Nitric Oxide: Understanding Air Pollution's Silent Killer

Nitric oxide (NO) is a colourless gas and one of the principal oxides of nitrogen. Nitrogen oxides (NOx) are a collective term for nitrogen monoxide (NO) and nitrogen dioxide (NO2). NOx gases are usually produced from the reaction between nitrogen and oxygen during the combustion of fuels, especially in car engines. In ambient conditions, nitric oxide is rapidly oxidised in the air to form nitrogen dioxide, which is a primary pollutant. NOx gases are also produced naturally by lightning.

Nitric oxide is oxidised to form nitrogen dioxide

Nitric oxide (NO) is a colourless gas and one of the principal oxides of nitrogen. It is a free radical with an unpaired electron, denoted by a dot in its chemical formula (•N=O or •NO). In mammals, including humans, nitric oxide is a signalling molecule in many physiological and pathological processes. It plays a role in a variety of biological processes and is a key vertebrate biological messenger.

Nitric oxide is produced from the reaction of nitrogen and oxygen gases in the air during combustion, especially at high temperatures. The higher the combustion temperature, the more nitric oxide is generated. At normal temperatures, oxygen and nitrogen gases do not react together. Nitric oxide is also produced naturally from lightning strikes, which can reach temperatures of roughly 30,000 Kelvin.

Nitric oxide is rapidly oxidised in the air to form nitrogen dioxide (NO2), a reddish-brown gas with a pungent, acrid odour. This oxidation process is facilitated by available oxidants such as oxygen, ozone, and VOCs. Nitrogen dioxide is heavier than air and has a low partial pressure in the atmosphere, preventing condensation so that it exists in the air in its gaseous form. In this form, nitrogen dioxide is volatile and has a characteristic odour that can be perceived from a concentration of 188 μg/m3 (0.1 ppm).

Nitrogen dioxide is a highly reactive gas and a primary pollutant. It is a strong oxidant, corrosive, and poorly soluble in water. It is produced from emissions from cars, trucks, buses, power plants, and off-road equipment. High outdoor NO2 levels originating from local traffic and other combustion sources can influence indoor levels. Breathing air with high concentrations of NO2 can irritate the airways in the human respiratory system, aggravate respiratory diseases, and potentially increase susceptibility to respiratory infections.

Nitrogen dioxide is a reddish-brown gas with a pungent odour

Nitrogen dioxide (NO2) is a reddish-brown gas with a pungent, acrid odour. It is one of the several oxides of nitrogen. NO2 is a primary pollutant and a contributing component for secondary pollutants formed from chemical reactions. It is produced from the reaction of nitrogen and oxygen gases in the air during combustion, especially at high temperatures. At normal temperatures, these gases do not react. However, nitrogen oxides are also produced naturally from lightning strikes, which can reach temperatures of around 30,000 Kelvin.

Road traffic and energy production are significant man-made sources of nitrogen oxides. In indoor environments, tobacco smoke and gas-, wood-, oil-, kerosene- and coal-burning appliances are the most important sources of nitrogen dioxide.

Nitrogen dioxide is heavier than air and has a low partial pressure in the atmosphere, preventing condensation so that it exists in the air in its gaseous form. It is a strong oxidant and corrosive, reacting with water and soluble in sulfuric and nitric acids. It is poorly soluble in water.

Nitrogen dioxide is a significant air pollutant, with ambient concentrations varying widely according to local sources and sinks. In dense urban areas, total nitrogen oxide concentrations can exceed 500 μg/m3. Short-term exposure to nitrogen dioxide can cause nausea, dyspnea and headaches, while long-term effects may include impaired immune and respiratory function.

Nitrogen dioxide is a primary pollutant

Nitrogen dioxide (NO2) is a reddish-brown gas with a pungent, acrid odour. It is one of the most abundant nitrogen oxides, along with nitrogen monoxide (NO). NO2 is a major contributor to smog and is a precursor to many harmful secondary pollutants, including ozone and particulate matter.

Nitrogen dioxide is formed through the combustion of fuel, such as emissions from cars, trucks, buses, power plants, and off-road equipment. It can also be produced through the oxidation of nitric oxide (NO), which is emitted during combustion. In ambient conditions, nitric oxide is rapidly oxidized in air to form nitrogen dioxide by reacting with oxygen, ozone, and volatile organic compounds (VOCs).

As a primary pollutant, NO2 is emitted in limited amounts through vehicles into the air. It is considered a primary pollutant because it is formed and emitted directly from specific sources, such as road traffic and energy production. However, NO2 is also a secondary pollutant, as it can be formed through the oxidation of nitric oxide.

