AnalysisMethods for Measurement of Air Pollution - SO2

Analysis Methods for Measurement of Air Analysis Methods for Measurement of Air PollutionPollution

(SO2)(SO2)

Sampling Of Gaseous Pollutants• Sampling Flow Rate is required as per test

method(0.2 – 1.0 lpm)• Unfiltered air is bubbled through reagents , which

either react or dissolve the gas of interest. • Impingers can be arranged in series or parallel. • Individual flow control.• Flow adjustment by Rotameter. • Ice tray.

Gaseous Sampling System

Gaseous Sampling Impinger

Monitoring of Gaseous PollutantsMonitoring of Gaseous Pollutants

Sampling Period • Sampling period are decided based on objectives. • Care is required in deciding sampling period it should be for duration of available

standard.

Deciding Sampling Reagent 10-30ml is reasonable volume need to be decided based on detection limit of pollutant, expected ambient concentration and flow rate decided by duration of sampling.

Criteria for valid samplesAccept sample if it has run for 75% of decided sampling duration otherwise reject the sample.

Sl. No. Period Rate of Sampling/lpm

1. 30 min 2

2. 1 hr. 1

3. 1-4 hr. 0.5

4. 8 hrs. 0.2

5. 8-24 hrs. 0.1-0.2

Wet Chemical Method for Measurement of Gaseous PollutantsWet Chemical Method for Measurement of Gaseous Pollutants

(Ambient Air)(Ambient Air)

PARAMETER ANALYTICAL METHOD

Sulphur Dioxide - T.C. M Method or Modified Wet & Gaeke Method.

Nitrogen Dioxide - (i) Sodium hydroxide-sodium Arsenite Method or Modified Jacob Hoceiser’s Method.

- (ii) Saltzman Griess Method

Ozone - (i) Neutral KI Method (ii) Alkaline KI Method

Hydrogen Sulphide - Alkaline CdSO4 Method

Chloride - Methyl Orange Method

Ammonia - Indophenol blue Method

Fluoride - Sodium hydroxide absorption Method Ion Selective Electrode or SPADNS analysis.

Phenol - 4-Amino antipyrene Method

Method for SOMethod for SO22 Measurement in Ambient Air Measurement in Ambient Air (Modified West & Gaeke Method)(Modified West & Gaeke Method)

Principle: SO2 in ambient air is collected in a solution of Tetrachloromercurate (TCM) with the formation of disulfitomercurate compelx. The disulfito mercurate is treated with formaldehyde and acid bleached pararosaniline to give a violet colour of pararosaniline methyl sulfonic acid. The intensity of the colour is measured on a spectrophotometer at 560nm wavelength.

Range & Sensitivity: SO2 in the range of 25-1050 µg/m3 can be measured by this method.

The lower detection limit can be increased by taking an increased volume of air. The analytical range of the method is 0.03-1.26 µg/ml .

Interferences: NO2 Concentration in the range of 2ppm induces a fading colour. NO2

interference is removed by adding sulfamic acid. • Ozone is eliminated by aging the sample • Upto 30 µg Mn, 10 µg Cr (III) & 22 µg Vanadium in 10ml absorbing

solutions eliminated by adding EDTA.

Analysis of Sulfur Dioxide TCM MethodAnalysis of Sulfur Dioxide TCM Method

Range = 25 to 1050 ug/m3(if a 30 litre air passed through 25ml absorbing reagent at Flow rate of 0.5 lpm; duration 60 min)

Detection Limit = 0.03 to 1.26 µg/ml

• Low concentration can also be monitored by sampling larger volume of air at specified flow rate for decided sampling duration.

• For changed conditions a slop test is must • Absorption efficiency of SO2 need to be calculated by connecting two impingers in series. • Lowest measurable concentration for specific condition.

0.03 x 25 x 1000For 1 hrs = ----------------------- = 25 µg/m3

1 x 60 x 0.5

0.03 x 25 x 1000For 8 hrs= ----------------------- = 7.81 µg/m3 or 8 µg/m3

8 x 60 x 0.2

0.03 x 25 x 1000 For 24 hrs = ---------------------- = 2.6 µg/m3 or 3 µg/m3

24 x 60 x 0.2

Analysis of Sulfur Dioxide TCM MethodAnalysis of Sulfur Dioxide TCM Method

Interferences- Minimization or Elimination

NOx = Add 1ml of 0.06% Sulfamic Acid

Ozone = Delay the analysis for 1hr after sampling.

Trace metals = 1drop of 0.01% EDTA in absorbing reagent prior to sampling.

