Big Cities: Pollution's Breeding Ground?

Air pollution is a pressing issue in cities worldwide, posing a significant threat to the health and well-being of citizens, the environment, and economic growth. Urban areas are often hotspots for poor air quality due to various factors, with traffic and industrialization being the most prominent contributors. The dense population in cities leads to increased emissions from vehicles, industrial activities, and energy consumption, all of which release pollutants into the atmosphere, causing short-term and long-term health issues. As a result, cities experience high levels of nitrogen dioxide (NO2) and particulate matter (PM2.5 and PM10), which have detrimental effects on respiratory and cardiovascular health. While urbanization has improved human life, it has also become a significant cause of air pollution, impacting the environment and human health.

Industrial activities and power plants

Power plants are not solely responsible for local air pollution; their emissions can travel long distances, affecting communities far from the source. This means that even cities located in high-income regions with relatively low PM2.5 levels can still be exposed to harmful pollutants from power plants. For example, a study by Lelieveld et al. in 2015 estimated that 0.65 million out of 3 million global deaths due to outdoor air pollution were from India, with power generation being the second biggest contributor at 14%.

In addition to power plants, industrial activities also play a significant role in air pollution in big cities. Factory processes such as dyeing or tanning clothes release toxic gas waste and chemical solvents into the atmosphere, contributing to the overall degradation of air quality. The industrial revolution in the 1850s led to a surge in air pollutants, with European countries and the US being the top global emitters at the time.

To combat the effects of industrial activities and power plants on air pollution, regulations and preventive measures have been enforced. These include the introduction of alternative fuels, zero-emission vehicles, and renewable energy technologies. Smart city planning, which utilizes advanced technologies to improve urban life, also offers an opportunity to address air pollution and enhance overall air quality in big cities.

While progress has been made in reducing emissions from the power sector, it continues to be a significant source of air pollution in big cities. The complex interplay between economic activities, power generation, and air quality means that targeted efforts to curb urban air pollution are essential to safeguard public health and the environment.

Vehicle emissions

In cities, the impact of vehicle emissions is particularly acute. Urban areas are often hotspots for poor air quality, and vehicle traffic is a major source of NO2 (nitrogen dioxide) in these areas. NO2 exposure has been linked to a range of negative health effects, including aggravating asthma symptoms and contributing to the development of asthma in children. It is also associated with organ and neurodevelopment issues during pregnancy, new-onset asthma in children, and lung function decline in older adults.

The problem is not limited to NO2 emissions. Vehicle emissions also produce PM2.5, or particulate matter, which includes soot, smoke, dust, and liquid droplets measuring less than 2.5 micrometres in diameter. These tiny particles can easily enter the lungs and even the bloodstream, impacting our health in various ways. PM2.5 pollution is of particular concern in large cities, with higher levels seen in populous cities in South Asia, East Asia, Southeast Asia, West Sub-Saharan Africa, and Andean and Central Latin America.

Heavy traffic congestion exacerbates the problem, increasing traffic flow and producing more O3 precursor emissions, which in turn leads to more adverse air quality issues. Research has shown that these negative impacts disproportionately affect drivers, commuters, and those living near major roads.

However, there are strategies to mitigate the impact of vehicle emissions on air pollution in cities. The implementation of intelligent traffic management systems and ride-sharing apps can help to reduce congestion and emissions by optimising traffic flow and promoting public transportation and alternative modes of transport. Cities can also encourage the use of electric vehicles and provide incentives to reduce emissions from petrol cars.

Another effective strategy is the implementation of Ultra Low Emission Zones (ULEZ), as seen in London. The ULEZ restricts vehicles that do not meet certain emission standards from driving in certain zones of the city or charges a daily fee for entry. This has significantly decreased the number of older, more polluting vehicles entering the city and reduced air pollution exposure levels. Between 2016 and 2020, central London saw an almost 50% decrease in nitrogen dioxide air pollution—a much faster reduction than in the rest of the United Kingdom.

Regulations and vehicle emission standards have also proven effective in reducing vehicle-related emissions. For example, the Clean Air Act has significantly reduced traffic-related air pollution levels, and research shows that for every dollar of compliance costs, over ten dollars are gained in environmental benefits.

