Shulou(Shulou.com)11/24 Report--

There is a group of people who, out of pure curiosity, carry scientific instruments with them to measure the amount of potentially harmful particles in the ambient air. Harmful air particles refer to tiny clumps of matter that can be inhaled in the air. "We're a lot like air pollution nerds, aren't we?" said Terry Gordon, an environmental health scientist at New York University.

A few years ago, one of his colleagues walked into the New York subway and found that the readings on the particulate matter concentration meter were astonishingly high. "he thought the instrument was broken," Gordon recalled. But this is not the case, and such a high reading has sparked a heated debate. So scientists conducted a study to investigate particulate matter concentrations in subway stations in New York, New Jersey, Philadelphia and other parts of the northeastern United States.

This is just one of many papers on the concentration of particulate matter in the air of the subway, and researchers have recently published a lot of papers on particulate pollution in the air of subway systems around the world. it reflects the growing concern that urban commuting environment may bring health risks. Earlier, prosecutors in Paris opened a criminal investigation into allegations that air pollution in the local subway endangered people's lives. Not only that, RATP, the operator of the Paris subway system, has been accused of deliberately underreporting the concentration of particulate matter in the subway air, which the company denies.

It is undeniable that the concentration of air particles in the subway is usually several times higher than that on the street. The friction of the metal wheels of the subway train on the track and the braking will produce tiny metal particles, which will be swept into the air while the train is running. The question is how the concentrations of particulate matter in different subway systems compare and whether science reveals whether there are real health risks for people who travel or work in these environments. As we all know, long-term inhalation of harmful air particles can cause a variety of heart and lung problems, and even lead to premature death.

However, Gordon was surprised to hear the charges made by prosecutors in Paris. "Paris is nothing compared to the concentration of particulate matter in the air of the London Underground," he said, adding that, at least according to his research, subway stations in and around New York have more particulate matter than anywhere else.

Gordon studied some subway stations in the northeastern United States and detected the highest ever measurements of air pollution. For example, at stations in Manhattan and New Jersey, there are about 1700 micrograms (μ g) of particles 2.5 microns or less in diameter-commonly known as PM2.5-per cubic meter of air. The reading is the average measured during two relatively short, about one-hour windows. PM2.5 is considered particularly dangerous because these very small particles can go deep into people's lungs and may even enter people's bloodstream. The World Health Organization recommends that people should not be exposed to more than an average of PM2.5 a day.

The Trans-Hudson Port Authority (Port Authority Trans-Hudson, PATH), the transportation system that belongs to those stations in Manhattan and New Jersey, said that in an independent assessment, the air quality at these stations was within the guidelines set by the Occupational Safety and Health Administration. "We will continue to take appropriate measures to ensure that the air quality of the PATH system is within regulatory standards," PATH said.

Another study published last year detailed the PM2.5 levels of all nine New York subway lines and 341 platforms at 287 stations. Although they fluctuate, with some readings as high as about 600, the average concentration on the platform is about 120 to 300.

A spokesman for the Metropolitan Transportation Authority of New York said: "We have conducted air quality tests on subway trains operated by our system before and found no health risks." He added that ensuring the safety of customers and employees was the highest priority of the Transport Bureau.

By contrast, an official study of airborne particulate matter concentrations in Paris subways published last year found that PM2.5 concentrations in Paris subways were about, already much lower than previously measured, but still about three times higher than outdoor PM2.5 concentrations in Paris. Between 2010 and 2018, PM2.5 concentrations began to decline gradually from 70%. According to another study, the average PM2.5 concentration on the Stockholm subway between 7 am and 7 pm on weekdays is 260, while the PM2.5 concentration on the Seoul subway platform is about 129.

It is worth noting that these studies are different in many aspects. Scientists use different monitors to measure at different times of the day and calculate the average of periods of different lengths, so they cannot directly compare the results. Not only that, seasonal differences also affect readings. As a study of particulate matter concentrations in Shanghai's subway system points out, the average reading of respirable particulate matter in autumn and winter is much higher, which may be due to winter haze, which affects many parts of China.

