Workshop on Air Quality Data Analysis and Interpretation

1
Workshop on Air Quality Data Analysis and
Interpretation

• Photochemical Assessment Monitoring Stations
  (PAMS) US Approach

2
PAMS Data Uses

• Corroborate precursor emission inventories
• Assess changes in emissions corroborate
  emissions reductions (control strategy
  evaluation)
• Assess ozone and precursor trends
• Provide input to models evaluate models
• Evaluate population exposure

3
PAMS Sampling Sites

• Type 1 Upwind and background characterization
• Type 2 Maximum ozone precursor emissions impact
• Type 3 Maximum ozone concentration
• Type 4 Extreme downwind monitoring

4
PAMS Sampling Sites Schematic
5
PAMS Sampling Considerations

• Site Location (Types 1-4)
• Number of Sites
• Ozone and Precursors
• Upper-Air Meteorology
• Sampling Frequency
• Hydrocarbons
• Carbonyl Compounds
• Upper-Air Meteorology

6
Ozone and Precursor Measurements

• Continuous measurements
• Ozone
• Nitrogen Oxides
• Total Non-Methane Organic Compounds
• Time integrated sampling
• Speciated NMOCs
• Carbonyl Compounds

7
PAMS Target VOCs

• COMPOUND AIRS code CAS code COMPOUND AIRS
  code CAS code
• 1. Ethylene 43203 74851 2.
  Acetylene 43206 74862
• 3. Ethane 43202 74840 4.
  Propylene 43205 115071
• 5. Propane 43204 74986 6.
  Isobutane 43214 75285
• 7. 1-Butene1 43280 106989 8.
  n-Butane 43212 106978
• 9. t-2-Butene 43216 624646 10.
  c-2-Butene 43217 590181
• 11. Isopentane 43221 78784 12.
  1-Pentene 43224 109671
• 13. n-Pentane 43220 109660 14.
  Isoprene 43243 78795
• 15. t-2-Pentene 43226 646048 16.
  c-2-Pentene 43227 627203
• 17. 2,2-Dimethylbutane 43244 75832 18.
  Cyclopentane 43242 287923
• 19. 2,3-Dimethylbutane 43284 79298 20.
  2-Methylpentane 43285 107835
• 21. 3-Methylpentane 43230 96140 22. n-Hexane
  43231 110543
• 23. Methylcyclopentane 43262 96377 24.
  2,4-Dimethylpentane 43247 108087
• 25. Benzene 45201 71432 26.
  Cyclohexane 43248 110827
• 27. 2-Methylhexane 43263 591764 28.
  2,3-Dimethylpentane 43291 565593
• 29. 3-Methylhexane 43249 589344 30.
  2,2,4-Trimethylpentane 43250 540841
• 31. n-Heptane 43232 142825 32.
  Methylcyclohexane 43261 108872
• 33. 2,3,4-Trimethylpentane 43252 565753 34.
  Toluene 45202 108883
• 35. 2-Methylheptane 43960 592278 36.
  3-Methylheptane 43253 589811

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Collection and Analysis of Speciated NMOCs

• Automated Approach Automated Field GC analysis
  of
• Sorbent tube samples
• Whole-air samples
• Manual Approach Laboratory GC analysis of
• Sequential sampler for Sorbent tube samples
• Whole-air samples

9
PAMs Target Carbonyls

• Compounds
• Formaldehyde 
• Acetaldehyde 
• Acetone 
• Propionaldehyde
• Crotonaldehyde 
• Butyr/isobutyraldehyde 
• Benzaldehyde 
• Isovaleraldehyde 
• Valeraldehyde 
• Tolualdehydes 
• Hexaldehyde 
• 2,5-dimethylbenzaldehyde 
• (Acrolein)

10
Collection and Analysis of Carbonyl Compounds

• Sequential Sampler collecting carbonyl compounds
  as DNPH derivatives
• Laboratory analysis of samples by HPLC

11
PAMS Sampling Frequency (during O3 season)

• Type 1 - Background
• 8 3 hr ave SNMOC samples every 3rd day and 1
  24 hr ave SNMOC sample every 6th day.
• Type 2 - Max. Emissions
• 8 3 hr ave SNMOC samples every 3rd day and 1
  24 hr ave SNMOC sample every 6th day.
• 8 3 hr ave carbonyl samples on the 5 peak O3
  days plus each previous day and 8 3 hr samples
  every sixth day.
• Type 3 Max. Ozone and Type 4 - Downwind
• 8 3 hr ave SNMOC samples every 3rd day and 1
  24 hr ave SNMOC sample every 6th day.