Urban population growth

The impact of urban population growth on pollution is twofold: the size and structure of cities change, and the population explosion leads to lasting air quality challenges. Urbanisation increases land use and anthropogenic emissions, affecting the concentrations and health risks of air pollutants.

Research has shown that larger populations are associated with increased vehicle usage and vehicle-kilometres travelled, which consequently boosts tailpipe emissions. Population density is also a useful reflector of transportation demand and the fraction of emissions inhaled by people.

The health risks related to urban population growth and pollution are significant. Air pollution in cities poses a major threat to the health and well-being of citizens, the environment, and economic growth. Poor air quality is linked to short-term discomforts like throat and eye irritation and minor illnesses like pneumonia or bronchitis. It can also cause long-term and more severe impacts on respiratory and cardiovascular health, such as increased risks of lung cancer and heart disease. Children, the elderly, and low-income communities are particularly vulnerable to these health impacts.

To address the issue of urban population growth and pollution, cities can implement intelligent traffic management systems and ride-sharing apps to reduce traffic congestion and emissions. Incentives for the use of electric vehicles and the development of more green infrastructure, such as green roofs and urban forests, can also help reduce air pollution in cities.

Fossil fuels

The burning of these fuels for electricity production, heating, transportation, and industry results in the emission of harmful substances, including carbon dioxide (CO2), nitrogen and sulfur dioxides, black carbon, polycyclic aromatic hydrocarbons (PAH), mercury, and volatile chemicals that form ground-level ozone (O3). These emissions have severe health impacts, particularly on children's health, with links to respiratory illnesses, cognitive and behavioral development issues, and other chronic diseases.

In big cities, the combustion of fossil fuels in vehicles, power plants, and industrial processes significantly contributes to air pollution. Vehicle emissions, including older diesel engines, are a significant source of particulate matter and nitrogen dioxide (NO2), which are harmful to human health. NO2 exposure is associated with adverse effects such as asthma development in children and aggravation of existing asthma symptoms.

Additionally, large-scale coal-fired power plants and industrial processes, such as dyeing or tanning clothes, release toxic gases and pollutants into the atmosphere, further contributing to the poor air quality in cities. The built environment, including heating buildings and construction, also plays a role in fossil fuel-related pollution, with nearly 70% of particulate matter attributed to these sources rather than transportation.

To address this issue, cities can transition to renewable energy technologies, such as solar, wind, and hydropower, to replace fossil fuels and reduce emissions. Implementing intelligent traffic management systems and promoting public transportation can also help reduce traffic congestion and lower emissions from vehicles.

Construction

Air Pollution

Air pollution is a significant issue associated with construction projects. Diesel engines power vehicles and heavy machinery, such as breakers, bulldozers, dumpers, and excavators, releasing pollutants like carbon monoxide, carbon dioxide, nitrogen oxides, and hydrocarbons. Additionally, land clearing, demolition, and drilling equipment generate high levels of dust from particulate matter, with particles smaller than 10 micrometers in diameter, significantly contributing to air pollution in construction zones.

The manufacturing of construction materials, especially cement, is energy-intensive and contributes to greenhouse gas emissions. According to the World Business Council for Sustainable Development, cement production alone accounts for around 5% of global CO2 emissions. The transportation of these materials to construction sites further emits CO2 and other pollutants.

Water Pollution

Water pollution is another concern arising from construction activities. Excavation, demolition, and drilling can release pollutants that contaminate water bodies such as rivers, lakes, and streams. Chemical pollution occurs when improperly disposed of materials, such as paints, solvents, and adhesives, flow into nearby waters. Sediment pollution happens when storm rains wash construction-site soil, sand, and debris into waterways, severely reducing water quality and disrupting aquatic ecosystems.

Soil Pollution

Soil pollution is also a consequence of construction activities. The deposition of waste materials can alter topography and affect local ecosystems. Hazardous materials uncovered or used during construction can contaminate the soil, compromising its health and the ecosystem it supports. Soil pollution can lead to weakened soil compaction, erosion, and destabilization, causing the soil to lose its structure and ability to retain water, resulting in soil degradation.

Noise Pollution

The impact of construction on the environment and human health is significant, and it is important to implement sustainable practices and regulations to minimize these adverse effects.

Frequently asked questions