AMS/ACSM Calibrations Overview

Phil Croteau – croteau@aerodyne.com

August 24, 2019 AMS Users Meeting Lund 1

Outline – Focus on PM1 vs. PM2.5 Lens and Standard vs. Capture Vaporizer Differences

• Inlet flow rate calibration – pressure to flow rate

• Particle lens alignment

• Velocity calibration – particle time-of-flight to size

• Vaporizer temperature calibration

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mg

m3

mass

volume

From Mass Spectrometer

Ionization Efficiency calibration

From volumetric flow rate

Particle Mass Loading

August 24, 2019 AMS Users Meeting Lund 3

Flow Meter

Low pressure drop

flow meter

Gilibrator™ or

equivalent soap film

meter10 Torr lens

pressure gauge

P

Aerodynamic Lens

Fine metering

valve

AMS Flow Rate Calibration Setup

Poiseuille equation relates pressure drop across Lens tube

to volumetric flow through the lens tube

Flow into

vacuum

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Flow Calibration

3.0

2.5

2.0

1.5

1.0

0.5

0.0

Flo

w (

cc/s

)

2.52.01.51.00.50.0

Pressure (torr)

U. Tokyo Cal at ARI

NOAA Cal at ARI

NOAA Cal at Boulder

NOAA Scaled to 760 torr

Particle lens pressure is used to measure mass flow rate

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PM1 and PM2.5 flow rate calibration

• PM2.5 lens operates at higher pressure

• Bigger ΔP for smaller Δflow with PM2.5

Standard flow

Research grade

TOF mass spectrometer

Thermal

Vaporization

&

Electron

Impact

Ionization

Aerodynamic

Lens

Beam

Chopper

Particle TOF Region

Pumps (x5)

Fast Data

System

Timers

DACs

Good lens alignment

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Research grade

TOF mass spectrometer

Thermal

Vaporization

&

Electron

Impact

Ionization

Aerodynamic

Lens

Beam

Chopper

Particle TOF Region

Pumps (x5)

Fast Data

System

Timers

DACs

Bad Lens Alignment

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AMSDMA

Atomizer

Drier

Setup for particle lens alignment

NH4NO3

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Vaporizer

Move lens while monitoring NO2+ signal

LENS

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Vaporizer

Move lens while monitoring NO2+ signal

LENS

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Vaporizer

Move lens while monitoring NO2+ signal

LENS

Measure here, “min”

Measure here, max

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Vaporizer

Move lens while monitoring NO2+ signal

LENS

Measure here, min

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Vaporizer

Move lens while monitoring NO2+ signal

LENS

Measure here, min

Measure here, max

𝐶𝑒𝑛𝑡𝑒𝑟 =min+𝑚𝑎𝑥

2

After calculating, move to Center and repeat for the other axis

August 24, 2019 AMS Users Meeting Lund 14

August 24, 2019 AMS Users Meeting Lund 15Yan Zheng, PKU 2017 AMS users meeting

Lens alignment with the capture vaporizerSame procedure but measure using m/z 30

• Almost all NO3 converts to NO when particles are captured

• NO2+ signal suggests

particles hit edges of vaporizer

Velocity CalibrationHow to go from time (what we measure) to size (what we care about)

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Velocity CalibrationHow to go from time (what we measure) to size (what we care about)

𝑓 𝐷𝑣𝑎 = 𝑉𝑔𝑎𝑠,𝑙𝑒𝑛𝑠 +𝑉𝑔𝑎𝑠,𝑒𝑥𝑖𝑡 − 𝑉𝑔𝑎𝑠,𝑙𝑒𝑛𝑠

1 + ൗ𝐷𝑣𝑎𝐷∗

𝑏

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AMSDMA

Atomizer

Drier

Setup for velocity calibration

NH4NO3

This is identical to the lens alignment setup.

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Velocity Calibration

We measure particle time-of-flight as a function of particle diameter.

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Velocity Calibration

We measure particle time-of-flight as a function of particle diameter.

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Velocity Calibration

𝑉𝑒𝑙𝑜𝑐𝑖𝑡𝑦 =𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒

𝑝𝑡𝑜𝑓

215-series:Distance = 0.295 m

255-series:Distance = 0.395 m

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Velocity Calibration

𝑓 𝐷𝑣𝑎 = 𝑉𝑔𝑎𝑠,𝑙𝑒𝑛𝑠 +𝑉𝑔𝑎𝑠,𝑒𝑥𝑖𝑡 − 𝑉𝑔𝑎𝑠,𝑙𝑒𝑛𝑠

1 + ൗ𝐷𝑣𝑎𝐷∗

𝑏

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PM1 and PM2.5 lens velocity calibration comparison

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• NaNO3 has higher density (2.26 g cm-3), which allows us to measure higher Dvawith same Dmob range

• Exercise caution interpreting measured ptof with PM2.5 for small particles; singly charged particles may not dominate or even be observed

Summary_VapT.pxp

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Standard Vaporizer – optimum temperature ~600C

Capture Vaporizer – optimum temperature ~550C

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Summary_VapT.pxp

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Red points – good thermocouple connectionBlue, Green, Pink – poor thermocouple connectionA disconnected thermocouple measurement can be off by 100s of degrees

Vaporizer power temperature relationship

AMSDMA

Atomizer

Drier

Setup for vaporizer temperature calibration

NaNO3

This is identical to the lens alignment setup and the velocity calibration setup, but with NaNO3.

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PToF traces for NaNO3 (m/z 30) give good temperature indication.

VapT_SN_100805.pxp

444°C

540°C

625°C

705°C

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Fit falling edge of PToF with single exponential. Plot tau vs amps. PToF are narrow by

1.1 A, or 700 to 750 C. Vaporizer is glowing dull orange from back (front is cooler than

back).

Summary_VapT.pxp

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Comparison of Standard Vaporizer and Capture Vaporizer heater power and temperature calibration

Weiwei Hu, CU, AMS Users Meeting 2016