Air Pollution Module 2 by SNz207M


									Air Pollution


– Ambient air pollution monitoring: techniques and
  instrumentation; monitoring stations
– Stack monitoring: techniques and instrumentation.
– Experimental analysis: gaseous and particulates;
  standards and limits.
Ambient Air Pollution Monitoring
• Most frequently occurring pollutants in an urban
  environment are particulate matters (suspended
  particulate matter i.e. SPM and respirable suspended
  particulate matter i.e. RSPM), carbon monoxide (CO),
  hydrocarbons (HC), sulfur dioxide (SO2), nitrogen
  dioxide (NO2), ozone (O3) and photochemical
      Monitoring of Air pollutants

             Source             Ambient
                              As per WHO ambient monitoring
     Point             Line       SOx             Essential
     SOX               CO         NOx
     NOX               NOx        SPM
     CO                HC         HC
     PM                RPM        CO              Additional
Source monitoring instruments
   Stack sampler (APM 620):            Parameters
   monitored are
           a. Pollutants
           b. Velocity (Isokinetic)
           c. Temperature
           d. Pressure
The recommended criteria for siting the
monitoring stations
   The site is dependent upon the use/purpose of the results of
   the monitoring programs.

   The monitoring should be carried out with a purpose of
   compliance of air quality standards.

   Monitoring must be able to evaluate impacts of new/existing air
   pollution sources.

   Monitoring must be able to evaluate impacts of hazards due to
   accidental release of chemicals.

   Monitoring data may be used for research purpose.
Type of ambient monitoring stations
Station type                                      Description
  Type A       Downtown pedestrian exposure station- In central business districts, in
               congested areas, surrounding by buildings, many pedestrians, average traffic flow >
               10000 vehicles per day. Location of station- 0.5 m from curve; height 2.5 to 3.5 m
               from the ground.
  Type B       Downtown neighbor hood exposure stations- In central business districts but not
               congested areas, less high rise buildings, average vehicles < 500 vehicles per day.
               Typical locations like parks, malls, landscapes areas etc.
               Location of station- 0.5 m from curve; height 2.5 to 3.5 m from the ground.
  Type C       Residential population exposure station – In the midst of the residential areas or
               sub-urban areas but not in central business districts. The station should be more
               than 100 m away from any street.
               Location of station- 0.5 m from curve; height 2.5 to 3.5 m from the ground.
  Type D       Mesoscale stations – At appropriate height to collect meteorological and air quality
               data at upper elevation; main purpose to collect the trend of data variations not
               human exposure.
               Location – roof top of tall buildings or broadcasting towers.
  Type E       Non-urban stations – In remote non-urban areas, no traffic, no industrial activity.
               Main purpose to monitor trend analysis.
               Location of station- 0.5 m from curve; height 2.5 to 3.5 m from the ground.
  Type F       Specialized source survey stations – to determine the impact on air quality at
               specified location by an air pollution source under scrutiny.
               Location of station- 0.5 m from curve; height 2.5 to 3.5 m from the ground.
Frequency of data collection

• Gaseous pollutants: continuous monitoring
• Particulates: once every three days
Number of stations
• Minimum number is three.
• The location is dependent upon the wind rose
  diagram that gives predominant wind directions
  and speed.
• One station must be at upstream of predominant
  wind direction and other two must at
  downstream pre dominant wind direction.
• More than three stations can also be established
  depending upon the area of coverage.
Components of ambient air sampling systems

