2.3 Quantification of aerosol mass

221 Pages·2015·12.58 MB·English

ETH Library
A new aerosol mass spectrometer
for long-term environmental
applications: performance
assessment and first deployment
at the Jungfraujoch
Doctoral Thesis
Author(s):
Fröhlich, Roman
Publication date:
2015
Permanent link:
https://doi.org/10.3929/ethz-a-010532721
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Diss. No. 22862
A new aerosol mass spectrometer for
long-term environmental applications:
performance assessment and
first deployment at the Jungfraujoch
Roman Fröhlich
2015

DISS. ETH NO. 22862
A new aerosol mass spectrometer for long-term environmental
applications: performance assessment and first deployment at
the Jungfraujoch
A thesis submitted to attain the degree of
DOCTOR OF SCIENCES of ETH ZURICH
(Dr. sc. ETH Zurich)
presented by
Roman Fröhlich
Dipl.-Phys. Univ.,
Technische Universität München (TUM), Germany
born on 04.08.1984
citizen of Germany
accepted on the recommendation of
Prof. Dr. Urs Baltensperger (examiner)
Prof. Dr. Alexander Wokaun (co-examiner)
Prof. Dr. Erik Swietlicki (co-examiner)
Dr. André S.H. Prévôt (co-examiner)
2015

