Ch 3 Earth s Modern Atmosphere Wednesday September 17 2014 4 10 PM Earth s Modern Atmosphere Atmosphere is a very thin layer of gases If earth is the size of an apple the atmosphere is the thickness of the skin Without it no life on earth It is a protective filter maintains the temperature Composition of the Atmosphere Nitrogen 78 Oxygen 21 CO2 0 039 Argon 0 9 Others 0 06 Atmospheric Pressure All of these gases are held down by gravity Gravity compresses air denser near the surface Air thins rapidly with altitude 50 of atmospheric mass is in bottom 5 5 km 99 9 is below 50 km Pressure decreases exponentially with height Atmospheric Profile Atmosphere extend to 32 000 km from surface Exosphere extremely few hydrogen helium atoms are held by gravity Thermosphere is at 480 km 1 Atmospheric Composition Heterosphere Outer atmosphere begins ar 80 km and goes up less than 001 of the atmosphere gases sorted by grav heterogeneous stratified by atomic weight Homosphere inner atmosphere gases evenly mixed concentrations are homogeneous extends from surface to 80 km 2 Atmospheric Temperature Thermosphere 80 km outward roughly same as heterosphere Temperatures very high 2200 degrees F but very little heat high vibration kinetic energy Mesosphere Temperature decreases with altitude lowest temperatures in the atmosphere 50 to 80 km Top of the mesosphere is the mesopause Stratosphere Temperature increases from 57 degrees C at bottom to 0 degreed C at the top the stratopause 18 to 50 km Troposphere Temperature decreases at rate of 6 4 degrees C per km Where all weather occurs extends from surface to about 18km Top is the tropopause but it s height varies Thickness of tropopause varies by latitude equator 18km poles 8km and by season thinner in winter Thicker in higher temperatures 3 Atmospheric Function Ionosphere Spans across mesosphere and thermosphere Changes incoming particles from atoms to ions Where auroras occur Absorbs cosmic rays gamma rays x rays and some UV rays Ozonosphere Part of the stratosphere What s important about the ozone Ozone Oxygen O2 in the stratosphere is split into two O atoms from exposure to light Photodisassociation O2 O3 light O O Oxygen atom quickly bonds with oxygen molecule forms ozone O O2 O3 Ozone absorbs UV radiation O3 UV O2 O Endless process that absorbs most of the harmful UV radiation Ozone Hole Not actually a hole but a thinning of the O3 layer Ozone layer normally only about 3mm thick Synthetic compounds from refrigerants propellants UV radiation strips chlorine Cl off CFCs which then splits O3 Cl O3 ClO O2 ClO O Cl O2 Chlorine is used and reused Montreal Protocol 1987 has reduced and phased out the use of CFCs Ozone hole may be getting smaller but too soon to say if it s recovering In 1960s the concentration of ozone was high and started decreasing until the late 80s and early 90s where the ozone concentration was stable In the early 2000s the concentration began to rise again Ozone layer protects us from UV radiation With very high level 8 10 UV radiation in Texas we need to minimize sun exposure and use sunscreen UV index in Texas was higher in the summer months than in the winter months Variable Atmospheric Components In addition to N2 O2 etc atmosphere also contains Variable gases Carbon dioxide monoxide methane sulfur Particles smoke ash dust pollen salt Chemicals smog Sources Natural Anthropogenic Transported Aerosols and Atmospheric Components Mount Pinatubo Eruption 1991 Philippines 15 20 million tons of sulfur dioxide into the stratosphere Mount Pinatubo erupts June 25 1991 From June January particles in the atmosphere increased Southern California Wildfires Natural Factors That Affect Air Pollution Winds Transport variable components Disperse pollution or concentrate it Saharan Dust The dust that arose along the China Mongolia border on March 8 2013 Arctic Haze due to anthropogenic air pollution in other parts of the world Local and regional landscapes Volcanic landscapes Mountain barriers Valleys Volcanic Smog Vog Temperature Inversion Temperature normally decreases throughout the troposphere Inversion layer layer where temperature suddenly increases The inversion layer traps the air so it cannot mix with the air above the layer Winter smoke in Shanghai China inversion layer Anthropogenic Pollution Anthropogenic human caused Small particles of dust soot and pollution aerosols from urban industrial fires Carbon monoxide CO From burning e g deforestation 90 of CO pollution is natural only 10 is anthropogenic Photochemical smog Primary anthropogenic pollutant From transportation Combination of sunlight car exhaust Industrial smog and sulfur oxides Pollutions from coal burning industries In virtually all industrialized countries Particulates Particulate Matter PM Fine dust particles harmful to people Can get into lungs and even bloodstream Distribution of Anthropogenic Pollution Automobiles account for 50 60 of anthropogenic air pollution Carbon monoxide s contribution comes from 77 1 transportation Nitrogen Oxide s contribution is 55 5 transportation Sulfur dioxide s contribution is 85 3 Fuel combustion Particulate Matter s contribution is 41 5 Industrial processes Volatile organic compounds contribution is 47 transportation