Wind rose diagrams

WIND ROSE
Wind rose is defined as "any one class of diagrams designed to show the distribution of wind direction experienced at a given location over a considerable period."

• Wind rose shows the prevailing direction of wind. 
• It consists of a circle from which eight or sixteen lines emerge
• Each line signifies a specific direction
• Length of a line is proportional to frequency of wind from that direction
• Frequency of calm conditions is entered in the center
• Wind roses are constructed from data obtained over a particular month, season or year
• Wind direction refers to the direction FROM which wind is blowing
• Sometimes, instead of wind speed, the parameters of precipitation, smoke, sulphur dioxide, smok, hydrocarbons, etc are attached to wid direction. These diagrams are known as POLLUTION ROSES.

Diagram of a typical wind rose is shown below:

Air quality standards

Air Quality Standards

• The current National Ambient Air Quality Standards were notified on 18 November 2009 by the Central Pollution Control Board.
• The National Ambient Air Quality Standards specified by the CPCB are mentioned in the table below for various pollutants

Lapse rates, inversion, types of inversion, atmospheric stability and dispersion of air pollutants

LAPSE RATE

In well mixed dry air, temperature falls by 3.3F for every increase in 100 ft altitude. This vertical temperature gradient is called 'lapse rate'.

The value mentioned above is called NORMAL LAPSE RATE or ENVIRONMENTAL LAPSE RATE.

INVERSION
If the cold layer of air at ground level is covered by warmer air at a higher level, the phenomenon is called inversion. During inversion, the vertical air movement is stopped and pollutants are concentrated in the inversion layer below. In this state, the atmosphere is stable and very less turbulence or mixing takes place. As a result, the pollutants in the air do not disperse. Inversion occurs typically in the months of October to February. The accumulation of smoke and other pollutants aggravates the problem of pollution by preventing the sun's rays from heating the ground and adjacent air. Fog is generally associated with inversions. Narrow valleys are favorable to inversions as horizontal air movement is restricted. During inversions visibility is greatly reduced and contaminant concentration is maximum.

TYPES OF INVERSION

1. Radiation inversion
• This type of inversion occurs at night
• It occurs when the vertical movement of air is stopped
• Fog forms in this type of inversion if air is moist and temperature is below the dew point
• It is common in winter due to longer nights
• It frequently occurs in valley areas
2. Subsidence inversion
• This type of inversion occurs at modest altitudes and remains for several days
• It is caused due to sinking of air in high pressure areas surrounded by low pressure areas
• As air sinks, it is compressed and gets heated to form a warm dense layer that prevents upward movement of contaminants
• Inversion height varies from ground layer to a height of 1600 m.
• At inversion height of 200 m, extreme pollution occurs.

If radiation and subsidence inversion occur simultaneously, the phenomenon is called "double inversion".

ATMOSPHERIC STABILITY
Stability is an important characteristic of the atmosphere. It is simply the ability to resist vertical motion. Stability affects the ability to disperse pollutants.
Lapse rate is the rate at which atmospheric temperature decreases with an increase in altitude.
Lapse rate is the negative of the rate of temperature change with altitude change.
Three different lapse rates are:

1. Dry adiabatic lapse rate
2. Moist adiabatic lapse rate and
3. Environmental lapse rate
   

The actual temperature profile of ambient air is the environmental lapse rate or atmospheric lapse rate or prevailing lapse rate. The environmental lapse rate varies from time to time and from place to place. A radiosonde is an instrument to measure environmental lapse rate.
Negative lapse rate is an inversion.
Static stability of the atmosphere can be determined by comparing the dry, moist and environmental lapse rates.
IF:

• ELR < MALR then the atmosphere is absolutely stable
• ELR > DALR then the atmosphere is absolutely unstable
• MALR < ELR < DALR then the atmosphere is conditionally unstable

