Urbanization's Impact: Air Pollution Explained

Urbanization has led to the world's biggest wave of urban growth in history. As of 2005, more than half of the world's population lived in cities, and by 2030, this number is expected to rise to about 5 billion. Urbanization spurs a unique set of issues, such as poverty and environmental degradation, and it is closely linked to air pollution. Air pollution is a prominent threat to global society, causing cascading effects on individuals, medical systems, ecosystem health, and economies. This paragraph will explore the relationship between urbanization and air pollution and discuss the impact on human health.

Urbanisation increases energy use, leading to greater air pollution

Urbanisation increases energy use, which, in turn, leads to greater air pollution. This is a well-known and researched phenomenon, with cities being centres of resource utilisation and major contributors to air pollutant and greenhouse gas emissions.

Urban areas consume about 75% of global primary energy and emit 50-60% of the world's total greenhouse gases. This is due to the concentration of people, resources, and wealth in cities, which drives up energy consumption and emissions. The increase in energy use is often a result of the transformation of the primary industry into secondary and tertiary industries, as well as the overall improvement in the standard of living of residents.

The energy used to power transportation infrastructure, buildings, and industrial processes in cities comes largely from the combustion of fossil fuels, which releases nitrogen oxides (NOx), volatile organic compounds (VOCs), and particulate matter into the atmosphere. These pollutants can cause lung problems and reduce visibility. In addition, the high population density and demands of urban environments lead to increased waste production, which can create multiple health hazards if not properly managed.

Furthermore, the unique urban landscape, with its contiguous built-up areas and street canyons, can trap pollution and increase the concentration of particulate matter, especially in compact cities with limited green spaces. This is known as the "big city disease", where traffic congestion, energy shortages, and air pollution are prevalent.

The impact of urbanisation on air pollution is particularly notable in developing countries, where the levels of pollution are often several orders of magnitude higher than in high-income or developed nations. However, it is important to note that strong city planning and sustainable urbanisation practices can play a crucial role in managing and reducing the air pollution caused by increased energy use in urban areas.

Urban areas are centres of resource consumption, contributing to air pollution

The concentration of people and economic activities in urban areas leads to increased resource consumption and energy use, which contributes to air pollution. Cities consume about 75% of global primary energy and emit 50-60% of the world's total greenhouse gases. The burning of fossil fuels for energy generation and industrial processes is a significant source of air pollutants like nitrogen dioxide (NO2) and particulate matter (PM2.5).

Transportation infrastructure also plays a role in air pollution within urban areas. The development of transportation networks can alleviate traffic congestion and reduce air pollution to some extent. However, it can also attract more traffic, increasing the pressure on the local road network and worsening air quality. Vehicle emissions, particularly from automobiles, contribute to elevated lead levels and particulate matter in the air.

In addition, the expansion of urban land use can affect air temperature and the height of the boundary layer, influencing the diffusion of air pollutants. Urban development can also result in the loss of green spaces and trees, which naturally absorb and reduce particulate matter in the air.

Furthermore, the initial stages of urbanisation are often accompanied by industrialisation, leading to large amounts of waste gas and wastewater emissions. The concentration of polluting industries in urban areas can exacerbate air pollution, particularly in low-income or developing countries where pollution levels tend to be higher.

Overall, the high consumption of resources and energy in urban areas, coupled with the emissions from transportation and industrial activities, contributes significantly to air pollution.

Industrialisation and urbanisation spread air quality concerns globally

Industrialization and urbanization have spread air quality concerns globally. Urban areas are centers of resource utilization and are major contributors to air pollutant and greenhouse gas emissions. Cities consume about 75% of global primary energy and emit 50–60% of the world's total greenhouse gases. As a result, urban residents may face issues such as poor air and water quality, insufficient water availability, waste-disposal problems, and high energy consumption.

The world is experiencing the biggest wave of urban growth in history. Currently, over 50% of the global population lives in urban areas, and by 2030, this number will rise to about 5 billion. Urbanization has driven China's rapid economic growth and competitiveness in international markets, but it has also increased resource consumption and caused environmental pollution problems. Similarly, the initial stage of urbanization is usually accompanied by industrialization, along with a large amount of waste gas and wastewater emissions.