But these studies do make people realize that the concentration of particulate matter is very high in the underground railway network as a whole. And some old, deeper subway stations, such as those in New York, tend to have relatively higher overall particulate matter concentrations.

London Underground is one of the most studied subway systems in the world. London Underground, which originated in 1863, is the oldest subway in the world. Hassan Aftabsheikh (Hassan Aftab Sheikh), a doctoral student at the University of Cambridge in the UK, recorded particulate matter concentrations at several subway stations and pointed out that the deepest and oldest lines tend to be the most polluted. He points out that the average concentration of particulate matter measured is about 300,400, but that concentration may soar to about 1000 when the subway rushes into the platform and blows up dust from the ground and around the tracks. The concentration that increases in a short period of time will soon decrease again.

Old-fashioned subway, Tuyuan Network last year Sheikh and colleagues studied the relatively high levels of iron oxide in particulate matter in London Underground. An analysis of the chemical composition of particulate matter in the London Underground suggests that it may have been around for many years. "this is not the usual iron oxide," Shaikh said. "it has been further oxidized because it has been in the subway system for too long."

There is a contrast between the London subway system and the Paris subway system, which has trains with rubber wheels on many lines. Shaikh also pointed out that the Paris subway system is relatively new and better ventilated than the London subway.

A spokesman for Transport London, which operates the subway, pointed out that safety is the agency's top priority, and staff have been working for years to reduce dust from the subway system. "this includes the use of industrial knapsack dust [vacuum] cleaners as part of our multimillion-pound subway cleaning programme," she added.

The last thing we don't know for sure is whether these particulates really cause people's health problems. In many cases, for many years, five days a week, many hours a day, millions of commuters travel by subway, and thousands of railway workers stay in the tunnel for even longer. However, among these people, no serious or acute health problems were found in a wide range of people, even if the concentration of air pollution in the subway exceeded the recommended standard. However, it is not clear whether subway particles have more subtle chronic effects on human health or on lung, brain and heart function.

Matthew Lockham, an air pollution toxicologist at the University of Southampton in the UK, said: "of course we can't rule out these factors. It's just that based on the current evidence, at least in the population surveyed, there seems to be no clear and obvious health risk." He and others co-authored a review of evidence of health risks in 2019, which concluded. He doesn't know if there will be any new evidence to overturn it.

Metal particles are common in subway air particles, especially iron particles, he added. Since metals are generally considered toxic, this fact may cause public concern. And the composition of particles is sometimes soluble, which means that these metal particles can dissolve in people's lungs and enter the body's cells.

"it's bad, but it's also possible that soluble ingredients can be removed more easily than solid particles," Lockham said, suggesting that some agglomerated particles may stay in people's lungs, which may cause health problems in the future. or maybe not.

He added that high levels of iron are indeed a problem, but our bodies are always dealing with iron; it is a key component of hemoglobin in our blood, so there is a mechanism in our bodies to regulate it. He stressed that it is not yet possible to determine whether these regulatory mechanisms have an effect on subway air particles. In addition, it is difficult to associate occasional high concentrations of respirable particles in the air of the subway with specific negative health outcomes, so don't jump to conclusions.

If people are worried that the air particles in the subway will endanger their health, they can wear masks that can filter the air particles. Where feasible, subway operators can consider installing screen doors on the platform to reduce the dust concentration raised by running trains to passengers. But even with this approach, there are other risks. A study on the use of the screen door in a Seoul subway station found that although it sometimes reduces the amount of particulate matter on the platform, it also increases the content of particulate matter in the train.

Gordon said it is difficult to say whether particulate matter in the subway air really poses a health risk to the human body, but he stressed the need for further research, including the need for long-term research on the health of subway workers for many years. Even their health after retirement should be paid continuous attention.

Author: CHRIS BARANIUK

Translation: sweeping monk

Revision: Tibetan idiots

Original text link:

The Filthy Truth about Subway Air

This article comes from the official account of Wechat: Institute of Physics, Chinese Academy of Sciences (ID:cas-iop), author: CHRIS BARANIUK

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.