ENV 4101/5105 Elements of Air Pollution
Reading: Chap 7.1 & 7.2
Air Quality
Monitoring
http://www.statcan.ca/english/freepub/16-254XIE/2007000/tablesgraphs/figure3-en.htm
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Air Quality Monitoring
 Monitoring Considerations
• Manual vs. automated (real-time, continuous) monitoring
• Sampling time
• Federal reference method (FRM) vs. equivalent method (EM)
 Monitoring of Ambient Air Pollutants
• SO2, NOx, CO, O3
• Hydrocarbons
• PM10, PM2.5
 Source Sampling and Monitoring
• Sampling train
• Isokinetic sampling
 Quality Assurance Programs
• Quality Assurance
• Quality Control
 Air Quality Monitoring Network
What’s the use of ambient air quality monitoring data?
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Monitoring Considerations
• Sampling location: limited number of fixed site
monitors whose locations reflect objectives of air
quality monitoring program
What are the objectives?
Examples of criteria for selecting ambient sampling locations?
• Lower limit of detection (LOD): a sufficient amount
of pollutant must be collected, f(sampling rate,
duration)
– Integrated sampling vs. real-time sampling
– Area sampling vs. personal sampling
• Collection efficiency of the instrument:
– Low flow rate for gas-phase contaminants (< 1 L/min)
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Differences in averaging times
associated with real-time data
Which duration should you use?
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National Ambient Air Quality Standards
Pollutant
Primary Stds.
Averaging Times
Secondary Stds.
CO
9 ppm (10 mg/m3)
8-hour(1)
None
35 ppm (40 mg/m3)
1-hour(1)
None
Pb
1.5 µg/m3
Quarterly Ave
Same as Primary
NO2
0.053 ppm (100 µg/m3)
Annual (Arith. Mean)
Same as Primary
PM10
Revoked(2)
Annual(2) (Arith. Mean)
150 µg/m3
24-hour(3)
15.0 µg/m3
Annual(4) (Arith. Mean)
35 µg/m3
24-hour(5)
0.08 ppm
8-hour(6)
Same as Primary
0.12 ppm
1-hour(7) (Applies only in
limited areas)
Same as Primary
0.03 ppm
Annual (Arith. Mean)
-------
0.14 ppm
24-hour(1)
-------
PM2.5
O3
SO2
-------
3-hour(1)
Why different durations?
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Same as Primary
0.5 ppm (1300 µg/m3)
http://www.epa.gov/air/criteria.html
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Federal Reference Methods for Criteria Pollutants
Pollutant
SO2
NO2
CO
O3
NMHCs
PM10
PM2.5
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Reference Method
Spectrophotometry (pararosanilne method)
Gas-phase chemiluminescence
Nondispersive infrared photometry
Chemiluminescence
Gas chromatography – FID (flame ionization detection)
Performance-approved product
Performance-approved product
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SO2
FRM - Spectrophotometry (pararosanilne method)
Air sample  potassium tetrachloromercurate solution 
HgCl2SO3-2  react with HCHO and colorless pararosaniline
hydrochloride  red-violet product  measured
spectrophotometrically  SO2 concentration
EM – FT- IR Spectrometry
(Absorption of IR by SO2 in
the air  SO2 concentration)
http://clu-in.org/programs/21m2/openpath/op-ftir/images/exhibit3.gif
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SO2
EM – UV Fluorescence
1) UV light excites SO2 to a higher energy state
SO2 + hv1  SO2*
2) Decay of the excited SO2*, emitting a characteristic radiation
SO2*  SO2 + hv2
www.cse.polyu.edu.hk/~airlab/so2.jpg
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NO – NO2 – NOx
FRM – Gas-Phase Chemiluminescence
Chemiluminescence: emission of light
from electronically excited chemical
species formed in chemical reactions.
NO + O3  NO2* + O2
NO2*  NO2 + hv
Measurement of NO2: conversion of NO2 to
NO, and subsequent measurement by
chemiluminescence.
2NO2 + Mo  3 NO + MoO3
Possible interference: N-containing
compounds  higher measured NO2
EM – FT- IR Spectrometry
www.k2bw.com/images/chem.gif
Can you design an instrument that can measure the
concentration of both NO and NO2 in the air?
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CO
FRM – Nondispersive Infrared (NDIR) spectrometry
CO strongly absorbs infrared energy at certain wavelengths.
Detection device: two cylindrical cells, a sample and a reference cell.
Difference in infrared energy in the two cells  concentration of CO
CO
Sample
Cell
~ IR ~
Reference
Cell
Detection
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O3
FRM – Chemiluminescence
Light emissions produced on reaction of O3 with ethylene (C2H4).
C2H4 flammable – replaced by Rhodamine B dye embedded in a disk
Rhodamine B does not attain a stable baseline rapidly after exposure to O3
EM – UV Photometry
Absorption of UV light (254 nm) by O3 and subsequent use of
photometry to measure the reduction of UV energy
O3
UV light (254 nm)
Detector
O3
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What would cause an
interference on a UV
photometry O3 monitor?
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NMHCs
Intensity
FRM – Gas Chromatography - FID
Time
Stationary and mobile phases
GC-Detector:
Generate an electronic signal when a gas other than the carrier gas elutes from the column.
