Supplemental Regional HazeRelated Data

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Supplemental Regional Haze-Related Data

• Rich Poirot, VT DEC
• Dallas RPO Mtg, December 2002

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• Collected, Distributed Archived with Other
  Objectives
• Large Domain Spatial Coverage (National -
  Global)
• High Spatial and/or Temporal Resolution
• Info on Aerosols Space, Time, Size Optical
  Properties

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• Regional Haze is a Complex 8-Dimensional Problem
• Aerosol Concentrations x Compositions x Size
  Distributions x Optical Properties x Latitude x
  Longitude x Altitude x Time,
• IMPROVE Data provide Site-Specific Information
  on Concentrations Compositions at the Surface,
• Information on Particle Size, Optical
  Properties, (3D) Spatial Temporal Patterns is
  limited.
• Sources of Supplemental Regional Haze-Related
  Data
• Collected, Archived Distributed (with Other
  Objectives)
• Large Spatial Coverage (National - Global)
• High Spatial and/or Temporal Resolution
• Extractable Information Content Space, Time,
  Size, Optics, etc.

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ASOS Data Availability Beginning 2004

• Around 1995 the human observed visibility was
  replaced by the automatic forward light
  scattering detectors, reporting every minute
  (ASOS)   
• Early evaluation by Richards et al in 1996/97
  showed that the ASOS signal compared favorably
  with continuous PM2.5 measurements, however, data
  truncation was a major problem     
• CAPITA analyzed 230 station - 5 month - 1
  minute data and found the network to be of high
  potential  value however, many sensors appeared
  to have poor absolute calibration
• A comparison with 26 hourly PM2.5 monitors over
  the country, was also favorable 
• As of 2003, NCDC provides (for a charge)
  real-time data access to 230 existing ASOS sites
• Beginning Sept 2003, NOAA/NWS is upgrading 880
  ASOS stations and will expose the real-time data
  through an FTP site, as well as through NCDC

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The ASOS Visibility Sensor

• The ASOS visibility sensor is a forward
  scattering instrument
• Replaced Hourly Human Observers in about
  1995-96
• Better Quality Extinction Data, But Need QA
  and Archived Data are Averaged,
  Binned, Truncated (Need Direct Access Routine
  Processing)

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ASOS Stations from FAA, NWS and Archived at NCDC
For this analysis (Husar, 2002) data for 220
stations were available from NCDC
These ASOS sites are mostly NWS sites, uniformly
distributed over the country (Imagine if we could
get the entire set, including the DOD sites, not
listed).
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Comparison of Sites with Duplicate ASOS Sensors

• Co-located ASOS sensors are installed at
  different runways of the same airport.
• Dual ASOS sensors (55) are distributed uniformly
  over the 800 station network
• Triple sensors are particularly useful for sensor
  calibration and consistency checking

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Duplicate Sensors Good Sites
Dallas-FW, TX
Erie, PA
San Diego, CA
Houston, TX

• At several duplicate sites the 2-sensor
  correlation is excellent and the absolute values
  also match.
• This indicates that the scattering sensor per se
  has high precision and temporal stability.

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Duplicate SensorsPoor Sites

• Duplicate sensors at some sites show significant
  deviation in scale and offset.
• The nature of these deviations indicate poor
  instrument calibration maintenance for the ASOS
  visibility sensors.

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ASOS Bext Threshold 0.05 km(-1)
Reported by NWS

• The Bext values below 0.05 km-1 are reported as
  0.05.
• For Koschmieder coeff K3.9, this threshold
  VR78km( 50 mile) for K2 VR40km(25mi)
• In the pristine SW US, the ASOS threshold
  distorts the cleaner day data
• Over the East and West, the (raw data) ASOS
  signal is well over the threshold most of the
  time (although Archived data are Truncated at 10
  mi.)

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Typical Diurnal Pattern of Bext, Temperature
Dewpoint

• Typically, Bext shows a strong nighttime peak due
  to high relative humidity.
• Most of the increase is due to water absorption
  by hygroscopic aerosols. At RH gt90 , the aerosol
  is mostly water
• At RH lt 90, the Bext is mostly influenced by the
  dry aerosol content the RH effect can be
  corrected.

Macon, GA, Jul 24, 2000
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Adopted RH Correction Curve (To be validated for
different locations/seasons)
RH is calculated from T Temperature, deg C and
D Dewpoint, deg C RH 100((112-(0.1T)D)/(112
(0.9T)))8

• The ASOS Bext value are filtered adjusted for
  high humidity
• Values at RH gt 90 are not used
• The Bext is also corrected for RH RHCorrBext
  Bext/RHFactor

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Seasonal Average Diurnal Bext Pattern

• For each minute of the day, the data were
  averaged over June, July and August, 2000
• Average Bext was calculated for
• Raw, as reported
• For data with RH lt 90
• RH lt 90 and RH Corrected
• Based on the three values, the role of water can
  be estimated for each location

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Location of ASOS and Nearby Hourly PM2.5 Sites

• There are no co-located ASOS and PM2.5 sites
• The stations are not co-located but in the same
  city
• Hourly PM2.5 data are compared to the filtered
  and RH-corrected one minute Bext

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ASOS-Hourly PM2.5 Allentown, PA

• RH-Adjusted Bext is a good surrogate for
  PM-2.5, and
• RH-Screened Bext is good surrogate for PM-2.5
  H2O

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Islip, Long Island, NY
San Diego, CA
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• Are There Areas of Common Interest between ASOS
  Data Providers RPOs?
• ASOS Sites are Spatially Dense (1000 sites),
  Evenly Distributed (airports everywhere just out
  of town, and Have High Temporal Resolution
• Currently Archived Data are Averaged (1-hour),
  Truncated (at gt 10 miles) and Binned (into VR
  categories lt 10 mi.) but,
• Are Useful for evaluating Episodes, even in
  their current form, but
• Require Expert Processing to extract aerosol
  haze-relevant Info, and
• Could be extraordinarily Useful if
• We could access them in near-real time (
  historical),
• In their raw, uncensored form (1-minute
  uncensored Bext RH),
• From any all sites, and Processed for
  Haze-Relevant Info, and
• Merge them with other Haze-Related data