Urban air pollution: Causes, impacts and solutions

Urban air pollution has become one of the main environmental and public health challenges of the 21st century. In an increasingly urbanised world, ensuring good air qualityAir quality refers to the state of the air we breathe and its composition in terms of pollutants present in the atmosphere. It is considered good when poll...
Read more in cities is essential not only for the well-being of their inhabitants but also to move towards more sustainable and resilient environments.

This article offers an in-depth analysis of the causes of urban air pollution, its impacts on health and the environment, and the most effective technological and management solutions to combat this global issue. From mobility to the use of air quality sensorMeasuring air quality is essential for improving human and environmental health. Changes in the natural composition of the air we breathe are common in ind...
Read mores, we explore how to transform our cities into cleaner and more liveable spaces.

Understanding urban air pollution

Urban air pollution refers to the accumulation of atmospheric pollutants in densely populated environments, resulting from intensive human activities and natural sources. Although it is a local phenomenon, its causes and effects have regional and global implications. From nitrogen dioxide (NO₂)Nitrogen dioxide (NO2) is a harmful gas whose presence in the atmosphere is mainly due to the use of fossil fuels in combustion vehicles and industrial act...
Read more and tropospheric ozoneTropospheric ozone (O3) or ground-level ozone is a gas found in the lowest layer of the Earth's atmosphere, the troposphere, which extends up to 10 kilomet...
Read more (O₃) to fine particulate matter (PM_2.5 and PM₁₀), pollutants originate from multiple sectors and affect millions of people daily.

According to the World Health Organization, 99% of the global population breathes air exceeding recommended quality limits. It is estimated that air pollution in urban areas contributes to over 4.2 million premature deaths annually, primarily from cardiovascular diseases, respiratory illnesses, and lung cancer (World Health Organization, 2021: Ambient air pollution: Health impacts).

The origin of this problem is multifactorial. Activities such as road traffic, industrial production, construction, domestic heating and even natural phenomena like desert dust make up a complex mix of emission sources. Meteorological and topographical factors also influence the dispersion or accumulation of pollutants.

Besides health effects, urban air pollution affects visibility, quality of life, educational and work performance, and contributes to climate change. Understanding its causes is the first step towards effective solutions.

What causes air pollution in urban areas?

Air pollution in urban areas results from a complex combination of local, regional, and even cross-border sources. Understanding these causes helps identify responsibilities and design effective strategies to improve air quality in cities. Below are the main emission sources in urban environments, classified by origin.

Traffic and transport emissions

The transport sector is one of the main causes of urban air pollution. Petrol and diesel vehicles generate large amounts of nitrogen dioxide (NO₂), carbon monoxide (CO)The carbon monoxide (CO) is an invisible gas (colorless and odorless) that, at the same time, is a silent killer because in just a few minutes it exhibits ...
Read more, particulates (PM₁₀ and PM_2.5), and volatile organic compounds (VOCs). In dense metropolitan areas, congestion and low-speed driving increase pollutant emissions per unit distance travelled.

Transport emissions are not limited to private cars. Buses, trucks, taxis and motorcycles also contribute significantly, especially in cities with slow fleet renewal and lax vehicle inspection regimes.

Solutions such as transport electrification, low emission zones, and promotion of sustainable mobility in cities can mitigate this impact, but require political will, investment and citizen engagement.

Industrial and energy sources

Industrial activities—from treatment plants to textile factories, steelworks, cement plants, or oil refineries—are also responsible for a considerable fraction of urban air pollution. Burning coal, gas or diesel in industrial processes and thermal power plants releases sulphur dioxide (SO₂)Sulphur dioxide (SO2) is a colourless gas with a pungent odour that causes an irritating sensation similar to shortness of breath. Its origin is anthropoge...
Read more, nitrogen oxides (NOₓ), particulates and heavy metals into the air.

The impact varies depending on the type of industry, technology used and proximity to residential areas. Often, industrial hubs are located within or near urban centres, increasing direct exposure for the population.

Electricity generation from fossil fuels also contributes, especially in regions where the grid relies on thermal power plants. Cleaner energy sources like solar, wind or nuclear help reduce these emissions, but their penetration is still uneven among countries and cities.

