EAS 4/8803: Experimental Methods in AQ

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EAS 4/8803 Experimental Methods in AQ

• Week 11
• Air Quality Management (AQM)
• Clean Air Act (History, Objectives, NAAQS)
• Emissions and Atmospheric Trends (Links)
• Principal Measurement Techniques (NOx, CO, SO2)
• Measurement of CO (Exp 5)
• NDIR Method (Interferences, Stability, DL,
  Precision, Accuracy)
• Controlling O3 and PM2.5
• Principal Measurement Techniques (O3, PM)
• Photochemical Processes (NOx vs VOC
  sensitivities, SOA)
• Ambient Measurements and Trends (World, USA, GA)
• Measurement of O3 (Exp 6)
• UV Absorption (Interferences, Stability, DL,
  Precision, Accuracy)

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Review CO Lab Experiment
CO Analyzer Calibration
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Review CO Lab Experiment
CO Method IR-Absorption
I I0 e-e c l
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Review CO Lab Experiment
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Review CO Lab Experiment
CO Analyzer Calibration and Zero-Trap Efficiency
COsensi (ppb/V) DCOnomi / DCOspani ZTeffi
(COspani COspani,0) / (COspani CO0) If ZTeff
lt 0.9, correct CO0 CO0 (V) CO0 / ZTeff
COipol (1/ZTeff-1) COnet (V) COraw
CO0ipol CO (ppb) COnet COsens DL (ppb) t
STD(CO0) COsens P () t STD(COsens) /
AVG(COsens) 100 A1 () (slopeDCOnomi /
DCOspani -1000) 100 A2 () S(s(Xj))2
(dCOsens/dXj)21/2 from error propagation
analysis.
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Emissions/AQ Trends O3
Secondary Product !!
old 1h NAAQS
new 8h NAAQS

• Potential Risks and Effects
• Acute health (respiration, asthma)
• Chronic health (obstructive pulmonary)
• Vegetation damage (chlorophyll)
• Agriculture (crop forest yields)
• Materials deterioration

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O3 Method Chemiluminescence
Disadvantage Need of Process Gases
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O3 Method UV Absorption
I I0 e-e c l e 308 cm-1 (_at_STP 0oC,
760Torr) l 38 cm
254 nm
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O3 Method ECC
Electro-Chemical Cell used in balloon
sondes Advantage size (8x8x14 cm) and weight (lt
300 g)
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Emissions/AQ Trends PM2.5
Primary Sources (2001)
Emissions
AQ

• Potential Risks and Effects
• Heart (arrhythmias, attacks)
• Respiratory (asthma, bronchitis)
• Among elderly and young
• Vegetation (ecosystem)
• Buildings, Materials
• Visibility

AQ influenced by Primary Secondary PM
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Sources and Mechanisms of Atmospheric PM
Meng et al., Science, 1997
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Secondary organic aerosol (SOA) Organic
compounds, some highly oxygenated, residing in
the aerosol phase as a function of atmospheric
reactions that occur in either gas or particle
phases. SOA formation depends on Precursors arom
atics (BTX, aldehydes, carbonyls) terpenes
(mono-, sesqui-) other biogenics (aldehydes,
alcohols) Presence of O3, OH, NO3, sunlight, acid
catalysts Mechanisms (with few hr
yields) Gas-to-particle conversion/partitioning e
.g. terpene oxidation Heterogeneous
reactions aldehydes via hydration,
polymerization, forming hemiacetal/acetal in
presence of alcohols Particle-phase
reactions acetal formation catalytically
accelerated by Meng et al., Science,
1997 particle sulfuric acid (Jang and Kamens,
EST, 2001)
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Other (Inorganic) Secondary PM2.5 Formation

• Secondary formation is a function of many factors
  including concentrations of precursors, other
  gaseous reactive species (e.g., O3, OH),
  atmospheric conditions, and cloud or fog droplet
  interactions. BUT Most secondary products
  remain semi-volatile and can evaporate back into
  the gas-phase!
• Gas-to-particle conversion (oxidation)
• SO2(g) HOSO3 H2SO4 2NH3
  (NH4)2SO4
• NOx(g) HNO3 NH3 NH4NO3
• Heterogeneous
• reactions

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Partitioning of Semi-Volatile Species

• Ambient PM2.5 is composed of primary and
  secondary components of particle-phase species.
  A large fraction of secondary PM in the
  atmosphere is in a fragile balance (equilibrium)
  between its gas-phase precursors and
  particle-phase products, meeting individual
  species vapor pressures and physical-chemical
  micro-environments at given ambient conditions.
  The gas-particle partitioning of these
  semi-volatile species can easily be altered
  during sample collection and analysis!

