Meteorology and air pollution

Meteorology and air pollution
Ravi Kumar GARRE

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
i. Meteorology
ii. Climatology

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

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

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

• 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

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:
o Analysis of wind direction
o Determination of frequency of wind in a
given wind direction
o Analysis for mean wind speed
o Preparation of wind rose diagram

Meteorology and air pollution

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