Air pollution has been one of the hottest topics in Shanghai's two sessions this year, as residents living in the Yangtze River Delta breathed the most polluted air in five years during the past two weeks.

The delta is working on a collaborative treatment plan on air pollution to reduce carbon emissions by 6 percent by 2015 in the region, according to Zhang Quan, director of Shanghai Environmental Protection Bureau. Zhang attended the Shanghai Municipal People's Congress, the city's top legislature's annual meeting that opened on Sunday.

Zhang said the plan will be released in the third quarter.

Transportation is a main source of air pollution in Shanghai. Twenty percent of the pollution is caused by vehicles, the same amount as by factory emission, said Zhang.

Shanghai's air quality index reached 250 several times in the past two weeks, indicating heavy pollution.

Fifty-eight of the 72 monitoring stations in Jiangsu province reported medium to heavy pollution on Saturday, and the province's capital, Nanjing, reported the worst air quality in five years.

"The control of air pollution is a long-term task for Shanghai and requires cooperation from neighboring cities in the Yangtze River Delta region. It will take a long time to see the effects," said Chen Zhaofeng, a lawmaker of the city.

"Sources of pollution, including emissions from factories and construction projects, should be continuously and efficiently shut down or moved out of urban areas," said Chen, who is also the vice-chairman of the city's top legislature's urban construction and environmental protection committee.

Wu Jiang, a deputy of the congress, said: "The recent smog was the inevitable result of the rapid industrialization of China, which reminded the related departments to pay more attention to control pollution."

The monitoring system of environmental protection should be restricted by regulations forcing factories to carry out regular check-ups of sources of pollution, added Wu, who is also vice-president of Tongji University.

"The central government should issue policies such as energy saving subsidies to encourage more enterprises to apply advanced renewable technologies to minimize the waste of energy," said Wu.

Chen Li, a member of the city's political advisory body, submitted a proposal to improve the city's air quality, calling for government organs to use new-energy vehicles to reduce emissions.

She also urged the authority to subsidize outdoor workers — such as sanitation workers, construction workers and traffic police — who are more likely "to be exposed to the polluted air".

Some experts are calling for more atmospheric pollution monitoring and improving early warnings for air pollution.

Yang Xin, an expert on atmospheric particulates and professor at Fudan University's Department of Environmental Science and Engineering, raised these issues in a proposal submitted to the congress.

Since 2012, Shanghai has established 10 stations citywide to monitor PM2.5, particulate matter of 2.5 microns or less in diameter. According to the local environmental bureau, the monitoring items now include PM10, PM2.5, sulfur dioxide, nitrogen dioxide, carbon monoxide and ozone, which reflect the overall situation of pollution and pollutant concentration.

"But the cause of the current pollution is very complicated, and its sources are also varied. To solely monitor the concentration of pollutants cannot explain its cause and fails to help further trace its source," Yang said.

"Besides that, the current monitoring system has its limitations on rapid detection of pollution and offering early warnings, especially during the days of heavy pollution," he added.

He said the government should establish advanced atmospheric pollution monitoring stations that can provide whole-journey records and monitoring.

Contact the writers at yuran@chinadaily.com.cn