Kiera Jefferson
Nitric acid is a highly corrosive and colourless inorganic compound that is commercially available and used in a wide variety of chemical processes. It is a common air pollutant that can be formed from the reaction between nitrogen and oxygen during the combustion of fuels, especially in car engines. This reaction produces nitrogen oxides, which react with water to form nitric acid. Nitric acid can also be formed during thunderstorms due to the extreme heating and cooling within a lightning strike. Additionally, nitric acid may form in small amounts wherever high temperatures are generated in the presence of air (nitrogen and oxygen) and water. Exposure to nitric acid fumes can cause severe respiratory issues, and it is known to contribute to acid rain.
| Characteristics | Values |
|---|---|
| Formation | Nitric acid is formed from the reaction of nitrogen oxide with oxygen in the air to form nitrogen dioxide, which then reacts with water to form nitric acid. |
| Air Pollutants | NOx gases, which include nitrogen oxide and nitrogen dioxide, are the most relevant for air pollution and contribute to the formation of smog and acid rain. |
| Health Effects | Exposure to nitric acid fumes can cause severe coughing, chest pain, shortness of breath, and corrosive burns on the skin. Inhalation of high concentrations can lead to pulmonary edema. |
| Vulnerable Groups | Children, the elderly, and people with asthma are particularly susceptible to the adverse effects of nitric acid pollution, including damage to lung tissue and reduced lung function. |
| Removal | Nitric acid can be removed from the atmosphere through wet and dry deposition methods, reducing its concentration in the air. |
| Regulatory Standards | Safe Work Australia sets workplace exposure standards for nitric acid, with a maximum eight-hour time-weighted average of 2 parts per million (5.2 mg/m3). |
What You'll Learn
Nitrogen and oxygen react during combustion of fuels
Nitric acid is an inorganic compound with the formula HNO3. It is a highly corrosive mineral acid that is colorless but tends to turn yellow over time due to decomposition into oxides of nitrogen. Nitric acid is formed from pollutants in the air through the combustion of fuels, which involves the reaction of nitrogen and oxygen.
Combustion is a chemical reaction that releases energy, typically in the form of heat and light. It occurs when a fossil fuel, such as a hydrocarbon, reacts with oxygen in the presence of a heat source. This reaction produces carbon dioxide (CO2) and water, with energy being released in the process. The water produced is in the gas state due to the high temperatures associated with combustion.
During the combustion of fossil fuels, nitrogen can be present in the form of nitrogen gas (N2) or nitrogen dioxide (NO2). When petroleum products, such as oil, are burned, they release nitrogen oxides (NO and NO2) and sulfur dioxide (SO2). Similarly, the combustion of coal and wood products can produce carbon monoxide (CO), a toxic gas, if there is an insufficient oxygen supply.
Nitrogen oxides formed during combustion can react with other atmospheric components to produce nitric acid. For example, nitrogen oxide (NO) reacts with oxygen in the air to form nitrogen dioxide (NO2), which then reacts with water to form nitric acid. This process contributes to the presence of nitric acid in the air, particularly in areas with high levels of combustion, such as near major cities.
Additionally, nitric acid can be formed during industrial processes. The Ostwald process, combined with the Haber process, is commonly used for the production of nitric acid. This method involves creating conditions under which anhydrous ammonia burns to form nitric oxide (NO) instead of dinitrogen (N2).
The presence of nitric acid in the air, whether from combustion or industrial processes, can have significant health impacts. Exposure to nitric acid fumes can cause respiratory issues such as coughing, dyspnea, and acute respiratory distress. It is essential to monitor and control nitric acid emissions to minimize potential health risks for individuals living or working in affected areas.
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Nitric acid is formed from nitrogen oxides reacting with water
Nitric acid is a highly corrosive inorganic compound with the formula HNO3. It is colourless but tends to turn yellow over time due to decomposition into oxides of nitrogen. Nitric acid is formed from nitrogen oxides reacting with water.
Nitric acid is present in the air in and around major cities, and people are exposed to trace amounts of it outdoors. It is found in exhaust fumes from motor vehicles, incinerators, and other chemical plants, especially when in contact with moisture in the air. It is also present in small quantities in rain in areas where nitric oxide, a product of combustion, reacts with ozone and water to form nitric acid.
Nitric acid may form in minute amounts wherever very high temperatures are generated in the presence of air (nitrogen and oxygen) and water. It is produced through the reaction of nitrogen oxides with water. Specifically, nitrogen dioxide (NO2) reacts with water to form nitric acid. This reaction occurs when nitrogen oxide reacts with oxygen in the air to form nitrogen dioxide.
The process of forming nitric acid from nitrogen oxides and water can be achieved through various methods. One historical method, devised by Johann Rudolf Glauber in the 17th century, involves distilling potassium nitrate with sulfuric acid. Another method, reported by Humphry Davy in 1806, involves electrolysis of distilled water using a high-voltage battery and non-reactive electrodes and vessels. This process produces nitric acid at the anode from dissolved atmospheric nitrogen gas.
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Nitrogen oxides are produced by lightning
Nitrogen oxides are naturally produced by lightning. Each lightning bolt carries electrical energy powerful enough to break atmospheric nitrogen bonds. The rapid heating and cooling of the gases within a lightning bolt produce nitric oxide (NO), which combines with oxygen to create nitrogen dioxide (NO2). Together, nitric oxide and nitrogen dioxide are referred to as nitrogen oxides (NOx).
