MODULE II
Learning Objectives
  • Ambient air pollution monitoring: techniques and instrumentation; monitoring stations
  • Stack monitoring: techniques and instrumentation.
  • Experimental analysis: gaseous and particulates; standards and limits.

Lecture 1 Lecture 2 Lecture 3

Experimental analysis: Gaseous & particulates; standards & limits

Principles of Sampling and Analysis

  • The components of an air pollution monitoring system include the
    -collection or sampling of pollutants both from the ambient air and from specific sources,
    -the analysis or measurement of the pollutant concentrations, and
    -the reporting and use of the information collected.
  • Emissions data collected from point sources are used to determine compliance with air pollution regulations, determine the effectiveness of air pollution control technology, evaluate production efficiencies, and support scientific research.
  • The EPA has established ambient air monitoring methods for the criteria pollutants, as well as for toxic organic (TO) compounds and inorganic (IO) compounds.
  • The methods specify precise procedures that must be followed for any monitoring activity related to the compliance provisions of the Clean Air Act.
  • These procedures regulate sampling, analysis, calibration of instruments, and calculation of emissions.
  • The concentration is expressed in terms of mass per unit volume, usually micrograms per cubic meter (µg/m3).
Particulate Monitoring
  • Particulate monitoring is usually accomplished with manual measurements and subsequent laboratory analysis.
  • A particulate matter measurement uses gravimetric principles. Gravimetric analysis refers to the quantitative chemical analysis of weighing a sample, usually of a separated and dried precipitate.
  • In this method, a filter-based high-volume sampler (a vacuum- type device that draws air through a filter or absorbing substrate) retains atmospheric pollutants for future laboratory weighing and chemical analysis. Particles are trapped or collected on filters, and the filters are weighed to determine the volume of the pollutant. The weight of the filter with collected pollutants minus the weight of a clean filter gives the amount of particulate matter in a given volume of air.
  • Chemical analysis can be done by atomic absorption spectrometry (AAS), atomic fluorescence spectrometry (AFS), inductively couple plasma (ICP) spectroscopy, and X-ray fluorescence (XRF) spectroscopy.

Atomic Absorption Spectrometry (AAS)

  • AAS is a sensitive means for the quantitative determination of more than 60 metals or metalloid elements.
  • Principle: This technique operates by measuring energy changes in the atomic state of the analyte. For example, AAS is used to measure lead in particulate monitoring.

Figure: Atomic absorption spectrometry

  • Particles are collected by gravimetric methods in a Teflon (PTFE) filter, lead is acid-extracted from the filter.
  • The aqueous sample is vaporized and dissociates into its elements in the gaseous state. The element being measured, in this case lead, is aspirated into a flame or injected into a graphite furnace and atomized.
  • A hollow cathode or electrode less discharge lamp for the element being determined provides a source of that metal's particular absorption wavelength.
  • The atoms in the unionized or "ground" state absorb energy, become excited, and advance to a higher energy level.
  • A detector measures the amount of light absorbed by the element, hence the number of atoms in the ground state in the flame or furnace.
  • The data output from the spectrometer can be recorded on a strip chart recorder or processed by computer.
  • Determination of metal concentrations is performed from prepared calibration curves or read directly from the instrument.