Domestic heating and biomass use

In colder climates or areas with energy poverty, the use of wood, coal, pellet or waste stoves for heating remains common. These systems emit large amounts of fine particulate matter (PM_2.5), polycyclic aromatic hydrocarbons (PAHs) and pollutants, especially when modern technologies or adequate ventilation systems are not used.

This issue is intensified in low-income urban areas, where access to clean energy is limited. In densely populated zones, domestic emissions can become a significant source of air quality degradation in cities.

Construction and urban dust

Construction and demolition activities create dust clouds which, when resuspended by wind or traffic, contribute to levels of suspended particulate matter. This often underestimated phenomenon significantly impacts air pollution in urban areas, especially in growing cities.

Public works, earthworks and the transport of uncovered materials are some of the practices that exacerbate this pollution source.

Implementing dust reduction protocols, applying water sprays, erecting physical barriers or covering materials can significantly reduce their impact.

Natural and imported pollution (e.g. Saharan dust)

Although most urban sources are anthropogenic, natural or external contributions exist. A notable example is the transport of Saharan dust to southern Europe and Latin America. These episodes can raise PM₁₀ levels far above legal limits, even in cities with normally good air quality.

This phenomenon is monitored by satellite systems, air quality sensor networks and atmospheric dispersion models. While unavoidable, it can be anticipated and better managed if a real-time alert and analysis system is in place.

Studies like the ESCAPE project have shown that the contribution of each source varies according to the city, local meteorology, and socio-economic profile of its inhabitants, making constant and accurate air quality monitoringControlling air quality is an essential task in order to enjoy optimal environmental conditions for healthy human development and to keep the environment i...
Read more essential (Querol et al., 2019).

Effects of urban air pollution on health and the environment

The effects of urban air pollution go beyond temporary nuisances like eye irritation or unpleasant odours. Scientific evidence has shown that sustained exposure to atmospheric pollutants has serious consequences for both human health and the balance of urban ecosystems. From respiratory and cardiovascular diseases to neurological developmental disorders in children, as well as loss of biodiversity and worsening local climate change, the impact is profound, cumulative, and often invisible.

Respiratory and cardiovascular impacts

Inhalation of pollutants such as fine particulate matter (PM_2.5), nitrogen dioxide (NO₂) and tropospheric ozone (O₃) can trigger a series of inflammatory reactions in the body. These substances penetrate the lungs and even reach the circulatory system, increasing the risk of diseases such as asthma, chronic bronchitis, chronic obstructive pulmonary disease (COPD), hypertension and acute myocardial infarction.

Acute exposure, such as during pollution peaks or thermal inversion episodes, can cause immediate symptoms in sensitive individuals. However, it is chronic exposure — living for years in a city with poor air quality — that poses the greatest risk. This prolonged exposure increases the incidence of non-communicable diseases and can shorten life expectancy even in healthy individuals.

A review published in the Journal of Allergy and Clinical Immunology highlights how the combined effects of biomass smoke and urban traffic pollution are associated with a significant increase in respiratory, cardiovascular problems and premature mortality (Laumbach & Kipen, 2012).

Impact on vulnerable groups and children

Air pollution does not affect everyone equally. Vulnerable groups such as children, the elderly, pregnant women, or individuals with chronic illnesses suffer its effects more severely.

In children, exposure during key developmental stages can affect lung growth, increase asthma risk and cause cognitive impairments. Recent studies have linked prenatal exposure to elevated PM_2.5 levels with negative neurodevelopmental outcomes, including attention problems and lower academic performance.

Older adults have weaker immune systems and a higher prevalence of cardiovascular and respiratory diseases, making them more susceptible to hospitalisations or worsening conditions during high pollution events.

Protecting these groups requires strict environmental monitoring policies and real-time air quality monitoring tools capable of anticipating risks and triggering preventive measures.

Ecosystem degradation and urban heat island effect

Beyond harm to human health, air pollution disrupts the ecological balance of cities. Atmospheric pollutants directly affect urban vegetation by reducing photosynthesis, damaging leaves and flowers, and diminishing trees’ capacity to absorb CO₂. This contributes to urban biodiversity loss, which is already threatened by urban development and habitat fragmentation.