Lightning-generated nitrogen oxides have a relatively small but potentially significant impact on ground-level ozone (O3), one of the primary air pollutants. The atmospheric chemistry changes caused by nitrogen oxides during a storm are what lead to the formation of ground-level ozone.
The impact of lightning on air pollution is determined by several factors in the atmospheric system, including the amounts and locations of human-produced air emissions. To better understand the contribution of natural sources like lightning to air pollution, researchers use innovative air quality models such as the Community Multiscale Air Quality Modeling System (CMAQ). CMAQ is a 'one-atmosphere' model that simulates the transport and fate of air pollutants across various geographic boundaries and time intervals.
The length and vertical structure of lightning flashes also influence the production of nitrogen oxides. Longer flashes release more NOx at lower altitudes compared to shorter flashes, and when lightning flashes are more frequent, each flash produces less NOx. The NASA Lightning Nitrogen Oxides Model (LNOM) uses Lightning Mapping Array (LMA) data to investigate the vertical distribution of LNOx.
Nitrogen oxides produced by lightning contribute to the nitrogen fixation process, where nitrogen in the atmosphere is transformed into a plant-usable form. Nitrogen dioxide, a product of nitrogen fixation, dissolves in water to create nitric acid, which then forms nitrates. These nitrates fall to the ground in raindrops and seep into the soil, providing plants with a usable form of nitrogen.
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Nitrogen oxides are produced by motor vehicles
As a result, combustion temperature tends to increase as the load on the engine increases, such as when accelerating rapidly or driving uphill. Interestingly, diesel cars sometimes feature lower combustion temperatures than gasoline engines because diesel combustion is much leaner, meaning the air-fuel mixture contains a higher proportion of air than fuel.
The production of nitrogen oxides in motor vehicles is not a new phenomenon. In fact, nitrogen oxide in cars has been known about for quite some time. While airborne nitrogen, in isolation, is not harmful to humans and makes up 80% of our atmosphere, it becomes an issue when it bonds with another element: oxygen. This bond forms nitrogen oxide, which has well-documented negative effects on public health and the environment.
To combat this issue, car manufacturers have been working on ways to reduce nitrogen oxide emissions. The Euro emissions standards, first introduced in 1992 alongside the mandatory inclusion of catalytic converters, have played a crucial role in reducing emissions. These standards dictate the maximum number of emissions that a car can legally produce. As a result, nitrogen oxide emissions have seen a significant decrease since 2001, with an 84% reduction as of 2017.
In addition to emissions standards, car manufacturers have introduced the three-way catalytic converter, which helps control nitrogen oxide emissions. This technology is inexpensive and has little to no impact on fuel economy, performance, drivability, or maintenance. It is also very effective, with modern gasoline-engine passenger cars exhibiting only negligible amounts of NOx present in the exhaust.
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Nitrogen oxides react with ammonia, moisture, and other compounds to form nitric acid
Nitrogen oxides (NOx) are formed from the reaction between nitrogen and oxygen during the combustion of fuels, such as hydrocarbons, in the presence of air and water. NOx is produced naturally by lightning and from human activities, especially in areas with high motor vehicle traffic. NOx contributes to air pollution and the formation of smog and acid rain.
NOx reacts with ammonia, moisture, and other compounds to form nitric acid (HNO3). This reaction occurs through various pathways. During the daytime, NO2 reacts with hydroxyl radicals (OH) to form nitric acid. This nitric acid can be removed through dry and wet deposition. At night, NO2 and NO can form nitrous acid (HONO) through a surface-catalyzed reaction. Nitrous acid can further react with water vapour or liquid water to form nitric acid.
The presence of ammonia and moisture in the air can facilitate the formation of nitric acid from NOx. While ammonia is not always present in the atmosphere, it can be emitted from agricultural activities, such as the use of fertiliser, or from industrial processes. Moisture in the air, in the form of water vapour or liquid water, is necessary for the reaction between NO2 and water to form nitric acid.
Other compounds can also influence the formation of nitric acid from NOx. For example, NOx reacts with volatile organic compounds in the presence of sunlight to form ozone. While not a direct precursor to nitric acid, ozone can indirectly impact its formation by affecting the concentration of other reactants and the overall atmospheric chemistry.
The reaction between NOx and ammonia, moisture, and other compounds to form nitric acid is complex and dependent on various factors, including temperature, humidity, and the presence of other pollutants. Nitric acid is a corrosive compound that can have adverse effects on human health, particularly the respiratory system, when present in high concentrations in the air.
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Frequently asked questions
Nitric acid is formed from the reaction of nitrogen oxides with volatile organic compounds in the presence of sunlight. Nitrogen oxides are produced from the reaction of nitrogen and oxygen during the combustion of fuels, especially in car engines.
Exposure to nitric acid can cause severe coughing, chest pain, shortness of breath, and corrosive burns to the skin. Inhalation of high concentrations of nitric acid can result in pulmonary edema, requiring hospitalisation.
Nitric acid is present in exhaust gases from motor vehicles, incinerators, and chemical plants. People living near industries that produce or use nitric acid may be exposed to low emissions. It is also formed naturally during thunderstorms and by lightning strikes.
