publishing real-time PM 2.5 levels in January 2012， later adding readings of ozone and carbon monoxide for the first time in May of last year on a trial basis. Real-time readings of these pollutants are accessible to the public on the website of Beijing Municipal Environmental Monitoring Center.
Ozone is not emitted directly into the air， but is instead created through chemical reactions between other pollutants such as nitrogen oxides and volatile organic compounds， and these reactions can take place in the presence of strong sunlight and high temperature.
Emissions of these two pollutants tend to mainly come from industrial facilities and electric utilities as well as exhaust fumes from motor vehicles， gasoline vapor and chemical solvents.
Although its presence is less apparent， ozone is more hazardous to human health than PM2.5， and more difficult to control， said Zhao Hualin， Director of the Pollution Prevention and Control Department at the MEP.
“Since ozone is produced by chemical reactions between nitrogen oxides and volatile organic compounds when they are exposed to ultraviolet light， we must simultaneously reduce nitrogen oxides and volatile organic compound emissions in order to reduce ozone levels，” said Tang Xiaoyan， a Peking University professor and academician with the Chinese Academy of Engineering.
hard to control
The 2012 State of China’s Environment report released by the MEP showed that emissions of nitrogen oxides in China continued to rise until 2011， and then dropped by 2.77 percent in 2012， exceeding 23 million tons in the year.
Although emissions of nitrogen oxides have been regulated by the government， volatile organic compounds are not included in emissions reduction targets of the 12th Five-Year Plan， China’s national social and economic development initiative for 2011-15， Tang said.
The 12th Five-Year Plan set goals to cut four of the major air pollutants， including sulfur dioxide and nitric oxide， by more than 10 percent each.
“Compared with the reduction of nitric oxide emissions， volatile organic compound emissions are more difficult to abate，” Tang said.
China has published several standards for volatile organic compound emissions， including standards for pollutants discharged during oil storage， certification standards for oil-based coatings， and mandatory standards for toxic substances contained in interior decoration materials.
But Tang warned that a wide range of sources can emit volatile organic compounds， with various industries emitting different compositions of these pollutants. Even in one production process， if different raw materials and production techniques are used， different types and concentrations of volatile organic compounds will be discharged.
For example， chemical products can emit volatile organic compounds during their production， storage and use. “Currently， many local governmental departments have not yet realized how hazardous volatile organic compounds are. In believing that chemical plants are less polluting than power and steel plants， they have given the green light to many chemical engineering projects without realizing the consequences，” Tang said.
Recently， the Chinese Government announced a plan to invest 1.7 trillion yuan（$277 billion） to combat air pollution in the next five years. The investment will mainly go toward helping highly polluted areas and areas with particularly high levels of PM2.5， said Wang Jinnan， Vice President of the Chinese Academy for Environmental Planning.
“Volatile organic compounds， ozone and PM2.5 are interrelated，” said He Kebin， a professor at the Tsinghua University’s School of Environment， adding that when ozone concentration is high， more nitric oxide and sulfur dioxide will be turned into PM2.5 pollutants.
If all pollutants are not effectively reduced together， reduction in one type of emission can be offset by an increase in another， He said.
However， many remain unaware of the mounting threat caused by increasing ozone levels. On hot and sunny days， ozone concentration on the ground is more likely to rise to an unhealthy level.
Chai Fahe， Vice President of the Chinese Research Academy of Environmental Sciences， said that ozone pollution is seasonal， and ozone levels are highest between May and October， with daily ozone level peaks between 2 and 3 p.m.
According to a recent air-quality report released by the Ministry of Environmental Protection （MEP）， ozone and PM 2.5， which is fine particulate matter measuring 2.5 microns or less in diameter， were the primary pollutants in June for 74 cities across China and three economically developed zones， namely the Beijing-Tianjin-Hebei region， the Yangtze River Delta and the Pearl River Delta.
The report also shows the areas monitored were polluted 45.2 percent of the first six months of this year. Ozone was found to be the primary pollutant 20.1 percent of the time， while PM 2.5 was the primary pollutant 64.3 percent of the time.
Imminent threat
With rising awareness of particulate matter’s health impacts， a growing number of Chinese urban residents have begun regularly checking PM2.5 levels to see whether they need to wear a mask when going outside. But since ground ozone is not as readily visible as the smog caused by particulate matter， the pollution has not caught public attention in the same way as PM 2.5.
