METEOROLOGY AND AIR POLLUTION JAI PRAKASH Civil Engineering IIT Delhi 1 AUGUST, 2011
METEOROLOGY Aerosols particles which are emitted from the sources they are transported and dispersed through meteorological and topographical condition of atmosphere. Meteorology is the study of atmospheric phenomenon. It is constantly changing, sometimes from hour to hour and other times day to day. Climate is an aggregate of weather condition, the sum of all statistical weather information. Basic meteorological parameters Temperature Relative humidity solar radiation Cloud Cover Rainfall Atmospheric pressure Wind speed and direction Atmospheric stability Mixing height These meteorological parameters effects the transport and dispersion of aerosols.
METEOROLOGY Meteorology movement of pollutants Vertical Movement how much pollutants will go high Horizontal Movement- wind speed and wind direction Causes of the vertical movement? 1. Change in density 2. Change in temperature So we will see the how the temperature changing vertically.
Horizontal Movement Vertical Movement Density decreases Pressure decreases Volume expansion Change in temperature When a small volume of air parcels is displaced upward in the atmosphere, it will encounter low pressure and undergo an expansion to low temperature. Let us assume No Transfer of heat
Lapse Rate If no heat transfer takes place between that parcels of air and surrounding atmosphere. This is called adiabatic expansion. The change in temperature with altitude that is due to the adiabatic expansion. Temperature gradient is also called lapse rate. The change in temperature with elevation that is due to the adiabatic expansion is determined the following manner.
Lapse rate (Contd..) Hydrostatic Equation dp/dz = - ƥ g ---------------------- (A) First law of thermodynamic dq = du+dw --------- (1) dq = CvdT+ PdV -----(2) Per unit mass of air PV = RT/Ma ------------(3) After differentiating PdV+VdP = RdT/Ma -----(4) In adiabatic process dq = 0 TOP BOTTOM
Lapse rate (Contd..) dq = 0 putting in eq. (2) CvdT = - PdV ------------------- (5) CvdT = -RdT/Ma + VdP ----- (6) dt/dp = V/(Cv+R/Ma) --------(7) Putting the value of V in eq. (7) from eq. (3) dt/dp = (RT/MaP)/(Cv+R/Ma) = RT/MaP (1/Cv+R/Ma) --- (8) from hydrostatic equation ------- dp/dz = - ƥ g ----------------(9) multiplying both eq. (8) and eq. (9) dt/dz = - g/(cv+r/ma) dt/dz = - g/ĉp ɼ = dt/dz = - g/ĉp 1 0 C /100 m ɼ is called adiabatic lapse rate.
Neutral Condition If some moisture in atmosphere than Cp will be more or less. Cp will be less. Then temperature lapse rate change. Its called Dry adiabatic lapse rate (DALR) Atmospheric lapse rate = Environmental lapse rate (ELR) DALR = ELR This situation is called Neutral condition and atmospheric stability is neutral. Z ELR DALR T
Stable Condition Z DALR ELR DALR > ELR when dry adiabatic lapse rate is greater than environmental lapse rate. Then atmosphere will be stable. there mixing of pollutant will be very less. They cant go up and stable condition happens normally in the night and early morning. T
Unstable Condition Z ELR DALR DALR < ELR when dry adiabatic lapse rate is smaller than environmental lapse rate. Then atmosphere will be unstable. there mixing of pollutant will be very high. They go up and disperse away from the source. unstable condition happens normally clear sky or afternoon. T
STRUCTRE OF ATMOSPHERE
CONTD.. Troposphere 0 to 15 km altitude The lowest region of the atmosphere, where life & weather exist. Temperature decreases with altitude. Long-wave radiations emitted from the Earth are absorbed by the atmosphere, the atmosphere becomes less dense with increasing altitude, less air to absorb Top of the troposphere is known as the tropopause Stratosphere 15 to 50 km altitude Temperature increases with altitude. Heating occurs because ozone (O3) absorbs ultraviolet radiation from the Sun. Top of the stratosphere is known as the stratopause
CONTD.. Mesosphere 50 to 90 km altitude Temperature decreases with altitude The lowest temperatures in the entire atmosphere are found in the mesosphere during summer at high latitudes, 130 K (-226 F). Top of the mesosphere is known as the mesopause Thermosphere 90 to 500 km altitude Temperature increases with altitude above 90 km, and is constant above 200 km. This heating is due to absorption of solar radiation (wavelengths less than 200 nm) by molecular oxygen (O2). The highest temperatures in the atmosphere can be found in the thermosphere, 2000 K can occur
Solar Radiation Solar radiation describes the visible and near-visible (ultraviolet and near-infrared) radiation emitted from the sun. The availability of energy is affected by location (including latitude and elevation), season, and time of day. All of which can be readily determined. However, the biggest factors affecting the available energy are cloud cover and other meteorological conditions which vary with location and time. sunlight that passes through the atmosphere annually, only 51% is available at the Earth's surface to do work. This energy is used to heat the Earth's surface and lower atmosphere, melt and evaporate water, Of the other 49%, 4% is reflected back to space by the Earth's surface, 26% is scattered or reflected to space by clouds and atmospheric particles, and 19% is absorbed by atmospheric gases, particles, and clouds.
Wind Measurement Wind is a primary mover of transport of aerosol particles. Wind speed decides how pollutant disperse and wind direction decides which direction pollutant will go. Energy is relevant to wind, because wind blow is the difference unequal heating of the earth surface, as temperature difference, pressure difference. Wind blows always high pressure to low pressure. Convection current occur the ground surface, that heated and its important phenomenon in air pollution meteorology and this convection (wind blow) decides where the pollutant grows. So, how will wind measure and how the wind represent.
N SOURCE E Wind is blowing from E (90 0 ) ---------------- Correct Wind is going from --------------------------- Incorrect
NW NNW N N N E N E WNW E N E W E WSW E S E SW S SW S S S E S E
It is graphical representation of wind direction and wind speed at given location. It gives prevalent wind direction. It gives maximum wind speed. It helps us locate or site or residential colony. calm condition where U < 0.5 m/s means where wind has no definite direction, it change time to time and location to location. there will be very poor condition. more pollutant chances to accumulate so we should avoid the install any industry and power plants. WIND ROSE
Temperature and Relative Humidity Wind Direction Wind Speed Solar Radiation WEATHER MONITORING STATION INSTALLED AT BLOCK-IV CIVIL ENGINNERING, IIT DELHI
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