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NMHC
• FID – Flame Ionization Detection:
– Combustion of organic substances
– Positive ions (+) and electrons (-) are formed when
burned – change in current
− Mass sensitive rather than
concentration sensitive
http://teaching.shu.ac.uk/hwb/chemistry/tutorials/chrom/gaschrm.htm
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Particulate Pollutants
• Impaction and filtration are the
primary PM collection principles
• Measure the weight of exposed
and clean filters
• High-volume sampler (Hi-Vol)
• Typical sampling duration – 24 h
Animation –
PM10 Sampler
PM10 Impactor
• Remove particles > 10 µm by
impaction on a greased surface
• Particles < 10 µm collected on a
quartz glass fiber filter
PM10 sampler with size-selective inlet
http://www.recetox.muni.cz/images/airsag/PM10.jpg
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What does the PM10 sampler
measure? Number or mass
concentration of particles?
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Dichotomous Sampler
Animation –
Virtual Impactor
TEOM Series 1400ab
Ambient Particulate Monitor
Thermo Electron Co.
http://crac.ucc.ie/images/sampler1.jpg
How can a Dichotomous sampler
measure coarse (PM2.5-10) and fine
(PM2.5) particles?
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Equivalent method: TEOM
• Measure PM10, PM2.5, TSP
• Tapered element oscillating
microbalance
• Real-time measurement of
particle mass collected on a
filter
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Animation –
Cascade Impactor
Cascade Impactor
Aerosol flow In
Clean air out
How can we collect
different sizes of particles
using cascade impactor?
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Source Sampling and Monitoring
Stack Sampling of PM
1) Probe inserted into the stack
2) Temperature sensor
3) Pitot tube – gas velocity and flow rate
4) Two-module sampling unit
Isokinetic Sampling
1) Particles – inertial forces
2) Samples must be collected at the
same rate of low as the stack gas
What’s the use of source emission data?
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Isokinetic Sampling
Fig 8 -2, Aerosol Measurement, 2nd Edition, 2001
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Continuous Emission Monitoring (CEM)
• Certain utilities and industrial sources are required
to measure stack emission continuously
• SO2, NO2, opacity, CO2, TRS, H2S, Hg
Opacity
• Compare plume darkness to
Ringlemann chart by trained
smoke readers
• Averages of measurements of ¼
or ½ minute over an hour
• Simple, low cost, legal
acceptance
Ringlemann chart
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Accuracy, Precision and Bias
Relative Error:
E r %  
Coefficient of variation:
OA
 Bias
 100
A
CV %  

 100
 Precision
X
Accuracy is a combination of random (precision) & systematic (bias)
errors. Which of the 3 cases has the highest accuracy? Why?
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Calibration
• Often used for adjusting bias-type errors
• Measured values are compared to standard reference
values (for pollutant concentration) or standard airflow
measuring techniques/devices (for volume air flow)
• Primary vs. secondary standard for flow: traceable to
the National Institute of Standards and Technology
(NIST)
– Primary: bubble meter
– Secondary: wet or dry test meters calibrated by bubble meter
• Gas standards: traceable to a NIST reference material
– CO, SO2, NO2, NO: available in cylinder gas or permeation tubes
– O3: NIST certified O3 generator
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Quality Assurance Programs
Goal: Valid and reliable air quality monitoring data
Quality Assurance (QA)
• Setting policy and overseeing management controls
• Planning, review of data collection activities and data use
• Setting data quality objectives, assigning responsibilities,
conducting reviews, and implementing corrective actions
Quality Control (QC)
• Technical aspects of data quality programs
• Implementation of specific QC procedures:
calibrations, checks, replicate samples, routine selfassessment, and audits
It is federal rule to document QA/QC efforts !
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Air Quality Monitoring Network
State and Local Air Monitoring Stations (SLAMS)
•
•
•
•
•
•
Highest pollutant concentrations
Representative concentrations in areas of high population density
Impact of major emission sources
Regional background concentrations
Extent of pollutant transport among populated areas
Welfare-related impacts in more rural and remote areas
National Air Monitoring Stations (NAMS)
• Urban area, long-term air quality monitoring network
• Air quality comparisons and trends analysis
Photochemical Assessment Monitoring Stations (PAMS)
• Monitor O3 and photochemical air pollutants
Clean Air Status and Trends Network (CASTNet)
• Primary source for rural O3 level and dry atmospheric deposition
National Atmospheric Deposition Program (NADP)
• Assess the problem of atmospheric deposition and its effects on aquatic
and terrestrial ecosystems (H+, NH4+, SO42-, NO3-, Cl-, Ca2+, Mg2+, K+, Hg)
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Quick Reflections
 Monitoring Considerations
• Manual vs. automated (real-time, continuous) monitoring
• Sampling time
• Federal reference method (FRM) vs. equivalent method
(EM)
 Monitoring of Air Pollutants
• SO2, NOx, CO, O3
• Hydrocarbons
• PM10, PM2.5
 Source Sampling and Monitoring
• Sampling train
• Isokinetic sampling
 Quality Assurance Programs
• Quality Assurance
• Quality Control
 Air Quality Monitoring Network
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