ELR     - Environmental Lapse Rate
MALR   - Moist Adiabatic Lapse Rate
DALR   - Dry Adiabatic Lapse Rate

During the day, the surface of the Earth get heated more due to insolation while at night, a terrestrial radiation loss causes a temperature inversion.
The range of stability indices are:

1. Very stable
2. Stable
3. Marginally unstable
4. Moderately unstable
5. Very unstable and
6. Extremely unstable

DISPERSION OF AIR POLLUTANTS

The degree to which air pollutants are discharged from various sources and their subsequent concentration in a particular area depends on meteorological conditions. Hence, the application of dispersal theory and knowledge of local weather conditions are essential for:

1. determination of required stack height and
2. evaluation of intensity of air pollution

Degree of air pollution varies spatially and temporally due to difference of meteorological conditions.

Adverse weather can trigger an air pollution episode like the "london killer smog". The important meteorological parameters that influence air pollution are:

1. Primary parameters
1. Wind speed and direction
2. Temperature
3. Atmospheric stability and
4. Mixing height
2. Secondary parameters
1. Precipitation
2. Humidity
3. Solar radiation and
4. Visibility

The above parameters vary as a function of

• Latitude
• Season and
• Topography

The following are the effects of air pollution on weather:

1. Reduced visibility
2. Frequent episodes of fog
3. Reduction in incoming solar radiation

Wind direction and speed influence the movement and diffusion of air pollutants discharged at ground level. high wind speeds diffuse pollutants from the source. Dispersed pollutants get rapidly diluted with increasing volume of air.

Gustiness is an important characteristic of surface winds is proportional to speed and determines the extent to which pollutants are mixed and diluted with surrounding air.

Concentration of a pollutant downwind is inversely proportional to wind speed.

Ambient air quality monitoring

Ambient air quality refers to the condition or quality of air surrounding us in the outdoors. National Ambient Air Quality Standards are the standards for ambient air quality set by the Central Pollution Control Board (CPCB) and is applicable nationwide.
The CPCB has been conferred this power by the Air (Prevention and Control of Pollution) Act, 1981.

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According to the National Ambient Air Quality Monitoring Program:

• The following factors influence site selection:

1. The site should be away from source and other interference (Inlet should be at least 15 m away from source or traffic artery)
2. Height of the inlet should be more than 3 m (preferably between 3 - 10 m) or double the height of nearby wall or obstruction.
3. The air at site should be free flowing and well mixed
4. The elevation angle should be less than 30 from inlet to top of building
5. Collocated samplers should be at least 2 m apart

• The following factors influence parameter selection

1. Sensitive location
2. Health impact stations (All pollutants)
3. Population and exposure in case of priority pollutants
4. Criteria pollutants and CO are typically sampled at traffic intersections
5. Concentration of criteria pollutants and ozone are accumulative and are sampled at 50 m from traffic intersections core commercial areas in the city

In case of manual monitoring, 

• Gravimetric methods are used to estimate the concentration of PM10 and PM2.5 
• Wet chemical methods are used to estimate the concentration OF SO2, NO2, NH3 and benzene
• Gravimetric method of sample processing and chemical analysis is done to estimate the concentration of Benzene, B(a)P, Ni, As and Pb in PM10

In case of automatic monitoring, 

• Sophisticated analysers are used for instant data generation, online data dissemination, air quality index, early warning system, forecasting, modeling of pollutants such as Sulphur dioxide, Nitrogen dioxide, particulate matter smaller than ten microns, particulate matter smaller than 2.5 microns, Ozone, Carbon monoxide, Ammonia and benzene.

Meteorology of air pollutants

Meteorology is the interdisciplinary scientific study of the atmosphere. Meteorological phenomena are weather events that are observed and they can be explained by the science of meteorology. These events are described and measured using variables of Earth's atmosphere such as temperature, air pressure, water vapour and bulk flow. These variables, their interaction and variability over time and space is used to describe and predict weather on a local, regional or global level.

