Week 9 - Atmosphere Flashcards
Importance of atmosphere to the Earth System
Protect and sustains the planet’s inhabitants by providing warmth and absorbing harmful solar rays
Contains O2 and CO2, which living things require to survive
Distributes energy and material globally, creates wind and weather systems
Atmosphere
A gaseous envelope that surrounds a planet or any other celestial body
Air
A mixture of gases and tiny suspended particles that makes up Earth’s atmosphere
The composition of air is often discussed in relative terms as density of air changes
Variable gases in the atmosphere
Aerosols
Water vapour (H2O)
(1-4% of air.)
Dry air
Composition is constant. Does not include variable gases.
N2, O2, and Ar make up 99.96% of dry air.
Trace gases
Gases present in small amounts in the atmosphere, including CO2, CH4, O3, N2O.
Composition of air
DRY AIR
78.08% Nitrogen
20.95% Oxygen
0.93% Argon
VARIABLE GASES
1-4% Water vapour (H2O) & Aerosols
ALL OTHER/ TRACE GASES
0.04% CO2, Ne, He, CH4, Kr, N2O, H2, O3
What are the Greenhouse gases (GHG)?
CO2, H2O, CH4, N2O
Function of GHG
Absorb and re-emit infrared radiation (IR)
Creates a near-surface environment that is warmer than it would be if they were absent from the atmosphere
Global atmospheric CO2 levels
280ppm (pre-industrial era/ 1760s) -> 320ppm (1960s) -> 442ppm (2024)
Keeling’s curve
Charles David Keeling
Describes the dynamics of atmospheric CO2 level
One of the most important discovery in 20th century
Long term trend of atmospheric CO2
Rising due to fossil fuels burning.
Coals and oil containing C pulled out of the atmosphere over millions of years are returned to the atmosphere in a few centuries due to humans
Tripled from 11 billion tons/year in 1960s to 36.6 billion tons/ year inn2023. Concentration growth tripled from 0.8 ppm/year to 2.4 ppm/year during 2010s.
Atmospheric CO2 never exceeded 300 ppm in the 800,000 years based on air bubbles trapped in ice cores. Before Industrial Revolution (mid 1700s), was 280 ppm or less.
CO2 levels today are higher than any point in human history.
Seasonal pattern of atmospheric CO2
Reflects activity of the biosphere
During northern hemisphere summer, decreases as vegetation photosynthesis > respiration
During northern hemisphere winter, increases as plant respiration > photosynthesis
GHG’s residence time (RT) / life time + global warming potential (GWP)
CO2 = 50-200 years RT, 1 GWP
CH4 = 12+-3 years, 21 GWP
N2O = 120 years, 310 GWP
Fluorinated gases (F-gases) = very long RT, very strong GWP
Hydrofluorocarbons (HFCs) = 1.5-209 years, 150-11,700 GWP
Perfluorocarbons (PFCs) = 2,600-50,000 years, 6,500-9,200 GWP
Sulfur Hexafluoride (SFs) = 3,200 years, 23,900 GWP
Global emission profiles
Emissions: CO2 - 75%, CH4 - 18%, N2O - 4%, F-gas - 2%
Warming impact: CO2 - 64%, CH4 - 19%, CFC - 8.1%, N2O - 7.8%
Singapore’s overall emission profile (2022)
56.8MgT (million tons) CO2-equivalent (less than 0.1% global GHG emissions
86% of emissions are CO2. 2nd largest is HFCs, due to growing use of refrigeration and air-conditioning equipment.
Singapore’s emission profile breakdown (2022)
Industry (primary +secondary) - 68%, Transport - 14%, Buildings - 12.6%, Household - 6.2%
Singapore’s goal/ journey to net zero
Net zero by 2050: clean energy (solar), green transport and building, regulate energy efficiency in industry
Singapore’s carbon tax
~80% of GHG emissions in SG are covered by carbon tax
S$5/tCO2eq (2019-2023)
S$25/tCO2eq (2024-2025)
S$45/tCO2eq (2026-2027)
S$50-80/tCO2eq (2030)
Aerosols
Solid or liquid particles, suspended in the air; very tiny remain in the atmosphere very easily (<1 micrometer in diameter)
Sources of aerosol
Natural and anthropogenic sources:
Volcanic ash
Smoke from forest fires
Blown sea salt
Blown dust
Loess and pollen
Most anthropogenic particulates are pollutants that originate from burning of fossil fuels
Impacts of aerosol on Earth System
Primarily a cooling effect on the Earth System
Ideal nucleation sites for water droplets and ice crystals to form clouds - white that can reflect sunlight
Scattering effect of aerosols - scatter incoming solar radiation
> Sulfur-bearing aerosols from large explosive volcanic eruption have a cooling effect on earth (Applies to above water volcanos. Submerged volcanos have the reverse effect as aerosols are unable to enter the atmosphere, pushing the GHG water vapour into the atmosphere instead.)
