Managing Urban Heat and Air Quality Challenges
Urban Heat Island Effect (UHIE)
The Urban Heat Island Effect (UHIE)
The Urban Heat Island Effect (UHIE) describes the phenomenon where urban areas experience higher temperatures than their rural surroundings due to human activities and the characteristics of built environment.
Why Do Cities Get Hotter?
- Materials: Concrete and asphalt absorb incoming radiation and re-radiate heat, unlike natural surfaces like soil or vegetation, which reflect more sunlight.
- Lack of Vegetation: Trees and plants provide shade and cool the air through evapotranspiration. Urban areas often lack this natural cooling.
- Human Activities: Cars, factories, and air conditioners release heat, further warming the city.
Think of a city as a sponge soaking up heat during the day and slowly releasing it at night, while rural areas act more like a mirror, reflecting sunlight and staying cooler.
Impacts of UHIE
- Increased Energy Demand: Higher temperatures lead to more air conditioning use, straining energy systems.
- Heat-Related Illnesses: Vulnerable populations, such as the elderly, face greater risks during heatwaves.
- Reduced Air Quality: Heat accelerates the formation of ground-level ozone, worsening pollution.
During a heatwave in Paris in 2003, the UHIE contributed to temperatures over 40°C, resulting in thousands of heat-related deaths.
Students often misinterpret the urban heat island effect (UHIE) as an absolute temperature increase in cities, rather than as a relative measure highlighting the temperature difference between urban areas and their surroundings. This effect is especially pronounced in temperate climates with nearby forests that cool the temperature, while in desert environments, the UHIE tends to be less noticeable due to already high baseline temperatures and minimal surrounding vegetation.
Air Pollution Patterns
Sources of Urban Air Pollution
- Vehicle Emissions: Cars and trucks release nitrogen oxides, carbon monoxide, and particulate matter.
- Industrial Processes: Factories emit pollutants like sulfur dioxide and volatile organic compounds.
- Construction Dust: Building activities generate fine particles that linger in the air.
PM10 refers to particulate matter smaller than 10 micrometers. These particles are a mixture of solids and liquids, including dust, dirt, soot, pollen, and smoke.
PM10 can be inhaled, reaching the lungs and potentially leading to respiratory problems, cardiovascular diseases, and other health issues.
Common sources of PM10 include incomplete process of combustion in coal-based power plants, vehicle emissions, construction activities, and natural phenomena like wildfires and wind lifting dust.
PM2.5 refers to particulate matter smaller than 2.5 micrometers, which can penetrate deep into the lungs and bloodstream. PM2.5 is more dangerous for human health than PM10.
Suspended particles of different sizes are most common component of air pollution in cities worldwide.
Impacts of Air Pollution
- Health Issues: Respiratory illnesses, cardiovascular diseases, and even cancer, as well as premature deaths.
- Environmental Damage: Acid rain and smog harm ecosystems and reduce biodiversity.
- Economic Costs: Healthcare expenses and lost productivity due to pollution-related illnesses.
Don't assume air pollution is only an outdoor problem. Indoor air quality can also be affected by pollutants from outside, as well as inside. Using poor quality cooking equipment is a most common source of indoor air pollution, especially in LICs.
Students often incorrectly classify carbon dioxide (CO₂) as an air pollutant, rather than understanding it as a greenhouse gas. While CO₂ is a significant contributor to climate change by trapping heat in the atmosphere, it is a natural component of air essential for processes like photosynthesis.
Management Strategies
Addressing the Urban Heat Island Effect
Green Roofs and Walls
- Vegetation on rooftops absorbs heat and provides insulation.
- Reduces energy consumption for cooling.
Toronto's Green Roof Bylaw requires new buildings to include green roofs, significantly lowering urban temperatures.
Urban Greenery, Trees and Forests
- Trees provide shade and cool the air through evapotranspiration.
- Improve air quality by absorbing pollutants.
Warsaw has initiated "One Million Trees" project increasing the number of trees in the city by 10%.
Reflective Materials:
- Cool roofs and pavements reflect sunlight instead of absorbing it.
- Helps lower surface temperatures in urban areas.
Los Angeles has experimented with reflective coatings on roads, reducing surface temperatures by up to 10°C.
Reducing Air Pollution
Widely Available and Clean Public Transport
- Promote public transport as a basic mean of transportation in cities - make it available, affordable, clean, and safe.
- Invest in electric buses, trams, and subways, and reduce reliance on fossil fuels.
Pedestrianization and Promoting Walking and Cycling
- Decrease reliance on motorized transport, leading to lower vehicle emissions and improved urban air quality.
- Making cities more compact, promoting mixed land use, and creating car-free zones encourages the development of vibrant public spaces, making neighborhoods more attractive for walking and cycling.
Low-Emission Zones
- Restrict high-polluting vehicles or allow only zero-emissions cars in certain areas.
- Encourage the use of cleaner transportation options.
London's Ultra Low Emission Zone (ULEZ) has reduced nitrogen dioxide levels by nearly 40% in central areas.
Transitioning to electric vehicles also requires clean energy sources to maximize environmental benefits.
Air Quality Monitoring Systems
- Real-time data helps identify pollution hotspots.
- Informs policy decisions and public health warnings.
Mobile apps that provide air quality updates can empower citizens to make informed choices about outdoor activities.
Beijing, China
The Problem
- High Levels of PM10 and PM2.5: Due to coal burning, traffic congestion, and industrial emissions.
- Health Impacts: Increased rates of respiratory and cardiovascular diseases.
Responses
- Closure of Coal-Based Power Plants: Shift towards cleaner energy sources like natural gas and renewables.
- Promotion of Electric Vehicles: Subsidies and incentives for EV adoption enhanced by expansion of charging infrastructure.
- Urban Tree Planting Programs: Large-scale afforestation projects to improve air quality and reduce heat.
How do cultural attitudes toward nature influence urban planning decisions? Consider how different cities prioritize green spaces or public transport.
Reflection and Broader Implications
- Urban heat and air quality challenges are interconnected, requiring holistic solutions.
- By combining green infrastructure, cleaner technologies, and effective policies, cities can create healthier, more sustainable environments.
