ISSAOS 2008

l‘Aquila, September 2008

Aerosol Mass Spectrometry:

General Principles and examples

Hugh CoeSchool of Earth, Atmospheric and Environmental Sciences

University of ManchesterReading:

• D Murphy, The design of single particle laser mass spectrometers, in: Mass Spectrometry Reviews, 2007, 26, 150-165.

• M. R. Canagaratna et al., Chemical and microphysical characterisation of ambient aerosols with the Aerodyne Aerosol Mass Spectrometer in: Mass Spectrometry Reviews, 2007, 26, 185-222.

• H. Coe and J. D. Allan, “Aerosol Mass Spectrometry” in “Atmospheric techniques” ed D. E. Heard, Blackwell Scientific Publishing, 2006

• http://cires.colorado.edu/jimenez/ams-papers.html

• thanks to Jose Jimenez for the slides showing component parts of aerosol mass spectrometers

I. General Introduction – the advantages of Aerosol Mass Spectrometry

II. The component parts of an aerosol mass spectrometer

III. Examples of different mass spectrometric methods

IV. Advantages and disadvantages of different mass spectrometric methods

General Outline

I. General Introduction – the advantages of Aerosol Mass Spectrometry

II. The component parts of an aerosol mass spectrometer

III. Examples of different mass spectrometric methods

IV. Advantages and disadvantages of different mass spectrometric methods

General Outline

I. General Introduction – the advantages of Aerosol Mass Spectrometry

II. The component parts of an aerosol mass spectrometer

III. Examples of different mass spectrometric methods

IV. Advantages and disadvantages of different mass spectrometric methods

General Outline

thanks to Jose Jimenez for the slides showing component parts of aerosol mass spectrometers

Aerosol Inlets

• Need to entrain aerosols from the atmosphere into a vacuum

Aerosol Inlets

• Need to entrain aerosols from the atmosphere into a vacuum

•Need to concentrate particles and remove the gas

2.5 x 1019 molecules cm-3 in ambient air

3.2 µg m-3 of particulate S = 10-7 moles m-3 of S

6.2x1023x10-7x10-6=6.2x1010 molecules cm-3

or around 2 ppb

Aerosol Inlets

• Need to entrain aerosols from the atmosphere into a vacuum

•Need to concentrate particles and remove the gas

2.5 x 1019 molecules cm-3 in ambient air

3.2 µg m-3 of particulate S = 10-7 moles m-3 of S

6.2x1023x10-7x10-6=6.2x1010 molecules cm-3

or around 2 ppb

• May need to introduce a size dependent velocity onto the particles

Effects on beam width

• non spherical particles may affect the ability of particle lens systems to focus the particle beam

Vaporization• Desorption/ionisation process can be coupled together

- This is certainly simpler but it is very difficult to quantify the mass of material detected

• A two step process of desorption followed subsequently by ionisation provides a way of more easily quantifying mass

However, this comes at a price - More volatile species may decompose- Refractory material (NaCl, dust, soot) will not

evapourate unless the temperature is very high

• Vaporisation may be performed by

-Thermal methods or

-IR laser absorption

Ionization Ideally should:• Produce ions from either solid or liquid particles or the desorbed gas

• Need to produce a high number of ions per molecule (high efficiency)

• Ideally the number of ions produced is proportional to the number of molecules

• The ionisation is selective and universal

• The molecular fragmentation is reproducible

Laser Desorption/Ionisation:• The LDI process on particles is poorly understood

•Laser wavelength is important

•Sulphuric acid hard to ionise – due to transparency in UV

•Dependent on laser beam cross sectional intensity

•Laser pulse width dependence

•In larger particles, not all particle may be ionized

•Laser power density -lower fluence reduces fragmentation-higher fluence allows improved ionisation

Ion Trap

• Can do MSn

• Can investigate ion-molecule reactions

I. General Introduction – the advantages of Aerosol Mass Spectrometry

II. The component parts of an aerosol mass spectrometer

III. Examples of different mass spectrometric methods

IV. Advantages and disadvantages of different mass spectrometric methods

General Outline

I. General Introduction – the advantages of Aerosol Mass Spectrometry

II. The component parts of an aerosol mass spectrometer

III. Examples of different mass spectrometric methods

IV. Advantages and disadvantages of different mass spectrometric methods

General Outline

Advantages/Disadvantages of laser and thermal systems:

laser based systems: thermal systems:-can ionise a wide range of - Can be used to deliver species quantitative mass

information

-deliver single particle info - deliver information on the and so enable estimates of particle ensemble mixing state -do not have consistent - Can be traced back to ionisation and suffer shot to well characterised ionisation shot variability libraries

Example: PALMS (Murphy et al NOAA)

Example: PALMS (Murphy et al NOAA)

Murphy, D.M., Thomson, D.S. & Mahoney, T.M.J. (1998b) In situ measurements of organics, meteoritic material, mercury, and other elements in aerosols at 5 to 19 kilometers, Science, 282 (5394), 1664–1669.

Example: Dall’Osto et al (Birmingham)

ATOFMS Identification of Hydroxymethanesulphonate during urban fog processing event

ART-2a analysis based on a neural network algorithm was used to identify a number of different particle classes

REPARTEE experiment in central London

Example: Dall’Osto et al (Birmingham)

ATOFMS Identification of Hydroxymethanesulphonate during urban fog processing event

Example: Jim Smith (NCAR)

Thermal Desorption Ionisation Chemical-Ionisation MS (TDICIMS) chemical analysis of ultrafine particles

Example: Jim Smith (NCAR)

Thermal Desorption Ionisation Chemical-Ionisation MS (TDICIMS) chemical analysis of ultrafine particles

Example: Jim Smith (NCAR)

Thermal Desorption Ionisation Chemical-Ionisation MS (TDICIMS) chemical analysis of ultrafine particles

Example: Jim Smith (NCAR)

Thermal Desorption Ionisation Chemical-Ionisation MS (TDICIMS) chemical analysis of ultrafine particles

Example: Jim Smith (NCAR)

Thermal Desorption Ionisation Chemical-Ionisation MS (TDICIMS) chemical analysis of ultrafine particles