What are streetcanyons and why are they important?

A street canyon, also known as an urban canyon, is a narrow street flanked by tall buildings on both sides. This urban form is common in densely built cities. Street canyons can have a significant impact on the local climate, air quality, and pedestrian comfort.

Impact on local climate:

Street canyons can trap heat and moisture, leading to higher air temperatures and humidity compared to surrounding areas. This effect is known as the urban heat island (UHI) phenomenon. The UHI can be exacerbated by the presence of dark-colored surfaces, such as asphalt and concrete, which absorb solar radiation and release it as heat.

Impact on air quality:

Street canyons can also trap air pollutants, such as particulate matter and nitrogen oxides, which are emitted from vehicles and other sources. This can lead to localized hotspots of poor air quality. The vertical walls of buildings can interfere with airflow, preventing pollutants from dispersing effectively.

Impact on pedestrian comfort:

Street canyons can create uncomfortable wind conditions for pedestrians. Strong winds can be funneled through the canyons, creating gusts and downdrafts that can make it difficult to walk or stand. In colder months, the trapped heat can make it feel warmer than the surrounding air.

If we build buildings like a pyramid or stair shape, would that effect the streetcanyon in terms of air quality

Building buildings in a pyramid or stair shape could help to improve air quality in street canyons. This is because these shapes would allow for better airflow and dispersion of pollutants.

Pyramid-shaped buildings would create a more open space at the street level, allowing for more sunlight and ventilation. This would help to reduce the concentration of pollutants in the air. Stair-shaped buildings would also help to improve airflow, as the steps would create an uneven surface that would disrupt wind patterns and prevent pollutants from becoming trapped.

In addition to the shape of the buildings, the materials used to construct them can also affect air quality. For example, using lighter-colored materials, such as white or light gray, can help to reflect sunlight and reduce the heat island effect. This can help to reduce the formation of pollutants, such as ozone.

Planting trees and other vegetation can also help to improve air quality in street canyons. Trees act as natural filters, removing pollutants from the air. They also provide shade, which can help to reduce the heat island effect.

By taking these measures, it is possible to create street canyons that are more livable and have a lower environmental impact.

How long can polluted air stay in a streetcanyon on average?

The amount of time that polluted air can stay in a street canyon depends on several factors, including the height and width of the buildings, the type of pollutant, and the wind conditions. In general, polluted air can stay in a street canyon for several hours or even days.

Factors affecting the residence time of polluted air in a streetcanyon:

  1. Street canyon geometry: The height and width of the buildings flanking the street significantly impact airflow and pollutant dispersion. Taller and narrower canyons restrict airflow, leading to longer residence times for pollutants.
  2. Pollutant type: Different pollutants have varying deposition rates and tendencies to mix with the surrounding air. Fine particulate matter (PM2.5) tends to remain suspended in the air for longer periods than coarse particulate matter (PM10).
  3. Wind conditions: Wind plays a crucial role in dispersing pollutants. Stronger winds can effectively mix polluted air with cleaner air, reducing its concentration in the street canyon.
  4. Atmospheric stability: Atmospheric stability refers to the resistance to vertical mixing of air. During stable conditions, when the air is stratified, pollutants tend to become trapped in the street canyon due to the lack of upward air movement.

Typical residence times of pollutants in streetcanyons:

  • PM2.5: Several hours to up to a day
  • PM10: Several hours
  • Nitrogen dioxide (NO2): Several hours to up to a day
  • Carbon monoxide (CO): Several hours

Strategies to reduce pollutant residence times in streetcanyons:

  1. Urban planning and design: Consider building shapes and street layouts that promote airflow and minimize pollutant trapping.
  2. Increased vegetation: Planting trees and other vegetation can help filter pollutants and improve airflow.
  3. Traffic management: Implementing measures to reduce traffic volume and promote cleaner transportation can lower pollutant emissions.
  4. Enhanced ventilation systems: Mechanical ventilation systems in buildings can help remove pollutants from indoor environments.
  5. Emission control technologies: Implementing stricter emission standards for vehicles and industries can significantly reduce pollutant sources.

If we have good ventilated building in cities but located in the streetcanyons, what will happen with the indoor air of these buildings?

The indoor air quality of well-ventilated buildings located in street canyons can still be affected by outdoor pollutants, but to a lesser extent than poorly ventilated buildings. This is because well-ventilated buildings have a higher rate of air exchange, meaning that fresh air is constantly being brought in and polluted air is being removed. This helps to dilute pollutants and reduce their concentration indoors.

