A Field Instrument for Measuring Rain Conductivity in Real

A Field Instrument for A Field Instrument for Measuring Rain Measuring Rain

Conductivity in RealConductivity in Real--timetime

Alfred M. Moyle and Dennis LambAlfred M. Moyle and Dennis LambMeteorology Department, 503 Walker BuildingMeteorology Department, 503 Walker Building

The Pennsylvania State UniversityThe Pennsylvania State UniversityUniversity Park, PA 16802University Park, PA 16802

What?What?DevelopDevelop an an economicaleconomical, real, real--time, single parameter monitor of time, single parameter monitor of precipitation quality as a precipitation quality as a supplementsupplement to NADP network to NADP network operations.operations.Ultimately, to build a network of Ultimately, to build a network of instrumentsinstruments; some co; some co--located at located at existing AIRMoN or NTN sites (validation) existing AIRMoN or NTN sites (validation) && some located some located betweenbetween existing network sites (interpolation).existing network sites (interpolation).

Why?Why?To provide data with high spatial To provide data with high spatial && temporal temporal resolutionresolution to to --

Guide the development of deposition models.Guide the development of deposition models.Improve our understanding of sourceImprove our understanding of source--receptor relationships.receptor relationships.

How?How?Take advantage of Take advantage of --

StrongStrong statistical links statistical links betweenbetween the concentration of sulfate, pH, the concentration of sulfate, pH, && the electrical conductivity of rainwater in the the electrical conductivity of rainwater in the northeasternnortheasternUnited States.United States.The fact that electrical conductivity, unlike pH, is relatively The fact that electrical conductivity, unlike pH, is relatively easy easy to measure to measure & conductivity& conductivity electrodes are inexpensive electrodes are inexpensive && robust.robust.

PA15 AIRMoN Data PA15 AIRMoN Data –– 1992 Thru 20071992 Thru 2007

Strong correlation between electrical conductivity & [H+] or [SO42-] ...

R2 = 0.9596

010

020

030

040

050

0

0 50 100 150 200 250 300

Conductivity, µS/cm

[H+ ],

µM

R2 = 0.9051

05

1015

2025

0 50 100 150 200 250 300


[SO

42-],

mg/

L

This is the basis for the Penn State conductivity instrument.

Contrast Contrast –– CO21 vs. PA15CO21 vs. PA15CO21 NTN data (1978-2007) exhibit distinctly different behavior ...

R2 = 0.9596

R2 = 0.3984

010

020

030

040

050

0

0 50 100 150 200 250 300


[H+ ],

µM

PA15 AIRMoN

CO21 NTN

H2SO4 Solution

IL11 IL11 AIRMoN AIRMoN –– Intermediate BehaviorIntermediate Behavior

Has characteristics of both northeastern & western sites ...

R2 = 0.7685

010

020

030

040

0

0 50 100 150 200 250Conductivity, µS/cm

[H+ ],

µM

Northeastern AIRMoN SitesNortheastern AIRMoN Sites

WV99 ...NY67 ...

R2 = 0.943

010

020

030

040

050

060

070

0

0 50 100 150 200 250 300 350 400


[H+ ],

µM

R2 = 0.9493

010

020

030

040

050

060

070

0

0 50 100 150 200 250 300 350


[H+ ],

µM

Strong correlation between conductivity and pH ... Similar to PA15.

An Earlier RealAn Earlier Real--time Instrumenttime Instrument

Kronmiller, et al (1990) Atmospheric Environment Kronmiller, et al (1990) Atmospheric Environment 24A24A, 525, 525--536 536 --Direct measurement of pH under full computer control ... RequireDirect measurement of pH under full computer control ... Requires frequent s frequent calibration of the pH meter calibration of the pH meter && careful storage of the pH electrode when in standby careful storage of the pH electrode when in standby mode.mode.Provides realProvides real--time measurements of pH time measurements of pH && conductivity conductivity && fractional event sampling fractional event sampling with refrigerated storage of samples for lab analysis.with refrigerated storage of samples for lab analysis.Instrument was large, relatively complex, Instrument was large, relatively complex, && relatively expensive relatively expensive -- thus limiting the thus limiting the number which could be deployed.number which could be deployed.Up side Up side –– direct measurement of pH applicable anywhere.direct measurement of pH applicable anywhere.

The Penn State Conductivity InstrumentThe Penn State Conductivity Instrument

Lid mechanism consists of an Lid mechanism consists of an MIC 300C wet sampler, on MIC 300C wet sampler, on loan from CAPMoN.loan from CAPMoN.Polypropylene funnel collects Polypropylene funnel collects falling precipitation and falling precipitation and channels it into the channels it into the instrument.instrument.


