Ambient air quality monitoring

The main objective of ambient air quality monitoring is to provide knowledge about the extent of pollution present against the standard laid down and take effective step to control the abnormal level of Air pollutant present in the ambient air.

Objective :a) Determining the extent of pollutant and their impact on human life, animal life and plants and property.

b) Trend study to identify the future problem and impact of control measure.

c) Pollution source identification and remedial measure.

d) Planning for priorities for environmental management by industries , government and urban authorities.

e) Provide baseline information for urban and industrial development project and predict the impact of this project. This is a part of EIA study and clearance for the project by MoEF.

Selection of sampling station for ambient air quality samples

a) Station based on predicted maximum concentration location of pollutant emanating for the emission sources.

b) Down wind location of sensitive areas like schools and hospitals.

C) Populated area

e) High rise building and other obstruction to dispersion to be outside 120 o angle of outsight of the obstruction.

f) Sampling station has to be always down wind preferably mid way of the wind trace angle.

g) Height of sampling point to be preferably the breathing height..

Net work and number of station:

i) Representative maximum concentration location as describe above.Ii) Representative Residential areaiii) Representative sensitive areaiv) Representative historical monumentsv) Industrial area

Sampling Instrument

1. High Volume Sampler : Suspended particulate matter

2. Respirable Particulate matter sampler : Respirable particulate matter ( Size less then 10 micron)

3. Non Dispersive Infrared Spectroscopy ( NDIR) : Carbon Monoxide

4. ASS( Atomic absorption spectrophometery ): Lead (Ammonia) 5. Chemiluminescence : NOx

6. Ultraviolet Fluorescence : SO2

7. Fine Particulate Sampler Monitoring of PM

8. Handy Sampler and Personal Sampler for aerosoles and gaseous pollutant

9. Organic Vapour Sampler : for organic vapour and CO

10. Stack Sampler : For monitoring particulate and gaseous pollutant in industrial stack emission

11. Micro Meteoro Monitor : for monitoring wind speed, wind direction, turbulence, temperature, relative humidity and rainfall.

1. High Volume Sampler : High volume sampler are the basic instrument used to monitor Ambient Air Quality. They are in wide spread use all over the world to measure dust pollution in industrial, residential, as well as in sensitive area.

In these sampler air borne suspended dust is measured by passing air at high flow rate of 1.1 to 1.7 m3 / min through high efficiency filter paper which retain the dust particles.

Amount of particulates collected on the filter paper is determined by measuring the change in weight of the filter paper

In HVS provision have been made for simultaneous sampling of gaseous pollutant like SO2, NO2, H2S etc.

Respirable Particulate matter sampler In India respirable dust has been included in the national ambient sir quality standard since April 1994.

Principle Operation

Ambient air ladden with suspended particulate enters the system through the inlet pipe.1) As the air pass through the cyclone , coarse, non respirable dust is separated from the air stream by centrifugal forces acting on the solid particles . These separated particles falls through the cyclones conical hopper2) and collect in the sampling bottle placed at it bottom. The fine dust forming the respirable fraction of the Total Suspended Particulate (TSP) passes through the cyclone and is carried by the air stream to the Filter Paper.3) Calmped between the Top Cover4) and Filter Adapter Assembly

5) Respirable dust is retained by filter and the carried air exhausted from the system through the blower . and is carried by the air stream to the Filter Paper.

Flow Rate : 0.9 1.4 m3/min. ( Free flow condition without filter)

Particle Size : A cyclone is used for fractionating the dust into two fraction. D-50 for the cyclone is at 10 microns. Particulate matter is accumulated on the filter paper while coarse dust is collected in a cup placed under the cyclone.

Recommended Filter : Whatman GF/ A for common and Wahtmans type No. EPM 2000 for special research.

Sampling Time : 28 hours (maximum)

Thermo Electrically Cooled Gaseous Attachment :

Monitoring of gaseous pollutants in ambient air using wet chemical methods is carried out by passing air at known flow rate through absorbing reagents kept in midjet impingers.

3. Non Dispersive Infrared Spectrometry

It is based on the principle that each gas absorbed particular band of infrared radiation.

When IR is led through a cell containing CO , part of energy radiation is absorbed by CO which can be co-related with the concentration of CO

To detect the pollution, gas is kept in sample cell and reference cell and light is passes through both cell.

There occur a pressure difference between two halve due to different intensity of incident solar radiation.

The pressure differences proportional to pollutant CO. If the pressure difference is more the concentration of CO will be more.

Atomic Absorption Spectrometry

It is based on the measurement of decreased in light intensity from a source (Hollow cathode lamp) when it pass through a vapour layer of atom of the analytic element.

The hollow cathode lamp produce intense electromagnetic radiation with a wavelength exactly the same absorbed by the atom.

X- Ray Fluorescence

It is based on the principle that when sample is bombarded with X rays , Y (gamma) rays or proton, it give rise to a secondary radiation as electron drop into vacant position in inner orbit.

The emitted X rays have the characteristics of particular atom.

The energy (wavelength) emitted give qualitative analysis of element while intensity yield quantitative analysis.

Chemiluminescence

It is based on the principle that when NO react with ozone, NO2 is formed .

When NO react with O3 NO2 is formed which remain in excited state and after completing reaction NO2 come down in ground state.

During coming down in ground state it emit (0.6 0.3 micro meter ) wavelenght band ( 3000 6000 nm)

By measuring the intensity of emitted light the amount of NOx can be measured.

NO + O3 ------------ NO2 +

NO2 + ---------------------- NO2 + hv

Flame Ionization Detector

It is based on the principle that mixture of H2 & air does not burn without ionization.

If hydrocarbon is used in very less quantity then ions are produced .

Number of ions produced are the proportional to the amount of hydrocarbon.

Stack Sampler

Monitoring of stack and vent emission now becoming a routine requirement not only for large but even in medium and small industrial units.

There has been growing realization that gaseous pollutants , chemical fumes and fine mist are hazardous as particulate ashes and dust.

In stack sampler VSSI simultaneous sampling for PM and gaseous pollutant can be carried out to save and efforts and time.

Principle of Operation

Flue gas enter the system through the nozzle at the tip of sampling probe pass through the filter thimble , where particulate matter is removed and reach the sampling panel.

Here the gas stream is split into two sections. One section passes at low flow rate (0.5 0.3 LPM) through a train of impingers loaded with suitable reagent to absorb gaseous pollutants, relevant to the emission source while the reaming gas stream bubbles through a distilled water impinger followed by silica gel.

On passing through the cold box section, the flue gases cool down, releasing any moisture or condensable present and scrubbed for corrosive or toxicant fraction.

Relatively clean gas pass through the flow meter and dry gas meter so that the volume of flue gas sampled is measured and are subsequently exhausted into the atmosphere through the vacuum pump.