Air Pollution's Global Reach: How Does It Spread?

Air pollution is a pressing issue that affects the health of the planet and humans alike. It consists of chemicals or particles in the air that can harm the health of humans, animals, and plants, and even damage buildings. Air pollution is distributed by air patterns and wind cycles around the world, but also through precipitation and transportation of food. While most air pollution is created by the burning of fossil fuels, it can also be caused by household combustion devices, motor vehicles, industrial facilities, and forest fires. This has led to an increase in greenhouse gas emissions, causing global warming and climate change. As a result, countries are phasing out the production of chemicals that deplete the ozone layer and implementing strategies to reduce air pollution. Despite these efforts, air pollution continues to spread and harm people's health worldwide, with low- and middle-income countries suffering the most.

Climate change and air quality

Air pollution and climate change are deeply interconnected. The chemical species that lead to a degradation in air quality are frequently co-emitted with greenhouse gases. Drier and hotter conditions can increase air pollution, particularly ozone, by increasing the rates of photochemical production. Climate change will also lead to more wildfires, which will increase emissions of harmful greenhouse gases and particulate matter.

Air pollution is distributed by air patterns and wind cycles around the world, but also through precipitation and the transportation of food. Research has found that ozone, particulate matter, nitrogen dioxide, and sulfur dioxide pollution from China have made their way to the west coast of the United States. This means that prolific polluters can harm the health of people in areas that do not pollute to the same extent.

The World Health Organization (WHO) promotes interventions and initiatives for healthy sectoral policies, addressing key risks to health from indoor and outdoor air pollution, and contributing to achieving health co-benefits from climate change mitigation policies. WHO provides technical support to its member states in the development of normative guidance, tools, and authoritative advice on health issues related to air pollution and its sources. WHO also monitors and reports on global trends and changes in health outcomes associated with actions taken to address air pollution at the national, regional, and global levels.

Research on climate change and air quality includes developing and verifying air pollution emissions inventories, modeling chemical transport of air pollutants emitted into the atmosphere, and quantifying the health and economic benefits of reducing air pollution and emissions of climate forcers.

Wildfires and air pollution

Air pollution is a global issue, and it is not limited to the communities where it originates. Air pollution travels through various means, including air patterns, wind cycles, precipitation, and transportation. Forest fires are a common source of air pollution, and wildfires, in particular, contribute significantly to the spread of harmful air pollutants.

Wildfires produce a range of dangerous air pollutants, from cancer-causing substances to minuscule particles that can aggravate pre-existing health issues and elevate the risk of heart attacks or strokes. The particulate matter (PM) from wildfire smoke is of utmost concern for public health, especially in the short term. These particles are incredibly small, measuring 2.5 micrometers or less in diameter, allowing them to infiltrate the lungs easily. The tiniest particles, known as ultrafine particles, can even enter the bloodstream directly. The correlation between PM2.5 exposure and adverse effects on heart and lung health is well-established in scientific research.

The particles generated by wildfires can be categorized into two main groups based on their aerodynamic diameter: coarse particles and fine particles. Coarse particles, denoted as PM10-2.5, typically have diameters larger than 2.5 micrometers but smaller than or equal to 10 micrometers. While coarse particles are predominantly associated with mechanical operations like construction and agriculture, they are also present in wildfire smoke to a lesser extent. On the other hand, fine particles, denoted as PM2.5, have diameters of 2.5 micrometers or less and constitute the primary pollutant released by wildfire smoke, accounting for approximately 90% of the total particle mass. These fine particles are of the utmost health concern, and this category includes ultrafine particles with diameters of less than 0.1 micrometers.

During wildfires, the concentration of particles in the air can increase significantly, becoming visible to the naked eye. This increase in particle pollution poses a severe health risk, especially to individuals with pre-existing cardiovascular or respiratory diseases, older adults, children, pregnant women, outdoor workers, and those of lower socioeconomic status. The health effects of exposure to wildfire smoke have been extensively studied, with research indicating similar adverse outcomes from fine particles attributed to wildfire smoke compared to those from other sources.

