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48 Cards in this Set
- Front
- Back
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Pressure gradient force
Coriolis force Friction force Centrifugal force |
– air moves from HP to LP air movement can generate HP and LP
– apparent force on air motions due to earth’s rotation – force acting in the reverse direction of air movement (more important at surface) – force directed outward from axis of rotation |
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Horizontal pressures
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-Pressure gradient force
-Coriolis force -Friction force -Centrifugal force |
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Vertical pressures
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-Pressure gradient force
-Gravity |
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Geostrophic Wind
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-Parallel to straight isobars
-Balance of pressure gradient force and coriolis force -Good approximation for the movement of air above the boundary layer (friction negligible) |
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Gradient Wind
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-Along curved isobars
-Balance of pressure gradient force, coriolis force and centrifugal force |
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Semi-permanent pressure centers:
Thermal pressure centers |
-Semi-permanent pressure centers:
Visible on a sea level isobar map most of the year Located over the ocean -Thermal pressure centers: Form over land seasonally Form in response to surface heating or cooling |
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Low pressure systems:
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-Cloudy sky, stormy weather, high winds
-Rising air: upward movement of air pollutants -Clouds suppress photochemistry -Rain -> wet deposition -Reduces air pollution (but: potentially more re-suspension of soil dust!) |
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High pressure systems:
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-Low wind speed
-Sinking air: confinement of air pollutants -Cloud free conditions, effective photochemistry -Enhances air pollution |
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Vertical pollutant transport
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-Adiabatic and environmental lapse rate
-Stability -Temperature inversions Radiation inversion Large-scale subsidence Marine inversion Small-scale subsidence inversion Frontal inversion |
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Adiabatic Process
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Process by which no energy is exchanged between a system (parcel of air) and its surroundings (atmosphere).
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Adiabatic Expansion in Unsaturated Air
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1. Rising air expands
2. Expanding air cools -Rising air cools -Unsaturated air cools +10 oC per 1 km rise in altitude - dry adiabatic lapse rate Gd = +10 oC/km |
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Adiabatic Expansion in Saturated Air
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-Saturated air cools +6 oC per 1 km rise in altitude
= +10 oC/km cooling due to expansion -4 oC/km warming due to latent heat release -Wet adiabatic lapse rate Gw = +6 oC/km |
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Horizontal pollutant transport
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-Large-scale pressure systems affect
Wind direction Wind speed -Examples for long-range transport of air pollutants: From Asia to the West coast US From the Sahara to the east coast From the US to Europe From Eastern Europe to Scandinavia -Role of chimneys |
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Role of cloud cover
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-Reduce the penetration of UV
Photolysis is reduced below them. Photolysis can be enhanced above them, because of the reflected radiation. -Pollutants dissolve in cloud droplets and can be rained out. |
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Effects of local meteorology on air pollution
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-Ground temperatures
Determine inversion height, convection, and temperature dependent reaction rates. Affects wind speeds at surface -> enhanced trapping or dispersion of pollutants -Soil moisture Affects ground temperature: Soil water cools the ground due to evaporation and due to enhancing the specific heat of the soil-air-water mixture. -Land cover - Urban heat island effect |
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Heat-Island Effect
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-In crease urban temperatures result in increased mixing depths, faster near surface winds, lower air pollution.
-Possibly responsible to enhanced thunderstorm activity. |
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Local winds
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-Sea Breeze
-Valley and Mountain Breeze -Even on smaller scales: Winds around buildings |
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sea breeze
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Sea Breeze (lake breeze, bay breeze)
During day, land heats up relative to water Rising air over land, diverges aloft Air moves from water toward the land |
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valley/mountain breeze
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-Valley and Mountain Breeze
-Mountain slope heats more than valley -Heating causes air on the mountain slope to rise, drawing air up from the valley to replace the rising air. -During night, mountain faces cool rapidly -> air drains downslope. |
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Methods of Producing Elevated Pollution Layers
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Upper return flow of sea-breeze circulation
Mountain-chimney effect Injection of fire plume into elevated inversion Nighttime titration of surface ozone |
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Solar Spectrum
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-Solar Spectrum: UV, VIS, near-IR
- UV: filtered at stratospheric Ozone - VIS: keeps the Earth warm, the distance we can see, colors in the atmosphere - Sun’s Peak radiation: green color ( ~ vision peak 550nm) - When Solar Radiation passes through the atmosphere, it is attenuated or redirected by absorption and scattering by gases and particles. |
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Processes affecting radiative transfer
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-The overall decrease in radiation intensity when radiation is passing through a medium such as the atmosphere is termed extinction.
