Methane is an important greenhouse gas that is over 28 times more potent than carbon dioxide at trapping heat. It contributes significantly to global warming despite low concentrations in the atmosphere. Natural sources like wetlands and human activities such as agriculture, landfills, and fossil fuel extraction release methane. Mitigation efforts aim to reduce emissions through measures like leak detection, manure management, landfill gas capture, and renewable energy adoption.

1. ATMOSPHERIC CHEMISTRY OF
METHANE GAS
CHEMISTRY OF ATMOSPHERE (ASL735)
Presented by : Nitish Singh (2023AST2529)
OUTLINE
WHAT IS METHANE?
HISTORY
METHANE AS A GREENHOUSE GAS
IMPORTANCE & COMPOSITION
MYSTERY RISE IN METHANE
SOURCES
FACTORS AFFECTING METHANE
CHEMISTRY OF METHANE
CHEMICAL REACTIONS INVOLVED
METHANE CYCLE
CoP26 CLIMATE BRIEF FOR METHANE
EFFECTS OF METHANE
MITIGATION OF METHANE

2. WHAT IS METHANE?
❏ Simplest of alkanes
❏ Odorless, colorless, tasteless gas that is lighter than air
❏ In sufficient amounts of oxygen, methane burns to give off carbon dioxide (CO₂) and water (H₂O). When it
undergoes combustion it produces a great amount of heat, which makes it very useful as a fuel source.
CH₄ + 2O₂ → 2H₂O + CO₂
Blue flame on
burning i.e.
complete
combustion.
Tetrahedral Structure

3. ❏ About 3.5 billion years ago, there was
1,000 times as much methane in the
atmosphere as there is now.
❏ The earliest methane was released into
the atmosphere by volcanic activity.
❏ These first, ancient bacteria added to the
methane concentration by converting
hydrogen and carbon dioxide into methane
and water.
❏ Oxygen didn’t become a major part of the
atmosphere until photosynthetic organisms
evolved later in Earth's history.
❏ With no oxygen, methane stayed in the
atmosphere longer and at higher
concentrations than it does today.
HISTORY OF METHANE

4. METHANE AS A GREENHOUSE GAS
❏ Very effective greenhouse gas. While its
atmospheric concentration is much less than
that of carbon dioxide, methane is 28 times
more effective (averaged over 100 years) at
trapping infrared radiation.
❏ Shorter atmospheric residence time of
approximately 9-15 years.
❏ Greater capacity to trap heat in the atmosphere
compared to CO2.
❏ Methane can contribute to positive feedback
loops in the climate system. For example, as
the Arctic permafrost thaws due to rising
temperatures, it can release stored methane,
which in turn accelerates warming.
❏ It is difficult to quantify methane emissions
since sources are spread out over large areas
and emission values are small and variable in
time and space.

5. What’s the big deal about methane?
Methane is the primary contributor to the formation of ground-level ozone, a
hazardous air pollutant and greenhouse gas, exposure to which causes 1 million
premature deaths every year. Methane is also a powerful greenhouse gas. Over a
20-year period, it is 80 times more potent at warming than carbon dioxide.Methane
has accounted for roughly 30 percent of global warming since pre-industrial times
and is proliferating faster than at any other time since record keeping began in the
1980s.
IMPORTANCE & COMPOSITION
Why is it important?
Methane is an important trace gas in Earth’s
atmosphere. Even though it only makes up
0.00017% (1.7 parts per million by volume) of the
the atmosphere, methane traps a significant
amount of heat, helping the planet remain warm
and habitable.

6. MYSTERY RISE OF METHANE

7. SOURCES

8. Natural Wetlands Paddy rice fields Emission from livestock production
systems (including intrinsic
fermentation and animal waste)
Biomass burning (including
forest fires, charcoal
combustion, and firewood
burning)
Anaerobic decomposition of organic
waste in landfills
Fossil methane emission during the
exploration and transport of fossil fuels

9. PRODUCTION, TRANSPORT, AND OXIDATION PROCESSES
OF CH4
IN WETLANDS

10. EMISSION FROM DRY VS FLOODED PADDY
RICE FIELDS
EMISSION FROM LIVESTOCK PRODUCTION
SYSTEMS (INCLUDING INTRINSIC
FERMENTATION AND ANIMAL WASTE)

11. FACTORS AFFECTING METHANE
1. Natural Sources:
- Wetlands: Natural wetlands are the largest natural source of methane. Microbial activity in waterlogged soils produces
methane.
- Termites: Termites produce methane as a byproduct of their digestion process.
- Geological: seafloor methane hydrates, mud volcanoes, and geological faults.
2. Human Activities:
- Energy Production: Production and transport of fossil fuels
- Agriculture: Livestock digestion (enteric fermentation), manure management, and rice cultivation
- Rice Cultivation
- Biomass Burning: Burning of biomass such as wood and crop residues
- Landfills: Organic waste decomposition in landfills
- Wastewater Treatment .
3. Climate and Temperature: Warmer temperatures can increase microbial activity in soils and wetlands, leading to higher
methane emissions.
4. Natural Sinks: The removal of methane from the atmosphere is primarily driven by the reaction with hydroxyl radicals
(OH) in the atmosphere. Changes in atmospheric OH concentrations can influence methane removal rates.

