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Systems to Measure Atmospheric Chemical Transport

Conditional samplers separate air into samples arriving from different directions. These segregated samples are accumulated according to their arrival direction as measured by a sonic anemometer. We have two software packages controlling two hardware organizations of pumps and valves (four basic combinations).

Software:

  • Relaxed Eddy Accumulation (REA) software segregates by vertical velocity. REA is used to measures trace gas exchange between the atmosphere and things on the ground. Arriving air is separated into: rising air, falling air and air with low vertical motion (MidBand).

  • Compass Sector Accumulation (CSA) software segregates by horizontal arrival direction. A configuration file defines three arrival sectors. The software uses the sonic anemometer information to direct the sample toward the correct accumulator: the one associated with the instant wind sector. CSA systems are sometimes used to determine the source direction of contaminates.

    Hardware:

  • Denuder type valve and pump hardware accumulates a target chemical species removing it from the passing air samples. After extraction, the balance of the air is discharged and of little importance in post accumulation analysis.

  • Whole air valve and pump hardware accumulates all of the segregated sample air putting it into two or three accumulators (usually Tedlar plastic bags). All of the air is available for broad spectrum post accumulation analysis.

    • Whole Air Conditional Samplers (REA and CSA) consists of:

    Options:
    • Analog-to-digital inputs, 16 bit resolution, 7 to 28 balanced input channels, data temporally correlated with REA sample rate, -10 to +10 Volt input range

    • Carbon dioxide, water vapor and heat flux measurement system - 20 Hz insitu results from the same air volume conditionally sampled - using Hampton Technologies' HTI-OP2.

    Standard Whole Air System Specifications:

    • Operational from 0 C to + 55C (optional sample heater)

      • Humidity: Any humidity lower than dew point

      • Sample Rate: 20, 10, 5, 2 and 1 sample/sec (configuration file)

      • Sample Rate: Compass Sector systems can sample intermittently

      • Flow Rate: 20 ml/min to 1000 ml/min

      • Flow Control: Computer controlled to within 5%

      • Pump: System Six uses a brushless DC pump motor

      • Power: less than 50 Watts, 10-30 VDC, Optional: 100-240 VAC @ 50/60 Hz

      • Data Storage: Compact Flash to 2 GByte each

      • Valve Latency: State change faster than 15 ms.

      • Inlet Delay: compensation from 300-5000 ms

      • Phase Jitter: Automatically corrects Sonic output jitter to 100 ms

      • Sample Size: Configurable from 3000 to 288,000 samples

      • Buffer Size: Rolling averaging set adjustable from 100 to 16,000 points

      • Purge Time: adjustable from zero to 5 hours

      • Start & Stop: Programable to days in advance or from keyboard

      • Status Log: Errors, Start/Stop, Sample Size, Pump & Valve use

      • Accumulators: Sets automatically change at end of sample period

      • Accumulator: Automatic compensation for sample transit time to accumulator

      • Materials: Sample contact, Teflon, Stainless, Tedlar, Viton, PPS

      • Cases: Aluminum (thick-wall), dust & water tight

      • Cooling: Surface convection only - no air through cases

      • Data Stored: Raw Sonic values, valve states, thresholds, errors, etc.

      • Display: High brightness LCD with some Sun shield

      • Keyboard: Most control uses 12 key-pad, PC-keyboard plugs in too

      • Cables: 20 meter data, power and control cables

      • GPS Receiver: Time to 15 microsecond and geographic locational to 20 meters

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