Units for Atmospheric Concentrations

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Units for Atmospheric Concentrations

• Conventional Units parts per million (ppm)
• ppmv (by volume - 1 part solute volume per
  million parts (airsolute) volume)
• ppmw (by weight)
• Current commonly used units - ?g / m³
• Micrograms of solute per m³ of air.
• These units can be converted into each other
• Conversion

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Relationship between ppmv and ? g/m3

• Consider volume of air (Vair) containing mA
  micrograms of A of molecular weight MA and molar
  volume VA. By Ideal Gas law, we have
• P VA (mA/MA) RT and therefore CA (? g/m3)
  (mA/Vair) (pMA/RT)(VA/Vair) (pMA/RT)(Cppm)
• Express R 0.08205 x 10-3 m3.atm/mol.K,
  atmospheric pressure P 1 atm, and ambient
  temperature T 298K then
• CA (?g/m3) (MA/0.024)(Cppm) 41.66 (Cppm)

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TYPES OF ATMOSPHERIC POLLUTANTS

• Airborne Particulates
• Aerosols
• Natural aerosols
• Fog, Mist, Dust, Biological Origin etc.
• Synthetic aerosols
• Sprays, mists, smoke etc.
• Classification
• Fine Dust (lt 100 ?m)
• Coarse Dust (gt 100 ?m)
• Smoke Fumes (0.001 lt d lt 1 ?m)
• Mist -liquid condensed on particles ( 0.1 lt d lt
  10 ?m)
• Composition of particulate varies with location
  
• Inorganic (mineral rich Fe, Al, Mg, Si, Pb
  etc.)
• Organic (from biological sources)
• Composition affects the pollution implication

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TYPES OF ATMOSPHERIC POLLUTANTS

• Primary Emissions
• Direct emissions
• SO2, CO2, CO, alkanes etc.Natural aerosols
• Secondary Emissions
• Indirect products of atmospheric reactions
• SO3, H2SO4, Ketones, aldehydes, acids, esters
• S compounds
• C compounds (organic)
• N compounds
• CO
• Halogenated compounds
• Radioactive compounds

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Effects of particulate pollutants

• Inhalation Hazard
• Enhances Chemical Reactions in the Atmosphere
• Visibility Reduction
• Fog Formation / Precipitation
• Solar Radiation Reduction
• Temperature and Wind Distribution Alteration

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AIR POLLUTION MEASUREMENTS

• Sampling instrumentation
• Sample?Collection Device?Detector?Pump?Vent
• Representative Sampling
• Ambient Monitoring
• Free access should be possible where
  concentrations are perceived to be maximum. EPA
  guidelines are strict.
• Source Testing (e.g. stack exit..)
• Isokinetic sampling.
• EPA methods 1-5 for particulate sampling.
  (http//www.epa.gov/epaoswer/hazwaste/test/main.ht
  m)
• Analytical Methods
• Measurement technique (or detector) varies with
  type of pollutant
• For some components, inline detectors exist to
  give real time measurement
• Other components must be accumulated over a
  period of time for measurement
• Method Detection limit (MDL) Concentration
  Averaging
• From real time continuous sampling data
• Accumulative sampling (e.g. particulate)

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GENERALIZED AUTOMATIC CONINUOUS AIR POLLUTION
MONITOR
TIMER
Air/liquid contactor
Adsorber to Remove interferents
Flow control monitoring
AMBIENT AIR
Air mover
Filter dryer
SPAN GAS
Zero gas adsorber
Measurement sensor
Reference sensor
Waste or cleanup
Absorption liquid
Electrical Comparison circuitry
Voltage signal
Fresh solution
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MODIFIED METHOD 5 SAMPLING TRAIN GENERAL
SCHEMATIC (EPA SW846 Method 0100)
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PROBLEMS OF CHOOSING A SAMPLING SITE
CO concentration Inside structure Is gt NAAQS
Air monitoring station
Downtown Air monitoring station
Governmental building
Parking structure
Office building
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Problem of on-line sampling for particulates
nozzle
Vn
Vs
Vn Vs
Cambient Csampled
Pollutant molar flow rate (molar flow rate of
gas) x (pollutant molar concentration in gas)
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Test Methods for Major Air Pollutants

• Particulate Matter (PM10) High volume sampler
  with nozzle (filter) designed to exclude
  particles greater than 10 microns diameter.
• Sulfur Dioxide West-Gaeke method air bubbled
  through tetrachloromercurate then treated with
  pararosaniline and determined by calorimetry.
• Ozone air reacted with ethylene to form a
  complex that is luminescent which is measured
  using a photomultiplier.
• Carbon monoxide Nondispersive infrared detector
  (NDIR)
• Hydrocarbons Gas chromatograph (GC) or high
  pressure liquid chromatograph (HPLC).
• Nitrogen Dioxide converted to No and reacted
  with ozone to form a chemi-luminescent material.
• Lead Similar to PM10 the filtered material is
  dissolved in nitric and hydrochloric acid and Pb
  determined using atomic absorption spectroscopy
  or inductively coupled plasma spectroscopy (ICP).

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High Volume Particulate Samplers
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EPA EMISSION FACTORS

• Emission Testing is Expensive,
• For Well defined sources (e.g. stacks)- Tedious
  but not difficult
• For Poorly defined sources (e.g.dust from unpaved
  roads or forest fires) Difficult to estimate
• For unknown or new sources - difficult
• Emission Factor Approach attempts to address
  these (EPA document AP-42, 1991)
  http//www.epa.gov/ttn/chief/ap42/
• An emissions factor is a representative value
  that attempts to relate the quantity of a
  pollutant released to the atmosphere with an
  activity associated with the release of that
  pollutant.
• General Equation for Emissions Estimation
• E EF x A x (1-ER/100)
• E emissions (mass of pollutant/unit quantity of
  activity)
• A Activity rate ( quantity of activity/ time)
• ER Emission reduction efficiency

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EPA EMISSION FACTORS

• Example Emissions From Bituminous Coal
  Combustion
• Obtain Activity Rate Coal Flow rate in this case

• Lookup Emission Factors for Specific Class of
  Pollutants
• Particulate Emissions Efparticulates x Coal
  Flow Rate
• SO2 Emissions EfSO2 x Coal Flow Rate
• NOX Emissions EfNOx x Coal Flow Rate

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EPA EMISSION FACTORS FOR COAL
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EPA EMISSION FACTORS
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EPA EMISSION FACTORS
http//www.epa.gov/ttn/chief/ap42/ch01/