Understanding Pm2.5 Pollution: Causes And Origins

Fine particulate matter (PM2.5) is a pollutant that causes serious health issues and even death. It is a mixture of solid and liquid particles that are 2.5 microns or smaller in size, which means they can enter the bloodstream through the lungs and cause issues with the respiratory and circulatory systems. Sources of PM2.5 include coal and other fossil fuel-burning power plants, vehicle emissions, industrial emissions, and human and natural sources. Urbanization and industrialization are the two main socioeconomic drivers of PM2.5, and population growth and migration have also contributed to the increase in PM2.5 pollution. While particulate pollution is harmful to everyone, certain populations are more vulnerable, including the elderly, infants, young children, and anyone with heart or lung disease.

Characteristics and Values of PM2.5 Pollution Causes

Urbanization and industrialization

Developing countries that are in the process of rapid urbanization and industrialization are suffering from severe air pollution, and their populations are exposed to high levels of particulate matter. For example, in January 2013, northern China experienced a prolonged smog event, during which PM2.5 levels peaked at over 800 μg/m3—32 times higher than the World Health Organization's guideline value.

In addition, the combustion of fuels, such as gasoline, oil, and diesel, which is commonly used in both urban and industrial settings, produces a significant amount of PM2.5 pollution. The particles emitted during combustion are often very small and can remain suspended in the air for long periods, contributing to haze and reduced visibility.

The relationship between urbanization, industrialization, and PM2.5 pollution is complex and influenced by various factors, including landscape patterns, land use, and economic development. Studies have shown that the composition and configuration of urban landscapes can impact air pollution levels. For example, narrower roads in historical urban areas have been associated with lower noise pollution but higher concentrations of certain pollutants due to the street canyon effect.

Population growth and migration

In India, for instance, the Financial Times analysed NASA satellite data and found that over 40% of Indians are exposed to particulate matter levels five times higher than the safe limit. This is partly due to crop-burning practices, which cause a significant increase in PM2.5 levels during the crop-burning season in November. The wind spreads a thick haze of smoke across the Indo-Gangetic Plain, affecting cities like Delhi.

Similarly, South Korea's proximity to China, a country with high emissions, contributes to its air pollution challenges. However, South Korea also faces issues due to its own industrial and human activities, demonstrating the impact of population growth and migration on PM2.5 pollution within a country's borders.

The correlation between population growth and PM2.5 pollution is evident in regions with weaker air pollution controls, such as East Asia. In contrast, regions like Europe and North America have seen a weakening correlation due to stricter controls and improved air quality. This highlights the importance of implementing strategies to reduce industrial emissions, transition to cleaner energy sources, and address transportation-related pollution to mitigate the impact of population growth and migration on PM2.5 pollution.

Furthermore, population ageing intersects with population growth to exacerbate the health impacts of PM2.5 pollution. Older adults are more vulnerable to the adverse health effects of air pollution, and as the global population ages, the health costs associated with PM2.5 exposure increase disproportionately. This highlights the urgency of addressing PM2.5 pollution, especially in regions with ageing populations, to mitigate the health and economic burdens on society.

Vehicle emissions

The impact of vehicle emissions on PM2.5 levels varies depending on spatial and temporal factors. For example, in certain cities like Beijing, Shanghai, Guangzhou, and Xi'an, traffic contributes about 7% of PM2.5 pollution, while in Warsaw, Poland, and Hamburg, Germany, traffic is responsible for about 18-21% of PM2.5 exposure. In the United States, the Environmental Protection Agency (EPA) estimates that transportation accounts for less than 10% of PM2.5 emissions, although other studies suggest that road transportation contributes to roughly a quarter of PM2.5-related mortalities in the country.

The adverse health effects of PM2.5 pollution are well-documented. Short-term exposures to high levels of PM2.5 have been linked to increased hospital admissions for heart and lung-related issues, acute and chronic bronchitis, asthma attacks, and respiratory symptoms, particularly in infants, children, and older adults with pre-existing heart or lung diseases. Long-term exposure to PM2.5 has even more severe consequences, including reduced lung function growth in children and increased risk of premature death, especially in individuals with chronic heart or lung conditions.