Although ozone high up in the strato- sphere protects life on Earth from the sun’s ultraviolet radiation， exposure to high levels of ozone at ground level can cause a wide range of health problems such as chest pain， coughing， throat irritation and permanent damage to the lungs. Increases in the risk of premature death from heart or lung disease can also be seen， according to experts.
The gas made up of three oxygen atoms is also one of the principal components of photochemical smog， which can reduce visibility.
Ground ozone and PM 2.5 were not included in China’s ambient air-quality standards until February 2012， when the State Council released new air-quality standards， which were to be put into effect in different regions at different times before the nationwide implementation scheduled for January 1， 2016. In 2012， the standards became effective in provincial capitals and municipalities that are directly under the Central Government， as well as key areas such as the BeijingTianjin-Hebei region， the Yangtze River Delta and Pearl River Delta.
This year， the standards are implemented in a further 113 cities that are either considered to be key cities for environmental protection or to be model cities for environmental protection. All prefecture-level cities are required to meet the same standards by 2015.
The new standards set the ceiling for the maximum allowable eight-hour average ozone level at 160 ppb， or parts per billion， for residential， commercial， cultural， industrial and rural areas and 100 ppb for areas such as nature reserves and scenic areas. The maximum permissible one-hour average ozone level for these two groups of areas is 200 ppb and 160 ppb， respectively.
Some cities， including Beijing， began to publish real-time PM2.5 readings to the pub- lic last year. However， most cities have not yet published real-time readings of their ozone levels.
Beijing began publishing real-time PM 2.5 levels in January 2012， later adding readings of ozone and carbon monoxide for the first time in May of last year on a trial basis. Real-time readings of these pollutants are accessible to the public on the website of Beijing Municipal Environmental Monitoring Center.
Ozone is not emitted directly into the air， but is instead created through chemical reactions between other pollutants such as nitrogen oxides and volatile organic compounds， and these reactions can take place in the presence of strong sunlight and high temperature.
Emissions of these two pollutants tend to mainly come from industrial facilities and electric utilities as well as exhaust fumes from motor vehicles， gasoline vapor and chemical solvents.
Although its presence is less apparent， ozone is more hazardous to human health than PM2.5， and more difficult to control， said Zhao Hualin， Director of the Pollution Prevention and Control Department at the MEP.
“Since ozone is produced by chemical reactions between nitrogen oxides and volatile organic compounds when they are exposed to ultraviolet light， we must simultaneously reduce nitrogen oxides and volatile organic compound emissions in order to reduce ozone levels，” said Tang Xiaoyan， a Peking University professor and academician with the Chinese Academy of Engineering.
hard to control
The 2012 State of China’s Environment report released by the MEP showed that emissions of nitrogen oxides in China continued to rise until 2011， and then dropped by 2.77 percent in 2012， exceeding 23 million tons in the year.
Although emissions of nitrogen oxides have been regulated by the government， volatile organic compounds are not included in emissions reduction targets of the 12th Five-Year Plan， China’s national social and economic development initiative for 2011-15， Tang said.
The 12th Five-Year Plan set goals to cut four of the major air pollutants， including sulfur dioxide and nitric oxide， by more than 10 percent each.
“Compared with the reduction of nitric oxide emissions， volatile organic compound emissions are more difficult to abate，” Tang said.
China has published several standards for volatile organic compound emissions， including standards for pollutants discharged during oil storage， certification standards for oil-based coatings， and mandatory standards for toxic substances contained in interior decoration materials.
But Tang warned that a wide range of sources can emit volatile organic compounds， with various industries emitting different compositions of these pollutants. Even in one production process， if different raw materials and production techniques are used， different types and concentrations of volatile organic compounds will be discharged.
For example， chemical products can emit volatile organic compounds during their production， storage and use. “Currently， many local governmental departments have not yet realized how hazardous volatile organic compounds are. In believing that chemical plants are less polluting than power and steel plants， they have given the green light to many chemical engineering projects without realizing the consequences，” Tang said.
Recently， the Chinese Government announced a plan to invest 1.7 trillion yuan（$277 billion） to combat air pollution in the next five years. The investment will mainly go toward helping highly polluted areas and areas with particularly high levels of PM2.5， said Wang Jinnan， Vice President of the Chinese Academy for Environmental Planning.
“Volatile organic compounds， ozone and PM2.5 are interrelated，” said He Kebin， a professor at the Tsinghua University’s School of Environment， adding that when ozone concentration is high， more nitric oxide and sulfur dioxide will be turned into PM2.5 pollutants.
If all pollutants are not effectively reduced together， reduction in one type of emission can be offset by an increase in another， He said.