Air Sampling & Instrumentation

Question 1

Absorption

Answer 1

The removal of gaseous constiutent from a gas stream by pentration of the gas molecules into a liquid or solid matrix. Needs bubbling to achieve good mixing.

Question 2

Properties/Types of Absorption Sampling

Answer 2

Properties
- Low volatility, low viscosity, low foaming, non flammable

Types
- Fritted Glass (MFGB), Impinger (MI)

Question 3

Adsorption

Answer 3

The removal of gaseous constituents from an airstream by a solid matrix in which the gas molecules are deposited on the surface of the adsorbent

Question 4

Factors affecting adsorption

Answer 4

• Nature of material (surface area, polarity, reactivity, etc.)
• Temperature
• Velocity of air stream
• Concentration of gases

Question 5

Active adsorption

Answer 5

air pulled thru tube
Break-thru criteria for chemical sampling media
NIOSH > 10% on back up
OSHA > 25% on back up section
―Migration – diffusion of sample from front to rear over storage time
5% on pre/post calibration of pumps = bad sample
Field Blanks: 10% of sample, Minimum 2

Question 6

Passive adsorption

Answer 6

relies on molecular diffusion (ficks first law)
Critical Air Velocity 0.2 m/sec
Performance affected by: Face velocity, temperature, humidity, pressure, and reverse
diffusion

Question 7

Common adsorbents

Answer 7

• activated charcoal
• silica gel
• porous polymers

Question 8

Conductivity:

Answer 8

Gases form electrolytes in solution and change conductivity of solution (NH3, SO2)

Question 9

Potentiometry:

Answer 9

Gases react with reagents to change pH of solution (O2, CO, H2S)

Question 10

Coulometry:

Answer 10

measurement of the number of electrons transferred across a solution/electrode interface

Question 11

Flame ionization:

Answer 11

measurement of conductivity of gas as a result of ionization of gas by flame (total Hydrocarbons)

Question 12

Thermal conductivity:

Answer 12

resistance of heated filament changes with temperature changes of filament caused by thermal conductance of gas flowing over filament (wheatstone bridge)

Question 13

Fume

Answer 13

Solid particles formed by condensation after heating (0.001-0.2 m)

Question 14

Dust

Answer 14

Solid particles formed by mechanical processes (0.5-50 m)

Question 15

Mist

Answer 15

A dispersion of liquid particles (40 - 400 m)

Question 16

Smoke

Answer 16

Solids from incomplete combustion

Question 17

Fog

Answer 17

Liquid formed by condensation

Question 18

Fiber

Answer 18

aspect ration of 3-1

Question 19

Aerosol behavior effected by

Answer 19

1) size
2) shape
3) density
4) Hygroscopic

Question 20

Stokes Law (particle settling rate)

Answer 20

Vs = 0.003SGd2(cm) Or Vs = 0.006 x SG x d2 ( m)

Terminal settling velocity is proportional to d2

Question 21

Filter medium - Forces Acting on an Aerosol

Answer 21

• Sedimentation – gravitational effects (based on Stokes Law)
• Impaction – Rapid changes in Air direction impacts particle on filter
• Diffusion – Random displacement due to air‘s Brownian Motion
• Interception – Airflow of particle past a collecting medium 1/2 particle size to be captured by ―touching” electromagnetic attraction (oil wipes this out)

Question 22

Filter medium - Forces promoting

retention

Answer 22

• Van der Waals
• Electrostatic charge
• Capillary forces due to liquids

Question 23

Three major types:

Answer 23

Filtering, Impaction, and impingement

Question 24

Impingement:

Answer 24

not commonly used as a technique anymore

• Greenberg-Smith: Flow rate 1 cfm, pressure drop 3”Hg
• Midget impinger: 0.1 cfm,
• Particle counting - (see Ocular microcopy for more information) Mppcf – million particles/cubic ft (6.4 mppcf = 1 mg/m3)

Question 25

MCEF

Answer 25

0.8 m, 37mm & 25 mm used for Not for Gravimetric 855 and 385 mm2 used for Metals, asbestos 100

Question 26

Glass

Answer 26

Analytical finish requires strong chemicals Benzidine, aldrine 32

Question 27

PVC

Answer 27

5 m typical, used for gravimetric tests Dust, Cr (IV) 15

Question 28

PTFE

Answer 28

5m typical, used for extraction/desorption Alkaline dust, formic acid 25

Question 29

Silver

Answer 29

Sample support medium for x-ray analysis | 2

Question 30

Types of Asbestos

Answer 30

- Amosite - Chrysotile - Most Common - Tremolite - Crocidolite - Blue Asbestos, Most Dangerous

Question 31

Inhailable particulate Mass (IPM)

Answer 31

any size within the respiratory tract (up to 100 m) (Inertial Impaction)

Question 32

Thoracic Particulate Mass (TPM)

Answer 32

Airway of lungs or gas exchange region (5-15 m) (Top Impaction, bottom diffusion and impaction)

Question 33

Reparable Particulate Mass (RPM)

Answer 33

Gas exchange region 5 m, sedimentation or diffusion dependent on size of particle (0.1 m)