How Subways Reduce Pollution And Improve City Life

Subway systems are crucial in reducing outdoor air pollution in large cities by helping to reduce motor-vehicle use. However, subway systems have been found to have unacceptably high levels of inhalable particulate matter (PM). A study from New York University found that the air on subway platforms is potentially unhealthy because it contains tiny, almost invisible particles of iron, an inevitable result of the friction between brakes, train wheels, and subway tracks.

The study noted that cities like New York have promoted mass transit to reduce traffic congestion and improve air quality. However, it said, the air quality inside the subway system is poor.

A study on the health effects of subway ventilation found that subway ventilation exerts a notable dual effect on environmental health in a subway station. On the one hand, ventilation controls temperature, humidity, and indoor air quality to ensure human comfort and health. On the other hand, ventilation also carries the potential risks of spreading air pollutants or fire smoke through the complex wind environment as well as produces continuous noise.

Another study found that subway air pollution disproportionately impacts New York City's minority and low-income commuters. The study revealed that longer commute times lead to higher exposure to hazardous air pollutants, a problem that disproportionately affects minority and low-income communities who endure more prolonged and frequent travel through the system.

Air quality in subway stations

Studies on Air Quality in Subways

Various studies have been conducted to measure and compare air quality in subway stations across different cities. One study found that New York's MTA had 251 micrograms per cubic meter of PM2.5, far beyond the safe level of 35. Another study by NYU researchers focused on river tunnel stations in New York City and found that these stations had significantly worse air quality than those farther away from river tunnels. The levels of PM2.5 in these river tunnel stations were up to 130% higher than in other stations.

Health Risks and Impact

The health risks associated with exposure to high levels of PM2.5 are well-documented. Long-term exposure to particulate matter has been linked to heart and lung problems, as well as premature death. However, the specific health impacts of spending time in subway stations are still being studied. While there are no widespread signs of severe health problems among commuters and transport workers, there may be more subtle, chronic effects on lung, brain, or heart function.

Improving Air Quality in Subways

To improve air quality in subway stations, better ventilation is necessary. This can be achieved by installing bigger fans and increasing the frequency of trains. Additionally, modern subway lines are being fitted with platform screen doors, which help reduce the ingress of contaminated tunnel air onto the platforms. These measures can help mitigate the health risks associated with spending time in subway stations.

While subways play a crucial role in reducing outdoor air pollution by reducing motor vehicle use, the air quality inside subway stations is a cause for concern. Further research and long-term studies are needed to fully understand the health impacts of exposure to particulate matter in subway stations and to develop effective strategies to improve air quality in these environments.

Air quality in subway trains

Sources of Particulates in Subways

Much of the particulate matter in subways comes from moving train parts, such as wheels and brake pads, as well as the steel rails and power supply materials. These particles are mostly iron-containing, but they can also include other metals such as manganese, copper, antimony, and chromium, which are known to be toxic to humans. The rubbing of metal wheels on tracks or brakes on wheels can shear off tiny metal particles that get kicked up into the air as trains move.

Factors Affecting Subway Air Pollution

Key factors that influence subway air pollution include station depth, date of construction, type of ventilation, types of brakes and wheels used on trains, train frequency, and the presence of platform screen doors. Older, deeper stations tend to have higher particulate levels, and natural ventilation systems can also contribute to higher particle concentrations. On the other hand, the use of air conditioning has been shown to reduce particle levels inside carriages.

Health Effects of Subway Air Pollution

There is currently no clear epidemiological indication of abnormal health effects on underground workers and commuters due to subway air pollution. However, studies have found that employees working on platforms with high particulate concentrations tended to have higher levels of risk markers for cardiovascular disease. Long-term exposure to particulate matter is known to be linked to various heart and lung problems, as well as premature death.

Reducing Subway Air Pollution

Some ways to reduce subway air pollution include the use of well-fitted filtering masks by commuters, platform screen doors to reduce the amount of dust blown towards commuters, and improved ventilation systems. Additionally, subway operating companies are becoming more aware of the link between cleaner air and better health for commuters, and are taking steps to improve air quality.