-Extinction of incoming radiation can be caused by the combined effects of scattering and absorption = extinction. -If the individual process is not addressed, the dominant physical process leading to an intensity decrease cannot be deter- mined. |
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Electromagnetic Waves
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- a bunch of types of radiation
-Radiation - traveling and spreading energy (Ex. Visible light: lamp, Radio waves: radio station) Ultra Violet (UV)Controls: photochemistry, skin color, can lead to cancer -Visible (VIS): -Infra Red (IR) |
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Solar Spectrum
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- Solar Spectrum: UV, VIS, near-IR
- UV: filtered at stratospheric Ozone - VIS: keeps the Earth warm, the distance we can see, colors in the atmosphere - Sun’s Peak radiation: green color ( ~ vision peak 550nm - When Solar Radiation passes through the atmosphere, it is attenuated or redirected by absorption and scattering by gases and particles. |
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extinction
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-The overall decrease in radiation intensity when radiation is passing through a medium such as the atmosphere
-Extinction of incoming radiation can be caused by the combined effects of scattering and absorption = extinction. -If the individual process is not addressed, the dominant physical process leading to an intensity decrease cannot be deter-mined. |
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Gas Absorption
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Radiative Energy (substance) Internal Energy Temp
-Gases selectively absorb radiation in different portions of the EM spectrum. - All absorb UV - a few absorb VIS - Photolysis |
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far uv
ozone |
far UV (<200nm): Absorbed by O2, N2 and O3
@ the Upper Stratosphere and the Mesosphere cannot reach the Troposphere Ozone (O3): absorbs UV and re-emits thermal-IR radiation + most UV-B (99%)is absorbed by O3 in the stratosphere + thinning of the ozone layer significant increase in the surface UV-B |
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other gases
Visible radiation absorbers |
Other Gases: (NO3, NO2, HCHO, HNO3, CO2 and H2O)
- Absorbs UV - too low concentrations to absorb significant UV radiation (in the stratosphere) - Visible radiation absorbers - NO2: polluted area / high mixing ratio - NO3: high conc. at night or in the early morning Reddish Brown color |
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Gas Absorption Extinction Coefficient
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the greater the absorption extinction
coefficient of a gas (σa,g,q) in the visible spectrum ↓ the more the gas reduces visibility The reduction in radiation intensity at a given wavelength with distance through an absorbing gas |
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Gas scattering
Rayleigh scattering |
Gas scattering: the redirection of radiation by a gas molecule without a net transfer of energy to the molecule
Rayleigh scattering: particle size << wavelength - Incident radiation is redirected symmetrically in the forward and backward direction. - All gas molecules are Rayleigh scatterers |
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- Aerosol:
- Hydrometeor particles: |
Aerosol:
Microscopic solid or liquid particles suspended in the atmosphere. (smokes, black carbon, mineral dust, sulfate - Hydrometeor particles: Any product of condensation or deposition of atmospheric water vapor, whether formed in the free atmosphere or at the Earth's surface; also, any water particle blown by the wind from the earth's surface. (ex. haze, cloud, fog, rain, freezing rain, snow, hail, |
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Absorbers of VIS radiation:
Absorbers of UV radiation |
Absorbers of VIS radiation:
* Black carbon (soot): - strongest VIS spectrum absorber - incomplete combustion of carbon-rich organic fuel * Hematite (Fe2O3): soil dust * Aluminum oxide: soil-dust and combustion particles. - Absorbers of UV radiation: * Black carbon, Hematite, Aluminum oxide * Nitrate aromatics, Polycyclic Aromatic Hydrocarbons (PAHs),… absorb UV radiation but little VIS radiation -Most PM are weak absorbers of VIS and UV: SiO2, NaCl, H2SO4 -Soil dusts are moderate absorbers of VIS and UV. |
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pollution
(dominated by UV absorption ptcls) |
-smog
-decrease in UV radiation -decrease in photolysis rates -decrease in ozone concentration |
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pollution
(dominated by UV scattering ptcls |
-smog
-increase in UV radiation -increase in photolysis rates -increase in ozone concentration |
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Reflection
Refraction Dispersion Diffraction Scattering |
-Reflection-The bounce off of light from an object at the angle of incidence