To mitigate the impact of vehicle emissions on PM2.5 pollution, various strategies have been implemented. These include air pollution removal measures, such as utilizing natural areas like forestlands and shrublands, which act as natural air purifiers. Additionally, source control measures, such as end-of-pipe control policies and energy-climate policies, have proven successful in improving air quality and reducing PM2.5 concentrations.

It is worth noting that the relationship between vehicle emissions and PM2.5 pollution is complex and influenced by various factors. While reducing emissions from vehicles is crucial, it is also important to address other sources of PM2.5 pollution, such as industrialization and urbanization, and population growth, to effectively improve air quality and protect public health.

Industrial emissions

In the context of industrial emissions, PM2.5 pollution primarily arises from two sources: industrial combustion and industrial processes. Industrial combustion refers to the burning of fuels on manufacturing and construction sites to generate energy for various industrial applications, such as powering machinery or creating heat for industrial processes. This practice can release fine particulate matter into the atmosphere, contributing to PM2.5 pollution levels.

Industrial processes and product use, on the other hand, encompass specific industrial production processes that often require fuel combustion. For example, the production of steel involves intense heat and energy, generating PM2.5 emissions. Additionally, the use of manufactured products, both industrial and non-industrial, can contribute to PM2.5 pollution. This includes the use of solvents, adhesives, and lubricants in industrial settings, as well as activities like cigarette smoking in non-industrial contexts.

The impact of industrial emissions on PM2.5 pollution varies across different regions. Developing countries undergoing rapid urbanization and industrialization, such as India, China, and Southeast Asian nations, tend to suffer from severe air pollution, including elevated levels of PM2.5. For instance, in 2013, northern China experienced a prolonged smog episode where PM2.5 levels exceeded the World Health Organization's guideline value by 32 times. Similarly, in 2013, Southeast Asia was engulfed by a severe haze that pushed PM2.5 accumulations to 329 μg/m3.

On the other hand, developed countries with high levels of urbanization and industrialization, such as the United States and Western Europe, have managed to maintain PM2.5 accumulation levels close to the natural background accumulation. This discrepancy is partly due to the implementation of air pollution controls and improved emission standards in developed countries, whereas developing countries may have more lenient regulations or face challenges in enforcing environmental protections.

Long-range transport of pollution

Long-range transport (LRT) of air pollutants from a range of sources can significantly increase background pollution levels, especially in urban areas. This can exacerbate high-pollution episodes and episodes of poor air quality.

In the Aburrá Valley (AV) in Colombia, and other cities in northern South America, biomass burning (BB), dust, and volcanic degassing have been identified as sources of long-range aerosol transport. BB contributed the most to PM2.5 levels during LRT events, with other substantial contributions from dust and volcanic events. African dust has been found to reach the Andean region via the Caribbean route. The Orinoco and the Middle Magdalena Valley have been identified as sizable sources of BB aerosols, and Nevado del Ruiz is a source of volcanic aerosols.

In China, PM2.5 driven by cold surges from the ground level has been found to travel up to 2000 km from northern to southern China within two days. In February 2015, two cold surges travelling from north China caused a temporary increase in the concentration of PM2.5 in Shanghai, with the concentration in Xiamen reaching 80 µg/m3, double the average. The transport distance of air pollutants depends on meteorological conditions, such as wind direction and speed, and varies with the lifespan, deposition velocities, and altitude of the pollutants. Pollutants with longer lifespans and lower deposition velocities can reach higher altitudes and be transported over greater distances.

Long-range transport of air pollution has also been observed in other regions. For example, Asian air pollution has been transported to North America, and Siberian biomass burning emissions have impacted surface ozone in western North America. South Korea has faced air pollution problems due to its proximity to China, as well as industrial and human activity within its own borders.

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