Air quality in subway systems in different cities

Subway systems are being expanded in major cities in China and other fast-growing economies to address worsening air pollution and traffic congestion. This article will discuss the air quality in subway systems in different cities and the factors that influence it.

Air Quality in Subway Systems

The air quality in subway systems can vary depending on the city and several factors. On average, the air quality in subway systems is poor and contains high levels of particulate matter (PM), which can be harmful to human health. The concentration of PM in subway systems is often higher than the recommended levels by the World Health Organization (WHO). The sources of PM in subway systems include moving train parts such as wheels, brake pads, steel rails, and power supply materials.

Factors Influencing Air Quality in Subway Systems

Several factors can influence the air quality in subway systems:

• Wheel materials and braking mechanisms: Different wheel materials and braking systems can affect the level of PM in subway systems. For example, rubber wheels may produce less PM than steel wheels.
• Ventilation and air conditioning systems: The type and efficiency of ventilation and air conditioning systems can impact the level of PM in subway systems. Well-designed and maintained ventilation systems can help reduce PM levels.
• Station depth, date of construction, and type of ventilation: Older stations with limited air volume and weak or poorly designed ventilation systems may have higher PM levels.
• Presence of platform screen doors: The absence of platform screen doors can allow contaminated tunnel air to enter the platform, increasing PM levels.
• Topography and elevation changes: Stations with topography that requires harder braking, such as elevation changes, may have higher PM levels.
• Frequency of trains: The more frequent the trains, the higher the PM levels are likely to be due to increased friction and wear.

Examples of Air Quality in Different Cities

• Barcelona: A study comparing air quality on subway, bus, tram, and walking journeys in Barcelona found that subway air had higher levels of PM than trams or walking but lower levels than buses. The levels of PM on the Collblanc platform in Barcelona were close to the European limits for outdoor air.
• Hong Kong, Mexico City, Istanbul, and Santiago de Chile: Studies in these cities showed lower PM levels in subway environments compared to other public transport modes.
• New York: A study by an NYU researcher found that the air quality in some New York City subway stations, especially in Washington Heights, was unhealthy due to high levels of PM.
• Beijing: The opening of new subway lines in Beijing has been associated with a reduction in air pollution levels, with an estimated 2-4% improvement in air quality.
• Shanghai: Shanghai is in the process of building its 15th subway line, which is expected to improve air quality by reducing motor-vehicle use.
• London, Paris, Tokyo, Moscow, and Beijing: These cities have a high number of subway users, and their air quality in subway systems may vary due to factors such as ventilation systems and train frequency.

Air quality in subway systems in different countries

Subways are vital for commuting in crowded cities, and their use is only expected to increase as the United Nations predicts that 75% of the world's population will be urban by 2050. They are also seen as a solution to reduce outdoor air pollution in large metropolises by helping to reduce motor-vehicle use. However, several studies have revealed unacceptably high levels of inhalable particulate matter (PM) in some subway systems. This article will discuss air quality in subway systems in different countries and offer recommendations for improving air quality and protecting commuters' health.

Air Quality in Different Subway Systems

A number of studies have monitored subway air quality across cities in Europe, Asia, and the Americas. While the database is incomplete, some comparisons can be made. For example, a study in Barcelona found that subway air had higher levels of air pollution (PM2.5 concentrations) than trams or walking in the street, but lower levels than buses. Similar findings were reported in Hong Kong, Mexico City, Istanbul, and Santiago de Chile.

Another study compared the air quality in subway systems in Athens, Helsinki, London, Prague, Stockholm, Taipei, and Shanghai. It was found that the levels of particulate matter (PM10 and PM2.5) varied significantly between these cities, with the highest concentrations observed in Athens and the lowest in Helsinki. The type of rolling stock, braking system, and ventilation system were identified as key factors influencing air quality.