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PAMS Surface Meteorological Monitoring

• At each monitoring site
• Wind direction
• Wind speed
• Ambient temperature
• Humidity (e.g., dew point or relative humidity)
• At least one network site
• Solar radiation
• Ultraviolet radiation
• Barometric pressure
• Precipitation

13
Capabilities and Limitations of Vertical
Profiling Systems
14
Example flow chart for data analysis
15
Purpose of Data Validation

• Definition
• "The purpose of data validation is to detect and
  then verify any data values that may not
  represent actual air quality conditions at the
  sampling station. Effective data validation
  procedures usually are handled completely
  independently from the procedures of initial data
  collection. Moreover, it is advisable that the
  individuals responsible for data validation not
  be directly involved with data collection." (U.S.
  EPA, 1984, Sec. 2.0.3, p.10)
• Why is Data Validation Important?
• Data validation is necessary to identify data
  with errors, biases, and physically unrealistic
  values before they are used for identification of
  exceedances, for analysis, or for modeling.

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Data Validation Definitions

• Outliers
• Data physically, spatially, or temporally
  inconsistent.
• Level 0 Data Validation
• Conversion of instrument output voltages to their
  scaled scientific units using nominal
  calibrations. May incorporate data logger
  inserted flags.
•  Level 1 Data Validation
• Observations have received quantitative and
  qualitative reviews for accuracy, completeness,
  and internal consistency. Final audit reviews
  required.
• Level 2 Data Validation
• Measurements are compared for external
  consistency against other independent data sets
  (e.g., comparing surface ozone concentrations
  with ozone concentrations from nearby aircraft
  flights, intercomparing radionsonde and radar
  profiler winds, etc.).
• Level 3 Data Validation
• Continuing evaluation of the data as part of the
  data interpretation process.

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Example of Quality Control Flags
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Data Validation Procedures

• Assemble Level I database.
• Place data in a common data format with
  descriptive information concerning variables,
  validation level, QC codes, and standard units.
• Ensure that results of and suggestions from final
  audit reports have been incorporated into the
  database.
• Review simple statistics for unrealistic maxima
  or minima and for consistency with nearby
  stations (still Level I)
• Perform spatial and temporal comparisons of the
  data (begin Level II).
• Perform intercomparisons of the data (e.g., from
  two different instruments). Data now Level III.

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VOC Data Validation Tools Tips

• OverallTotal VOC --gt Species groups --gt
  Individual species
• Inspect every species
• Time SeriesInspect time series for the
  following
• Large "jumps" or "dips" in the concentrations
• Periodicity of peaks, calibration carryover
• Expected diurnal behavior (i.e., isoprene)
• Expected relationships among species
• High single-hour concentrations of less abundant
  species

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VOC Data Validation Tools Tips (continued)

• Scatter PlotsPrepare scatter plots of the
  following
• Total NMOC vs. species group totals, vs.
  individual species
• Benzene vs. Toluene, Acetylene, Ethane
• Species that elute close together
• Isomers
• Other
• FingerprintsPrepare and inspect fingerprint
  plots for the following
• Identify calibration data.
• Investigate hours surrounding suspect and invalid
  data.
• Obtain overall view of diurnal changes.

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VOC Data Validation Tools Tips (continued)

• Additional DataTo further investigate outliers,
  use
• Wind direction data
• Other air quality data (e.g., ozone, NOx)
• Subsets of data (e.g., high ozone days only)
• Industrial or agricultural operating schedules
• Traffic patterns
• Other