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Marianne Advanced and Applied > Passive samplers IAQ2 > Flashcards

Passive samplers IAQ2 Flashcards

1
Q

What are the basic principles of passive samplers?

A
  1. Pollutant sampled onto medium - - at rate controlled by molecular diffusion
    - without pump
  2. After exposure (days to weeks), sampler closed and returned to laboratory
  3. Absorbed pollutant determined
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2
Q

What are the two methods used to determine the absorbed pollutant?

A
  1. Spectrophotometry
  2. ion chromatography
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3
Q

What is the operating principle of the passive sampler?

A
  1. NO2 diffuses up tube and absorbed on TEA (Triethanolamine) coated mesh
  2. Identified reaction product - triethanolamine N-oxide
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4
Q

What is the reaction scheme of the operating principle of the passive sampler?

A

2NO2 + N(CH2CH2OH)3 + 2OH- ->2NO2- + -O-N+(CH2CH2OH)3 +H2O
- Reaction will not occur in extremely dry air
- OH- occurs from dissociation of TEA in water

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5
Q

In what formations does the NO2 participate in?

A
  1. Troposphere O2
  2. Peroxyacyl nitrate (PAN)
  3. Nitrate aerosols
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6
Q

What are the advantages of passive samplers?

A
  1. Simple
  2. Lightweight
  3. Cheap devices
  4. Operate with no power source
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7
Q

How is the preparation done for NO2 monitoring?

A
  1. 2 stainless steel wire meshes placed into coloured cap
  2. 50 μl of 20% w/v TEA injected on meshes
  3. 0.5 ml wetting agent added to 20 ml of TEA (aq) - acts as absorbent of NO2
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8
Q

What is the chemical formula of Triethanolamine (TEA)?

A

N(CH2CH2OH)3

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9
Q

How are the samplers positioned?

A

3 samplers positioned at 1.5 - 4m from surface

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10
Q

What is the purpose of the three samplers in NO2 monitoring?

A
  • 2 samplers exposed, without colorless cap
  • 1 sampler col.cap not removed, used used as field black
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11
Q

What is the exposure time of the passive samplers?

A

4 weeks

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12
Q

Using spectrophotometry what are the observations made on NO2 using passive samplers?

A
  1. Nitrite in solution, NO2 extracted as nitrite ion from TEA
  2. Reacts with sulphanilamide, forms diazonium compound
  3. On coupling with NEDA forms purple azo dye
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13
Q

Reaction done in spectrophotometry for NO2 monitoring?

A

2NO2 + N(CH2CH2OH)3 + 2OH- -> 2NO2- + -O-N + (CH2CH2OH)3 + H2O

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14
Q

What is NEDA?

A

N-1-naphthylethyldiamine dihydrochloride

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15
Q

How long does it take for full color development and at what wavelength is it spectrophotometrically measured?

A

15 minutes required before optical absorbance is measured at 543 nm

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16
Q

How is the Nitrogen Monoxide determined?

A

Does not react with Saltzman reagent.
- Oxidizes using acidified potassium permanganate

17
Q

How does the analysis of NO2 occur using spectrophotometry?

A
  • colorless cap removed
  • Saltzman reagent added containing:
    a) 2% w/v solution sulphanilamide in b) 5% w/v orthophosphoric acid
    c) 0.14 % NEDA solution
18
Q

How is the concentration of ambient NO2 calculated?

A

By the amount of extracted nitrite for samplers.

19
Q

What method is used to analyze NO2 in short term exposure?

A

Using chemiluminescence analyzer
1. Luminol in alkaline solution reacts with gaseous NO2
2. Produces intense chemiluminescence with maximum emission at 425 nm
3. for sensitive NO2 analyzers
4. detection limit: <30ppt

20
Q

What equipment is used in ion chromatography?

A
  1. Dionex chromatograph
  2. anion separator
  3. conductivity detector
21
Q

What is used in ion chromatography analysis?

A
  1. anion exchange column
  2. solution of sodium bicarbonate
  3. sodium carbonate (Dionex eluent solution)
22
Q

How to calculate the NO2 concentration?

A

NO2 = 1.67 x 10^3 W/t
W: nitrite (μg) subtracted from black value
t: collection time (hrs)

23
Q

How is the NO determined using Analyst samplers?

A
  1. NO oxidised to NO2
  2. Absorbed as nitrite by ion chromatography
  3. NOx conc. calculated
  4. NO subtracted from NOx and NO2 determined by passive samplers
    NOx = NO + NO2
24
Q

What is the equation to calculate NOx?

A

NOx = 2.89 x 10^3 W/t (μg/m3)

25
Q

What are the two properties of NO?

A
  1. Thermodynamically favored species at HIGH temperature
  2. Reason why NOx in combustion exhausts
25
Q

What are the two properties of NO2?

A
  1. Thermodynamically favored at LOW temperatures
  2. The dominant species in ambient air
25
Q

How do you calculate the total uptake of a sampler ΔM (g)?

A

Depends on conc. of pollutant Co (g/cm3), and exposure time Δt (s).
ΔM = S x Co x Δt
S: sampling rate (cm3/s) - depends on geometry

26
Q

What is the passive sampling equation?

A

S = D A / L
S: sampling rate
D: diffusion coefficient
A: area
L: length

27
Q

What is the equation for the volume of a passive sampler and the concentration?

A

V = S x t = DA/L x t
C = m/V = m/ (DA/L x t)

Marianne Advanced and Applied (17 decks)

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