A review of more than 160 relevant studies across over 20 countries found that particulate matter, aromatic hydrocarbons, carbonyls, and airborne bacteria were the primary air pollutants inside metro systems. It was also noted that the number of metro commuters has continuously increased in recent years, with the metro system becoming the primary public transportation mode in some cities.

Factors Affecting Air Quality in Subway Systems

The air quality in subway systems is influenced by various factors, including the type of brakes and wheels used on the trains, station depth, ventilation system, train frequency, and the presence of platform screen doors. The age of the system and the topography of the area can also play a role, with older systems having more accumulated particulate pollutants and areas with elevation changes requiring harder braking.

The use of air conditioning in trains has been shown to improve air quality, while the ability to open windows can have the opposite effect, especially when entering tunnels at high speed. The materials used in construction can also affect the types of particles present on platforms worldwide.

Health Effects of Subway Air Pollution

To date, there is no clear epidemiological indication of abnormal health effects on underground workers and commuters due to subway air pollution. However, a study of employees working on the platforms of the Stockholm underground, where PM concentrations were highest, found that they tended to have higher levels of risk markers for cardiovascular disease than ticket sellers or train drivers.

Recommendations for Improving Air Quality and Protecting Commuter Health

• Use of public transport, especially subways, should be encouraged to reduce motor-vehicle use and outdoor air pollution.
• Improve ventilation systems in subway stations, taking into account the local conditions of each station.
• Use intelligent ventilation systems to control the exchange between outdoor and underground air masses, avoiding sourcing air from traffic hotspots.
• Install platform screen doors to reduce the ingress of contaminated tunnel air into the platform.
• Conduct night maintenance as early as possible and use dust suppressants when laying ballast.
• Further research is needed to assess the toxicity of inhalable friction-generated polymetallic particles from brakes and copper-bearing catenary systems.

Air quality in subway systems over time

Air quality in subway systems has been a growing concern for researchers and commuters alike. Studies have shown that the air in subway systems can contain high levels of particulate matter, which can have negative impacts on human health.

The impact of subways on urban air pollution

The impact of subways on urban air pollution is complex and depends on various factors. On average, particulate concentrations remain unchanged or show a tiny decrease after the introduction of a subway system. However, in cities with higher initial pollution levels, subways can lead to a reduction in particulates, with the effect being more pronounced near the city center. This effect persists over several years, providing a significant external mortality benefit.

Particulate matter in subway systems

Particulate matter, especially PM2.5, is a major concern in subway systems. These tiny particles, often produced by the friction between train wheels and tracks or the braking system, can be inhaled and pose health risks. Studies have found PM2.5 levels in subway systems to be well above the recommended limits, with some stations showing incredibly high pollution levels.

Factors influencing subway air pollution

Several factors influence the air quality in subway systems:

• Station design: Older, deeper stations tend to have higher pollution levels. Stations with limited air volume, weak ventilation systems, and lack of platform screen doors tend to have worse air quality.
• Train design: The type of brakes and wheels used on trains can impact air quality. Trains with electromagnetic brakes and rubber wheels tend to generate less particulate matter.
• Ventilation: The type and power of ventilation fans play a crucial role in air quality. Proper ventilation can reduce particulate matter concentrations inside carriages.
• Other factors: The presence of biological aerosols, outdoor air quality, and maintenance practices can also influence subway air quality.

Health impacts of subway air pollution

The health impacts of long-term exposure to particulate matter in subway systems are not yet fully understood. While there is no clear epidemiological indication of abnormal health effects on underground workers and commuters, the high levels of certain pollutants, such as iron and organic carbon, are concerning. These pollutants have been linked to respiratory conditions, lung cancer, and heart disease.

Improving subway air quality

To improve subway air quality, researchers have suggested:

• Using less toxic materials for train parts
• Optimizing ventilation systems
• Implementing platform screen doors
• Enhancing maintenance practices, such as using dust suppressants

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