•       Four main components are:
    –     Inlet manifold
    –     Air mover
    –     collection medium
    –     flow measurement device
Inlet manifold transports sampled pollutants from ambient air to
collection medium or analytical device in an unaltered condition.
The manifold should not be very long. Air mover provides force
to create vacuum or lower pressure at the end of sampling
systems. They are pumps. The collection mediums are liquid or
solid sorbent or dissolving gases or filters or chamber for air
analysis (automatic instruments). The flow device like rotameters
measure the volume of air sampled.
Characteristics for ambient air sampling
•       Five important characteristics are:
    –     collection efficiency
    –     sample stability
    –     recovery
    –     minimal interference
    –     understanding the mechanism of collection
The first three must be 100% efficient. For e.g. for SO2, the
sorbent should be such that at ambient temperature it may
remove the SO2 from ambient atmosphere 100%. Sample must
be stabled during the time between sampling and analysis.
Recovery i.e. the analysis of particular pollutant must be 100%
    Basic considerations for sampling
•     Sample must be representative in terms of time,
      location, and conditions to be studied.
•     Sample must be large enough for accurate analysis.
•     The sampling rate must be such as to provide
      maximum efficiency of collection.
•     Duration of sampling must accurately reflect the
      fluctuations in pollution levels i.e. whether 1-hourly,
      4-hourly, 6-hourly, 8-hourly, 24-hourly sampling.
•     Continuous sampling is preferred.
•     Pollutants must not be altered or modified during
Errors in sampling by HVS
 • Particulates may be lost in sampling manifold – so
   not too long or too twisted manifold must be used.

 • If ’isokinetic’ conditioned are not maintained,
   biased results may be obtained for particulate
Advantages of HVS

 High flow rate at low pressure drop
 High particulate storage capacity
 No moisture regain
 high collection efficiency
 Low coast
 Not appreciable increase in air flow resistance
 Filter is 99% efficient and can collect the particles as
 fine as 0.3 μm
 Absorption principle is 99% efficient in collecting the
Stack Monitoring: techniques & instrumentation
 Stack Sampling
• The sample collected must be
  representative in terms of time
  and location.
• The sample volume should be
  large enough to permit accurate
• The sampling rate must be
  such as to provide maximum
  efficiency of collection.
• The contaminants must not be
  modified or altered in the
  process of collection.
Diagrammatic view of stack sampling
• Impingers are glass bubble tubes designed for the
  collection of airborne particles into a liquid medium
  (Figure 1).
• When using an air sampler, a known volume of air
  bubbles is pumped through the glass tube that
  contains a liquid specified in the method.
• The liquid is then analyzed to determine airborne

              Figure 1: Glass Impinger
 Selection of sampling location
• The sampling point should be as far as
  possible from any disturbing influence,
  such as elbows, bends, transition pieces,
• The sampling point, wherever possible
  should be at a distance of 5-10 diameters
  down-stream from any obstruction and 3-5
  diameters    up-stream     from    similar
Size of sampling point

• The size of the sampling point may be made in
  the range of 7-10 cm, in diameter.
Traverse points
• For the sample become representative, it should be
  collected at various points across the stack.
• The number of traverse points may be selected
  with reference to Table 1.

        Table 1: Traverse Points
        Cross-section area of stack sq. m   No. of points
                       0.2                       4
                    0.2 to 2.5                   12
                 2.5 and above                   20
In circular stacks, traverse points are located at the center of equal
annular areas across two perpendicular diameters as shown in
Figure 2

                                                    Figure 2

In case of rectangular stacks, the area may be divided in to 12 to 25
equal areas and the centers for each area are fixed. (Figure 3)

                             Figure 3
Isokinetic conditions
• Isokinetic conditions exist when the velocity in the
  stack ‘Vs’ equals the velocity at the top of the probe
  nozzle ‘Vn’ at the sample point (Figure 4).

