Questions and Answers
What size range do particulate matter typically fall into according to their diameter?
Which of the following oxides of nitrogen are considered important air pollutants?
What is the primary natural source of oxides of nitrogen in the atmosphere?
Which hydrocarbon compounds are typically found in the atmosphere within the range of C1 to C10?
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Which group of hydrocarbons has raised significant environmental concerns due to their structure?
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What percentage of carbon monoxide emissions can be attributed to motor vehicles on a global basis?
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Which process is primarily responsible for the conversion of atmospheric carbon dioxide to oxygen?
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What is the principal source of oxides of carbon related to air pollution?
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What does the term 'fine particulate matter' specifically refer to in terms of diameter?
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How are hydrocarbons formed during combustion characterized?
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Study Notes
Radiation and the Troposphere
- Radiation reaching the troposphere is filtered by molecular oxygen (O2) and ozone (O3) via the Chapman cycle.
- O3 can photolyze under UV radiation, producing oxygen (O2) and atomic oxygen (O).
- The reaction of atomic oxygen with water vapor (H2O) generates hydroxyl radicals (OH), which play a critical role in atmospheric chemistry.
Nitrogen Oxides as Air Pollutants
- Nitric oxide (NO) and nitrogen dioxide (NO2) are the primary nitrogen oxide air pollutants.
- NO is a by-product of combustion processes, formed from the high-temperature reaction of nitrogen (N2) and oxygen (O2).
- The Zeldovich mechanism describes the formation of nitric oxide:
- Reaction 1: N2 + O → NO + N (has high activation energy)
- Reaction 2: N + O2 → NO + O
Photochemical Processes in the Troposphere
- Nitrogen dioxide (NO2) is crucial for photochemical reactions as it can be photolyzed by solar radiation (290–423 nm) to produce nitric oxide (NO) and atomic oxygen (O).
- Subsequently, atomic oxygen can react with molecular oxygen to form ozone (O3) in the troposphere.
Role of Nitrous Acid and Alkyl Nitrites
- Nitrous acid (HONO) is significant in photochemical reactions.
- Alkyl nitrites (RONO) photolyze rapidly into alkoxy radicals (RO) and nitric oxide (NO), indicating their transient nature in the atmosphere.
Formaldehyde and Acetaldehyde Photolysis
- Formaldehyde (HCHO) photolyzes in the wavelength range of 290–356 nm through two pathways:
- HCHO + hν → HCO + H
- HCHO + hν → H2 + CO
- Acetaldehyde (CH3CHO) can undergo photolysis through three distinct pathways.
Particulate Matter in the Atmosphere
- Particulate matter sizes range from 0.1 to about 25 micrometers; less than 2.5 micrometers are termed fine particles, while those larger are coarse.
- Particles are essential in atmospheric chemistry and can originate from both natural and anthropogenic sources.
Composition of the Atmosphere and Nitrogen
- Diatomic nitrogen (N2) constitutes approximately 78% of the atmosphere and is essential for the chemistry of living organisms.
- Trace levels of nitrogen exist in various forms like ammonia (NH3), nitrous oxides, NO, and NO2.
- Natural processes (bacterial action, lightning, volcanic eruptions) and human activities (fossil fuel combustion) contribute to nitrogen oxide emissions.
Air Pollution from Carbon Compounds
- Key pollutants include carbon monoxide (CO) and hydrocarbons, primarily from fossil fuel combustion.
- The carbon cycle captures the conversion of atmospheric CO2 into oxygen and biomass, returning to CO2 through decomposition.
- Motor vehicles are responsible for over 55% of global carbon monoxide emissions.
Hydrocarbons in the Atmosphere
- Volatile hydrocarbons range from C1 to C10 compounds and include both unburned hydrocarbons from combustion and natural emissions from vegetation.
- Polynuclear aromatic hydrocarbons (PAHs) are concerning due to their association with fine particulate matter and originate from incomplete combustion processes.
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Description
Explore the crucial processes of atmospheric chemistry focusing on the role of ozone in the troposphere and the implications of nitrogen oxides as air pollutants. This quiz covers photolysis, the Chapman cycle, and reactions involving hydroxyl radicals. Test your knowledge on these important environmental concepts.
