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PM2.5 density at Beijing's subway lines higher than open field: survey

Passengers travel on the Yanfang subway line in Beijing. Photo: Xinhua

A survey showed that people cannot take air pollution problems lightly at Beijing's subway lines, which serve millions of commuters every day.

The average concentration of PM2.5, an atmospheric particulate matter detrimental to human respiratory system, stood at 154 micrograms per cubic meter at Beijing's 10 subway lines during the heating season in 2016 and 2017, higher than the average 103 micrograms per cubic meter in the open air, according to the Air Quality Monitoring Report released recently by the Rock Environment and Energy Institute, a Beijing-based independent think tank. The air samples were collected during the rush hours of every Friday.

Subway Line 8 had the highest PM2.5 density, which reached 195 micrograms per cubic meters, while Subway Line 13 had the lowest PM2.5 density of 106 micrograms per cubic meter, said the report. The air quality readings at all subway lines surpassed the national standards for air quality.

Besides, the report found that many Beijing citizens had misunderstanding about air quality at subways. Seventy-six percent of people surveyed thought that air quality at subways was better than open field, while 36 percent of respondents said that they did not use mask at subways, showed the report.

"Beijing people spend 1.95 hours on subways on average. The bad air at subways is undisputedly detrimental to their health," said Zhao Ang, director of the Rock Environment and Energy Institute.

Currently, the Beijing government has installed glass separators splitting platform and tunnel at the platforms of some subway stations on safety grounds. The separators can also be helpful in partly preventing fine particulate matters in the tunnel from spreading to the platforms, say some experts.

China does not have air quality standards specially for subways. In 2002, the country validated its first indoor air quality standards, which are only applied to residential and office buildings. Chinese cities have lagged behind Seoul, which is considering including the PM2.5 concentration into a 2008 underground space management regulation, which already stipulated that the PM10 density cannot surpass 150 micrograms per cubic meter at underground space.

In April, the Shanghai Municipal Center for Disease Control and Prevention designed its subway air quality standards which are still awaiting approval. The standards will include indexes of temperature, humidity, carbon dioxide and PM10.

In the recent years, China has ramped up efforts to combat air pollution. The country has made a three-year action plan to win the battle for better air quality, with a focus on the Beijing-Tianjin-Hebei region and its surrounding areas, the Yangtze River Delta and other polluted areas.

One of the key targets set by the action plan is for cities to achieve good air quality on 80 percent, or about 292 days, of a year by 2020, when the average density of PM2.5 in the cities which fail to reach the air pollution reduction standards would drop by 18 percent compared with the figures in 2015.

In 2017, Beijing had better air quality than other pollution-stricken northern cities. The number of days with good air quality increased to 226 days from 198 days in 2016. The annual average concentration of PM2.5 dropped 20 percent to 58 micrograms per cubic meter last year from 2016, according to the data.

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