To mitigate the health risks associated with wildfire smoke, it is crucial to prioritize staying indoors with windows and doors closed when air quality deteriorates to dangerous levels. For those with central-ducted air conditioning and heating systems, setting the system to "on" ensures constant air filtration. Additionally, installing high-efficiency air filters (MERV 13 or higher) and using air cleaners can significantly reduce indoor particle levels. During evacuation, it is imperative to follow official orders, operate vehicles with closed windows and the air conditioner set to recirculate, and avoid outdoor exercises or activities that could increase indoor pollution, such as burning candles or using gas stoves.

Air pollution in large cities

The primary sources of outdoor air pollution in large cities are vehicle emissions, coal-burning power plants, industrial emissions, and residential energy use. The burning of fossil fuels, such as coal, natural gas, and oil, releases harmful chemicals and particles into the atmosphere, which can have detrimental effects on human health and the environment. Fine particulate matter, for example, can cause respiratory issues, heart disease, and lung cancer. The small size of these particles means they can easily enter the lungs and even the bloodstream.

Large cities with dense populations tend to have higher levels of vehicle usage and, consequently, higher tailpipe emissions. Population density also influences transportation demand, with more people travelling longer distances, further adding to emissions. Economic development and growth also play a significant role in air pollution in large cities. As economic activities increase, so do energy consumption and industrial processes, contributing to higher levels of air pollution.

Air pollution does not remain localised and can spread globally through air patterns and wind cycles. For example, air pollution from China has been carried by westerly winds to the west coast of the United States, increasing ozone pollution in that region. This demonstrates how air pollution in large cities can have far-reaching impacts, affecting areas with lower levels of local pollution.

Interventions targeting pollution at the local level have proven effective in some large cities. For instance, Beijing, China, managed to reduce PM2.5 levels by 36% in five years by implementing controls on power plant and industrial emissions, as well as introducing new fuel quality and vehicle emission standards. Similarly, London's Ultra Low Emission Zone initiative resulted in a significant reduction of NO2 levels in just six months. These examples highlight the importance of local policies and initiatives in improving air quality in large cities.

Indoor air pollution

The use of such fuels and technologies in poorly ventilated dwellings can result in indoor smoke containing fine particles at levels 100 times higher than what is considered acceptable. Women and children, who typically spend the most time near the domestic hearth and are responsible for household chores like cooking and collecting firewood, bear the brunt of the health impacts. The exposure to indoor air pollution has been linked to non-communicable diseases, including stroke, ischaemic heart disease, chronic obstructive pulmonary disease (COPD), and lung cancer. It can also exacerbate existing conditions such as asthma.

To address indoor air pollution, the WHO has developed guidelines for indoor air quality and household fuel combustion. These guidelines provide recommendations on the types of clean fuels and technologies that can be used to protect health. Additionally, organizations like the US Environmental Protection Agency (EPA) offer resources and guidance on improving indoor air quality. They emphasize the importance of testing for and reducing radon levels, preventing mold, maintaining a smoke-free environment, installing carbon monoxide alarms, and properly ventilating homes.

The impacts of indoor air pollution can be severe and far-reaching, affecting not only the individuals directly exposed but also contributing to the global burden of air pollution. It is, therefore, crucial to prioritize initiatives that promote the adoption of cleaner household fuels and technologies, raise awareness about the risks of indoor air pollution, and implement effective strategies to improve indoor air quality worldwide.

Outdoor air pollution

The impact of outdoor air pollution is particularly severe in low- and middle-income countries, where 89% of premature deaths related to this type of pollution occur. This is due to a combination of indoor and outdoor factors. Indoor pollution rates tend to be high in low-income countries due to the reliance on solid fuels, such as firewood, crop waste, and dung for cooking and heating. As countries industrialize and transition from low to middle-income levels, outdoor air pollution tends to increase. This is because industrialization often leads to greater energy use and production, which are major sources of air pollution.

The good news is that regulatory and voluntary actions can reduce anthropogenic (human-caused) emissions, leading to improved air quality. For example, the United States has achieved significant reductions in air pollution levels of sulfur dioxide, particulate matter (PM10), nitrous oxides, and volatile organic compounds. Additionally, the WHO provides support to member states by offering evidence-based policies, building institutional capacity, and leveraging health arguments to address air pollution.

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