PM2.5 Measurement Challenge
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Separating PM2.5 at Sample Inlet
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Potential Gas/Particle Interactions at a Filter
Surface
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Discrete PM2.5 Sampling Method, e.g. FRM
Ambient sample air containing PM2.5 (aerosol)
passes through a filter, which collects the
particle phase then through an adsorber, which
traps the gas phase compounds. This method
suffers from potential positive and mostly
negative artifacts !!
Filter
Adsorber
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Denuder (Diffusion Tube) Application
Air passes through an annular diffusion tube
(gas phase) then through a filter (particle
phase) then through an adsorber to trap the
compounds released from the surface of the
particles. The denuder is coated with a material
that will trap the gas phase molecules. Each
sampling medium is extracted separately for
direct quantification of NH3, HONO, HNO3, SO2,
Formic, Acetic, Oxalic Na, NH4, Cl-, NO2-,
NO3-, SO4, Formate, Acetate, Oxalate EC, OC,
and SVOC
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Denuder Difference Method
Air passes through an annular diffusion tube
(gas phase) then through a filter (particle
phase) then through an adsorber to trap the
compounds released from the surface of the
particles. The denuder is coated with a material
that will trap the gas phase molecules.
Indirect determination of gas phase
concentrations from PM-difference.
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Utilizing Fast Gas Diffusion to Walls
Denuder Fluid Dynamics and Efficiency (for
annulus)
where
and making gas molecules stick!
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Diffusion Coefficients Gas vs PM
D (cm2/s)
NH3 0.24 HONO 0.17 HNO3 0.15 NO2 0.14 SO2 0.1
3 HCOOH 0.18 CH3COOH 0.15 (COOH)2 0.13 0.01 5.20E
-4 0.05 2.33E-5 0.1 6.71E-6 0.5 6.24E-7 1.0 2.
72E-7 1.6 1.61E-7
Reactive gases
Particles with diameter (mm)
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Providing Large Wall Surface for Gas Adsorption
Possible Denuder Configurations
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Making Gases Stick Scanning electron
photomicrograph of an uncoated sandblasted glass
denuder fragment
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Making Gases Stick Scanning electron
photomicrograph of a denuder fragment coated with
ground XAD-4 adsorbent
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Particle Loss in a Denuder
h 1 - 0.910exp(-7.54m) - 0.0531exp(-85.7m) -
0.0153exp(-249m)
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Assessing Particle Loss in a Denuder
Ambient Aerosol or PSL
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Particle Composition Monitor (PCM) KB
Channel 1 NH3 Na, K, NH4, Ca2 Channel
2 HF, HCl, HONO, HNO3, SO2, HCOOH, CH3COOH,
(COOH)2 F-, Cl-, NO3-, SO4, HCOO-, CH3COO-,
C2O4 Channel 3 EC, OC, SVOC
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PM2.5 Mass from Teflon Filter Gravimetry
Equilibration of Teflon filter samples in Class
1000 Clean Room PM lt 1000/scf, T 21 -0.5
oC, RH 33 -3 Mettler Toledo MT5 Electronic
Micro-Balance Exp. DL 1.2 -0.02 mg P -
0.4 _at_ 1 mg A -0.001 1-500 mg
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Effects of Water Vapor on PM2.5 Mass
Dehydration of denuded Teflon filter samples
(ch1), Griffin Jan-Jul 2002
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EPAs FRM Samplers
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Andersen RAAS Sampler
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Met-One SASS Sampler
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URG MASS Sampler
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RP Speciation Sampler
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URG VAPS Sampler
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SEARCH/ARIES-PCM EE
Figure 3
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Atlanta Super-Site Experiment Aug99
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PM2.5 Mass Concentrations Comparison of
Different Filter Samplers During ASSE 99
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PM2.5 Mass Concentrations Comparison of
Different Filter Samplers During ASSE 99
Period Averages for Mass and Chemical Components
for Time-Integrated Samplers
Pearson Correlation Coefficients (r) for Test
Samplers vs Relative Reference
Solomon et al., JGR, 2003
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ASSE 99 PM2.5 Mass
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ASSE 99 PM2.5 Sulfate
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ASSE 99 PM2.5 Ammonium
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ASSE 99 PM2.5 Nitrate
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Why Nitrate Scatter?

• Three Potential Artifact Reactions
• 2 NO2 H2O ? HNO3 HONO
• Surface mediated hydrolytic reaction,
  disproportionating N(IV) to N(III) N(V)
• NO2 Salkaline ? NO2-surface
• Reductive surface conversion of NO2 to nitrite
• NO2-surface O3 ? NO3-surface O2
• Secondary surface oxidation of nitrite to nitrate
• Plus volatility
• HNO3 NH3 NH4NO3

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ASSE 99 PM2.5 Organic Carbon
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ASSE 99 PM2.5 Elemental Carbon