Meteorology and air pollution

meteorology and air pollution
meteorological factors
factors influencing air pollution in atmosphere
temperature
atmospheric pressure

1. Meteorology and air pollution Ravi Kumar GARRE

2. Meteorology The study of atmosphere The branch of atmospheric sciences, mainly aimed for weather forecasting. Also helpful for forecasting intensity of air pollution at a particular location. Atmospheric sciences Meteorology Climatology

3. Layers of atmosphere

4. Layers of atmosphere In meteorology, the atmosphere is considered up to 120 km from earth surface. Troposphere – 0 to 12km Stratosphere – 12 to 50km Mesosphere – 50 to 80km Thermosphere – 80 to 700km

5. Meteorological factors The meteorological factors which influence air pollution and dispersion of air pollutants at an area are: The primary factors: Wind direction and speed Atmospheric temperature Atmospheric pressure The secondary factors: Precipitation Humidity Solar radiation

6. Meteorological factors The dispersion or transport of air pollutants from their sources, depends upon behaviour of meteorological factors. The study of meteorological factors help in the determination of stack height or height of chimney is required at a particular place. The parameters widely vary as a function of latitude, season and topography. As weather influences air pollution, air pollution also influences weather. Like: visibility reduced, fog frequency and duration increased, incoming solar radiation may be decreased .

7. Wind direction and speed The direction and speed of winds governs drift and diffusion of air pollutants discharged into atmosphere. Higher the wind speed, dispersion, transport and diffusion, dilution and mixing of air pollutants will be high.

8. Wind direction and speed Gustiness is the important parameter of wind like wind speed. Gustiness determines the extent to which pollutants mixed and diluted with surrounding air. Mixing height is the height to which related air pollutants can extend, primarily through action of turbulence. Wind direction, wind speed and wind turbulence will decides the mixing height of air pollutants in atmosphere.

9. Atmospheric temperature The dispersion of air pollutants influenced by the atmospheric temperature. Higher the atmospheric temperature without any humidity, higher the dispersion in vertical direction. Lower the atmospheric temperature with atmospheric fog or during winters, the vertical dispersion of pollutants will be blocked. And in such atmosphere, the pollutants tend to accumulate near their source of emission itself.

10. Atmospheric pressure Low pressure systems (i.e. cyclones) occurred in atmosphere, lead to good mixing and rapid dispersion of pollutants. Hence such cyclones, usually accompanied by rains and storms, prove to be better for dispersion of pollutants.

11. Atmospheric pressure High pressure systems (i.e. anticyclones) occurred in atmosphere, could cause serious air pollution problems. Hence such anticyclone conditions, accompanied by clear skies and light winds, prove to be bad for dispersion of pollutants.

12. Precipitation Rainfall or precipitation exerts a cleansing action on the pollutants discharge into atmosphere. It accelerates the deposition of particulate matter on the ground. It also helps to remove the concentration of gaseous pollutants which are soluble in water. The process of removal of SOx and NOx , leads to fall of acid rain. This increases rate of corrosive nature and decreases pH of water bodies.

13. Humidity Humidity is the concentration of water vapour present in the atmosphere. Humidity can be expressed in three ways: Absolute humidity: water content in air – gm/kg (or) gm/cubic m Relative humidity: expressed as percentage (%) Specific humidity: the ratio of water vapour mass to total moist air parcel mass Humidity affects air quality primarily by blocking solar radiation during day times and earths radiation during nights. Humidity also leads to formation of fogs.

14. Solar radiation Solar radiation can heat air near the earth surface which can affects dispersion of air pollutants. Also can accelerate photochemical reactions. Photochemical produces photochemical smog and Ozone in ambient atmosphere. During winters. Solar radiation helps for dispersion by increasing heat energy.

15. Wind rose diagrams Wind rose is defined as “ Any one of a class of diagrams designed to show the distribution of wind direction experienced at a given location, over a considerable period ”. “ A diagram showing the relative frequency of wind directions at a place ”. Wind rose shows prevailing direction of wind. Wind roses may be constructed from the data obtained over a given time period such as a particular month or season or a year.

16. Wind rose diagram

17. Wind rose diagram

18. Wind rose diagram The modern wind rose gives the % of time the wind blows from each direction during the observation period. The concentric circles represent percentage of time. 8 or 16 lines emerge from centre, one for each direction.

19. Wind direction refers to from wind is blowing. Colour bars refer to speed of wind. Concentric circles - % time No. s around – compass points or direction

20. Wind rose diagram Wind rose diagram provides the graphical summery of distribution of wind direction wind speed over a period of time. Steps to develop a wind rose diagram from hourly observations are: Analysis of wind direction Determination of frequency of wind in a given wind direction Analysis for mean wind speed Preparation of wind rose diagram