Question

For each of the following gases, make a list of known or possible naturally occurring sources: (a) \(\mathrm{CH}_{4}\), (b) \(\mathrm{SO}_{2}\), (c) \(\mathrm{NO}\), (d) \(\mathrm{CO}\).

Short answer

Natural sources of the given gases are as follows: (a) Methane (\(\mathrm{CH}_{4}\)): Wetlands, termites, oceans, freshwater bodies, and natural gas deposits. (b) Sulfur Dioxide (\(\mathrm{SO}_{2}\)): Volcanic activity, hot springs, biological decay, and oceanic release. (c) Nitric Oxide (\(\mathrm{NO}\)): Soil bacterial activity, lightning, forest fires, and volcanic activity. (d) Carbon Monoxide (\(\mathrm{CO}\)): Forest fires, volcanic activity, oceanic release, and biological decay.

Step-by-step solution

(a) Methane (\(\mathrm{CH}_{4}\))

Methane is an organic compound, and its main natural sources include: 1. Wetlands: Methane is produced by microorganisms called methanogens, which are anaerobic bacteria that release methane during the decomposition of organic matter. 2. Termites: Methane is produced in the digestive systems of termites as a byproduct of breaking down the cellulose present in wood. 3. Oceans: Methane is produced in ocean sediments due to microbial activity. 4. Freshwater bodies: Methane is produced in lakes and rivers as a result of microbial activity in oxygen-depleted environments. 5. Natural gas deposits: Methane is the primary component of natural gas and can be found in underground deposits formed by the decomposition of ancient organic material.

(b) Sulfur Dioxide (\(\mathrm{SO}_{2}\))

Sulfur dioxide is a compound of sulfur and oxygen, and its main natural sources include: 1. Volcanic activity: When volcanoes erupt, they release sulfur dioxide into the atmosphere, along with other gases and particles. 2. Hot springs: Sulfur dioxide is released in geothermal areas, where hot, mineral-rich water flows out of the ground. 3. Biological decay: The decomposition of organic matter containing sulfur can release sulfur dioxide into the atmosphere. 4. Oceanic release: Sulfur dioxide can be emitted from the ocean surface due to the breakdown of sulfur-containing compounds by marine bacteria.

(c) Nitric Oxide (\(\mathrm{NO}\))

Nitric oxide is a compound of nitrogen and oxygen, and its main natural sources include: 1. Soil bacterial activity: Nitrogen-fixing bacteria in the soil convert nitrogen compounds to nitric oxide and release it into the atmosphere. 2. Lightning: During thunderstorms, high-energy reactions between nitrogen and oxygen molecules in the atmosphere produce nitric oxide. 3. Forest fires: When vegetation burns, nitric oxide is released as a byproduct of combustion. 4. Volcanic activity: Nitric oxide can be emitted in volcanic gases, along with other nitrogen oxides.

(d) Carbon Monoxide (\(\mathrm{CO}\))

Carbon monoxide is a compound of carbon and oxygen, and its main natural sources include: 1. Forest fires: When vegetation burns, carbon monoxide is released as a byproduct of incomplete combustion. 2. Volcanic activity: Carbon monoxide can be emitted in volcanic gases, along with other gases and particles. 3. Oceanic release: The photodissociation of atmospheric organic compounds over the ocean surface can release carbon monoxide into the atmosphere. 4. Biological decay: The decomposition of organic matter in low-oxygen environments can produce carbon monoxide.

Key concepts

Methane Sources

Methane (CH₄) is an important greenhouse gas found naturally in our environment. It arises from a variety of sources, largely from biological processes.

• Wetlands: These are the most significant natural contributors to atmospheric methane. Microorganisms called methanogens thrive in the oxygen-free (anaerobic) environments of wetland soils, decomposing organic matter and producing methane in the process.
• Termites: Surprisingly, termites rank high on the list of natural methane sources. They produce methane as a byproduct while digesting cellulose from wood.
• Oceans: In underwater sediments, especially in the deep sea, microbial activity can lead to methane formation.
• Freshwater bodies: Similar to wetlands, lakes and rivers with low-oxygen conditions can foster microbes that emit methane.
• Natural gas deposits: These underground reservoirs of methane result from the decomposition of ancient organisms. Occasional seepages can release methane into the atmosphere naturally.

Sulfur Dioxide Sources

Sulfur dioxide (SO₂) is a gas that, while best known for its human-made sources, also emanates from various natural processes.

• Volcanic activity: Volcanoes are a dramatic and powerful source of sulfur dioxide. During eruptions, they discharge this gas in large quantities.
• Hot springs: The Earth's geothermal activity releases sulfur dioxide, noticeable around natural hot springs.
• Biological decay: As organisms containing sulfur compounds decompose, they can release sulfur dioxide, albeit in smaller amounts than other sources.
• Oceanic emission: Seas and oceans release sulfur dioxide due to the action of marine bacteria on sulfur compounds.

Nitric Oxide Sources

Nitric oxide (NO), along with nitrogen dioxide (NO₂), makes up what we refer to as NOx, a group of highly reactive gases. Natural sources of nitric oxide are diverse and include both terrestrial and atmospheric processes.

• Soil bacterial activity: Nitrogen-fixing bacteria in the soil generate nitric oxide as they process nitrogen in the ground.
• Lightning: The high temperatures and energies from lightning strikes cause the nitrogen and oxygen in the air to combine and form nitric oxide.
• Forest fires: Wildfires contribute to the natural production of nitric oxide due to the high-temperature combustion of plant matter.
• Volcanic activity: Though not as significant a source as others, volcanic emissions contribute to atmospheric levels of nitric oxide.

Carbon Monoxide Sources

Carbon monoxide (CO) is a colorless, odorless gas that is produced from the incomplete combustion of carbon-containing materials. It occurs naturally in the Earth's atmosphere through several processes.

• Forest fires: One of the largest natural contributors to atmospheric carbon monoxide is forest fires, which produce CO through the burning of wood and foliage.
• Volcanic activity: Eruptions can release a mixture of gases, including carbon monoxide, from the depths of the Earth.
• Oceanic processes: Photodissociation of organic compounds on the ocean's surface contributes to the natural occurrence of carbon monoxide in the environment.
• Biological decay: The breakdown of organic matter in environments where oxygen is scarce can also generate carbon monoxide.