中国地质大学武汉环境化学02Atmosphericstructureandcomposition.ppt

Chapter two,Atmospheric Structure and Composition,1. Atmospheric Structure,The atmosphere Atmospheric Structure Troposphere Stratosphere Mesosphere Thermosphere Ionosphere atmospheric pressure Wind and pressure Atmospheric Circulation,The atmosphere,The atmosphere is a thin blanket of gas that envelops the earth. The gases that make up the atmosphere are held close to the earth by the pull of gravity. With increasing distance from the earths surface, the temperature, density, and composition of the atmosphere gradually change On the basis of air temperature, the atmosphere can be divided vertically into four major layers.,The atmosphere functions as,A highly effective regulator of heat and radiation, the principal sources of energy for life. A radiator: Protects the biosphere (where life is foundabout 21 km thick) from harmful forms of incoming solar radiation As a heat regulator, the atmosphere slows the loss of heat from earth, a process called the GREENHOUSE EFFECT,Atmospheric Structure,Atmospheric Structure,Troposphere,The troposphere is the layer from the earths surface to the tropopause, which is at 10-15 km altitude depending on latitude and time of year. (Mt. Everest 8.85km) As altitude increases, air temperature decreases at a rate of about 3.5o per 1000 ft. The tropopause has a temperature of about 57oC. The lower part of the troposphere interacts directly with the surface of the earththis part of the troposphere is generally called air. The atmosphere in this layer is heated from below by convection and radiation from the earths surface. Most of our weather occurs in the troposphere.,Troposphere Structure,Stratosphere,The stratosphere is the layer above the troposphere and extends to about 50km. The temperature rises with increasing altitude, reaching a maximum of about 1oC at the stratopause. The ozone layer is in the stratosphere. Ozone absorbs UV, causing the rising temperature with altitude in this layer. The temperature structure keeps the air calm in this layer. (Thats why jet aircraft fly in the lower stratosphere!),The lower atmosphere,The troposphere and the stratosphere together are called the lower atmosphere. The lower atmosphere account for 99.9% of total atmospheric mass The lower atmosphere is the domain of main interest from an environmental perspective. Ozone depletion (stratosphere) Air pollution (troposphere),Mesosphere,The mesosphere extends from the top of stratopause to 80 km. In the mesosphere, the temperature decreases with altitude.,Thermosphere,The layer of air above mesosphere is called thermosphere. In the thermosphere, temperature rises with altitude, caused by absorption of UV solar radiation by N2 and O2.,Ionosphere,Ionosphere is a region where ions and electrons are most abundant. This region is located at altitude above 60km, therefore lie within the mesosphere and above.,Ionosphere,Ionosphere acts as a conducting layer in the upper atmosphere that would allow a transmitted electromagnetic signal to be reflected back toward the Earth.,Ionosphere: Northern light (1),Ionosphere: Northern light (2),Energetic events on the Sun can turn the solar wind into an intense solar “gale” which injects large numbers of energetic particles in the Earth's magnetosphere.,Ionosphere: Northern light (3),The charged particles travel along the field lines with so much energy that they penetrate the ionosphere, where they hit gas atoms and molecules. These collisions give off energy that we see as colored light.,Base on Composition,Homosphere vs. Heterosphere 均质层和非均质层 Transition zones between layers Tropopause对流层顶 Stratopause平流层顶 Mesopause中间层顶,Atmospheric pressure,The atmospheric pressure is the weight exerted by the overhead atmosphere on a unit area of surface,A,B,h,vacuum,Mercury barometer,Air pressure is greatest at earths surface, 14.7 lbs/sq. in, about 1013.2 millibars As you climb higher, air temperature decreases. Typically, air temperatures decrease about 3.6 F per 1,000 feet of elevation.,Mass of the atmosphere,Ps: the global mean pressure at the surface, Ps=9.84x104Pa. R=6400 km, the earth radius g=9.8m2/s, acceleration of gravity,Results: ma = 5.2x1018kg,Pressure profile,Pressure profile,Barometric law,Where Ma: the molecular weight of air g: acceleration of gravity R: gas constant T: temperature z: altitude,What fraction of total atmospheric mass is in the troposphere?,The troposphere contains all of the atmospheric mass except for the fraction P(tropopause)/P(surface) that lie above the tropopause.,P(tropopause) = 100 hPa P(surface)=1000hPa Result: Ftrop =0.90,Units for pressure,International System of Units: Pascal (N/m2) Hectopascal (hPa) mm Hg or Torr Millibar (mbar) psi (lb/in2),1 atm = 1.01325 x 105 Pascal (Pa) = 1.01325 x 103hPa 1 atm = 760 mmHg = 760 Torr 1 atm = 1013.25 mbar 1 atm = 14. 