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**Session 2, Unit 3 Atmospheric Thermodynamics**

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Ideal Gas Law Various forms

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Hydrostatic Equation Air density change with atmospheric pressure

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**First Law of Thermodynamics**

For a body of unit mass dq=Differential increment of heat added to the body dw=Differential element of work done by the body du=Differential increase in internal energy of the body

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Heat Capacity At constant volume At constant pressure

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Heat Capacity Relationships

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**Concept of an Air Parcel**

An air parcel of infinitesimal dimensions that is assumed to be Thermally insulated – adiabatic Same pressure as the environmental air at the same level – in hydrostatic equilibrium Moving slowly – kinetic energy is a negligible fraction of its total energy

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Adiabatic Process Reversible adiabatic process of air

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**Lapse Rate Combine hydrostatic equation and ideal gas law**

For adiabatic process

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Lapse Rate Therefore dT/dz is Dry Adiabatic Lapse Rate (DALR)

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**Dry Adiabatic Lapse Rate**

Dry adiabatic lapse rate (DALR) Or on a unit mass basis Or the expression in the textbook:

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**Lapse Rate Effect of moisture Because**

Wet adiabatic lapse rate < DALR (temperature decreases slower as air parcel rises) Condensation

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**Lapse Rate Superadiabatic lapse rate (e.g., 12oC/km)**

Subadiabatic lapse rate (e.g., 8oC/km) Atmospheric lapse rate Factors that change atmospheric temperature profile Standard atmosphere (lapse rate ~ 6.49 oC/km or 3.56 oF/1000 ft)

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**Potential Temperature**

Current state: T, P Adiabatically change to: To, Po Set Po = 1000 mb, To is potential temperature If an air parcel is subject to only adiabatic transformation, remains constant Potential temperature gradient

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**Session 2, Unit 4 Turbulence and Mixing Air Pollution Climatology**

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**Atmospheric Turbulence**

Turbulent flows – irregular, random, and cannot be accurately predicted Eddies (or swirls) – Macroscopic random fluctuations from the “average” flow Thermal eddies Convection Mechanical eddies Shear forces produced when air moves across a rough surface

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**Lapse Rate and Stability**

Neutral Stable Unstable

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**Richardson Number and Stability**

Stability parameter Richardson number Stable Neutral Unstable

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**Stability Classification Schemes**

Pasquill-Gifford Stability Classification Determined based on Surface wind Insolation Six classes: A through F Turner’s Stability Classification Wind speed Net radiation index Seven classes Feasible to computerize

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**Inversions Definition Types Fumigation Radiation inversion**

Evaporation inversion Advection inversion Frontal inversion Subsidence inversion Fumigation

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**Planetary Boundary Layer**

Turbulent layer created by a drag on atmosphere by the earth’s surface Also referred to as mixing height Inversion may determine mixing height

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**Planetary Boundary Layer**

Neutral conditions Mixing height Increased wind speed and surface roughness cause higher h.

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**Planetary Boundary Layer**

Unstable conditions Mixing height

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**Planetary Boundary Layer**

Stable conditions Mixing height

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**Surface Layer Fluxes of momentum, heat, and moisture remain constant**

About lower 10% of mixing layer

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**Surface Layer Monin-Obukhov length**

Monin-Obukhov length and stability classes

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**Surface Layer Wind Structure**

Neutral air

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**Surface Layer Wind Structure**

Unstable and stable air

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Friction Velocity Measurements of wind speed at multiple levels can be used to determine both u* and z0

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**Power Law for Wind Profile**

Wind profile power law Value of p

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**Estimation of Monin-Obukhov Length**

For unstable air For stable air Bulk Richardson Number

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**Air Pollution Climatology**

Meteorology vs. climatology Meteorological measurements and surveys Pollution potential -low level inversion frequency in US

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**Air Pollution Climatology**

Mean maximum mixing height determined by Morning temperature sounding Maximum daytime temperature DALR Stability wind rose

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