Gaseous pollutant monitoring

  • Gaseous pollutant monitoring can be accomplished using various measurement principles.
  • Some of the most common techniques to analyze gaseous pollutants include
    -Spectrophotometry,
    -Chemiluminescence,
    -Gas chromatography-flame ionization detector (GC-FID),
    - Gas chromatography-mass spectrometry (GC-MS), and
    - Fourier transform infrared spectroscopy (FTIR).
  • With all sampling and analysis procedures, the end result is quantitative data.
  • The validity of the data depends on the accuracy and precision of the methods used in generating the data.
  • The primary quality control measure is calibration.
  • Calibration checks the accuracy of a measurement by establishing the relationship between the output of a measurement process and a known input.
Table 1. Methods of Measuring and Analyzing Air Pollutants
Method
Variable Measured
Principle
Gravimetric
PM10, PM2.5
Particles are trapped or collected on filters, and the filters are weighed to determine the volume of the pollutant.
Atomic absorption spectrometry (AAS)
more than 60 metals or metalloid elements (e.g. Pb, Hg, Zn)
This technique operates by measuring energy changes in the atomic state of the analyte.  Emitted radiation is a function of atoms present in the sample.
Spectrophotometry
SO2, O3
Measure the amount of light that a sample absorbs.  The amount of light absorbed indicates the amount of analyte present in the sample.
Chemiluminescence
SO2, O3
Based upon the emission spectrum of an excited species that is formed in the course of a chemical reaction.
Gas chromatography (GC) - flame ionization detector (FID)
VOC
Responds in proportion to number of carbon atoms in gas sample.
Gas chromatography-mass spectrometry (GC-MS)
VOC
Mass spectrometers use the difference in mass-to-charge ratio (m/z) of ionized atoms or molecules to separate them from each other.
Fourier Transform Infrared Spectroscopy (FTIR)
CO, VOC, CH4
Sample absorbs infrared radiation and difference in absorption is measured.

Spectrophotometry

  • A spectrophotometer measures the amount of light that a sample absorbs.
  • The instrument operates by passing a beam of light through a sample and measuring the intensity of light reaching a detector.
  • Spectrophotometry commonly used to measure sulfur dioxide (SO2) concentrations.
  • The amount of light absorbed indicates the amount of sulfur dioxide present in the sample.

Figure: Schematic of a UV-VIS spectrophotometer

Chemiluminescence

  • An ambient air sample is mixed with excess ozone in a special sample cell. A portion of the NO present is converted to an activated NO2 which returns to a lower energy state and in the process emits light. This phenomenon is called chemiluminescence.

Figure: Chemical reaction to determine oxides of nitrogen by chemiluminescence

  • Chemiluminescence methods for determining components of gases originated with the need for highly sensitive means for determining atmospheric pollutants such as ozone, oxides of nitrogen, and sulfur compounds.
  • The intensity of this light can be measured with a photomultiplier tube and is proportional to the amount of NO in the sample. A second reaction measures the total oxides of nitrogen in the air sample and in turn, the concentration of NO2 can be calculated.

Gas Chromatography (GC)

  • Gas chromatography (GC) coupled with a flame ionization detector (FID) is employed for qualitative identification and quantitative determination of volatile organic compounds (VOCs) in air pollution monitoring.
  • The GC, consists of a column, oven and detector. In the gas chromatograph, a sample goes to the column, separates into individual compounds and proceeds through the hydrogen flame ionization detector.

Figure: Schematic gas chromatography

  • The flame in a flame ionization detector is produced by the combustion of hydrogen and air.
  • When a sample is introduced, hydrocarbons are combusted and ionized, releasing electrons.
  • A collector with a polarizing voltage located near the flame attracts the free electrons, producing a current that is proportional to the amount of hydrocarbons in the sample.
  • The signal from the flame ionization detector is then amplified and output to a display or external device.
  • Gas chromatography-mass spectrometry (GC-MS) instruments have also been used for identification of volatile organic compounds. Mass spectrometers use the difference in mass-to-charge ratio (m/z) of ionized atoms or molecules to separate them from each other. Mass spectrometry is useful for quantification of atoms or molecules and also for determining chemical and structural information about molecules.

Fourier Transform Infrared Spectroscopy

  • FTIR can detect and measure both criteria pollutants and toxic pollutants in ambient air
  • FTIR can directly measure more than 120 gaseous pollutants in the ambient air, such as carbon monoxide, sulfur dioxide, and ozone.
  • The technology is based on the fact that every gas has its own "fingerprint," or absorption spectrum.

Figure: FTIR can directly measure both criteria pollutants and toxic pollutants in the ambient air.