Fe (III) = 6 µg/ml these concentration if built up in Mn(II) = 1 µg/ml solution do not give positive Cr(III) = 1 µg/ml interferences while analysis.

• 10 µg copper (II), 22 µg of vanadium in 10ml of solution are also not interfere in analysis

• There is no interference of NH3, Sulphides and Aldehydes.

Determination of Sulfur Dioxide Concentration Determination of Sulfur Dioxide Concentration (Modified West and Gaeke Method) (Modified West and Gaeke Method)

(As recommended by CPCB, Govt. of India)(As recommended by CPCB, Govt. of India)

Ste 1 Preparation of Reagent A. For Sampling

Absorbing Reagent (TCM): Dissolve 10.86g mercuric chloride, 0.066g EDTA and 6.0g potassium chloride in 1 liter distilled water CAUTION:- Highly poisonous if spilled on skin, flush off with water immediately.

B. For Analysis 1. Sulphamic Acid (0.6%): Dissolve 0.6g sulphamic acid in 100ml distilled water. 2. Formaldehyde Solution (0.2%): Take 5ml formaldehyde solution (36-38%) and dilute by adding 1 litre distilled water. 3. Working Para- rosaniline Solution (PRA): a) Dissolve 0.5gm of specially purified para -rosaniline in 100ml of distilled water and keep for 48hrs (Stock Solution) b) Mix 10ml of stock PRA (from 3a) with 15ml Conc. HC1 and make up to 250ml with distilled water.

Note: Prepare PRA solution 2 days before analysis.



A. For Preparation of Calibration Curve1. Iodine Solution (0.01N): Dissolve 1.27g iodine and 4g potassium iodide in water. Stir and make upto 1 litre with distilled water. 2. Starch Indicator Solution: Make paste by dissolving 0.4g soluble starch and 0.002g mercuric iodide with a little water and make up to 200ml with boiled water. 3. Sodium Thiosulphate (0.01N):- a) Primary Standard Potassium Iodate: Dissolve 1.5g Potassium Iodate (dried at 180°C) in 500ml distilled water.b) Stock Sodium Thiosulphate (0.1N): Dissolve 25g Sodium Thiosulphate and 0.1g Sodium Carbonate in 1litre boiled and cooled distilled water. (Allow the solution to stand for one day before standardization)



c) Standardization: i) Pipette 50ml of Iodate solution in 250ml Iodine flask. ii) Add 2g Potassium Iodide and 10ml Hcl (1:10).iii) Put stopper on the flask and allow to react for 5 min. iv) Titrate with stock sodium thiosulphate solution to a pale yellow color. v) Add 5ml starch indicator. It shall give blue color. vi) Continue Titrate upto disappearance of blue color. vii) Calculate the Normality as follows:

(2.80 x W)N= -----------------------

VWhere V= Volume of Thiosulfate consumed (ml)W= Weight of Potassium Iodate (g)



d) Sodium Thiosulphate (0.01N): Dilute Sufficient amount of standardized stock sodium thiosulphate solution to 250ml with freshly boiled, cooled, distilled water.

4. Working Sulphite – TCM Solution: a) Stock Sulphite Solution: Dissolve 0.3gm Sod. Metabisulphite in 500ml

recently boiled, cooled distilled water.



b) Determination of Sulphite Solution Strength. Iodine Flask A (Blank) Iodine Flask B (Sample)

Pipette 50ml of 0.01N Pipette 50ml of 0.01N Iodine Solution

Add 25ml distilled water Add 25ml Stock Sulphite Solution

Stopper the flask and allow to react to 5 minutes

Titrate each flask in turn to a pale yellow with standard Sod. Thiosulphate Solution (0.01N)

Add 5ml starch solution to each flask (blue color)

Titrate continue until the disappearance of blue colour



c) Strength of Sulphite Solution (V1 – V2) x N x K

C = ------------------------------V

Where C = Concentration of SO2 (microgram/ml)

V1 = Volume of Thiosulphate for Blank (ml) V2 = Volume of Thiosulphate for Sample (ml)N = Normality of Sodium Thiosulphate Solution K = 32000 m. eq.wt. of SO2

d) Working Sulphite – TCM Solution (2µg/ml): Dilute sufficient amount of stock sulphite solution to 250ml with TCM.