-Refraction-Bending of light as it travels between media of different density -Dispersion-Separation of white light into colors -Diffraction -Bending of light around objects -Scattering-Combination of reflection, refraction, dispersion, diffraction. The deflection of light in random directions. |
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Aerosol and hydrometeor particle scattering
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redirection of incident energy by a particle without
a loss of energy to the particle. reflection, refraction, and diffraction |
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Reflection
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- Change in direction of a radiation at an interface between two different media
- The angle of incidence will be equal to the angle of reflection (Billiard) - No energy is lost during reflection - The colors of most objects that we see are due to preferential reflection of certain wavelengths by the object. |
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Refraction
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- Change in direction of a radiation due to a change in its speed
(commonly seen when a wave passes from one medium to another; different density) - Changing the angle of the incident wave relative to a surface normal - If a wave travels from a medium of one density to a medium of a higher density, it bends toward the surface normal. -waves cannot pass through the interface; total reflection |
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Huygens' principle
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-Each point of an advancing wavefront may be
considered the source of a new series of secondary waves |
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single-particle scattering efficiency:
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the ratio of the effective scattering cross section of a particle to its actual cross section. Can be above unity since portion of radiation diffracted around particle can be intercepted and scattered.
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single-particle absorption efficiency
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the ratio of the effective absorption cross section of a particle to its actual cross section. Can be above
unity since portion of radiation diffracted around particle can be intercepted and scattered. |
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visibility
visual range |
Visibility:
- a measure of how far we can see through the air * To describe maximum visibility Visual Range - the actual distance at which a person can discern an ideal dark object against the horizon sky. |
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Prevailing visibility
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-Prevailing visibility - the greatest visual range a person can see along 50%(180o) or more of the horizon circle(360o) but not necessarily in
continuous sectors around the circle. (half the area around an observation point may have visibility worse than the prevailing visibility) -Meteorological range (standard visibility) - A concept developed to keep consistency of the visibility measurement. |
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Effects of gases on visibility
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-N2, O2 mixing ratios do not change much between clean and polluted air
- MR does not change much -when the NO2 mixing ratio increased from .01 to .25 ppmv visibility↓↓ -MR decrease: Rayleigh Scattering << NO2 absorption - NO2 attenuates visibility in urban air when its mixing ratios are high Ptcl scattering dominated on both days -(less polluted) gas scattering, gas absorption and ptcl absorption- small effect -(polluted) ptcl scatt. > ptcl absorp. > gas absorp. > gas scatt. |
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Red sunset and blue skies
Rainbows White Hazes and Clouds |
preferential scattering of light by gas molecules
interactions of light with raindrops water drops scatter all wavelengths of VIS with equal intensity |
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Reddish and Brown Colors in smog
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-- Preferential absorption of blue and some green light by NO2
-- Preferential absorption of blue, light by PAHs and nitrated aromatics in particles -- when soil dust concentrations are high preferentially absorb blue and green light |
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Models Predict
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-Increase in avg. surface T
-Increase in avg. precipitation at equator and poles, but decrease at mid-latitudes -Decrease in sea ice extent -Decrease in ocean pH (more acidic) |
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natural greenhouse effect
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-Warming of the Earth’s atmosphere due to natural gases that transmit the sun’s radiation, but absorb the Earth’s IR radiation.
-These gases are mainly water vapor and CO2. Others are CH4, O3, N2O, CH3Cl. |