Contents
Summary ix
Zusammenfassung xi
1 Introduction 1
1.1 Atmospheric aerosols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1.1 Definition and sources . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1.2 Aerosol chemical composition . . . . . . . . . . . . . . . . . . . . . . . 3
1.1.3 Impacts of aerosols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1.3.1 Climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1.3.2 Health . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.2 Instrumentation and techniques . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.2.1 Aerosol chemical speciation monitor (ACSM) . . . . . . . . . . . . . . 10
1.2.1.1 Operational principle . . . . . . . . . . . . . . . . . . . . . . 11
1.2.1.2 ACSM mass spectra & quantification . . . . . . . . . . . . . 13
1.2.2 PMF / ME-2 organic source apportionment . . . . . . . . . . . . . . . 15
1.3 Thesis motivation and overview . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2 The ToF-ACSM 21
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.2 Apparatus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.2.1 Operational principle. . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
2.2.2 Time-of-flight mass analyser . . . . . . . . . . . . . . . . . . . . . . . . 26
2.2.3 Data acquisition and analysis . . . . . . . . . . . . . . . . . . . . . . . 26
2.3 Quantification of aerosol mass . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.3.1 Calibrations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.3.1.1 Inlet flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.3.1.2 Baseline and detector . . . . . . . . . . . . . . . . . . . . . . 28
2.3.1.3 m/Q . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.3.1.4 Signal-to-mass . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.3.2 Detection limits. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
2.4 First data set and intercomparisons . . . . . . . . . . . . . . . . . . . . . . . . 34
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Contents
2.4.1 General information . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
2.4.2 Intercomparisons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
2.4.2.1 Q-ACSM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
2.4.2.2 C-ToF-AMS . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
2.4.2.3 Scanning mobility particle sizer and nephelometer . . . . . . 41
2.4.3 High-resolution peak fitting with low-res mass analyser . . . . . . . . 43
2.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
3 Aerosol properties at the Jungfraujoch (3580 m a.s.l.) 49
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
3.2 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
3.2.1 Measurement site . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
3.2.2 Instrumentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
3.2.3 Bilinear factor analysis with the multilinear engine (ME-2) . . . . . . 54
3.2.4 Back dispersion (BD) clustering . . . . . . . . . . . . . . . . . . . . . 55
3.2.5 Characterising air masses: influence of the planetary boundary layer . 55
3.2.6 Saharan dust events . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
3.3 Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
3.3.1 Time series & concentrations . . . . . . . . . . . . . . . . . . . . . . . 58
3.3.1.1 Seasonal variations . . . . . . . . . . . . . . . . . . . . . . . . 58
3.3.1.2 Diurnal variations . . . . . . . . . . . . . . . . . . . . . . . . 62
3.3.1.3 Free tropospheric concentrations . . . . . . . . . . . . . . . . 64
3.3.1.4 Geographical aerosol origins . . . . . . . . . . . . . . . . . . 65
3.3.2 Organic mass spectra . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
3.3.2.1 ME-2 results . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
3.3.2.2 f44 vs f43 triangle plots. . . . . . . . . . . . . . . . . . . . . 76
3.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
3.5 Supplementary information . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
4 Intercomparison of ME-2 source apportionment of ACSM data 95
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
4.2 Methodology and instrument description . . . . . . . . . . . . . . . . . . . . . 98
4.2.1 Site description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
4.2.2 Aerosol mass spectrometers . . . . . . . . . . . . . . . . . . . . . . . . 99
4.2.3 Aethalometer, NO analyser and PTR-MS . . . . . . . . . . . . . . . . 100
x
4.2.4 ME-2 and SoFi tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
4.2.5 Model input and data preparation . . . . . . . . . . . . . . . . . . . . 103
4.2.6 Optimisation of ME-2 constraints . . . . . . . . . . . . . . . . . . . . . 104
4.3 Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
4.3.1 Organic time series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
4.3.2 Organic mass spectra . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
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Contents
4.3.3 HR-ToF-AMS source apportionment . . . . . . . . . . . . . . . . . . . 109
4.3.4 ACSM (UMR) source apportionment . . . . . . . . . . . . . . . . . . . 112
4.3.5 Intercomparison of source apportionment results . . . . . . . . . . . . 115
4.3.5.1 Time series . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
4.3.5.2 Profiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
4.3.5.3 Contributions . . . . . . . . . . . . . . . . . . . . . . . . . . 119
4.3.5.4 ACSM specific recommendations . . . . . . . . . . . . . . . . 122
4.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
4.5 Supplementary information . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
4.5.1 Supplementary equations, tables and figures . . . . . . . . . . . . . . . 125
4.5.2 UpdateoftheQ-ACSMPMFexportfunctioninrecentanalysissoftware
update (version 1.5.5.0) and its influence on the presented dataset . . 146
4.5.3 HR-AMS PMF analysis diagnostics . . . . . . . . . . . . . . . . . . . . 148
4.5.3.1 4 factor unconstrained PMF . . . . . . . . . . . . . . . . . . 148
4.5.3.2 5 factor unconstrained PMF . . . . . . . . . . . . . . . . . . 151
4.5.3.3 8 factor unconstrained PMF . . . . . . . . . . . . . . . . . . 153
4.5.3.4 4 factor constrained PMF . . . . . . . . . . . . . . . . . . . . 157
4.5.3.5 5 factor constrained PMF . . . . . . . . . . . . . . . . . . . . 158
4.5.3.6 Residuals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160
4.5.4 ACSM PMF analysis diagnostics . . . . . . . . . . . . . . . . . . . . . 163
5 Thesis conclusions & outlook 165
List of Tables I
List of Figures I
References V
Acknowledgements XXXIII
Curriculum vitae XXXV
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Summary
Aerosols cause adverse effects on human health and may play an important (cooling) role
in the ongoing climate change, counteracting part of the observed global warming which is
caused mainly by atmospheric greenhouse gases. The extent of the effects due to aerosol is
still poorly determined. More knowledge about physical and chemical properties of aerosols
in all parts of the atmosphere is necessary to reduce the uncertainties and to improve global
model simulations. Aerosol chemistry and composition can vary on seasonal scales but also
on much shorter time scales e.g. during a day, depending on meteorological processes and
location or on nearby sources. For the investigation of the effects, long-term measurements
on the order of several months to years with sufficient time resolution to detect variations
during a day are necessary. The aerosol chemical speciation monitor (ACSM), a robust on-line
mass spectrometer for non-refractory, submicron particulate matter was developed exactly for
this task. It combines minimised maintenance requirements, i.e. the possibility of long-term
operation with a time resolution of minutes and is able to separate the main constituents of
atmospheric aerosol: sulphate, nitrate, ammonium, organics and chloride.
Aerosol mass concentrations at very remote sites typically are on the order of µg/m3 or
less, too low to measure with the original ACSM (using a quadrupole mass spectrometer)
without loosing valuable time resolution. Therefore, the ToF-ACSM equipped with a more
sensitive time-of-flight (ToF) mass spectrometer was developed. Performance and suitability
for autonomous operation at a remote site (Jungfraujoch, CH, 3580 m a. s. l.) was investigated
in this work. A manifold improvement of detection limits compared to the Q-ACSM and good
covariance with other, established measurement methods could be demonstrated together
with uncomplicated long-term (14 months) operation. Additionally, it was shown that the
new ToF technique enabled basic access to enhanced ion separation exceeding the unit mass
resolution of the Q-ACSM.
Furthermore, the14monthsofToF-ACSMmeasurementattheJungfraujoch(JFJ)provided
valuable insights into the Alpine aerosol. The unique location of the JFJ in the central Swiss
Alps at an elevation well above typical heights of the planetary boundary layer (PBL) away
from all sources makes it an interesting place to study the aerosol of the lower free troposphere
(FT), a location where clouds are forming and thus is very important for climate relevant
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