Ste II: Preparation of Calibration Curve (SO2) i) Pipette 0.0 (blank) 1.0, 3.0, 5.0, 7.0, 9.0 ml to a series of 25ml

volumetric flasks. ii) Add sufficient TCM solution to each tube to bring the volume upto

10ml. iii) Add 1 ml of sulphamic acidiv) Allow to react for 10min to destroy the nitrite resulting from oxides of

nitrogen. v) Add 2ml formaldehyde solution vi) Add 2ml working pararosanilne solution vii) Make up-to 25ml with distilled water. viii) Mix Thoroughly ix) Measure the absorbance at 560nm after 30min but before 60min

against reagent. x) Plot the absorbance versus concentration at different strengths.



Ste III: Analysis 1. Mix Thoroughly the sampling bottle by shaking it several

times.2. Take two 25 ml volumetric flask (Blank and Sampler) 3. Pippete 10ml unexposed TCM solution in Blank and 10ml

exposed TCM in sample) 4. Add 1ml of Sulphamic acid. 5. Allow to stand for 10minutes. 6. Add 2ml formaldehyde solution 7. Add 2ml working pararosailine solution. 8. Make upto 25ml with distilled water.

Note:- Mix thoroughly after addition of each reagent. 9. Measure the absorbance at 560nm against the blank reagent

by suing spectrophotometer.



(As – Ab) x CF x Vs Concentration = ---------------------- = µg/m3

Va x Vt As = Absorbance of SampleAb = Absorbance of reagent BlankCF = Calibration FactorVa = Volume of air Sampled =Avg. Flow Rate x Sampling PeriodVs = Volume of Reagent taken for samplingVt = Volume of Reagent taken for analysis

Analysis of Sulfur Dioxide- Major PrecautionsAnalysis of Sulfur Dioxide- Major Precautions

• Sampling and Analysis – 0.5 – 2.0 litre/min through midjet impinger containing 20ml reagent. – Sampling period need to decided such so that 3-30 µg SO2 is

accumulated in the solution while sampling for best reliable results. – If sample is to be analysed after a day or more store sample at 5°C in

a refrigerator. Ensure that sample is kept at low at temperature even during transit/Transportation.

– Sodium sulfite solution need to prepared fresh as it is unstable. – Always use KCI salt in place of NaCI as it is available in more purer

form – If heavy metals expected add 0.07 gm EDTA disodium salt in

absorbing reagent. – Formaldehyde solution (HCHO) need to be prepared daily for

analysis. – Sulfamic Acid need to protected from air and it is stable for 1 week

only.

Analysis of Sulfur Dioxide- Major PrecautionsAnalysis of Sulfur Dioxide- Major Precautions

– Use pure sigma make p-rosaniline – Calibration curve preparation and sample analysis need to

be done at similar temperature and it shall not differ more than few degrees.

– The Intercept with vertical axis of the line best fitting the points usually within 0.02 absorbance unit of the blank.

– Prepare calibration curve also by adding sulfamic acid. – Delay analysis by 20 minute to over come impact of O3. – Temperature effect on blank 0.017 absorbance/°C any

change in temperature upward/downward cause increase and decrease in absorbance value.

– Best results are obtained in constant temp bath.

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Methods for Analysis of Gaseous Pollutants in Ambient and SourceMethods for Analysis of Gaseous Pollutants in Ambient and Source S. No. Pollutant BIS No. Method CPCB EPA No.

1. SO2 Ambient 5182-Part-II As BIS 704

Source Emission Regulation Part-III, Isopropanol Method

6

2. NOx Ambient 5182-Part-II Jacob Hochheiser Method Emission Regulation Part-III, Jacob Hochheiser modified method

-

Source - - 7 Phenol disalphonic Acid Colorimetric

3. O3 Ambient & Source

5182 – Part – (ix) - -

4. HCI,HBr,HI,HF Ambient & Source

Specific Electrod Method - 26

5. F2

Ambient & Source

11225-Part-V

SPADNS-Zirconium lead indicator

Emission Regulation Part-III, APHA Method Selective Ion Electrod

Emission Regulation Part-III EPA Method Selective Ion Electrod

ENV-Method

-

6. CI2

Ambient & Source

5182-Part-XIX Methyl Orange NaOH titrated with standard Hypo

-

ENV Method

-

7. NH3

Ambient & Source

11225-Part-VINessler Reagent

- -

8. H2S

Ambient & Source

5182- Part –III Methylene Blue Method - -

9. Mercaptons Ambient & Source

From Handbook of Air Pollution - -

10. COAmbient & Source

5182-Part-X I2O5 Method Indicator Tube Method NDIR Method Gas Chromatography

- -

11. Pb Ambient & Source

ISO 9855-1993(E) - -

AnalysisMethods for Measurement of Air Pollution - SO2

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