Atmospheric chemistry and Ocean circulation Flashcards
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.
Ocean Temperature Patterns
1) Latitudinal Variation
Warmer waters are found near the equator (25–30°C) due to concentration sunlight and lack of sea ice.
2) Depth Variation (Thermocline Effect)
Surface waters (top 100–200 m): Warmer due to solar heating. Deep ocean (>1000 m): Uniformly cold (~0–4°C).
3) Seasonal Changes
Summer: Warmer surface waters, deeper thermocline.
Winter: Cooling and mixing of surface layers, weakening the thermocline.
Thermocline
The layer in the ocean where temperature rapidly decreases with depth, acting as a boundary between the warm surface layer and the cold deep ocean (strongest in tropical regions).
Ocean Salinity Patterns
1) High Salinity Areas (>35 ppt)
-Subtropics (20°–30° latitude): High evaporation and low precipitation (e.g., Atlantic Ocean).
-Enclosed seas (e.g., Mediterranean, Red Sea): Limited freshwater input, high evaporation.
2) Low Salinity Areas (<34 ppt)
-Polar regions: Melting sea ice and high precipitation dilute seawater.
-Near large rivers (e.g., Amazon, Ganges, Mississippi): Freshwater inflow reduces salinity.
Ocean Currents and Circulation
1) Surface Currents (Wind-Driven)
-Controlled by global wind patterns, Coriolis effect, and landmasses.
-Form gyres (large circular systems):
Clockwise in the N. Hemisphere and the other way in the S. Hemisphere.
2) Major Warm and Cold Currents
-Warm Currents (equator to poles):
For example, Gulf Stream (North Atlantic) and Kuroshio Current (North Pacific).
-Cold Currents (opposite direction)
3) Deep Ocean Currents (Thermohaline Circulation)
-Driven by temperature and salinity differences.
-Cold, salty water sinks at the poles and moves toward the equator.
Why Does the Thermocline Exist?
The thermocline forms due to the uneven heating of ocean water by the Sun and limited mixing between surface and deep layers.
Factors Affecting the Depth of the Thermocline.
- Latitude (Solar Energy Distribution)
- Seasonal Changes
- Ocean Circulation & Upwelling
- Weather & Climate Events
How does the depth of the thermocline vary with latitude.
Tropics (0°–30°): Strong, permanent thermocline (~100–500 m deep) due to intense solar heating.
Mid-Latitudes (30°–60°): Seasonal thermocline varies with seasons (deeper in summer, weaker in winter).
Polar Regions (60°–90°): Weak or absent thermocline due to cold surface water mixing with deeper layers.
How does the thermocline vary with seasons.
Summer: Stronger and deeper thermocline due to warm surface water.
Winter: Weaker thermocline as storms mix surface and deep water.
How does the thermocline vary with Ocean Circulation & Upwelling.
Upwelling Zones (e.g., off West Coasts of continents): Cold, nutrient-rich deep water rises, weakening or erasing the thermocline.
Downwelling Zones: Warm water sinks, deepening the thermocline.
How does the thermocline vary with Weather & Climate Events.
El Niño: Weakens or disrupts the thermocline in the Pacific.
La Niña: Strengthens the thermocline, making it more pronounced.
The mixed layer (topmost ocean layer stirred by winds) can suppress or deepen the thermocline depending on storm activity and wind strength.
What is the Meridional Overturning Circulation (MOC)?
The MOC, also called the Global Conveyor Belt, is a system of deep and surface currents that transport heat, salt, and nutrients across the Atlantic, Pacific, Indian, and Southern Oceans.
Ocean Circulation in Icehouse conditions.
-Stronger thermohaline circulation due to high salinity from ice formation.
-Deep water formation is strong, especially in polar regions.
-More nutrient cycling due to increased upwelling.
-Weaker tropical circulation as heat transport is less efficient.
-Cold, oxygen-rich deep waters dominate, supporting deep-sea ecosystems.
Ocean Circulation in Hothouse conditions.
-Weaker or absent thermohaline circulation due to less polar ice and lower salinity.
-Stronger stratification, meaning less mixing between surface and deep water.
-More sluggish deep-ocean circulation, leading to oxygen-poor (anoxic) conditions in deep waters.
-Higher sea levels and warmer oceans, leading to stronger equatorial currents.
-Frequent extreme weather due to stronger atmospheric convection.
Explain the factors that give western Europe a mild climate.
Western Europe’s mild climate results from warm ocean currents, prevailing westerly winds, and the Atlantic Ocean’s stabilizing effect. These factors prevent extreme cold, making the region much warmer than other areas at similar latitudes.