Structure of the atmosphere - Troposphere
Bottommost layer of the atmosphere, extends to 6-16km
Tropopause (top of the troposphere) is higher in the tropics due to stronger convection.
Contains 80% of the air mass
Temperature decreases with altitude as air at bottom is warmed by IR emitted by land and ocean
Most weather is a consequence of thermal motion of air in the troposphere
Rise in tropopause (top of troposphere)
Potential reasons:
1. Tropospheric warming due to increasing GHGs
2. Stratospheric cooling due to stratospheric ozone depletion
Maximum increase found around 30-40°N, reasons unknown.
Potentially caused by tropical expansion and enhanced tropospheric warming in mid-latitudes.
Jet streams
A narrow, fast moving current air close to the Tropopause and generated due to temperature gradient between air masses across latitudes
Rising tropopause makes it difficult to locate jet streams. Uneven increase may weaken jet streams.
Structure of the atmosphere - Stratosphere
Higher than Troposphere
Location of most ozone, temperature increases with altitude due to absorption of incoming UV radiation by ozone.
Extends up to 50 km above the land surface.
Structure of the atmosphere - Mesosphere
Above Stratosphere
Temperature decreases with altitude, the coldest layer of the atmosphere, reaching a minimum of 100°C.
No ozone, limited absorption of solar energy
Extends up to 85 km above the surface
Structure of the atmosphere - Thermosphere
Above Mesosphere
Increasing temperature with altitude, reaches the highest temperature (direct absorption of sunlight and bombardment of gas molecules by protons and electrons from the sun)
Extends to 500 km, very little air mass
Hosts ionosphere, where auroras occur
Ozone (O3) in the Stratosphere
Photochemical reaction involving O2
Converts UV into heat, without net loss of O3. Absorption of UV radiation by O3 causes temperature in stratosphere to be higher than tropopause.
O3 mostly produced by chemical reactions in the atmosphere over the tropics (where there are more sunlight) and then distributed towards the poles by air circulation.
Ozone hole
An area where O3 concentrations drop below the threshold of 220 Dobson Units (1 Dobson Units = 10 nanometer)
In the upper stratosphere, UV light causes CFCs to break apart and release chlorine, a very reactive atom that repeatedly catalyses ozone destruction.
Full recovery of ozone expected in 2040-2050
Ozone trend
Though over Antarctica has been closing, ozone has been thinning at the lower latitudes, wheee sunlight is stronger.
Mostly produced over the tropics (where there is more sunlight) and then distributed towards the poles by air circulations.
Warming trends could be strengthening air circulation, moving more ozone to the poles and leaving less at lower latitudes.
Structure of the atmosphere - Moisture
Saturation: the maximum concentration of water vapour in the air; a balance of evaporation and condensation
Actual amount of water vapour in the air is referred to as vapour pressure (unit: kPa)
Maximum amount of water vapour in the air is referred to as saturated vapour pressure (SVP; unit: kPa)
Increases with temperature: molecular kinetic energy is greater under higher temperature, more molecules can escape into the air
Ratio of vapour pressure/SVP is relative humidity (RH)
Adiabatic lapse rate
Type of thermodynamic process which occurs WITHOUT transferring heat or mass between the system and its surroundings
Expansion in air volume decrease air temperature and vice versa.
Dry adiabatic lapse rate: 10°C/km in altitude
Moist adiabatic lapse rate: 6°C/km in altitude (on average)
Air parcel rises, water vapour saturates and condenses, releases latent heat to warm air
Foehn / Chinook/ Zonda wind
Cool, moist air approaches the windward side of mountains
Clouds form and rain falls, causing air to get dryer as it rises
Turbulence over mountains draws more moisture out of the air and forces it downwards; Dryer air from higher altitudes can join in
As the air travels down the leeward side of the mountains, dry, sunny conditions and increased air pressure combine heat and strengthen winds
Warm, dry Foehn winds are formed
Clouds
Visible aggregations of minute water droplets and ice crystals
Most are in troposphere, where most moisture stays.
Formed when air rises and becomes saturated with moisture due to adiabatic cooling
Reasons for air lifting
- Density lifting: warm, low density air rises convectively and displaces cooler, denser air
- Frontal lifting: two flowing air masses of different density and temperature meet
- Orographic lifting: flowing air is forced upwards as a result of passing over a sloping terrain
- Convergence lifting: flowing air masses converges and are forced upwards
Cloud types
Cumulus: puffy, globular, individual clouds (density lifting)
Stratus: sheets of cloud cover at 2-15 km altitude (frontal lifting)
Cirrus: highest clouds in the troposphere, fine, wispy feather like; mostly ice crystals
Stratocumulus: cumulus clouds coalesce to form a puffy layer; shape like a combination of stratus and cumulus
Cumulonimbus: large cumulus clouds rise to the top of the troposphere and expand horizontally — thunderstorms
Nimbostratus: cloud blanket of stratus is thick and the day is dark and dreary
