Is the air quality inside the subway better than outside？ Survey： Not necessarily, generally worse than outdoor.

[Survey] The public pays little attention to the air in the subway.

The subway is becoming a mode of transportation for more and more people. According to the statistics of Beijing Municipal Transportation Commission, in 2017, the proportion of green travel in downtown Beijing reached 72%, and the average daily passenger traffic of rail transit network reached 10.3 million. According to the statistics of Beijing Metro Company, on March 27th this year alone, the daily passenger traffic of 16 operating lines under the jurisdiction of Beijing Metro Company reached 10,008,800 passengers.

What followed was the increase in people’s time on the subway. According to incomplete statistics, Beijing subway passengers spend an average of two hours in the subway every day. Therefore, how the air quality in the subway becomes very important and what adverse effects it may have should be paid enough attention by the public.

Volunteers conducted a questionnaire survey in the subway.

However, the reporter’s random survey found that the public paid little attention to this. Not long ago, Beijing issued the first blue warning of dust this year, and the air quality in the whole city reached the level of heavy pollution. At Guangqumennei Station of Metro Line 7, many people naturally took off their masks after entering the subway station. The reporter interviewed a girl in her twenties at random. She told reporters: "Wearing a mask for a long time feels very oppressive, and there is no way for the air outside to be heavily polluted. When you enter the subway station, you don’t have to wear it. " She believes that there is air conditioning in the subway, which will filter pollutants in the air.

The reporter also asked some subway passengers. Most people think that the air in the subway is better than that outside. Is this really the case? The reporter interviewed Zhao Ang, the director of Panshi Institute of Environment and Energy and the main person in charge of the subway air pollution research project.

[Truth] There are obvious differences between different subway lines.

Panshi Institute of Environment and Energy recently released the information map of "Investigation on the Characteristics of Air PM2.5 Exposure and Coping Behavior of Beijing Subway Commuters". In 2017, they successively conducted a series of surveys and assessments on the differences in air pollution exposure levels of commuters in Beijing subway and the corresponding health impacts.

"We conducted a questionnaire survey on 618 people in the Beijing subway." Zhao Ang said that 76% of the respondents thought the outdoor air quality was worse than that in the subway. But the actual monitoring situation is the opposite. During the investigation in the subway, the daily average concentration of PM2.5 was 154 μ g/m3 in winter heating season and 127 μ g/m3 in non-heating season, while the daily average in outdoor Beijing was 103 μ g/m3 and 69 μ g/m3, respectively.

Through monitoring, experts also found that not only the air quality in the subway is generally worse than that outside, but also the differences between the lines are obvious. "By horizontally comparing the average concentration of PM2.5 in different subway lines, we found that the air quality of Line 13 was the best and Line 8 was the worst within half a year of project monitoring." Zhao Ang said.

According to statistical analysis, Metro Line 2 and Line 13 have the lowest concentration of PM2.5, and Line 8 has the highest concentration of PM2.5. "The monitoring results of this time are similar to those of the subway air monitoring in our’ measuring the air in the corner’ project in 2015." Zhao Ang said that it seems that this situation has not changed.

"If we compare the outdoor air quality of Line 13 and Line 8, we can find that the PM2.5 concentration level of Line 13 is close to the outdoor during the monitoring period of up to 6 months, especially in the non-heating season. This may be related to the long outdoor part of the line, good ventilation and relatively slow speed. "

Zhao Ang told reporters that the concentration of PM2.5 in Line 8 is always higher than that outside, whether in heating season or non-heating season. Similarly, Line 6, with poor air quality, also shows a greater difference from outdoor air quality.

[Response] Over 7 adults are willing to pay for improving the air.

"The actual situation of subway air quality is inconsistent with the cognition of many citizens, which also requires the public to strengthen this awareness." Zhao Ang said that the relationship between knowledge and action is an important field of decision-making science and behavioral science research. "When we analyze the survey data, we see that the respondents understand the inconsistency between air pollution and coping behavior, and also understand that there are many factors that affect the relationship between knowledge and action."

Zhao Ang said that although most people think that air pollution has a noticeable impact on people’s lives, the proportion of people who wear masks when taking the subway is not high. "When taking the subway, the proportion of people who never wear masks is as high as 36%, and only 7% of people always wear masks."

He believes that this inconsistency in cognition and behavior is largely related to people’s ignorance of the reality that the air quality in the subway is worse than that outside. On the other hand, it is also related to people’s judgment on the pollution protection effect of wearing masks. "More than two-thirds of the respondents believe that masks have no obvious protective effect."

In addition, the research group also found that there is a significant positive correlation between income level and education level and willingness to pay for air purifiers. In this regard, Zhao Ang explained that the higher the education level or income level, the higher the willingness to pay for air purifiers. There is no correlation between these two factors and the willingness to pay for purchasing anti-haze masks.

According to the survey report, among the 618 respondents, 88.2%(545 people) think that increasing the consumption of renewable energy (such as wind power and solar power) is helpful to alleviate the air pollution in Beijing. Among them, 478 people are willing to increase their monthly electricity bill in order to improve the air quality in Beijing.

[Tips] Wearing a mask is the best protection.

"The best way is to wear a mask in the subway." Zhao Ang said, "Because it takes a long time to control air pollution, personally, the most effective means of protection is probably to wear masks often, especially when taking the subway."

Zhao Ang told reporters that cardiovascular disease is one of the main health risks caused by air pollution exposure. Fudan University once asked 30 young college students to do relevant experiments to evaluate the potential cardiovascular health benefits brought by wearing a mask (model: 3M-8210V) that can block PM2.5 fine particles.

The experimental results show that wearing a mask in a short time can improve Heart Rate Variability (HRV) and reduce ambulatory blood pressure and circulating biomarkers, indicating that wearing a mask can alleviate the harm of air pollution to cardiovascular diseases. On the contrary, if you don’t wear a mask, the inhaled particles will increase, which will lead to the decrease of HRV parameters, which is potentially harmful to cardiovascular diseases.

"Of course, this experimental study also has some limitations." Zhao Ang said, for example, due to the small sample size, this study is exploratory in nature; Because the personal exposure to PM2.5 has not been detected, it is inevitable that errors will occur when measuring exposure; The monitoring device is not calibrated by gravity measurement, and some indoor factors, such as human activities, will affect the exposure concentration of individual PM2.5.

"Although there are some limitations, this randomized controlled crossover experiment still provides preliminary evidence that wearing masks can be used as an effective practical tool to protect individual cardiovascular health, thus reducing the harm of air pollution."

(The original title is "Green Living Lab | Is the air inside the subway better than outside? Not necessarily! 》）