The presence of NO2 in the air can have significant health impacts. Breathing air with high concentrations of NO2 can irritate the airways in the human respiratory system and aggravate respiratory diseases, especially asthma. Prolonged exposure to high levels of NO2 may contribute to the development of asthma and increase susceptibility to respiratory infections. People with existing respiratory conditions, such as asthma, are more susceptible to the harmful effects of NO2 pollution.

To mitigate the health risks associated with NO2 pollution, comprehensive air quality monitoring is essential. Portable and fixed air monitoring devices can help identify areas of heavy NO2 concentration and provide real-time data to inform decision-making and develop strategies to reduce NO2 emissions.

Nitrogen dioxide can cause respiratory issues

Nitrogen dioxide (NO2) is a reddish-brown gas with a pungent, acrid odour and is one of the several oxides of nitrogen. It is a highly reactive gas and a primary pollutant. NO2 primarily gets in the air from the burning of fuel, especially at high temperatures. The most common sources of NO2 emissions are cars, trucks, buses, and other vehicles, followed by industrial processes such as oil and gas production, power plants, industrial boilers, and coal-fired plants.

Breathing air with a high concentration of NO2 can irritate the airways in the human respiratory system. Exposure to NO2 over short periods can aggravate respiratory diseases, especially in people with pre-existing conditions such as asthma, chronic obstructive pulmonary disease (COPD), and cardiovascular disease. This can lead to respiratory symptoms such as coughing, wheezing, or difficulty breathing, and may result in hospital admissions and emergency room visits.

In addition to the immediate health impacts, longer-term exposure to elevated levels of NO2 may contribute to the development of respiratory issues. Prolonged exposure to high concentrations of NO2 has been linked to an increased risk of asthma, respiratory infections, and other health problems. Scientific evidence suggests that exposure to NO2 is likely associated with heart and lung harm, affected pregnancy and birth outcomes, and an elevated risk of kidney and neurological harm, autoimmune disorders, and cancer.

While everyone is at risk of the harmful effects of nitrogen dioxide pollution, certain subpopulations are more vulnerable. People living near emission sources, such as heavily travelled roadways or industrial sites, are at a higher risk of exposure. Additionally, individuals with pre-existing medical conditions, such as asthma or other respiratory diseases, are more susceptible to the adverse effects of NO2.

To mitigate the health risks associated with NO2 pollution, it is crucial to monitor air quality and implement measures to reduce emissions. Real-time air quality monitoring can help identify areas with high levels of NO2, enabling individuals to make informed decisions about their exposure. Additionally, regulatory efforts, such as the Clean Air Act in the United States, have contributed to a nationwide improvement in air quality by driving down nitrogen dioxide emissions from power plants, industrial sites, and on-road vehicles.

Nitrogen dioxide is a contributing component of secondary pollutants

Nitrogen dioxide (NO2) is a reddish-brown gas with a pungent, acrid odour. It is one of the most abundant nitrogen oxides (NOx) and is produced from the reaction of nitrogen and oxygen gases in the air during combustion, especially at high temperatures. At normal temperatures, oxygen and nitrogen gases do not react together. NO2 is a primary pollutant, but it is also a contributing component of secondary pollutants.

Nitrogen dioxide is formed from emissions from cars, trucks, buses, power plants, and off-road equipment that burn fuel. It is also produced by high-temperature combustion in vehicles, industries, and power-generating facilities. The burning of fossil fuels like coal, oil, and gas is a significant source of NO2.

NO2 combines with volatile organic compounds (VOCs) in the presence of sunlight and heat to create ozone (O3), a major secondary pollutant. Photochemical smog, common in sunny and dry locations, is created when NO2 from gas combustion is exposed to sunlight, releasing an oxygen ion (O). This released oxygen ion combines with another oxygen molecule (O2) to form ozone.

Ozone is a harmful pollutant that can cause respiratory problems such as coughing, wheezing, and difficulty breathing. It is also linked to asthma and other respiratory conditions. In addition to ozone, other secondary pollutants formed through reactions with NO2 include particulate matter, acid rain, and other toxic chemicals.

The health risks associated with NO2 exposure are significant. Breathing air with high concentrations of NO2 can irritate the airways and aggravate respiratory diseases, especially asthma. Longer exposures to elevated NO2 levels may contribute to the development of asthma and increase susceptibility to respiratory infections. People with asthma, children, and the elderly are generally at greater risk for the adverse health effects of NO2.

Frequently asked questions