Lecture 4

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University of Toronto Scarborough
Environmental Science
Tanzina Mohsin

Lecture 4: Atmosphere-Climate System Composition and Structure of the Atmosphere • The very early atmosphere probably consisted of gases, mainly hydrogen and helium, which was abundant in the solar system • Then came the geologic control o Under geologic control, a secondary atmosphere was formed: Out gassing from cooling magma Emissions from volcanoes o Essentially no atmospheric O2, and highly corrosive o Highly energetic-lightning, volcanic activity, high UV radiation • Then the biological control o Anaerobic conditions “Age of Bacteria” o Anaerobic bacteria developed about 3.5 to 4 bya o Could survive in absence of oxygen and began the slow conversion of CO2 to O2 • Gaia Hypothesis o James Lovelock, not about environmental control, life modifies the environment to best suit itself o Atmospheric constituents have been controlled by life to optimize conditions for life o Abrupt change occurred 2.3 bya, Os started to appear o As O2 started to become abundant, some was broken down by the sun’s radiation into atomic O2 and eventually formed ozone O3 o Life started to appear o Evolution of the Atmosphere Once rocks at surface were sufficiently oxidized, more oxygen could remain free in atmosphere There was switch from anaerobic to aerobic condition 2.3 bya 2.3 bya solar output increased and earth was becoming too warm, the switch to aerobic life, reduce the greenhouse gases and cooled the planet Now have lower levels of CO2 in atmosphere than early earth O2 stabilizes at 21%, which is optimal for life on earth • Then came the Anthropogenic control o During Carboniferous Period (290-360mya) life appears on land Sun’s energy converted to plant material (photosynthesis) Decaying plants not fully oxidized Converted to coal and oil under geologic pressure, stored for millions of years We used these fossil fuel for our comfort o Composition now Atmosphere currently consists of water vapour, aerosols (gaseous suspensions of find solid or liquid particles) Water vapour- less than 0.0001% of all the water on earth Aerosols O2 21%, N2 78% Ar 1% If all water vapour in atmosphere converted to liquid would cover entire earth surface by 1 inch (25mm) smooth layer Greenhouse Effect and Radiation • 2 types of radiation: short wave and long wave • GHG is atmospheric constituent that traps outgoing terrestrial radiation • Water vapour is the most important GHG in atmosphere • Understand the difference between GHG and enhanced GHE www.notesolution.com • Some of Sun’s radiation absorbed by natural GHG o If there is no GHG, earth will be very cold (-33), GHG absorb radiation and keeps earth warm o Enhanced GHG, is causes by burning fossil fuel, CO2 emitted, CH4, O2, N2O, CFCs o Helping the inducing of water vapour by increasing GHG into the atmosphere- positive feedback loop • Water vapour is most important GHG in atmosphere • Understand the difference b/w greenhouse effect and enhanced greenhouse effect Atmospheric Moisture • Standard atmosphere o To understand the changes within the atmosphere, have to have a standard o Pressure: 1013.25mb, temperature: 15 degree Celsius, air density: 1225 g m-3 o Air density changes with altitude, it changes rapidly o 4 layers in atmosphere Troposphere- 0-10 temperature decrease with altitude, at surface, heated by sun’s ray Stratosphere- 20-50, temperature increase with altitude, have ozone that absorb UV radiation and turns into kinetic energy of motion Mesosphere- very unstable zone where there is high mixing Thermosphere- lots of O2 and O3, absorbs sun’s rays and turns into kinetic energy of motion o Variations with latitude Troposphere thicker in the tropics, thickness decreases as it goes towards the poles o Latent heat is released when one state changes to another state o Most water vapour enters atmosphere over the oceans o Relative humidity: indicates the amount of water vapour that can still enter the air mass before being saturated o Warm air holds more water vapour o Clouds form as warm air rises, expands, cools- holds less moisture o Lapse rate: change in temperature with heights that is associated with pressure, as pressure decreases, volume increases and temperature drops Warm air rises and it expands- volume increases Air parcel at 0m has a temperature of -10 degrees, it rises at dry adiabatic lapse rate. What is temperature of air parcel at 1km is -20 degrees, if air parcel drops 1 km, it is 0 degree o The adiabatic lapse rate: measure of how much air decreases in
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