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Reading: Chap 7.1 & 7.2. Air Quality Monitoring. ENV 4101/5105 Elements of Air Pollution. Monitoring Considerations Manual vs. automated (real-time, continuous) monitoring Sampling time

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air quality monitoring

Reading: Chap 7.1 & 7.2

Air Quality Monitoring

ENV 4101/5105 Elements of Air Pollution

Aerosol & Particulate Research Lab

air quality monitoring2

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

Air Quality Monitoring

What’s the use of ambient air quality monitoring data?

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monitoring considerations
Monitoring Considerations

What are the objectives?

Examples of criteria for selecting ambient sampling locations?

  • 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)

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differences in averaging times associated with real time data
Differences in averaging times associated with real-time data

Which duration should you use?

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national ambient air quality standards
National Ambient Air Quality Standards

Why different durations?

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federal reference methods for criteria pollutants
Federal Reference Methods for Criteria Pollutants

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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)


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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

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no no 2 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

NO – NO2 – NOx

EM – FT- IR Spectrometry

Can you design an instrument that can measure the concentration of both NO and NO2 in the air?

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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







~ IR ~


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UV light (254 nm)



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


What would cause an interference on a UV photometry O3 monitor?

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FRM – Gas Chromatography - FID




Stationary and mobile phases


Generate an electronic signal when a gas other than the carrier gas elutes from the column.

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  • Mass sensitive rather than concentration sensitive

  • FID – Flame Ionization Detection:
    • Combustion of organic substances
    • Positive ions (+) and electrons (-) are formed when burned – change in current

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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 Impactor

  • PM10 Sampler
  • Remove particles > 10 µm by impaction on a greased surface
  • Particles < 10 µm collected on a quartz glass fiber filter

Particulate Pollutants

What does the PM10 sampler measure? Number or mass concentration of particles?

PM10 sampler with size-selective inlet

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dichotomous sampler

Animation – Virtual Impactor

TEOM Series 1400abAmbient Particulate Monitor

Thermo Electron Co.

Dichotomous Sampler

  • Equivalent method: TEOM
  • Measure PM10, PM2.5, TSP
  • Tapered element oscillating microbalance
  • Real-time measurement of particle mass collected on a filter

How can a Dichotomous sampler measure coarse (PM2.5-10)and fine (PM2.5) particles?

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cascade impactor

Aerosol flow In

Clean air out

Animation – Cascade Impactor

Cascade Impactor

How can we collect different sizes of particles using cascade impactor?

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source sampling and monitoring
Source Sampling and Monitoring
  • Stack Sampling of PM
  • Probe inserted into the stack
  • Temperature sensor
  • Pitot tube – gas velocity and flow rate
  • Two-module sampling unit
  • Isokinetic Sampling
  • Particles – inertial forces
  • 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
Isokinetic Sampling

Fig 8 -2, Aerosol Measurement, 2nd Edition, 2001

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continuous emission monitoring cem
Continuous Emission Monitoring (CEM)


  • 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

Certain utilities and industrial sources are required to measure stack emission continuously

SO2, NO2, opacity, CO2, TRS, H2S, Hg

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accuracy precision and bias

 Bias

 Precision

Relative Error:

Coefficient of variation:

Accuracy, Precision and Bias

Accuracy is a combination of random (precision) & systematic (bias) errors. Which of the 3 cases has the highest accuracy? Why?

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  • 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 self-assessment, and audits

Quality Assurance Programs

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

Air Quality Monitoring Network

  • 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

Quick Reflections

Aerosol & Particulate Research Lab