Boundary-Layer Meteorology and Atmospheric Dispersion Dr. J. D. Carlson Oklahoma State University Stillwater, Oklahoma

Mechanisms of Heat Transfer in the Atmosphere-Earth System Radiation (no conducting medium) Sensible Heat Transfer (large-scale movement of heated material) Latent Heat Transfer (change of phase associated with water) Conduction (molecule to molecule)

in the Earth-Atmosphere System RADIATION in the Earth-Atmosphere System

Shortwave Radiation Longwave Radiation SUN EARTH

Longwave Shortwave

THE GREENHOUSE EFFECT

MERCURY VENUS Sunlit Side = 800 F Dark Side = -279 F NO Greenhouse Effect VENUS Surface Temp = 900 F Large Greenhouse Effect

RADIATION AT THE EARTH’S SURFACE SW SW LW LW Shortwave (solar) radiation reaches a portion of the earth’s surface (SW ) A portion of that solar is reflected back (SW ) Albedo (α) = the fraction of solar radiation reflected (SW = α SW ) Albedo values: Dark soil 0.05-0.15 Dry sand 0.25-0.40 Meadow 0.10-0.20 Forest 0.10-0.46 Water 0.05-0.10 Fresh snow 0.7-0.9 Old snow 0.4-0.7 The surface receives longwave (infrared) radiation from the sky (LW ) The surface emits longwave radiation to the sky (LW ) The sum of the four radiation terms is often called “Net Radiation” (R)

(How is the net radiation partitioned at the earth’s surface ?) SURFACE ENERGY BUDGET (How is the net radiation partitioned at the earth’s surface ?)

SURFACE ENERGY BUDGET DAY NIGHT SW = shortwave radiation received SW = shortwave radiation reflected LW = longwave radiation received LW = longwave radiation emitted H = sensible heat transfer by turbulence, advection, convection LE = latent heat transfer (change of phase: evaporation, condensation, freezing, thawing) G = heat transfer through the submedium (conduction) SW + SW + LW + LW + H + LE + G = rate of warming or cooling of surface DAY LE G Energy Units +20 -4 +4 -11 -1 -4 -2 = +2 (surface warming) +9 -7 NIGHT LE G Energy Units +4 -11 +1 +3 +1 = -2 (surface cooling) -7 +5

ATMOSPHERIC BOUNDARY LAYER Daily Behavior under High Pressure Regimes

= LAPSE RATE ∂T T2 – T1 ∂z z2 – z1 Typical Vertical Profiles of Wind and Temperature during the Course of a 24-h Fall Day with Clear Skies (note formation and growth of temperature inversion during the night) “Inversion” = temperature increases with height =

T2, z2 LAPSE RATE ∂T T2 – T1 ∂z z2 – z1 T1, z1 =

Surface Radiation Inversion

Temperature Profile Radiation Inversion

Subsidence Inversion HIGH PRESSURE

Temperature Profile Subsidence Inversion

ATMOSPHERIC DISPERSION 1. General mean air motion that transports the pollutant a. horizontally - “advection” b. vertically - “convection” 2. Turbulence - random velocity fluctuations that disperse the pollutant in all directions 3. Molecular diffusion - due to concentration gradients

Mechanical (wind-related) 2. Thermal (temperature-related) TURBULENCE Mechanical (wind-related) 2. Thermal (temperature-related)

MECHANICAL TURBULENCE Speed shear Directional shear Surface frictional effects

THERMAL TURBULENCE

DENSITY DEPENDS ON TEMPERATURE Ideal Gas Law: PV = nRT (P = pressure, V = volume, n = # moles, R = Universal gas constant, T = Absolute Temp) Can be rewritten: P = rRT, where r = Density For two air parcels at the same pressure, the warmer parcel has the lower density: r = P / RT

without any heat exchange) ADIABATIC LAPSE RATE (rate of temperature change that an air parcel experiences as it changes elevation without any heat exchange) (dT/dz)adiab = Γ = - g/cp = -1C/100 m = -5.4F/1000 ft z T

ENVIRONMENTAL LAPSE RATE (actual rate of temperature change with height of the current atmosphere) (∂T/∂z)env = environmental lapse rate z T

(∂T/∂z)env < Γ (∂T/∂z)env = Γ (∂T/∂z)env > Γ

THERMAL STABILITY (∂T/∂z)env < Γ Unstable (∂T/∂z)env = Γ Neutral (∂T/∂z)env > Γ Stable

TYPES OF ATMOSPHERIC DISPERSION Weather Factors Side View (vertical dispersion) Top View (horizontal dispersion) UNSTABLE ATMOSPHERE NEUTRAL STABLE TYPES OF ATMOSPHERIC DISPERSION

PLUME BEHAVIOR

Unstable Atmosphere – Good Dispersion

LOOPING Larger scale convective turbulence dominates Γ (adiabatic) environmental Larger scale convective turbulence dominates Strong solar heating with generally light winds Super-adiabatic lapse rates

Neutral Atmosphere – Moderate Dispersion

CONING Γ Near neutral conditions (adiabatic lapse rates) Overcast days or nights Moderate to strong winds Small-scale mechanical turbulence dominates

Stable Atmosphere – Poor Dispersion

FANNING Γ Strong inversion (large positive lapse rate) at plume height Extremely stable conditions (buoyancy suppression) Typical of clear nights with light winds

Special Cases

LOFTING Γ Inversion layer below plume Pollutants dispersed downwind with minimal surface concentration Sometimes a transition to a fanning plume

FUMIGATION Γ Opposite of lofting Inversion lies above plume with unstable air below Typical of early morning as inversion breaks up from below Short duration, high surface concentrations

TRAPPING Γ Subsidence inversion aloft (well above plume) with unstable air below Typical of weather conditions featuring high pressure

Six types of plume behavior, under various conditions of stability and instability. At left: broken lines: dry adiabatic lapse rate; full lines: existing environmental lapse rates.

PLUME RISE

Minimal plume rise due to strong winds

DIFFERENT PLUME HEIGHTS

Example of Complex Shear Flows along a Coastline Salem, Mass. Oil-fired power plant looking south on a winter morning. Lower steam plume from two 250-ft stacks trapped by inversion. Upper plume from a 500-ft stack. East Atlantic Ocean Shoreline Inland West

Types of Air Pollutants Gases Particulate Matter PM10 (< 10 microns dia.) PM2.5 (< 2.5 micron dia.)

Types of Emission Sources

GAUSSIAN PLUME MODELING

Emissions from Pollutant Sources Emission Rate (amount/time) Height of release Plume rise (thermal effects) Plume descent (gravitational effects)

σz σy Diagram showing Gaussian distribution of pollutant plume. σy and σz are standard deviations of the horizontal and vertical concentration distributions, respectively.

Physical system Model system Bounded space; plume Unbounded space; no reflection

Class A results in the most dispersion, while Class F has the least. Category A represents very unstable conditions; B, moderately unstable; C, slightly unstable; D, neutral; E, slightly stable; and F, stable. Night refers to the period from one hour before sunset to one hour after sunrise. The neutral category, D, should be used regardless of wind speed for overcast conditions, day or night. Thermal turbulence dominates (buoyancy enhancement) Mechanical turbulence only Thermal effects dominate (buoyancy suppression) Classes E-F Class A results in the most dispersion, while Class F has the least.