• Atmospheric processes such as movement of air and exchange of heat (convection and radiation) dictate the fate of pollutants as they go through the stages of transport, dispersion, transformation and removal.
• Air pollution meteorology is the study of how these atmospheric processes  affect the fate of air pollutants.
• Knowledge of air pollution meteorology helps to manage and control the release of pollutants in the atmosphere
• Knowledge of air pollution meteorology is essential to understand the fate and transport of air pollutants
• Air pollution problems involve three parts:
• The pollutant source
• The dispersion of pollutant and
• The recepient
• Transport of the pollutant is determined by the meteorological conditions
• Air pressure difference causes movement of air
• Air moving parallel to the ground is called wind whereas air moving up or down is called a current

• Calm conditions, emissions from low elevations, temperature inversion, high buildings and narrow streets prevent air circulation and concentrate air pollutant into specific regions.
• Turbulent atmospheric conditions, areas with thick vegetation, emission at elevated positions using smoke stacks and rain lower air pollution by creating conditions that encourage circulation and eventually remove pollutants from the atmosphere.
• As air rises, it encounters lower pressure. However, the air parcel that rises has higher pressure than surrounding molecules. This means that more force is exerted by the inside the parcel than the particles outside. Hence the parcel expands. For the parcel to expand the particles inside the parcel must use some internal energy to do this work.
• Since the internal energy decreases, temperature decreases (temperature is a function of internal energy).
• Hence, the rising parcel expands and cools. This is called adiabatic cooling

Sources, classification and effects of air pollutants

Air pollution
Air pollution is defined as the presence of any undesirable substance in the environment in an excessive concentration for an excess duration that causes damage to the living and non-living components of the environment.

The undesirable substance is termed as "air pollutant". The source of air pollution is any activity that causes pollutants to be emitted in the air. Natural sources of air pollution are called "biogenic" sources while pollutants generated due to human activities are called "anthropogenic" sources.

Air pollutants can be classified in the following ways:

• Based on the source of pollutants, air pollution is classified as:
• Natural air pollution. Examples are
• Forest fires
• Volcanic eruptions
• Biological decay
• Disintegration of rocks
• Artificial air pollution. Examples are
• Vehicular pollution
• Cooking (domestic and industrial) 
• Industries
• Based on movement of air polluting source, air pollution is classified as
• Stationary source
• Stationary sources are inturn classified as
• Point sources. Examples are
• Industrial processes
• Power plants
• Volcano

• Area sources. Examples are
• Domestic heating of coal and gas
• Onsite incineration

• Mobile source
• Mobile sources are inturn classified as 
• Line sources. Examples are
• Highway vehicles
• Railways

• Area sources. Examples are
• Railway station
• Bus stand
• Airports

The term used to describe a variety of vehicles, engines and equipment that generate air pollution and can be moved from place to place is Mobile sources

Mobile sources are in-turn classified as 

• On-road sources and
• Non-road sources

On road sources are used on road for transportation of passengers or freight. Examples are:

• LDVs (Light Duty Vehicle or passenger car)
• HDVs (Heavy Duty Vehicle used for transportation of freight) and
• Motorcycles

Non-road sources include gasoline and diesel powered vehicles, engines and equipment used for construction, agriculture, transportation, recreation and several other purposes.
Mobile sources contribute to air pollution by way of combustion and evaporation of fuel.
Petrol and diesel are mixtures of hydrocarbons. Complete combustion of fuel gives carbondioxide and water while incomplete combustion (which occurs mostly in every engine) yields unburnt hydrocarbons, oxides of nitrogen, carbon monoxide, carbon dioxide and water.

Air pollution is also classified based on state of pollutant as

• Gaseous pollutant. Examples are
• Carbon monoxide (CO)
• Oxides of Nitrogen (NOx)
• Oxides of sulphur (SOx), etc
• Particulate pollutant. Examples are
•  Fumes
• Mist
• Fog
• Smoke
• Dust, etc

Gaseous pollutants mix with air and normally do not settle. Particulate pollutants consist of finely divided solid or liquid particles and often exist in colloidal state as aerosols.

