环境化学英文课件6教学内容

1、环境化学英文课件6Cloud Greenhouse Forcing: WarmingLongwave radiationWhen a cloud absorbs longwave radiation emitted by the Earths surface, the cloud re-emits a portion of the energy to space and a portion back toward the surface. This process is called cloud greenhouse forcing and, taken by itself, tends to

2、 cause a heating or positive forcing of the Earths climate.Overall effect of all clouds Cloud albedo forcing cooling Cloud greenhouse forcing warming The overall effect of all clouds together is that the Earths surface is cooler than it would be if the atmosphere had no clouds The dominate factor in

3、 the global albedo is clouds.Aerosol: Definition Aerosol is a suspension of solid or liquid particles in a gas. Atmospheric aerosols consist of small particles of liquid and solid material suspended in the air. Bioaerosol: An aerosol of biological origin. (Examples: viruses, bacteria, fungi, spores,

4、 and pollens.) Aerosol sizes are usually measured in the unit of micrometer (mm) 1 mm = 106 m 1 mm = 104 angstrom ()Typical Particle Diameters (mm)Photochemical aerosols0.01-1Tobacco smoke0.25Coal fly ash1-50Flour dust15-20Pollens15-70Human hair: 25-100 mmExample images of atmospheric particlesSourc

5、e: http:/www.mpch-mainz.mpg.de/kosmo/Aerosol sourcesAerosol sources Windblown dust from Desert Sulfate aerosol from volcano eruption, fuel combustion and microbial activities. Seasalt aerosol from seaspray and bubble bursting Soot from fuel combustion Secondary organic aerosol from volatile organic

6、compoundsAerosol Radiative Forcing: direct effect The effect of aerosol on the energy flux of the atmosphere depends on particle size and composition. Dark particles (sootcontaining) tend to absorb light, thus warming Earths atmosphere. Small particles tend to scatter light, thus increasing the albe

7、do of the atmosphere.Aerosol and cloud condensation nuclei (CCN) Cloud Condensation Nuclei (CCN) are particles that can become activated to grow to fog or cloud droplets in the presence of a supersaturation of water vapor. If the Earths atmosphere were totally devoid of particles, clouds could not f

8、orm.Aerosol radiative forcing: indirect effectAn increase in the number of atmospheric particles would increase the number of cloud condensation nuclei, therefore more cloud cover and higher albedo Ship tracking phenomenonVolcanoes and climate changeLarge volcano eruptions provide dramatic evidence

9、of the ability of aerosols to affect global climate.Mt. Pinatubo eruption made 1992 the coolest year since 1986Red line: modeled temperature changes Blue line: temperature changes observed from meteorological ground stationsVolcanic CoolingLarge volcanic eruptions can cool the Earth by increasing th

10、e albedo. Calculate the expected temperature change if the albedo increases from 30 to 30.5 percent. Compare this estimate with the temperature record after the Mt. Pinatubo eruption.(Textbook, pp150).1816-the year without a summer In 1815, Tambora in Indonesia exploded and the volcano dust blankete

11、d the Northern Hemisphere. The following year, 1816, daily minimum temperatures were abnormally low in the northern hemisphere from late spring to early autumn. Famine was widespread because of crop failures. An estimated 82,000 were killed indirectly by the eruption by starvation, disease, and hung

12、er. Sulfate aerosol formation from volcano eruptions Large amount of SO2 is injected into the atmosphere from the force of the volcano eruption. SO2 can be converted to sulfate in gas and aqueous phase. In gas-phaseSO2 + .OH + M HOSO2. + MHOSO2. + O2 HO2. + SO3SO3 + H2O + M H2SO4 + M Sulfate aerosol

13、 formation from volcano eruptions (Continued) In aqueous phase, dissolved SO2 is oxidized to sulfate by O3(dominant pathway when pH5) H2O2 (dominant pathway when pH5) organic peroxides O2 catalyzed by iron and manganese The oxidation of SO2(aq) by H2O2 proceeds as follows: HSO3- + H2O2 SO2OOH- + H2O

14、 SO2OOH- + H+ H2SO4Sulfate formation from biogenic gases Dimethylsulfide (DMS): CH3SCH3 Marine origin Produced in plankton by the enzymatic cleavage of dimethylsulfonopropionate, a compound that help plankton achieve osmotic balance in the salty ocean water. Oxidation of DMS SO2 sulfate H2S Terrestr

15、ial origin Produced by sulfate-reducing bacteria.Example: Kuwait Oil Fires Air temperatures below the plumes were reported to be about 7oC lower than in adjacent areas without smoke. Coldest May in 35 years. Average temperatures were about 4oC lower than normal. Aerosol Effects on ClimateDirect Effects Aerosols scatter and absorb visible and infrared radiation Overall effect: cooling Light scattering depends on size distribution and index of refraction of the particl