Urban Pollution: What Are The Main Culprits?

Urban pollution is a pressing issue that affects almost every city worldwide. Air pollution, in particular, poses a significant threat to human health and the environment. While natural sources such as volcanic eruptions and wildfires contribute to air pollution, human activities are the primary culprits. Cities, with their dense populations and industrialization, have become hotspots for poor air quality. Various factors, including transportation, construction, and industrial activities, release harmful substances into the atmosphere, making them the leading causes of air pollution in urban areas.

Vehicle emissions

The combustion of fossil fuels, such as gasoline, natural gas, oil, coal, and wood, releases carbon monoxide, a highly toxic, colourless, odourless, and tasteless air pollutant. The largest anthropogenic source of carbon monoxide is vehicle emissions. When vehicles burn gasoline and diesel, the exhaust from the tailpipe contains toxic pollutants, including smog-causing volatile organic compounds, sulfur dioxide, formaldehyde, and benzene. Heavy-duty vehicles, which make up about 10% of all vehicles on the road, generate more than 25% of global warming emissions, 45% of NOx emissions, and nearly 60% of direct PM2.5 emissions from on-road vehicles.

To reduce vehicle emissions, cities can implement measures such as the Ultra Low Emission Zone (ULEZ) in London, which restricts vehicles that do not meet certain emission standards from certain zones in the city. Research has found that the ULEZ has significantly decreased the number of older, more polluting vehicles entering the city and reduced air pollution exposure levels. Another strategy is to improve public transportation systems and make alternative forms of transportation, such as biking and light rail, more feasible for residents. This can help reduce the number of cars on the road and encourage the use of more environmentally friendly modes of transport.

Industrial activities

In addition to air pollution, industrial activities also generate solid and liquid waste that can pollute water bodies. This wastewater contains heavy metals and other toxic chemicals, which can have detrimental effects on aquatic ecosystems and human health. The exponential increase in industrialization has led to the consumption of large areas of agricultural land, causing serious environmental degradation of soil.

Furthermore, global changes in industrialization and urbanization are expected to increase the amount of ocean litter and microplastics. The production and use of petrochemicals, power generation, heavy industry, and mining activities contribute to environmental pollution, affecting the air, water, and soil.

Interventions targeting pollution at the local level have shown success in some cities. For example, Beijing, China, reduced its PM2.5 levels by 36% in five years by implementing controls on power plant and industrial emissions, as well as improving fuel quality and vehicle emission standards. Similarly, London's Ultra Low Emission Zone initiative resulted in a 36% reduction in NO2 levels in the first six months after its launch in 2019.

Construction

Air pollution is a major issue in construction, with diesel engines powering vehicles and heavy machinery like breakers, bulldozers, and excavators. These diesel engines release pollutants such as carbon monoxide, carbon dioxide, nitrogen oxides, and hydrocarbons. In addition, dust generated during construction and demolition activities, including excavation, loading, and unloading, contains particulate matter and volatile organic compounds (VOCs) that can be spread by wind, affecting both construction workers and nearby residents. The production of concrete also generates a significant amount of carbon dioxide emissions, contributing to the sector's carbon footprint.

Water pollution is another concern in construction sites. Chemical pollution occurs when paints, solvents, adhesives, oils, and other chemicals are improperly disposed of or spilled, contaminating nearby water sources. Sediment pollution is also an issue, as rain can wash construction site soil, sand, and debris into waterways, impacting aquatic life and water quality. Additionally, wastewater from concrete mixing or site cleanup can pollute local water bodies if not properly treated or managed.

Noise pollution is a significant issue in construction sites, with heavy machinery, hammering, drilling, and beeping disrupting urban tranquillity and affecting human well-being and wildlife. Construction activities also generate substantial waste, including scrap materials, packaging, and old building components, which can further impact the environment if not properly managed.

While construction is necessary for progress, addressing its environmental and health impacts is crucial. This includes implementing measures to reduce emissions, following proper waste management practices, and seeking out environmental air quality solutions to minimise the harmful effects of construction activities on the air we breathe and the ecosystems we depend on.

Commercial cooking

The indoor PM2.5 concentrations in commercial kitchens can also affect the outdoor environment adjacent to them, leading to higher PM2.5 concentrations in those areas. This can result in respiratory health issues for residents, such as asthma, emphysema, COPD, and lung cancer. To address this issue, many restaurants are opting to install pollution control units (PCUs) or grease exhaust scrubbers to remove grease, smoke, and odors from the kitchen exhaust air stream and reduce outdoor air pollution. These units are specially designed filtration systems that can help improve air quality and reduce the harmful effects of pollution on human health.

It is important to note that the emission characteristics of PM2.5 from different cooking styles in commercial kitchens can vary, and more studies using real-time measurements are needed to fully understand the impact of commercial cooking on air pollution. However, the current research suggests that commercial cooking is a significant contributor to air pollution in cities and that measures should be taken to mitigate its impact on the environment and human health.

Local interventions and policies have been successful in improving air quality in some cities. For example, two air quality management districts in California have implemented restrictions on commercial cooking emissions, and many cities have introduced ultra-low emission zones to reduce NO2 levels. These initiatives demonstrate a growing awareness of the impact of commercial cooking on air pollution and a commitment to improving air quality in cities.

Residential heating

The impact of residential heating on air pollution varies across different regions. For instance, a study focusing on the London boroughs of Lambeth and Southwark found that heating buildings, along with construction and associated traffic, contributed significantly more to particulate matter (PM) pollution than transportation used by residents for navigating the city. This highlights how the sources of air pollution are intricately linked to the specific characteristics of each city.

Wood burning in homes, a form of residential heating, has been identified as a more prevalent source of air pollution than previously thought. A study in London revealed that wood burning contributed to higher levels of PM2.5 pollution, which is of particular concern due to its ability to penetrate deep into the lungs and cause respiratory issues. Additionally, the incomplete combustion of wood releases carbon monoxide, a colorless, odorless, and toxic gas.

To address the issue of pollution from residential heating, several strategies can be implemented. Education can play a vital role, encouraging residents to consider alternative options before increasing the thermostat during colder weather. For instance, wearing warmer clothing or using extra blankets can help reduce the reliance on heating systems. Additionally, the adoption of renewable energy sources, such as solar panels, can contribute to more sustainable residential heating practices.

Furthermore, implementing green infrastructure initiatives can help mitigate the heat island effect commonly observed in cities. This effect occurs when cities replace natural land cover with heat-absorbing surfaces like pavement and buildings, leading to higher temperatures in urban areas compared to their surrounding regions. Green roofs, urban forestry, and the incorporation of vegetation within communities can help reduce the heat island effect, thereby decreasing energy costs and improving air quality.

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