Atmospheric chemistry and Ocean circulation Flashcards
(38 cards)
What is the stratosphere?
The layer above the troposphere (temperature increases with height). This temperature increase in the stratosphere is directly related to the absorption of ultraviolet (UV) radiation by ozone and oxygen at wavelengths between 220-310nm.
What happens to UVB and UVC in the stratosphere?
UVB- absorbed but some gets through reaching the outer skin and producing vitamin D.
UVC- experiences total absorption and scattering (this is good as it destroys nucleic acids so is very harmful).
What is the Chapman cycle?
It is a cycle that describes the photochemical reactions that create and destroy ozone in the stratosphere.
What is the fist step of the Chapman cycle?
1) Oxygen Photolysis:
O2+ℎ𝜈 ⟶2O
Molecular oxygen (O₂) absorbs high-energy UV radiation (λ < 242 nm) and dissociates into two oxygen atoms.
What is the second step of the Chapman cycle?
2) Ozone Formation:
O+O2+𝑀 ⟶ O3+𝑀
Atomic oxygen (O) reacts with molecular oxygen (O₂) in the presence of a third body (M), typically nitrogen or oxygen, to form ozone (O₃).
The third body (M) absorbs the excess energy released, stabilizing the newly formed ozone.
What is the third step of the Chapman cycle?
3) Ozone Photolysis (UV Absorption):
O3+ℎ𝜈 ⟶ O2+O
Ozone absorbs UV radiation, mainly in the Hartley band (200-310 nm), splitting into molecular oxygen and atomic oxygen.
This absorption of UV radiation heats the stratosphere.
What is the fourth step of the Chapman cycle?
Recombination of Oxygen:
O+O3 ⟶ 2O2
Atomic oxygen can also react with ozone, regenerating molecular oxygen
Which steps of the Chapman cycle are fast and which are slow?
Steps 1 and 4 are slow and steps 2 and 3 are fast.
How does the formation of ozone effect the temperature profile?
Heating Effect: The absorption of UV radiation by ozone occurs primarily between 15 and 50 km, with the highest concentration of ozone occurring around 20-25 km.
Temperature Increase: The absorbed UV energy is converted into kinetic energy, causing the surrounding air to warm, leading to an increase in temperature with altitude in the stratosphere.
Peak Heating Zone: Maximum heating occurs in the mid-to-upper stratosphere where ozone concentration and UV absorption are highest.
Explain the role of chlorine compounds in modifying stratospheric ozone concentrations.
Chlorine perturbs the chapman cycle as it steals bonds with oxygen. This process destroyed 2 ozone molecules forming 3 molecular oxygen molecules whilst leaving the chlorine free to keep interfering. (catalytic cycle.)
What is the role of CFCs?
CFCs add atmospheric chlorine which enters the stratosphere and acts as a catalytic cycler.
Explain qualitatively the formation of the Antarctic ozone hole.
Once in the air CFCs are concentrated poleward by the polar vortex. Cold subsiding air and jet stream isolates the area further.
1) The cold air (-80°C) crystalises water HNO3 into ice forming polar stratospheric clouds (PSCs).
2) This releases Cl2 and and HOCl via denitrification and dehydration.
3) ClO and Cl are formed in spring when the sun rises and UV breaks down the Cl2 and HOCl.
4) This results in localised catalytic depletion of ozone.
Primary pollutants
Emitted directly into the atmosphere.
-NO and CO (from engines)
-Hydrocarbons
-SO2
-NH3
-Particulate matter
Secondary pollutants
Formed from reactions in the atmosphere.
-Sulfuric and Nitric acid
-Ozone
Secondary particulate matter (condensation of acids)
-Organic aerosols
Explain how ozone is a pollutant.
Ozone is good in the stratosphere (blocks UV) however it is bad in the troposphere as it is and oxidant, irritant and can cause respiratory disease.
Explain the ozone–NO x cycle in the troposphere.
Tropospheric ozone (O₃) is a secondary pollutant formed through complex photochemical reactions involving nitrogen oxides (NOₓ, which includes NO and NO₂) and volatile organic compounds (VOCs) in the presence of sunlight. The ozone–NOₓ cycle describes how NOₓ regulates the formation and destruction of ozone in the troposphere.
Ozone Formation in the Troposphere
Step 1: Photolysis of NO₂
NO2+ℎ𝜈(𝜆<420 nm) ⟶ NO+O
Sunlight breaks down nitrogen dioxide (NO₂) into nitric oxide (NO) and atomic oxygen (O).
Step 2: Ozone Formation
O+O2+𝑀 ⟶ O3+𝑀
The free oxygen atom reacts with molecular oxygen (O₂) to form ozone (O₃), with M (a third body, often N₂ or O₂) stabilizing the reaction.
Ozone Destruction in the Troposphere
What little UV radiation that does react the troposphere can photolyze ozone producing excited oxygen radicals.
O3+UV ⟶ O2+O* *=excited
Most of the O* reacts with N2 or O2 and reforms O3. Some can react with H2O to form hydroxyl radicals (very reactive).
Role of VOCs in Ozone Accumulation
If volatile organic compounds are present, they react with hydroxyl radicals to form peroxy radicals (RO₂ and HO₂).
These peroxy radicals react with NO to convert it to NO₂ without destroying ozone:
RO2+NO ⟶ RO+NO2
Since NO is converted to NO₂ without ozone destruction, more NO₂ photolysis occurs, leading to ozone build-up.
Thus, high VOCs and NOₓ levels lead to ozone pollution (photochemical smog), especially in urban areas. (e.g. Great smog of London)
Meteorological Effects on Air Quality
Meteorology plays a crucial role in the dispersion, transport, and removal of pollutants.
For example:
-Strong winds disperse pollutants, improving air quality.
-Higher temperatures enhance photochemical reactions, leading to more ozone and smog formation.
-Rain removes pollutants through wet deposition.
Emissions and Their Role in Air Quality
Local emissions (traffic, industry) affect urban air quality.
Regional transport spreads pollutants over long distances (e.g., wildfire smoke, transboundary pollution).
Describe the components of the Earth’s hydrosphere.
- Oceans and Seas (97%)
Largest component of the hydrosphere, covering about 72% of Earth’s surface. Salinity comes from chemical weathering and upwelling (55% chloride and 21% sodium). - Freshwater (3%)
Glaciers and Ice Caps (68.7%), Groundwater (30.1%), Surface Water (1.2%). - Atmospheric Water (~0.001%)
Origin of Ocean Salts
Weathering of Rocks (Primary source) and upwelling from hydrothermal vents/volcanoes.
Ocean salts are 55% chloride, 31% sodium and the rest is sulphate, magnesium, calcium and potassium.
Origin of Ocean Water
1) Volcanic Outgassing (Primary Source)
-Water vapour condensed to form oceans by at least 3.8Ga
-Volcanoes such as Momotombo (Nicaragua) emit up to 97% of their gases as water vapour.
2) Extra-terrestrial Contributions (Secondary Source)
-Ice in comets has double the deuterium than ocean water.
-Meteorites contain 10 times more xenon than the atmosphere.