However, even with good ventilation, it is not possible to completely eliminate the impact of outdoor pollutants on indoor air quality. This is because some pollutants, such as particulate matter, can enter buildings through cracks and openings around windows and doors. Additionally, if the outdoor pollutant concentration is very high, even a well-ventilated building may not be able to keep up with removing all of the pollutants from the air.

Here are some additional factors that can affect the indoor air quality of well-ventilated buildings in street canyons:

  • The location of the air intake: If the air intake is located near a source of pollution, such as a busy street, it is more likely to be contaminated with pollutants.
  • The type of air filtration system: Some air filtration systems are more effective than others at removing pollutants from the air.
  • The maintenance of the air filtration system: A poorly maintained air filtration system will not be as effective at removing pollutants from the air.

In general, well-ventilated buildings with good air filtration systems will have better indoor air quality than buildings with poor ventilation. However, it is important to be aware that even well-ventilated buildings can be affected by outdoor pollutants.

Indoor air is a cumulation of the polluted outside air from a streetcanyon, the building materials, the indoor activities and humans?

Outdoor air pollution can enter buildings through cracks and openings around windows and doors, as well as through ventilation systems. Outdoor pollutants can include particulate matter, nitrogen dioxide, sulfur dioxide, and carbon monoxide.

Building materials can also release pollutants into indoor air. These pollutants can include formaldehyde, radon, and volatile organic compounds (VOCs). Formaldehyde is a common pollutant in manufactured wood products, such as plywood and particleboard. Radon is a radioactive gas that can enter buildings through the foundation. VOCs are released from a variety of sources, including paints, solvents, and cleaning products.

Indoor activities can also generate pollutants. These pollutants can include smoke from cooking and burning candles, dust from carpets and furniture, and pet dander.

Humans also contribute to indoor air pollution by breathing out carbon dioxide and other pollutants.

The concentration of pollutants in indoor air can be higher than the concentration of pollutants in outdoor air, especially in tightly sealed buildings with poor ventilation. This is because pollutants can build up indoors over time, especially if there are not enough fresh air exchanges.

Exposure to indoor air pollution can cause a variety of health problems, including respiratory problems, heart disease, and cancer. It is important to take steps to improve indoor air quality, such as ventilating your home regularly, using low-VOC products, and avoiding smoking indoors.

The amount of time that indoor air is more polluted than outdoor air in buildings located in polluted street canyons can vary depending on a number of factors, including:

  • The type of building
  • The ventilation system
  • The outdoor air quality
  • Indoor activities
In general, indoor air can be up to 5 times more polluted than outdoor air, and sometimes even more. This is because pollutants can become trapped indoors and build up over time.

On which building floor should i live to get a minimum effect of the polluted air of a streetcanyon?

The best floor to live on in a street canyon to minimize the effects of polluted air depends on a number of factors, including the height of the buildings, the width of the street, and the type of pollutants in the air. However, in general, higher floors in a street canyon will have lower levels of pollution than lower floors. This is because pollutants tend to become trapped in the lower levels of a street canyon.

The following factors can affect the distribution of pollutants in a street canyon:

  • Building height: Taller buildings create narrower street canyons, which can trap pollutants more effectively.
  • Street width: Wider streets allow for better air circulation, reducing pollutant concentration.
  • Pollutant type: Heavier pollutants, such as particulate matter, tend to settle closer to the ground, while lighter pollutants, such as nitrogen oxides, can disperse more evenly.
  • Wind patterns: Wind can help to disperse pollutants, but it can also channel them through street canyons, increasing pollution levels in certain areas.

Based on these factors, here are some general recommendations for choosing a floor to live on in a street canyon to minimize exposure to pollution:

  • Choose a higher floor: Upper floors will generally have lower pollution levels than lower floors.
  • Consider the building shape: If possible, choose an apartment in a building with a setback or a stepped design, as this can help to reduce pollutant trapping.
  • Avoid apartments near traffic sources: Apartments located directly above or near busy streets will likely have higher pollution levels.
  • Monitor indoor air quality: Consider using an indoor air quality monitor to track pollution levels in your apartment and make adjustments as needed.

Remember that even on higher floors, it is still important to take steps to reduce your exposure to indoor air pollution. This includes ventilating your apartment regularly, using air filters, and avoiding indoor pollution sources such as smoking and harsh cleaning products.

If you are concerned about the air quality in your apartment, you can consult with an indoor air quality professional to assess your risk and develop a plan to improve your indoor air quality.

The Scientific explanation