 Based on Origin, air pollutants are classified as primary or secondary pollutants.

• Examples of primary air pollutants are
• Carbon monoxide (CO)
• Carbon dioxide (CO2)
• Sulphur dioxide (SO2)
• Suspended Particulate Matter (SPM) and
• Halogen compounds
• Examples of secondary air pollutants are
• Ozone (O3)
• Peroxy Acetyl Nitrate (PAN)
• Smog
• Formaldehyde, etc

Primary pollutants are emitted from identifiable sources while secondary pollutants are produced by reaction between two or more primary air pollutants or between primary air pollutants and constituents of the atmosphere with or without sunlight as a catalyst.

Effects of air pollutants:

• Effects of air pollutants on human beings
• Carbondioxide is the primary pollutant responsible for global warming
• Carbonmonoxide causes asphyxiation (breathlessness) and in high doses forms carboxyhaemoglobin that results in unconsciousness, coma and death.
• Other pollutants irritate the respiratory tract, cause allergic reactions, lead to eye-watering, poor visibility
•  Sulphur dioxide (SO2) is found in association with particulate matter and is mainly released into the air by combustion of sulphur containing fuels. It causes significant respiratory damage.
• Oxides of Nitrogen (NOx) originate from both natural and anthropogenic sources. It is produced by burning fuel in automobiles and power plants. It affects the respiratory system of human beings. It causes pneumonia and bronchitis.
• Hydrocarbons (HC) are found in fossil fuels. They cause eye irritation, coughing and drowsiness. Hydrocarbons with high molecular weight cause mutagenic or carcinogenic problems
• Presence of excess lead causes behaviour disorders in children and adults. In high concentrations it causes coma, severe and irreversible brain damage. Lead poisoning weakens the central nervous system resulting in convulsions, uncontrolled mental disturbances, coma and eventually death.
• Cadmium is present in urban atmosphere and cigarette smoke. It causes cardiovascular diseases, hypertension, kidney and liver failure.
• Mercury present in the gaseous form causes neurological damage, birth defects, damage to the cerebellum and cortex.
• Effects of air pollutants on materials
• Air pollutants like NO2, CO, SO2, acids and aerosols cause discoloration and deterioration of limestone and building materials.
• SO2 in the form of acid (dry deposition) or gas reduces the tensile strength of textiles
• Ozone (O3) and other oxidants are responsible for cracking and loss of strength of rubber
• CO, O3, SO2, H2S and SPM cause discolouration, surface erosion and soiling of paints
• SO2, acids and gases cause embrittlement and discolouration of paper
• NO2, SO2, acids and gases are responsible for corrosion, tarnishing and loss of strength in metals
• SO2 and acid gases are responsible for disintegration and loss of strength of leather.
• Effects of air pollutants on vegetation
•  SO2 causes chlorosis (disappearance of chlorophyll and yellowing of leaves)
• NO2 causes premature fall of leaves and suppressed growth of plants resulting in reduced yield
• Ozone causes necrosis (dead areas on leaves), leaf damage and reduced yield
• PeroxyAcetylNitrate(PAN) causes premature fall of leaves, discoloration and epinasty (downward curvature of leaves)
• Effects of air pollutants on animals
• Animals ingest fluorides in air through plants. This affects their bones and a reduced production of milk
• Lead particulates in air lead to lead poisoning in animals
• Extreme air pollution leads to paralysis of animals.
• Effects of air pollutants on physical properties of atmosphere
• Air pollution leads to 
• Decrease in visibility
• Reduction of solar radiation
• Affects weather conditions and
• Affects the atmospheric composition

Manufacturing processes & Wastewater characteristics for Dairy industry