Meter Ology

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Air Pollution METEOROLOGY

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Transcript of Meter Ology

Air Pollution Meteorology

Air Pollution METEOROLOGYWhat is atmospheric thermodynamics? What are the variables of atmospheric thermodynamics? What is lapse rate? What is atmospheric stability and the various methods that define atmospheric stability? What are the effects of meteorology on plume dispersion? What is wind velocity profile? What is wind rose diagram and what are the uses of it? Determination of mixing height.Atmospheric thermodynamics

Atmospheric stability

Effect of meteorology on plume dispersionAir Pollution MeteorologyPollution cloud is interpreted by the chemical composition and physical characteristics of the atmosphereConcentration of gases in the atmosphere varies from trace levels to very high levelsNitrogen and oxygen are the main constituents. Some constituents such as water vapor vary in space and time.Four major layers of earths atmosphere are:TroposphereStratosphereMesosphereThermosphere

AtmosphereA parcel of air is defined using the state variablesThree important state variables are density, pressure and temperature The units and dimensions for the state variables are

Atmospheric ThermodynamicsDensity(mass/volume) gm/cm3 ML-3Pressure (Force/Area) N/m2 ( Pa ) ML-1T-2Temperatureo F, o R, o C, o K

THumidity is the fourth important variable that gives the amount of water vapor present in a sample of moist airLapse Rate:Lapse rate is the rate of change of temperature with heightLapse rate is defined as = -T zValue of varies throughout the atmosphere

The ability of the atmosphere to enhance or to resist atmospheric motions

Influences the vertical movement of air.

If the air parcels tend to sink back to their initial level after the lifting exerted on them stops, the atmosphere is stable.

If the air parcels tend to rise vertically on their own, even when the lifting exerted on them stops, the atmosphere is unstable.

If the air parcels tend to remain where they are after lifting stops, the atmosphere is neutral.Atmosphere StabilityThe stability depends on the ratio of suppression to generation of turbulence

The stability at any given time will depend upon static stability ( related to change in temperature with height ), thermal turbulence ( caused by solar heating ), and mechanical turbulence (a function of wind speed and surface roughness). Atmospheric StabilityAtmospheric Stability ALR < DALR ThenSuperadiabatic meaning unstableALR = DALR ThenNeutral DALR < ALR < 0 ThenSubadiabatic meaning stable (weakly stable) DALR < 0 < ALR ThenInversion - meaning strongly stableAtmospheric StabilitySuperadiabatic

Atmospheric Stability Subadiabatic

Atmospheric Stability Inversion

Atmospheric stability can be determined using adiabatic lapse rate. Atmospheric Stability > d Unstable = d Neutral < d Stable is environmental lapse rate (ambient lapse rate)d is dry adiabatic lapse rate (10c/100 m) and dT/dZ = -10c /100 mSurface WindSpeed (m/s)Daytime InsolationNighttime cloud coverStrongModerateSlightThinly overcast or 4/8 low cloud3/8< 2AA - BB--2 - 3A - BBCEF3 - 5BB - CCDE5 - 6CC - DDDD> 6CDDDDPasquill-gifford Stability Categories

Source: Met Monitoring Guide Table 6.3Sigma Theta stability classificationCATEGORYPASQUILL CLASSSIGMA THETA (ST)EXTREME UNSTABLEAST>=22.5MODERATE UNSTABLEB22.5>ST>=17.5SLIGHTLY UNSTABLEC17.5>ST>=12.5NEUTRALD12.5>ST>=7.5SLIGHTLY STABLEE7.5>ST>= 3.8MODERATE STABLEF3.8>ST>=2.1EXTREMELY STABLEG2.1>ST

Source: Atmospheric Stability Methods & Measurements (NUMUG - Oct 2003)Temperature Difference (T)

Source: Regulatory guide; office of nuclear regulatory research- Table 1

Fig. 12-12, p.33317FIGURE 12.12 The inversion layer prevents pollutants from escaping into the air above it. If the inversion lowers, the mixing depth decreases and the pollutants are concentrated within a smaller volume.

Temperature Inversion

TemperatureTemperature InversionAltitudePollution trapped below inversion18The trapping of emissions beneath the noccturnal inversion is the reason why haze concentrations are highest in the late night and early morning hours.19InversionsInversion: when a layer of the atmosphere has an inverted temperature profile; temperature increases with altitudeHighly stable layer of airSuppresses vertical movement of airPollution accumulates within or below inversion20Application: StabilityLoopingFanningConingFumigationLoftingstableunstableneutralelevated inversionground inversionStability is a measure of the tendency for air to move vertically.Emission plumes can be an estimator of the stabilityVertical mixing influences ground level concentrations.RAQ Train the TrainerFebruary 26-28, 20072021Application: StabilityLoopingFanningConingFumigationLoftingstableunstableneutralelevated inversionground inversionStability is a measure of the tendency for air to move vertically.Emission plumes can be an estimator of the stabilityVertical mixing influences ground level concentrations.RAQ Train the TrainerFebruary 26-28, 200721Fluctuations in wind flow which have a frequency of more than 2 cycles/ hr

Types of TurbulenceMechanical TurbulenceConvective TurbulenceClear Air TurbulenceWake TurbulenceTurbulenceA power law profile is used to describe the variation of wind speed with height in the surface boundary layer

U = U1 (Z/Z1)pWhere, U1 is the velocity at Z1 (usually 10 m) U is the velocity at height Z. The values of p are given in the following table.

Wind VelocityStability ClassRural pUrban pVery Unstable0.070.15Neutral0.150.25Very Stable0.550.30This scale is helpful in getting an idea on the magnitude of wind speed from real life observationsBeaufort ScaleAtmosphericconditionWind speedCommentsCalm < 1mphSmoke rises verticallyLight breeze 5 mphWind felt on faceGentle breeze 10 mphLeaves in constant motionStrong 25 mphLarge branches in motionViolent storm 60 mphWide spread damageWind Rose Diagram (WRD)

Wind Direction (%)Wind Speed (mph)WRD provides the graphical summary of the frequency distribution of wind direction and wind speed over a period of timeSteps to develop a wind rose diagram from hourly observations are:Analysis for wind directionDetermination of frequency of wind in a given wind direction Analysis for mean wind speed Preparation of polar diagram

Wind Rose Diagram (WRD)

A Wind Rose% Frequency = Number of observations * 100/Total Number of Observations

Direction: N, NNE, ------------------------,NNW, Calm

Wind speed: Calm, 1-3, 4-6, 7-10, -----------

Calculations for Wind RoseSteps to determine the maximum mixing height for a day are:Plot the temperature profile, if neededPlot the maximum surface temperature for the day on the graph for morning temperature profileDraw dry adiabatic line from a point of maximum surface temperature to a point where it intersects the morning temperature profileRead the corresponding height above ground at the point of intersection obtained. This is the maximum mixing height for the dayDetermination of Maximum Mixing HeightDetermination of Maximum Mixing Height

Power plant Plumes

Power plant Plumes