Conductivity electrode Conductivity electrode mounted in a cast acrylic, flowmounted in a cast acrylic, flow--through cell.through cell.Trap on downstream side of Trap on downstream side of cell insures that the electrode cell insures that the electrode remains wet and free of air remains wet and free of air bubbles.bubbles.Tipping bucket rain gauge Tipping bucket rain gauge (0.0045” of precipitation per (0.0045” of precipitation per tip) provides rain rate tip) provides rain rate information.information.


Utilizes offUtilizes off--thethe--shelf, NISTshelf, NIST--traceable digital conductivity traceable digital conductivity meter, modified to provide for meter, modified to provide for computer data logging.computer data logging.Meter calibrated using Meter calibrated using commercially available standards.commercially available standards.Data logging system Data logging system uses SD uses SD memory cards to recordmemory cards to recordconductivity, cell temperature, conductivity, cell temperature, tipping bucket signal, and MIC tipping bucket signal, and MIC 300C signals (lid open/closed, 300C signals (lid open/closed, sensor wet/dry, and error sensor wet/dry, and error conditions).conditions).

Case Study: 19 Case Study: 19 –– 21 August 200721 August 2007

Warm front approaching PA15

from the southwest.

August 19, 2007 – 7:00 AM EST


Both stratiform and convective features observed during this

rain event.

Stratiform Rain

Convective Rain

PA15


Chemical signature of stratiform rain -

0

50

100

150

200

Con

duct

ivity

(µS

/cm

)

3.5

4

4.5

5

5.5

pH

12:00 18:00 00:00 06:000

1

Tipp

ing

Buc

ketS

igna

l

Local Time (EDT), 19 - 20 August 2007

λ = 22.1 S/cmµ

pH = 4.35

PA15 AIRMoNConductivity (µS/cm) -Conductivit

0

100

200

Conductivit

pH -

3.5

4.5

5.5

Tipping Bucket Signal -Conductivit

0

1

Local Time (EDT), 19 – 20 August 200712:00 18:00 00:00 06:00

25.5 µS/cm

4.34


Chemical signature of convective rain -

0

50

100

150

200

Con

duct

ivity

(µS

/cm

)

3.5

4

4.5

5

5.5

pH

12:00 18:00 00:00 06:000

1

Tipp

ing

Buc

ketS

igna

l

Local Time (EDT), 20 - 21 August 2007

λ = 31.4 S/cmµ

pH = 4.21

ConductivitConductivit

Conductivit

Conductivity (µS/cm) -

pH -

Tipping Bucket Signal -

Local Time (EDT), 20 - 21 August 200712:00 18:00 00:00 06:00

0

100

200

3.5

4.5

5.5

0

1

PA15 AIRMoN

25.2 µS/cm

4.37


Adapted from Ahrens (1994)

Chemical Quality of Rains from a Warm Front

CONVECTIVEBANDS

(intermittant rains)

STRATIFORMREGION

(steady rain)

Front

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****

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Clean

Outflow

Mic

ro

physical

proc

essing

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*****

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******

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Clean Cloud

Polluted Inflow

Dirty Rain Clean Rain

ConclusionsConclusions

The electrical conductivity of rain can be measured automaticallThe electrical conductivity of rain can be measured automatically y andand in real time.in real time.Using conductivity as a surrogate for rain pH is appropriate forUsing conductivity as a surrogate for rain pH is appropriate fordecisively acidic precipitationdecisively acidic precipitation that that we see in the northeast.we see in the northeast.This technique provides high temporal resolution results which This technique provides high temporal resolution results which allow us to see allow us to see the details “insidethe details “inside” AIRMoN data.” AIRMoN data.Initial results suggest a strong relationship between the Initial results suggest a strong relationship between the conductivity of rain and any “processing” which the precipitatioconductivity of rain and any “processing” which the precipitation n has experienced.has experienced.

Future StepsFuture StepsDevelop a more compact version of the instrument and deploy Develop a more compact version of the instrument and deploy multiple units at AIRMoN or NTN sites in the northeastern multiple units at AIRMoN or NTN sites in the northeastern United States.United States.Eventually expand operations up to the mesonet scale for the Eventually expand operations up to the mesonet scale for the purpose of testing chemical deposition models.purpose of testing chemical deposition models.

AcknowledgementsAcknowledgementsFunding for this project was provided by the NOAA Air Funding for this project was provided by the NOAA Air Resources Laboratory.Resources Laboratory.We thank Bob Vet and Dave MacTavish of the Canadian Air We thank Bob Vet and Dave MacTavish of the Canadian Air and Precipitation Monitoring Network for lending the MIC and Precipitation Monitoring Network for lending the MIC 300C collector used in this project.300C collector used in this project.

Documents

A Field Instrument for Measuring Rain Conductivity in Real