Moreover, certain particulate matter and gases like ozone exacerbate the urban heat island effect, raising average temperatures in densely built areas. This not only increases energy demand and heatwave risks but also creates a vicious cycle where greater air conditioning needs lead to higher emissions and thus more pollution.

Addressing urban air pollution effects requires an integrated vision of public health, urban planning, and environmental management. Only then can resilient, healthy, and liveable cities be designed for all.

Air quality monitoring in cities

Air monitoring in cities is a fundamental tool to diagnose the urban environmental status, protect public health, and design effective policies. Thanks to technological advances, it is now possible to complement traditional methods with more versatile, precise, and accessible solutions.

Traditional stations vs smart sensors

Historically, cities have relied on fixed reference stations to assess air quality. While these stations are extremely accurate and certified, they have a high cost and limited spatial coverage, making it difficult to fully understand pollution variability within the city.

In contrast, low-cost smart sensors allow for the deployment of denser monitoring networks, capable of capturing local variations in real time. Although individually they may be somewhat less precise, their combination with traditional stations results in hybrid networks offering the best of both worlds: scientific robustness and high spatial resolution.

This approach enables coverage of school zones, parks, busy avenues and industrial areas, providing a more complete picture of the urban environment. According to Kumar et al. (2015), the expansion of these systems has been a turning point in local environmental management, especially in developing countries’ cities.

Companies like Kunak provide advanced technological solutions combining multipoint sensors with scientific calibration and advanced platforms for data analysis and remote network management.

The importance of real-time data for public health

Access to real-time data enables rapid identification of high pollution episodes, activation of alert protocols, and reduction of exposure for vulnerable populations. Mobile apps, information panels, and early warning systems empower both citizens and urban managers.

This type of monitoring also plays a key role in public decision-making, from traffic restrictions to school schedule changes or issuing health recommendations.

In a context of rapid urbanisation and climate crisis, having an accessible and intelligent sensor network is not just an advantage, but a necessity.

Technology to make air pollution visible

For decades, air pollution has been an invisible enemy. However, thanks to advances in smart air quality monitoring, it is now possible to map, visualise and analyse pollution levels in cities in real time.

Air quality data, once limited to fixed reference stations, is now complemented by distributed sensor networks, mobile technologies and digital platforms that build high spatial and temporal resolution maps. Tools such as urban dashboards and environmental visualisation platforms offer authorities, researchers and citizens deeper and more accessible understanding of their surroundings.

Companies such as Kunak, specialised in multiparameter air quality sensors with traceable calibration, are deploying low-cost yet highly accurate solutions in industrial, school, and high-traffic areas. Other platforms like World’s Air Pollution offer open air quality data, encouraging citizen participation and collective empowerment in environmental decision-making.

This democratisation of environmental data is key to making informed decisions, activating public health protocols and raising social awareness of urban air pollution challenges.

How to improve air quality in cities

Reducing air pollution in cities is not the result of a single measure but requires a multisectoral strategy that combines regulation, urban planning, transport, and technology. Below are the fundamental pillars for building cleaner and healthier urban environments.

Governance, regulation, and public awareness

Political action is the first step. The implementation of strict environmental regulations, such as the European Union Air Quality Directives, has proven effective in reducing pollutant levels like NO₂ and particulates. These rules should be accompanied by green taxation, penalising the most polluting sources and promoting sustainable solutions.

Additionally, public awareness campaigns are essential to drive behavioural changes: from reducing private vehicle use to using cleaner stoves or avoiding agricultural burning.

An informed citizenry is key to the success of any environmental strategy.

Urban planning and access to nature

City design also determines air quality. Expanding green areas, creating ecological corridors, and facilitating urban ventilation through appropriate building layouts are strategies that help dilute pollutants and reduce average temperatures.

Urban green infrastructure, such as parks, vertical gardens, or green roofs, not only absorb CO₂ and particulates but also improve thermal comfort and the psychological wellbeing of residents.

