Air Pollution's Nitrogen Problem: How Much Is Too Much?

Nitrogen pollution is a pressing issue threatening the environment, human health, climate, and ecosystems. Nitrogen is the most abundant element in Earth's atmosphere, with 78% of the air we breathe comprising nitrogen. However, human activities have disrupted the natural nitrogen cycle, leading to excessive nitrogen waste and pollution. Nitrogen dioxide (NO2), a significant component of traffic-related air pollution, is a major contributor to poor air quality, particularly in densely populated urban areas. NO2 is formed by burning fossil fuels such as coal, oil, gas, or diesel at high temperatures, and it poses various health risks, including respiratory issues and adverse effects on lung development in children. Additionally, nitrogen in its active form, such as in fertilizers, contributes to climate change by releasing nitrous oxide, a greenhouse gas with a warming potential 300 times greater than carbon dioxide. The impact of nitrogen pollution is economically significant, costing the global economy up to $3.4 trillion annually. Addressing nitrogen pollution requires a multifaceted approach, including sustainable nitrogen management and collaborative efforts among countries to reduce nitrogen waste and limit harmful emissions.

Nitrogen dioxide (NO2) is a major air pollutant

Nitrogen is the most abundant element in our atmosphere, making up 78% of it. However, this nitrogen is unusable by most organisms. In the past 150 years, human-driven flows of reactive nitrogen have increased tenfold, contributing to a dangerous accumulation of unused reactive nitrogen. Nitrogen pollution is a pressing issue, threatening our environment, health, climate, and ecosystems.

NO2 is formed when fossil fuels such as coal, oil, gas, methane, or diesel are burned at high temperatures. It is a major component of vehicle exhaust and is often used as a proxy for tracking traffic-related air pollution. Trucks, buses, and cars are the largest sources of NO2 emissions, followed by industrial processes such as oil and gas production, and coal-fired power plants. NO2 levels are higher on or near heavily traveled roadways, with some of the highest levels seen in high-income countries, North Africa, and the Middle East.

NO2 exposure can irritate the airways and is linked to more frequent and severe asthma symptoms. It may also increase a child's likelihood of developing asthma and can impair lung development. Scientific evidence suggests that exposure to NO2 could be linked to asthma in children and is associated with emergency department and hospital admissions. In 2021, exposure to NO2 was linked to 177,000 healthy years of life lost for children and adolescents.

NO2 is formed by burning fossil fuels

Nitrogen pollution is one of the most pressing pollution issues today, threatening the environment, human health, climate, and ecosystems. Nitrogen dioxide (NO2) is a gaseous air pollutant composed of nitrogen and oxygen. NO2 is formed when fossil fuels such as coal, oil, methane gas (natural gas), liquified petroleum gas (LPG), kerosene, or diesel are burned at high temperatures.

NO2 is one of a group of related gases called nitrogen oxides or NOx. The combustion of fossil fuels releases NOx gases, which are highly reactive and poisonous. The two major nitrogen oxides produced during combustion are nitric oxide (NO) and NO2. The higher the combustion temperature, the more nitric oxide is generated. Typically, 90-95% of nitrogen oxides are emitted as nitric oxide, and only 5-10% as nitrogen dioxide. However, in ambient conditions, nitric oxide rapidly oxidizes in the air to form nitrogen dioxide, which is then considered the primary pollutant.

NO2 is primarily produced outdoors through the burning of fossil fuels by trucks, buses, cars, and industrial sources such as power plants, industrial boilers, and coal-fired power plants. Monitors show that large urban regions, such as the Northeast corridor, Chicago, and Los Angeles, have the highest concentrations of outdoor NO2. Levels are also higher on or near heavily traveled roadways. Indoors, NO2 is produced by burning fuels like wood, gas, kerosene, and coal for cooking, heating, or other purposes, especially if the appliances are not fully vented to the outside.

NO2 and other nitrogen oxides contribute to particle pollution and the formation of ozone in the atmosphere. They are also greenhouse gases that intensify the greenhouse effect, increasing the Earth's average air temperatures. Additionally, NO2 has harmful effects on human health, particularly the respiratory system, and can increase the likelihood of hospital admissions. Scientific evidence suggests that exposure to NO2 may cause asthma in children.

NO2 is a pungent reddish-brown gas

Nitrogen is the most abundant element in our atmosphere, making up about 78% of the air we breathe. However, most organisms cannot use this nitrogen in its atmospheric form. In the past 150 years, human activities have caused a tenfold increase in the amount of reactive nitrogen in the atmosphere, contributing to a growing pollution problem. Nitrogen dioxide (NO2) is one of the main pollutants, a chemical compound composed of nitrogen and oxygen.

NO2 is a reddish-brown gas with a pungent odour. It is heavier than air and has a boiling point of 21.15°C. In its liquid form, NO2 is colourless to brown. At room temperature, it is a volatile gas and has a pungent odour at concentrations as low as 0.1 ppm.

NO2 is formed when fossil fuels such as coal, oil, gas, diesel, and methane are burned at high temperatures. It is also a product of combustion processes such as internal combustion engines and industrial production. As a result, road traffic is the primary outdoor source of NO2 pollution, with trucks, buses, and cars being the largest emitters. Other significant sources include industrial processes, such as oil and gas production, and coal-fired power plants.