Air pollution often plagues industrialized cities, particularly during their early development. For example, episodes of high levels of sulfurous smog killed or sickened thousands in Donora, Pennsylvania, in 1948, and in London in 1952. As governments controlled more traditional pollution sources, a different type of air pollution also arose: photochemical air pollution. This type of air pollution results from photochemical reactions involving nitrogen oxides (NOx) and volatile organic compounds (VOCs) that produce ozone (O3) and particulate matter, both of which cause lung problems.

Urbanization affects air pollutants through urban expansion and emission growth, thereby changing the health risks involved with air pollutants. Urban land use has been shown to increase air temperature and boundary layer height, contributing to the diffusion of PM2.5. The monthly average surface PM2.5 concentrations decreased by 10.8 µg m−3 (7.6 %) in January, while the monthly average daily maximum 8-hour average (MDA8) O3 concentrations increased by 10.6 µg m−3 (6.0 %) in July.

Transportation infrastructure can also play a role in air pollution. While better infrastructure can relieve traffic congestion and reduce air pollution, it can also cause a "siphoning effect" on transportation in neighboring cities, increasing the pressure on the local road network and worsening air quality. Climate variables such as wind speed, rainfall, and temperature can significantly affect the generation and dispersion of air pollution.

Developing sustainable urbanization practices is crucial for addressing the challenges of pollution caused by urbanization. Governments should consider health and environmental protection in urbanization construction and evaluation and introduce low-carbon measures to guide the practices of sustainable urbanization.

Urbanisation causes traffic congestion, trapping pollution inside street canyons

Urbanisation has a significant impact on air quality, and one of the key ways in which this occurs is through the development of "street canyons". Street canyons are characterised by narrow streets with continuous rows of high buildings on either side. The combination of high population density and heavy traffic volume in these areas can result in extremely high levels of air pollution.

As urban areas develop and expand, they often experience an increase in traffic congestion. This is particularly common in cities with a high population density, where the number of vehicles on the road can far exceed the capacity of the road network. As a result, cities become plagued by slow-moving traffic and even gridlock. This congestion has a significant impact on air quality.

When streets are congested with slow-moving or stationary vehicles, the pollutants emitted by those vehicles become trapped within the street canyon. The high buildings on either side of the street restrict the dispersion of pollutants, leading to a build-up of harmful substances in the air. This phenomenon is known as the "street canyon effect". The geometry of the canyon, including the height and proximity of the surrounding buildings, influences the airflow and can result in the formation of vortexes that further concentrate pollutants within the canyon.

The impact of traffic congestion on air quality is particularly pronounced in urban canyons due to the high volume of traffic and the restricted airflow. The concentration of pollutants, including vehicle emissions and airborne particles, can reach levels that are significantly higher than those found in other urban settings or the surrounding countryside. This heightened level of pollution has a direct impact on the health of those who live and work in these areas.

Pedestrians, cyclists, and office workers in areas with street canyons are at an increased risk of exposure to harmful pollutants. The narrow confines of the canyon mean that individuals are exposed to higher concentrations of pollutants for more extended periods. This exposure has been linked to adverse health effects, including respiratory issues and chronic diseases. Therefore, addressing traffic congestion and improving air quality in urban canyons is crucial for protecting public health and ensuring the well-being of city dwellers.

Urban vegetation can help mitigate air pollution

Urbanisation has various impacts on human health and the environment. It is associated with economic development, which can lead to increased resource consumption and a gathering of polluting industries, causing environmental pollution problems. Urban areas are centres of resource utilisation and are major contributors to air pollutant and greenhouse gas emissions. Urbanisation can increase urban land use and anthropogenic emissions, affecting the concentrations and health risks of air pollutants.

Urban vegetation has been found to reduce the growth of air pollutant concentrations, with reduction rates of 16.5% to 26.7% for PM, 13.9% to 36.2% for nitrogen oxide (NOx), and 20.5% to 47.8% for sulfur dioxide (SO2). However, it has not been shown to significantly mitigate ground-level ozone (O3). The effectiveness of air phytoremediation in cities requires more synthesis to inform environmental management, and the overall effectiveness of GI remains unclear. Nevertheless, urban vegetation is widely regarded as a cost-effective and nature-based approach to meeting clean air standards.

To optimise air pollution mitigation by green infrastructure, it is important to consider the scale of the intervention, the context and conditions of the site, and the target air pollutant type. The selection of plant species that exhibit certain biophysical traits can enhance the mitigation of air pollution. Additionally, the literature suggests that the inclusion of green spaces in urban planning can help reduce air pollution.

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