Sustainable transport and emissions control

One of the most effective actions to reduce air pollution in cities is transforming mobility. This includes the renewal of public and private vehicle fleets, electromobility, the use of sustainable biofuels, and the creation of Low Emission Zones (LEZs) restricting access to polluting vehicles.

Intelligent traffic management systems, promotion of remote working, and clean urban logistics are complementary measures that also help reduce transport emissions.

Sustainable mobility: alternatives to the private car

Transforming urban mobility is one of the most powerful tools to improve air quality and advance towards the Sustainable Development Goals (SDG 11: Sustainable Cities and SDG 13: Climate Action). Betting on a more efficient, equitable, and clean transport system means diversifying available options and encouraging their use.

Cycling infrastructure and walking promotion

Creating networks of safe, continuous, and connected cycle lanes, alongside pedestrian streets and accessible pavements, makes it easier for more people to choose active travel. This reduces emissions, improves health, and boosts local commerce.

Cities like Paris, Bogotá, and Mexico City have demonstrated that with political will and smart design, cycling can be integrated as a daily mode of transport.

Public transport efficiency and coverage

A reliable, affordable, and extensive public transport system is essential to reduce car dependence. Investments in metro, trams, commuter trains, and electric buses help meet urban mobility demand with lower emissions and better accessibility.

Integrated payment systems, real-time tracking apps, and social subsidy policies are key factors to increase public transport use.

Shared mobility and electrification

Shared mobility —such as carsharing, electric scooters, or public bikes— offers flexibility and reduces the need to own a car. Combined with robust charging infrastructure, urban transport electrification is a major lever for decarbonising mobility.

Together, these measures not only improve air quality but also reduce noiseImagine waking up every morning at 5:00 a.m. to the relentless roar of a motorway just metres from your window. Experiencing such high-intensity noise is n...
Read more, free up public space, and build fairer, healthier, and more resilient cities.

The 15-minute city: everything within easy reach

The concept of the 15-minute city, developed by Franco-Colombian urbanist Carlos Moreno, proposes a model where citizens can access all essential services —work, health, education, shopping, and leisure— within a 15-minute walk or bike ride from home. This idea, which gained prominence post-pandemic, aims to make cities more sustainable, resilient, and human-centred.

Applying this approach drastically reduces private car dependency by minimising long journeys and fostering sustainable mobility in cities. This not only lowers emissions of pollutants like NO₂ and PM but also improves public health and strengthens urban social fabric.

Cities such as Paris, under Mayor Anne Hidalgo, have embraced this model by transforming streets into pedestrian zones, promoting cycling, and encouraging decentralised service provision. Barcelona, with its superblocks programme, has begun implementing similar strategies, limiting traffic in residential areas to prioritise pedestrians and cyclists.

According to Moreno et al. (2021), this urban model promotes local identity, spatial equity, and emissions reduction, all aligned with the principles of sustainable urban development.

Low emission zones (LEZs) and clean air policies

What are LEZs and how do they work?

Low emission zones (LEZs) are urban areas where access is restricted for the most polluting vehicles, according to their environmental classification. These measures aim to reduce atmospheric pollutant concentrations, especially in areas with high population density or traffic.

LEZs usually operate through control cameras, environmental badges, differentiated fees or driving bans. The goal is to promote the use of less polluting vehicles, public transport, and alternative modes.

Impact of LEZs on air quality

Several studies have shown that implementing LEZs helps reduce nitrogen dioxide (NO₂) and particulate matter (PM)Atmospheric particulate matter are microscopic elements suspended in the air, consisting of solid and liquid substances. They have a wide range of sizes an...
Read more levels, particularly on main avenues and urban centres. They also improve public perception of air quality and encourage changes in mobility habits.

The success of these zones depends on proper planning, communication, enforcement, and smart air quality monitoring systems that allow for real-time evaluation and policy adjustments.

Implementation in the UK and Europe

London pioneered its Ultra Low Emission Zone (ULEZ), which has cut NO₂ emissions by over 40% since inception. Madrid and Milan have implemented similar zones with significant improvements in urban air quality, especially in historic and school areas.

The push for LEZs is part of a broader European trend to meet climate neutrality goals, protect public health, and comply with EU air quality directives.

Frequently asked questions about urban air pollution

What is the main cause of pollution in cities?