12. Chemistry of Atmospheric Methane
❏ Source of CO (Carbon Monoxide)
CH4
+ OH → CO + H2
O
❏ Source of H2
(Hydrogen)
CH4
+ OH → H2
O + H2
❏ Source of HCHO (Formaldehyde)
❏ Source of Water Vapor
CH4
+ OH → CH3
+ H2
O
CH3
+ O2
→ HCHO + H
HCHO + OH → H2
O + CO

13. ❏ Sink for Cl (Chlorine) in Stratosphere:
The presence of methane in the stratosphere can lead to the formation of methane chlorine radicals (CH3
Cl, CH2
Cl2
, etc.)
through photochemical reactions, which can help deactivate chlorine and reduce its ozone-depleting potential.
❏ Source/Sink of O3
(Ozone):
Methane has complex interactions with ozone (O3
) in the atmosphere.
Methane itself does not directly produce ozone, but it can indirectly affect ozone levels. When methane is oxidized in the
atmosphere, it can produce ozone precursors like NOx
(nitrogen oxides), which can lead to both ozone production (source)
and destruction (sink) depending on the atmospheric conditions.
High methane concentrations can contribute to ozone production when sufficient NOx
is present, but methane can also lead
to ozone depletion in the stratosphere by reacting with hydroxyl radicals (OH), which is a key factor in stratospheric ozone
chemistry.

14. CHEMICAL REACTIONS
1. Combustion Reactions:
CH4
+ 2O2
→ CO2
+ 2H2
O
2. Reaction with Hydroxyl Radicals (OH·):
CH4
+ OH· → CH3
OH (methanol)
- This reaction initiates the breakdown of methane in the atmosphere, leading to the formation of methanol.
3. Reaction with Cl and Br Radicals:
- Methane can react with chlorine (Cl) and bromine (Br) radicals in the stratosphere, contributing to ozone depletion.
CH4
+ Cl· → CH3
Cl + H·
CH4
+ Br· → CH3
Br + H·
4. Methane Oxidation Chain Reaction:
CH4
+ OH → CH3
+ H2
O
CH3
+ O2
→ HCHO + H
HCHO + OH → HCOOH + H2
O

15. 5. Photochemical Reactions:
- Methane can participate in photochemical reactions, especially in the presence of sunlight.
- It can contribute to the formation of ground-level ozone (tropospheric ozone) and other secondary pollutants in smog.
6. Formation of Methane Sulfonic Acid (MSA):
- In marine environments, methane can react with sulfur dioxide (SO2
) to form methane sulfonic acid (MSA).
CH4
+ SO2
+ H2
O → CH3
SO3
H (methane sulfonic acid)
7. Methane Hydration Reaction:
- In cold environments, methane can react with water vapor to form methane hydrates (methane clathrates), which are
crystalline structures containing trapped methane molecules.
CH4
(g) + 6H2
O(l) → CH4
·6H2
O (methane hydrate)
8. Reaction with Nitrogen Oxides (NOx
):
- In the presence of nitrogen oxides (NOx
), methane can contribute to the formation of tropospheric ozone and other
secondary pollutants.
- These reactions are relevant in urban environments with high levels of NOx
emissions.

16. METHANE CYCLE
The methane cycle begins in the soil where
methane gas is created by microbes.Soil methane
is consumed by methanotrophs, microorganisms
that feed on methane.
Sources of Methane:
1. Wetlands
2. Livestock
3. Rice paddies
4. Natural gas production
5. Landfills
6. Termites
7. Oil production
8. Wetland emissions
9. Biomass burning
10. Permafrost
Sinks of Methane:
1. Hydroxyl radicals
(OH)
2. Soil uptake
3. Stratospheric loss
4. Chemical
reactions
5. Oxidation in the
atmosphere
6. Microbial
consumption in
sediments
7. Methanotrophic
bacteria
8. Ocean uptake
9. Vegetation uptake
10. Abiotic oxidation

17. CoP26 CLIMATE BRIEF FOR METHANE
❏ To stay well below 2°C and
limit global warming to 1.5°
C, the global community
must take decisive action
to reduce methane
emissions from the energy
sector and transition to
alternative energy sources.
❏ Global methane emissions
must be reduced by
between 40-45 per cent by
2030 to achieve least cost
pathways that limit global
warming to 1.5°C this
century
❏ Readily available targeted
measures can reduce 2030
methane emissions by 30
per cent

18. EFFECTS OF METHANE
EFFECTS ON HUMANS
❏ Health Impacts: Headaches, nausea, dizziness, and in extreme cases, asphyxiation.
❏ Air Quality: Produce ground-level ozone, a harmful air pollutant that can exacerbate respiratory problems like asthma
and other lung diseases.
❏ Safety Concerns: Highly flammable and can lead to explosions and fires
EFFECTS ON ENVIRONMENT
❏ Greenhouse Gas: Higher heat-trapping capacity per molecule compared to carbon dioxide (CO2) leading to global
warming
❏ Climate Change: Lead to rising temperatures, melting ice, sea-level rise, and more frequent extreme weather events
❏ Positive Feedback Loop: Methane release from thawing permafrost and methane hydrates on the ocean floor could
create a positive feedback loop. As the planet warms, more methane is released, further accelerating global warming.
❏ Ocean Acidification: Harm marine ecosystems, particularly those with calcium carbonate-based organisms like corals
and shellfish.
❏ Air Quality: Can damage crops, reduce agricultural yields, and harm ecosystems
❏ Methane's Interaction with Other Pollutants
❏ Methane Hydrates

19. MITIGATION OF METHANE
1. Leak detection and repair
2. Natural gas infrastructure upgrades
3. Livestock management
4. Manure management
5. Improved rice cultivation method
6. Landfill gas capture
7. Renewable energy adoption
8. Energy efficiency
9. Methane oxidation catalysts
10. Regulatory measures
11. Methane emissions monitoring
12. Carbon pricing
13. Wetland conservation
14. Methane hydrate research
15. International laws and conventions

20. References
❏ National Oceanic and Atmospheric Administration
❏ IPCC (2001)
❏ Wikipedia
❏ United Nations Framework Convention on Climate Change (UNFCCC)
❏ CoP26