  • The FTIR sensor monitors the entire infrared spectrum and reads the different fingerprints of the gases present in the ambient air.
  • Carbon monoxide is monitored continuously by analyzers that operate on the infrared absorption principle.
  • Ambient air is drawn into a sample chamber and a beam of infrared light is passed through it.
  • CO absorbs infrared radiation, and any decrease in the intensity of the beam is due to the presence of CO molecules.
  • This decrease is directly related to the concentration of CO in the air.
  • A special detector measures the difference in the radiation between this beam and a duplicate beam passing through a reference chamber with no CO present.
  • This difference in intensity is electronically translated into a reading of the CO present in the ambient air, measured in parts per million.
National Ambient Air Quality Standards
POLLUTANTS
AVERAGE TIME
CONCENTRATION
sulphur dioxide (SO2)

Annual average
24 hour

60 µg/cubic m
80 µg/cubic m

Oxides of Nitrogen (NO2)

A.A
24H

60 µg/cubic m
80 µg/cubic m

Suspended Particulate Matter (SPM)

A.A
24H

140µg/cubic m
200µg/cubic m

Lead

A.A
24H

0.75 µg/cubic m
1.0 µg/cubic m

Carbon Monoxide

A.A
24H

2.0 µg/cubic m
84.0 µg/cubic m

Respirable Particulate Matter (RPM)

A.A
24H

60 µg/cubicm
100 µg/cubic m



NAAQS by USEPA 2006


Pollutant
Primary Stds.
Averaging Times
Secondary Stds.
Carbon Monoxide
9 ppm (10 mg/cubic m)
8-hour(1)
None
35 ppm (40 mg/cubic m)
1-hour(1)
None
Lead
1.5 µg/cubic m
Quarterly Average
Same as Primary
Nitrogen Dioxide
0.053 ppm (100 µg/cubic m)
Annual (Arithmetic Mean)
Same as Primary
Particulate Matter (PM10)
Revoked(2)
Annual(2) (Arith. Mean)
150 µg/cubic m
24-hour(3)
Particulate Matter (PM2.5)
15.0 µg/cubic m
Annual(4) (Arith. Mean)
Same as Primary
35 µg/cubic m
24-hour(5)
Ozone
0.08 ppm
8-hour(6)
Same as Primary
0.12 ppm
1-hour(7) (Applies only in limited areas)
Same as Primary
Sulfur Oxides
0.03 ppm
Annual (Arith. Mean)
-------
0.14 ppm
24-hour(1)
-------
-------
3-hour(1)
0.5 ppm (1300 µg/cubic m)
    (1)Not to be exceeded more than once per year.
    (2)Due to a lack of evidence linking health problems to long-term exposure to coarse particle pollution, the agency revoked the annual PM10 standard in 2006 (effective December 17, 2006).
    (3) Not to be exceeded more than once per year on average over 3 years.
    (4) To attain this standard, the 3-year average of the weighted annual mean PM2.5 concentrations from single or multiple community-oriented monitors must not exceed 15.0 µg/cubic metre.
    (5) To attain this standard, the 3-year average of the 98th percentile of 24-hour concentrations at each population-oriented monitor within an area must not exceed 35 µg/cubic metre (effective December 17, 2006).
    (6) To attain this standard, the 3-year average of the fourth-highest daily maximum 8-hour average ozone concentrations measured at each monitor within an area over each year must not exceed 0.08 ppm.
    (7) (a) The standard is attained when the expected number of days per calendar year with maximum hourly average concentrations above 0.12 ppm is < 1, as determined by appendix H. (b) As of June 15, 2005 EPA revoked the 1-hour ozone standard in all areas except the fourteen 8-hour ozone nonattainment Early Action Compact (EAC) Areas.
WHO Air Quality Guidelines Value

POLLUTANTS
AVERAGE TIME
AQG value
Particulate matter
PM2.5

PM10
1 year 24 hour(99th percentile)
1 year 24 hour(99th percentile)

10 µg/cubic metre
25 µg/cubic metre
20 µg/cubic metre
50 µg/cubic metre

Ozone, O3

8 hour, daily maximum

100 µg/cubic metre

Nitrogen dioxide, NO2

1 year 1 hour

40µg/cubic metre
200µg/cubic metre

Sulfur dioxide, SO2

24 hour 10 minute

20 µg/cubic metre
500 µg/cubic metre



References

USEPA, 2007. Online literature from www.epa.gov
WHO, 2005. WHO air quality guidelines global update 2005, WHOLIS number E87950.
CPCB 2006, Central Pollution Control Board. http://www.cpcb.nic.in/standard2.htm