Indoors, exposure to NO2 arises from tobacco smoke and the burning of fuels like wood, gas, oil, kerosene, and coal in appliances like stoves, ovens, heaters, and fireplaces. Cooking with a gas stove, in particular, is associated with poor indoor air quality and increased NO2 concentrations, which can lead to respiratory issues and diseases.

NO2 is a harmful pollutant that can cause changes in lung function and increase the likelihood of hospital admissions for respiratory issues. Scientific evidence suggests that exposure to NO2 may cause asthma in children. It is also one of the gases that contribute to the formation of ozone and acid rain, which harm ecosystems such as lakes and forests.

NO2 is a health risk, especially for children

Nitrogen Dioxide (NO2) is a pungent gas that contributes to the reddish-brown haze that hangs over cities like Los Angeles and is a major component of smog. NO2 is formed when fossil fuels such as coal, oil, gas, diesel, or natural gas are burned at high temperatures. It is also produced from tobacco smoke, gas-, wood-, oil-, kerosene- and coal-burning appliances, and industrial processes such as oil and gas production.

NO2 is a significant health risk, especially for children. Children are at particular risk because they have a higher breathing rate relative to their body weight and typically spend more time outdoors. Several studies have shown that long-term exposure to NO2 during childhood can lead to smaller lungs at maturity, with higher levels of exposure linked to reduced lung function. Controlled human exposure studies have also found that NO2 exposure can intensify responses to allergens in allergic asthmatics, and epidemiological studies have demonstrated associations between NO2 exposure and premature death, cardiopulmonary effects, respiratory symptoms, and emergency room visits for asthma.

The Pollution and the Young (PATY) project assembled health and exposure data for 58,561 children from 12 countries and found robust evidence for associations between NO2 and respiratory symptoms, particularly for inhalation allergies. Increased levels of NO2 were related to a higher risk of allergy to pets and sensitivity to inhaled allergens, with odds ratios consistently higher in older children. Several studies have also reported greater NO2 effects in girls, although the evidence is mixed.

In addition to the health risks posed by NO2 itself, it is important to note that NO2 contributes to the formation of other harmful air pollutants, including ozone (O3), particulate matter, nitric acid (HNO3), and nitrate (NO3-) -containing particles. These pollutants can have further detrimental effects on respiratory health, particularly for children with asthma, who have a greater degree of airway responsiveness compared to adult asthmatics.

Given the health risks associated with NO2 exposure, particularly for children, it is essential to address the sources of nitrogen pollution and implement strategies to reduce NO2 emissions. The US EPA, for example, identifies areas that do not meet national NO2 standards and works with state, local, and tribal governments to develop plans to improve air quality.

Nitrogen pollution is a global crisis

Nitrogen is the most abundant element in our atmosphere, accounting for about 78% of the air we breathe. However, this atmospheric nitrogen is not directly usable by most organisms. Through natural and artificial processes, nitrogen can become "reactive," leading to the production of fertilizers and a subsequent increase in global food production. While this has revolutionized agriculture, it has also contributed to a dangerous accumulation of unused reactive nitrogen.

One of the primary forms of nitrogen pollution is nitrogen dioxide (NO2), a pungent and corrosive gas that contributes to smog and poor air quality. NO2 is formed when fossil fuels like coal, oil, gas, or diesel are burned at high temperatures. It is a major component of vehicle exhaust and industrial emissions, with trucks, buses, and cars being the largest sources of NO2 emissions. As a result, NO2 levels are particularly high in large cities and urban areas, posing health risks for much of the world's population. Exposure to NO2 irritates the airways, exacerbates asthma, and may increase the likelihood of children developing asthma. It is also linked to more frequent and severe asthma symptoms, impaired lung development in children, and increased susceptibility to respiratory infections.

Another critical aspect of nitrogen pollution is agricultural ammonia emissions. When animal manure and synthetic fertilizers are used, stored, or spread, they release ammonia into the atmosphere. While ammonia itself is not a greenhouse gas, it acts as a base for emissions of nitrous oxide (N2O), a potent greenhouse gas. Nitrous oxide is 300 times more effective at warming the atmosphere than carbon dioxide and persists in the atmosphere for over 100 years. Additionally, agricultural ammonia emissions, combined with vehicle exhaust pollution, create dangerous particulate matter in the air, exacerbating respiratory diseases and reducing air quality.

The impact of nitrogen pollution is far-reaching and devastating. It contributes to climate change, harms human health, degrades air and water quality, and disrupts ecosystems. The economic costs are also significant, with nitrogen pollution costing the global economy between US$340 billion and US$3.4 trillion annually. Recognizing the urgency of the situation, governments and organizations are taking steps to address nitrogen pollution. The United Nations Environment Assembly has adopted resolutions on sustainable nitrogen management, aiming to significantly reduce nitrogen waste globally by 2030 and beyond. Local initiatives, such as London's Ultra Low Emission Zone, have also shown promising results in reducing NO2 levels. However, there is still much work to be done to mitigate the harmful effects of nitrogen pollution and protect the planet for future generations.

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