The Harmful Impact Of Gases: Which Pollutes More?

Air pollution is a major concern, causing millions of deaths each year. It is caused by the presence of dangerous substances in the atmosphere, including gases, at concentrations high enough and for long enough durations to cause harm. These gases are emitted from both human-made and natural sources. Human-made sources include vehicle emissions, fuel oils, natural gas, and by-products of manufacturing and power generation. Natural sources include smoke from wildfires, ash and gases from volcanic eruptions, and gases emitted from decomposing organic matter in soils. The gases that cause the most air pollution include nitrogen oxide (NOx), volatile organic compounds (VOCs), carbon dioxide (CO2), sulphur oxide (SOx), and fluorinated gases such as hydrofluorocarbons and perfluorocarbons. These gases can have direct and indirect impacts on human health, leading to respiratory and cardiovascular problems, cancer, and even death.

Nitrogen oxide (NOx)

NOx gases are primarily emitted from vehicles burning gasoline and diesel, with trucks, buses, and cars being the biggest sources of nitrogen dioxide emissions. They are typically found in areas with heavy traffic, such as large cities, where they can have detrimental effects on people and the environment. Exposure to NOx gases can cause headaches and respiratory problems, and they also contribute to the formation of ground-level ozone, smog, and acid rain.

In addition to vehicle emissions, industrial processes such as oil and gas production, power plants, and boilers also contribute to NOx pollution. The combustion of nitrogen-containing fuels like coal and the use of nitrogen-fixing plants in agriculture further increase NOx levels in the atmosphere. NOx gases react with other compounds to form particulate matter, such as PM2.5, which is harmful to human health due to its ability to penetrate sensitive and deep parts of the lungs.

Furthermore, NOx plays a role in the formation of ground-level ozone, often referred to as the "'bad'" ozone. This type of ozone is formed when NOx reacts with volatile organic compounds (VOCs) and sunlight, creating a dense barrier that traps heat and reduces visibility. Ground-level ozone is of particular concern for children, the elderly, and people with lung diseases, as it can exacerbate breathing difficulties and other respiratory issues.

While human activities are a significant source of NOx pollution, it is worth noting that NOx can also be produced naturally by lightning. However, the occurrence of lightning-produced NOx depends on geographic location and seasonal variations.

Volatile Organic Compounds (VOCs)

VOCs are of particular concern in indoor environments, where concentrations can be up to 10 times higher than outdoors. VOCs can cause serious health issues such as eye, nose, and throat irritation, headaches, nausea, dizziness, and difficulty breathing. Long-term exposure to VOCs can damage vital organs, including the liver and kidneys, and the central nervous system, and some VOCs are linked to cancer. They may also worsen symptoms for people with asthma and COPD.

The high vapor pressure of VOCs is due to their low boiling point, which relates to the number of the sample's molecules in the surrounding air, known as volatility. VOCs with lower boiling points are more likely to be emitted from products or surfaces and are found mostly as gases in the air rather than in materials or on surfaces.

The European Union defines a VOC as "any organic compound as well as the fraction of creosote, having at 293.15 K a vapour pressure of 0.01 kPa or more, or having a corresponding volatility under the particular conditions of use". The VOC Solvents Emissions Directive was the main policy instrument for reducing industrial emissions of VOCs in the European Union, covering activities such as printing, surface cleaning, and vehicle coating.

Carbon dioxide (CO2)

The amount of carbon dioxide in the atmosphere has increased alongside human emissions since the start of the Industrial Revolution in 1750. Before this time, emissions were very low, and growth in emissions was slow until the middle of the 20th century. By 1950, the world emitted 6 billion tonnes of CO2 annually, which quadrupled to over 20 billion tonnes by 1990. This number has continued to grow, and we now emit over 35 billion tonnes of CO2 each year. The annual rate of increase in atmospheric carbon dioxide over the past 60 years is about 100 times faster than previous natural increases. The global average carbon dioxide set a new record high in 2023 at 419.3 parts per million.

Human activities, such as industry and transportation, are the main drivers of increasing carbon dioxide emissions. Each year, human activities release more carbon dioxide into the atmosphere than natural processes can remove. While emissions from fossil fuels have not yet peaked, they have increased rapidly over the last 50 years. Fossil fuel emissions are still rising, and current policies to reduce or slow the growth of CO2 emissions have only slightly curbed the problem. The world needs to decarbonize and reach net-zero emissions to stabilize or reduce concentrations of CO2 in the atmosphere.

Carbon dioxide in the atmosphere can have several negative effects on human health and the environment. High concentrations of CO2 and other gases in the air can cause undesirable health, economic, or aesthetic effects. Direct exposure to certain gases can have acute effects on health, especially for people with existing respiratory conditions such as asthma or chronic obstructive pulmonary disease (COPD). Additionally, carbon dioxide contributes to the formation of particulate matter, which is made up of smaller particles that can enter our lungs, airways, and bloodstream, causing respiratory and cardiovascular problems, including cancer, strokes, and heart attacks.

Sulphur oxide (SOx)

SOx emissions are regulated by the UN Convention on Long-range Transboundary Air Pollution (CLRTAP) and the UN Framework Convention on Climate Change (UNFCCC). Regulation 14 provides limit values and means of compliance for SOx emissions. For instance, the regulation requires fuel oil suppliers to state the sulphur content of the fuel on the bunker delivery note. This is to ensure that the fuel oil used does not exceed the applicable limit for sulphur content.

SOx emissions have decreased in recent years due to the introduction of pollution controls and a shift away from coal in some regions. In 2020, global SO2 emissions had almost halved since their peak in 1979, with significant reductions in Europe, North America, and China. Technologies that filter or "scrub" SO2 from smokestacks in coal plants have contributed to this decline.

Sulphur oxides are emitted into the atmosphere from both natural and anthropogenic sources. Volcanic activity is the largest natural source of SOx on a global scale. Anthropogenic sources include the combustion of sulphur-containing fuels, such as coal and fuel oil, and industrial processes using sulphur-containing raw materials and additives. Sulphur dioxide is used in various industries, such as a bleach, disinfectant, and food preservation.

Fluorinated gases

F-gases are considered greenhouse gases with a strong global warming potential, and their use is regulated due to their environmental impact. They have a high global warming potential (GWP), and some F-gases are extremely long-lived in the atmosphere, with HFCs remaining for decades and PFCs and SF6 persisting for millennia. As of 2015, HFC-134a (1,1,1,2-Tetrafluoroethane) was the most abundant HFC in Earth's atmosphere, while PFC-14 (Carbon tetrafluoride) was the most prevalent PFC.

The production and use of F-gases have increased rapidly since the mid-twentieth century, marking the beginning of their industrial-scale utilization. In 2019, these man-made gases were responsible for about one-tenth of the direct radiative forcing from all long-lived anthropogenic greenhouse gases. To address their potential contribution to global warming, the European Union enacted legislation in 2006, such as the F-gas Regulation, to control their use and promote containment and recovery.

International efforts to regulate F-gases have also been made. The Kigali Amendment under the Montreal Protocol, signed in 2016, mandates a phased elimination of CFC gases. The United States, under the American Innovation and Manufacturing Act, aims for an 85% reduction in HFC refrigerant production and consumption by 2035. Additionally, the US has proposed a joint initiative with Mexico and the Federated States of Micronesia to reduce HFCs by 2030.

While F-gases are ozone-friendly and relatively safe for the public due to low toxicity and flammability, their impact on global warming and long atmospheric lifetimes make them a significant concern in the context of climate change and environmental sustainability.

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