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Reading: Chap 7.1 & 7.2. Air Quality Monitoring. ENV 4101/5105 Elements of Air Pollution. http://www.statcan.ca/english/freepub/16-254-XIE/2007000/tablesgraphs/figure3-en.htm. Monitoring Considerations Manual vs. automated (real-time, continuous) monitoring Sampling time - PowerPoint PPT Presentation
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Air Quality Air Quality MonitoringMonitoring
ENV 4101/5105 Elements of Air Pollution
04/21/23 1Aerosol & Particulate Research Lab
http://www.statcan.ca/english/freepub/16-254-XIE/2007000/tablesgraphs/figure3-en.htm
Reading: Chap 7.1 & 7.2
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
04/21/23 2Aerosol & Particulate Research Lab
What’s the use of ambient air quality monitoring data?
Monitoring Considerations
• Sampling location: limited number of fixed site monitors whose locations reflect objectives of air quality monitoring program
• 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)
04/21/23 Aerosol & Particulate Research Lab 3
Examples of criteria for selecting ambient sampling locations?
What are the objectives?
4
Differences in averaging times associated with real-time data
04/21/23 Aerosol & Particulate Research Lab
Which duration should you use?
5
National Ambient Air Quality StandardsPollutant 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)
PM2.5 15.0 µg/m3 Annual(4) (Arith. Mean) Same as Primary
35 µg/m3 24-hour(5)
O3 0.08 ppm 8-hour(6) Same as Primary
0.12 ppm 1-hour(7) (Applies only in limited areas)
Same as Primary
SO2 0.03 ppm Annual (Arith. Mean) -------
0.14 ppm 24-hour(1) -------
------- 3-hour(1) 0.5 ppm (1300 µg/m3)
http://www.epa.gov/air/criteria.html
04/21/23 Aerosol & Particulate Research Lab
Why different durations?
Federal Reference Methods for Criteria Pollutants
Pollutant Reference Method
SO2Spectrophotometry (pararosanilne method)
NO2Gas-phase chemiluminescence
CO Nondispersive infrared photometry
O3Chemiluminescence
NMHCs Gas chromatography – FID (flame ionization detection)
PM10Performance-approved product
PM2.5Performance-approved product
04/21/23 6Aerosol & Particulate Research Lab
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)
04/21/23 7Aerosol & Particulate Research Lab
http://clu-in.org/programs/21m2/openpath/op-ftir/images/exhibit3.gif
04/21/23 Aerosol & Particulate Research Lab 8
SO2
EM – UV Fluorescence1) 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
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
Can you design an instrument that can measure the concentration of both NO and NO2 in the air?
www.k2bw.com/images/chem.gif
04/21/23 9Aerosol & Particulate Research Lab
EM – FT- IR Spectrometry
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
SampleCell
ReferenceCell
CO
~ IR ~
Detection04/21/23 10Aerosol & Particulate Research Lab
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
O3What would cause an interference on a UV photometry O3 monitor?
04/21/23 11Aerosol & Particulate Research Lab
NMHCsFRM – Gas Chromatography - FID
Time
Inte
nsi
ty
Generate an electronic signal when a gas other than the carrier gas elutes from the column.
GC-Detector:
Stationary and mobile phases
04/21/23 12Aerosol & Particulate Research Lab
NMHC• FID – Flame Ionization Detection:
– Combustion of organic substances– Positive ions (+) and electrons (-) are formed when
burned – change in current
04/21/23 Aerosol & Particulate Research Lab 13
http://teaching.shu.ac.uk/hwb/chemistry/tutorials/chrom/gaschrm.htm
− Mass sensitive rather than concentration sensitive
Particulate Pollutants
http://www.recetox.muni.cz/images/airsag/PM10.jpg
PM10 sampler with size-selective inlet
• 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
PM10 Sampler
• Remove particles > 10 µm by impaction on a greased surface
• Particles < 10 µm collected on a quartz glass fiber filter
What does the PM10 sampler measure? Number or mass concentration of particles?
Animation – PM10 Impactor
04/21/23 14Aerosol & Particulate Research Lab
Dichotomous Sampler
http://crac.ucc.ie/images/sampler1.jpg
How can a Dichotomous sampler measure coarse (PM2.5-10) and fine (PM2.5) particles?
Animation – Virtual Impactor
TEOM Series 1400abAmbient Particulate MonitorThermo Electron Co.
Equivalent method: TEOM• Measure PM10, PM2.5, TSP• Tapered element oscillating
microbalance• Real-time measurement of
particle mass collected on a filter
04/21/23 15Aerosol & Particulate Research Lab
Cascade ImpactorAnimation – Cascade Impactor
How can we collect different sizes of particles using cascade impactor?
Aerosol flow In
Clean air out
04/21/23 16Aerosol & Particulate Research Lab
Source Sampling and Monitoring
Stack Sampling of PM1) Probe inserted into the stack2) Temperature sensor3) Pitot tube – gas velocity and flow rate4) Two-module sampling unit
Isokinetic Sampling1) Particles – inertial forces2) Samples must be collected at the
same rate of low as the stack gas
04/21/23 17Aerosol & Particulate Research Lab
What’s the use of source emission data?
Isokinetic Sampling
04/21/23 Aerosol & Particulate Research Lab 18
Fig 8 -2, Aerosol Measurement, 2nd Edition, 2001
Continuous Emission Monitoring (CEM)• Certain utilities and industrial sources are required
to measure stack emission continuously
• SO2, NO2, opacity, CO2, TRS, H2S, Hg
04/21/23 Aerosol & Particulate Research Lab 19
Opacity
Ringlemann chart
• 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
Accuracy, Precision and Bias
Accuracy is a combination of random (precision) & systematic (bias) errors. Which of the 3 cases has the highest accuracy? Why?
04/21/23 20Aerosol & Particulate Research Lab
100%
A
AOErRelative Error:
Coefficient of variation: 100% X
CV
Bias
Precision
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
04/21/23 Aerosol & Particulate Research Lab 21
Quality Assurance Programs
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
Goal: Valid and reliable air quality monitoring data
Quality Control (QC)• Technical aspects of data quality programs• Implementation of specific QC procedures:
calibrations, checks, replicate samples, routine self-assessment, and audits
It is federal rule to document QA/QC efforts !
04/21/23 22Aerosol & Particulate Research Lab
Air Quality Monitoring NetworkState 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
04/21/23 23Aerosol & Particulate Research Lab
National Atmospheric Deposition Program (NADP)• Assess the problem of atmospheric deposition and its effects on aquatic
and terrestrial ecosystems (H+, NH4+, SO4
2-, NO3-, Cl-, Ca2+, Mg2+, K+, Hg)
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
04/21/23 24Aerosol & Particulate Research Lab