Lecture 11 - Air Pollution Meteorology

Question 1

Layers of the Atmosphere

Answer 1

troposphere (0 - 10km) mixing happens in 2- 3 days, pressure and density decrease rapidly with height
stratosphere (10-30km) much less mixing

planetary boundary layer - part of the troposphere influence by earth’s surface (coriolis force etc). higher than you have geostrophic winds

Question 2

main forces on pollutants

Answer 2

general mean motion from advection, turbulent diffusion - (due to random wind motion forming eddies), mass diffusion (due to concentration gradients, fickian diffusion, much less important than turbulent diffusion),

Question 3

key factors influencing pollutant concentrations

Answer 3

wind speed and direction: pressure gradients, convective circulation, coriolis force, surface friction
turbulence: determined by temperature profiles, wind profiles, atmospheric stability, turbulence, mixing, dilution, concentration

Question 4

Winds

Answer 4

pressure gradient force (from high to low),
convective circulation - winds result from imbalance in moisture, temperature, pressure or moisture, pressure gradients, gravity, friction, coriolis force

surface winds shift clockwise as you increase in z

Question 5

Coriolis force

Answer 5

comes from spinning earth. winds deflect to the right in the northern hemisphere. directed 90deg to to the right of the direction of motion, 0 at the equator

Question 6

why is wind speed important in dispersion modeling

Answer 6

travel time, dilution, plume rise, building downwash (generally we want to guess wind speed at plume center)

Question 7

wind speed profile

Answer 7

use the power law for wind speed extrapolations, exponent is based on atmospheric stability determination

Question 8

wind rose ….

Answer 8

…. there are also pollution roses. frequency of calms is also important to note

Question 9

scale of motion for winds

Answer 9

macroscale - 1000km - highs and lows - days weeks
mesoscale - 10 - 100km - sea breeze urban heat island, mountain valley wind,
microscale - 1 - 10km - plume meandering, building downwash

Question 10

Macroscale flows

Answer 10

anticyclonic flows - high pressure region, air subsiding down, outward, clockwise at surface, associated with air pollution episodes

cyclonic flows - low pressure region , air rise and cool, precipitation, counter-clockwise at surface

Question 11

Mesoscale flows

Answer 11

associated with rough terrain, urban heat island (low wind speeds also allow for recirculation in the immediate area), sea breeze, mountain breeze (Affected by orientation with respect to sun & direction and strength of prevailing winds. Strong winds will suppress features.)

Question 12

Microscale flows

Answer 12

caused by mechanical and thermal turbulence, results in wind field deformations, separated flows, isolation surface, cavity (region of separated flows)

downwash (downward dispersion of a plume, results in high concentrations near the ground surface, can be avoided with larger stacks, can be terrain or building induced)

city canyon effect, valley wind (katabatic wind)

Question 13

Inversions

Answer 13

sea breeze -
frontal - uncommon, warm air slides up
subsidence - high pressure, air pollution episodes
nocturnal - common in desert

Question 14

Plume behavior

Answer 14

during the day, at night, in different types of eddies (small eddies, large eddies, varied eddies)

fanning, fumigation, looping, coning, lofting, trapping

Question 15

Environmental Lapse Rate

Answer 15

unstable, nuetral, stable, isothermal (inversions happen when lapse rate is positive)

can have both dry (unsaturated air) or wet (saturated air) adiabatic lapse rate

an air parcel stops moving when its density is equal to the surrounding air

stability, adiabatic process (no heat transfer) [compression and warming of air moving down, expansion and cooling of air moving up], absolute / relative humidity, saturated vapor pressure,

Question 16

neutral atmosphere, stable atmosphere

Answer 16

netural dry adiabatic lapse rate = wet adiabatic lapse rate. ball on a table.

stable = environment < standard (Parcel rising cools following dry adiabatic lapse rate has a lower temperature than surrounding air, thus higher density. Thus air doesn’t move). ball in a valley

unstable = parcel rising cools slower than surroundings, thus it keeps rising. ball on top of a hill

Question 17

Mixing height

Answer 17

the vertical extent of dilution, persistent low mixing heights associated with air pollution events. also has seasonality. measured by weather balloon and radiosode