                         Figure 4
      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,
   – 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 further 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)
Atomic Absorption Spectrometry (AAS)
• AAS is a sensitive means for the quantitative
  determination of more than 60 metals or metalloid
• 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 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                                          Principle
                                                Particles are trapped or collected on filters, and
Gravimetric               PM10, PM2.5           the filters are weighed to determine the volume of
                                                the pollutant.
                          more than 60          This technique operates by measuring energy
Atomic absorption         metals or metalloid   changes in the atomic state of the
spectrometry (AAS)        elements (e.g. Pb,    analyte. Emitted radiation is a function of atoms
                          Hg, Zn)               present in the sample.
                                                Measure the amount of light that a sample
Spectrophotometry         SO2, O3               absorbs. The amount of light absorbed indicates
                                                the amount of analyte present in the sample.
                                                Based upon the emission spectrum of an excited
Chemiluminescence         NO2, O3               species that is formed in the course of a chemical
Gas chromatography
                                                Responds in proportion to number of carbon
(GC) - flame ionization   VOC
                                                atoms in gas sample.
detector (FID)
Gas chromatography-                             Mass spectrometers use the difference in mass-to-
mass spectrometry         VOC                   charge ratio (m/z) of ionized atoms or molecules to
(GC-MS)                                         separate them from each other.
Fourier Transform
                                                Sample absorbs infrared radiation and difference
Infrared Spectroscopy     CO, VOC, CH4
                                                in absorption is measured.
• 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

• 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

• 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
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      Figure: FTIR can directly measure
  "fingerprint,"    or   absorption    both criteria pollutants and toxic
  spectrum.                            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
• 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
• 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
• This difference in intensity is electronically translated into
  a reading of the CO present in the ambient air,
  measured in parts per million.
Ambient Air Quality standards & Limits
Central Pollution Control Board 2006
           National Ambient Air Qu ality Standards

           Sulphur dioxide (SO2)        Annual average   60 µg/m 3
                                           24 hour       80 µg/m 3

           Oxides of Nitrogen
                                              A.A        60 µg /m 3
                                              24H        80 µg /m 3

           Suspended Particulate
                                              A.A        140 µg/m 3
           Matter ( SPM)
                                              24H        200 µg/m 3

           Lead                               A.A        0.75 µg/m 3
                                              24H         1.0 µg/m 3

           Carbon Monoxide                    A.A        2.0 µg/m 3
                                              24H        4.0 µg/m 3

           Respirable Particulate
                                              A.A        60 µg/m 3
           Matter (RPM)
                                              24H        100 µg/m 3
  NAAQS by USEPA 2006
  Pollutant                       Primary Stds.                Averaging Times                                 Secondary Stds.

  Carbon Monoxide                 9 ppm (10 mg/m3)             8-hour(1)                                       None

                                  35 ppm (40 mg/m3)            1-hour(1)                                       None

  Lead                            1.5 µg/m3                    Quarterly Average                               Same as Primary
  Nitrogen Dioxide                0.053 ppm (100 µg/m3)        Annual (Arithmetic Mean)                        Same as Primary
  Particulate Matter (PM10)       Revoked(2)                   Annual(2) (Arith. Mean)
                                  150 µg/m3                    24-hour(3)
  Particulate Matter (PM2.5)      15.0 µg/m3                   Annual(4) (Arith. Mean)                         Same as Primary
                                  35 µg/m3                     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/m3)
(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/m3.
(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/m3 (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
Pollutant                     Averaging time                 AQG value

Particulate matter
PM2.5                         1 year                         10 µg/m3
                              24 hour(99th percentile)       25 µg/m3

PM10                          1 year                         20 µg/m3
                              24 hour(99th percentile)       50 µg/m3

Ozone, O3                     Ozone, O3                      100 μg/m3
                              8 hour, daily maximum
Nitrogen dioxide, NO2
                              1 year                         40 μg/m3
                              1 hour                         200 μg/m3

Sulfur dioxide, SO2           24 hour                        20 μg/m3
                              10 minute                      500 μg/m3

Source: WHO, 2005. WHO air quality guidelines global update 2005, WHOLIS number E87950.
•   USEPA, 2007. Online literature from
•   WHO, 2005. WHO air quality guidelines global update 2005, WHOLIS
    number E87950.
•   CPCB 2006, Central Pollution Control Board.

To top