The main cause of urban air pollution is motorised traffic. Combustion vehicles emit nitrogen oxides, fine particles, and other pollutants that accumulate in heavily trafficked areas. Industrial sources, domestic heating, construction, and meteorological conditions that hinder dispersion also contribute. In many cities, urban design and lack of efficient public transport add to excessive private car use.

How does pollution affect citizens’ health?

Air pollution in cities is directly linked to respiratory diseases such as asthma, bronchitis and COPD, as well as cardiovascular diseases and even cancer. Prolonged exposure can also impact neurological development in children and reduce life expectancy. According to WHO, it causes millions of premature deaths annually. The most vulnerable groups are children, the elderly, pregnant women, and residents near busy roads.

Which cities have the worst air quality?

Cities with the poorest air quality are often in rapidly urbanising countries with dense traffic and weak industrial regulation. Some of the worst affected include Delhi, Dhaka, Lahore, and Mexico City. However, severe pollution episodes also occur in European cities during winter. Air quality varies daily, so smart air quality monitoring is essential to understand actual exposure at each location.

Can smart monitoring improve urban air quality?

Yes. Air monitoring in cities using smart sensors helps detect hotspots, identify pollution sources, and trigger corrective actions in real time. This facilitates more effective decision-making by local authorities and empowers citizens with accessible information. Sensor networks such as those provided by Kunak support public policies, low emission zones, and health alerts based on reliable and updated data.

What can individuals do to reduce pollution?

At an individual level, you can help by choosing sustainable mobility in cities: walking, cycling, or using public transport. Reducing car use, avoiding waste burning, improving home insulation, and using clean energy for heating are also key measures. Additionally, staying informed, supporting environmental policies, and demanding transparency in air quality data can create positive pressure to achieve healthier urban environments.

Conclusion – towards cleaner and healthier cities

Urban air pollution is a complex challenge requiring integrated responses. This article has explored its multifactorial causes —from traffic and industry to domestic heating and urban design— and its harmful effects on health, environment, and quality of life.

Viable and mature solutions exist to monitor, mitigate and prevent atmospheric pollution in urban areas. Combining smart sensors, effective regulation, transport transformation, and new urban models —like the 15-minute city and low emission zones— offers hope for a cleaner, more resilient future.

But achieving this change requires more than technology. It demands active collaboration among governments, businesses, scientific communities, and citizens. Municipalities must make bold decisions, companies must embrace sustainability strategically, and individuals must inform themselves and act responsibly.

Clean air is not a privilege: it is a basic environmental right and a necessary condition to achieve the Sustainable Development Goals. Investing in innovation, participation, and environmental justiceEnvironmental justice on air quality issues is crucial to ensure that all communities, especially those in areas of high traffic and industrial activity, a...
Read more will not only improve air quality but also make our cities more livable, equitable, and future-ready.

The transformation is already underway. The time to act is now.

References

1. World Health Organization. (2021). Ambient air pollution: Health impacts.
   https://www.who.int/news-room/fact-sheets/detail/ambient-(outdoor)-air-quality-and-health
2. Querol, X., Amato, F., Alastuey, A., et al. (2019). Monitoring the impact of air pollution on human health in urban environments: The ESCAPE Project. Science of The Total Environment, 685, 963–975. https://doi.org/10.1016/j.scitotenv.2019.05.274
3. Laumbach, R., & Kipen, H. (2012). Respiratory health effects of air pollution: Update on biomass smoke and traffic pollution. Journal of Allergy and Clinical Immunology, 129(1), 3–11. https://doi.org/10.1016/j.jaci.2011.11.021
4. Kumar, P., Morawska, L., Martani, C., et al. (2015). The rise of low-cost sensing for managing air pollution in cities. Environment International, 75, 199–205.
   https://doi.org/10.1016/j.envint.2014.11.019
5. Moreno, C., Allam, Z., Chabaud, D., Gall, C., & Pratlong, F. (2021). Introducing the “15-minute city”: Sustainability, resilience and place identity in future post-pandemic cities. Smart Cities, 4(1), 93–111. https://doi.org/10.3390/smartcities4010006