7 psi,Wind and pressure,Wind is driven by differences in pressure Air in a high pressure area compresses and warms as it descends. The warming inhibits the formation of clouds, meaning the sky is normally sunny in high-pressure areas. But haze and fog still might form. Just the opposite occurs within an area of low atmospheric pressure,Global pressure belts,Semipermanent暂时的 pressure systems Belts of pressure that more or less encircle the globe depending on latitude Origins Thermalheating and cooling of surface and atmosphereheat (low pressure), cool (high pressure) Dynamicfrom wind movement, as when 2 systems meet and the air is forced up (low pressure), or when air flow forces wind down (high pressure),Atmospheric Circulation,Global circulation Governed by two factors Uneven solar heating The rotation of the earth Coriolis(法国数学家) effect,Hadley cells Ferel cells Polar cells,Equatorial low pressure system The first belt of pressure Intertropical convergence zone (ITC) Converging wind systems along the Equatorial low pressure system Coriolis effect An apparent force resulting from the earths rotation,Surface wind and pressure,Wind patterns,Doldrums赤道无风带 Intertropical convergence zone or ITCZ热带集中带 Horse latitudes大西洋无风带 Trade winds信风 Westerlies西风带 Polar easterlies极地东风带 Geographic equator地理赤道 Meteorologic equator气象赤道,wind,Monsoon 季候风 Sea breeze 海风(白天吹向内陆地) Land breeze 陆地吹向海上的风 Storms 暴风 Cyclones 飓风 Tornado 龙卷风/台风,2. Atmospheric Composition,Composition of the atmosphere Water vapor in the air Expressing the amount of substances in the atmosphere Origin of the Atmosphere Relative Humidity,Composition of the atmosphere,Water vapor in the air,The % volume of Water vapor is variable, depending on temperature, precipitation, rate of evaporation and other factors at a particular location. The percentage of water vapor ranges from 0.1-5%. Generally it is 1-3% (the 3rd most abundant constituents in the air).,Expressing the amount of substances in the atmosphere,Concentration the amount (mass, moles, molecules, etc) of a substance in a given volume divided by that volume. The example concentration units are mg/m3, mol/m3, molecules/cc, and etc. Mixing ratio the ratio of the amount of the substance in a given volume to the total amount of all constituents in that volume.,Mixing Ratio,ni is the molar concentration of i and ntotal is the total molar concentration of air. parts per million (ppm) 10-6 mmol mol-1 parts per billion (ppb) 10-9 nmol mol-1 parts per trillion (ppt) 10-12 pmol mol-1,Conversion between ppm and mg/m3,ni: mol/m3 mi: mg/m3 Mi: g/mol,Pressure unit and R Constant: P= 1.01325x105 pascal R= 8.314 J/k.mol for P in Pa and volume in m3,Example:,The Hong Kong Air Quality Objective for ozone is 240 mg/m3. The U.S. National Ambient Air Quality Standard for ozone is 120 ppb. Which standard is stricter at the same temperature (25oC) and the pressure (1atm)?,Typical mixing ratios for some compounds of environmental importance,ppm in solution vs. ppm as mixing ratio for airborne substances,solution,air,Important gases for Environ. Changes,Carbon dioxide An important heat absorbing gas. Plays an important role in the Greenhouse effect. Since the Industrial Revolution in the 18th century, has increased by about 30% (from 280 to 365 pts/million) from increasing amounts of carbon-based fossil fuel use.,Ozone: As atmospheric oxygen increased, this led to the formation of the ozone layer. This layer, approximately 8 to 30 km above the surface, helps to filter the ultra-violet portion of the incoming solar radiation spectrum. Therefore, as levels of harmful ultraviolet radiation decreased, so plants were able to move to progressively higher levels.,Water vapor Mainly through evaporation from the oceans, That depends on air temperature: the warmer air is the greater amount of water vapor, and vice versa. Airborne particles Liquid particles are water droplets in cloud and fog Solid particles are dust from soil erosion and volcanic eruptions, pollen from plants, salt crystals from ocean spray, air pollution,Origin of the Atmosphere,Volcanoes release H2, CO2, H2Ov, N2, NH3, CH4 No O2 or O3, so no land organisms! One-celled aquatic organisms release CO2 to atmosphere when breaking down food through fermentation发酵 Simple aquatic plants took in CO2 and released O2 to atmosphere via photosynthesis O3 formed from the O2,CO2 gets stored in shells and decaying plants N2 builds up in atmosphere,Relative Humidity,Definition: ratio of the partial pressure of water to its saturation vapor pressure at the same temperature.,y: mole fraction of water vapor at temperature T ys: mole fraction of saturation water vapor at Temperature T,Calculation of H2O mixing ratio in ppm from RH,= p exp13.3185a - 1.976 a2 - 0.6445 a3 -0.1299 a4 Where, p = 1 atm and a = 1-(373.15/T).,