Supplemental information
A New Laser Induced Incandescence – Mass Spectrometric
Analyzer (LII-MS) for Online Measurement of Aerosol
Composition Classified by Black Carbon Mixing State
T. Miyakawa1, 2, N. Takeda3, K. Koizumi3, M. Tabaru3, Y. Ozawa1, 4, N.
Hirayama3, and N. Takegawa1, 5
1
Research Center for Advanced Science and Technology, The University of Tokyo,
Tokyo, Japan
2
Now at Department of Environmental Geochemical Cycle Research, Japan Agency for
Marine-Earth Science and Technology, Kanagawa, Japan.
3
Fuji Electric Co., Ltd., Tokyo, Japan
4
Now at Graduate school of Science, The University of Tokyo
5
Now at Graduate School of Science and Engineering, Tokyo Metropolitan University
Laboratory and ambient experiments
Transmission efficiency of the LII-vaporizer
Transmission efficiency of aerosol particles sampled and analyzed by LII-analyzer
was evaluated by the experimental setup as given by Figure S1a.
Using dry
mono-disperse polystyrene latex (PSL, Size Standard Particles, JSR Corporation)
particles generated by a nebulizer with a differential mobility analyzer (DMA, model
3081, TSI, Inc.) and diffusion dryer (model 3062, TSI, Inc.), the size-dependent
transmission efficiency can be calculated as the ratio of the number concentration of
PSL particles sampled via LII-analyzer to that via the bypath line. The diameters of
the PSL particles tested in this study were 0.104, 0.294, 0.506, and 0.791 µm.
The
number concentrations of PSL particles were measured by a condensation particle
counter (CPC, model 3022, TSI, Inc.).
It should be noted that ultrafine aerosol
particles (smaller than 0.1 µm) are significantly lost by the diffusion process even in the
sampling tube of the bypath line.
Transmission and detection efficiencies of the PT-LDMS
Size-dependent transfer function of the PT-LDMS can be described as a product of
the transmission efficiency of aerosol particles transported from the ADL assembly to
the particle trap (TEADL) and the detection (particle collection and vaporization)
efficiency of the sampled aerosol particles (EffMS).
The product of these parameters
was evaluated using the experimental setup given by Figure S1b, and described by the
following equation.
TE ADL  Eff MS 
M PT  LDMS
M CPC
(S1)
The product of TEADL and EffMS is a function of the aerodynamic diameter in the
transition regime (Da).
Da has been used in this study to discuss the detection
efficiency of the LII-MS compatibly with the conventional sizing techniques such as an
inertial impactor and cyclone.
MCPC is the mass of a selected compound accumulated
during the sampling time, which is predicted by the number concentration of
size-selected aerosol particles measured by the CPC. The flow rate of the sample and
sheath flow in the DMA was 0.41 and 4.0 liter per minute (lpm).
The mass of a
selected compound accumulated during the sampling time (typically 5-10 min),
MPT-LDMS, can be quantified using the calibration curve (i.e., the relationship between
Qm/z and mass of sampled particles).
In this study, the transmission efficiency of the
aerosol particles with Dmob (Da) of 0.25 (0.35~0.40) µm is assumed to be unity. This
assumption is valid for the ADL with the current operating pressure (~2 torr) as seen in
the previous studies (e.g., Takegawa et al., 2009).
The size-dependence of
MPT-LDMS/MCPC has been quantified by changing Dmob in the DMA. Multiply-charged
fraction of MPT-LDMS and MCPC at the selected Dmob has been corrected using the method
given by Wang et al. (2010) and Takegawa et al. (2012).
Ammonium sulfate (AS) and
potassium nitrate (PN) were selected as the material of particles for evaluating the
size-dependence of MPT-LDMS/MCPC.
Detection efficiency of the BC-containing particles by the LII-analyzer
The detection efficiency of BC-containing particles size-selected by the DMA was
evaluated by the experimental setup shown in Figure S1b and S1c. Fullerene (stock#:
40971, lot#: G25N20, Alfa Aesar Inc.) and propane flame soot particles generated by
the real smoke generator (RSG-miniCAST 5200, Jing Ltd.) were introduced into both
CPC and LII-analyzer.
The detection efficiency of the selected BC aerosols has been
determined by as a part of the experiments given in the section 4.
A thermodenuder
(model 3065, TSI, Inc.) was placed behind the nebulizer or RSG-miniCAST 5200 for
stripping off non-BC materials on the generated particles.
The temperature of the
thermodenuder was 300˚C (±2 ˚C). Denuded fullerene particles classified by the DMA
were introduced into the LII-analyzer using the setup as shown in Figure S1b.
The
diffusion dryer was placed behind the nebulizer for dehumidifying the sample air and
generating the undenuded dry BC particles.
Undenuded fullerene particles classified
by the DMA were also introduced into the LII-analyzer via the diffusion dryer (Figure
S1b). The sheath flow rate was set to be 4 lpm.
Propane flame soot particles coated
with oleic acid (OL) was prepared by a tandem DMA system (Figure S1c) as given in
Takegawa et al. (2012).
lpm, respectively.
Sheath flow rates for first and second DMAs were 4 and 3
An example of LII signals for fullerene particles classified by the
DMA, which was obtained before starting the ambient measurements, was shown in
Figure S2.
Detection of carbonaceous aerosols using the PT-LDMS
Dry, mono-disperse (Dmob = 0.25 µm) azelaic acid (C9di, Wako Chemicals), fullerene,
and propane flame soot particles have been introduced into both CPC and LII-MS
system (Figure S1b) to examine the response of the PT-LDMS to carbonaceous
aerosols.
Evaluations of the LII-MS
Laboratory characterizations
The LII-MS was evaluated with laboratory experiments to verify (1) the vaporization
of organics internally mixed with BC and (2) the persistence of non-light absorbing (i.e.
BC-free) particles.
The effect of (3) the vaporization of non-core-shell structure of BC
was on the quantification of chemical composition classified by the BC mixing state
also investigated.
For the purpose (1), propane flame soot particles coated with OL were introduced
into the LII-MS with changing the core and outer diameters of the test particles.
The
selected core diameters of BC particles (DC) were 0.1, 0.15, and 0.25 µm. The coating
thickness of coated-BC particles were 0.05 and 0.075 µm (only 0.05 µm-coating for
particles with DC = 0.1 and 0.25 µm). Figure S1c depicts the experimental setup for
this experiment.
For the purpose (2), mono-disperse fullerene and AS aerosols are individually
generated by two sets of nebulizers and DMAs and mixed before introduced into the
LII-MS (Figure S1d).
Sheath flow rates for both DMAs were 2 lpm.
The diameters
of both denuded fullerene and dry AS particles were set to 0.25 µm in Dmob. The
number concentration of AS particles were estimated by subtracting the number
concentration of fullerene particles from that of fullerene and AS particles, where the
former was measured by the LII-analyzer and the latter was measured by the CPC.
For the purpose (3), fullerene particles coated with OL were introduced into the
LII-MS with changing the shell diameters.
Figure S1e depicts the diagram of the
experimental setup to examine the changes in the number concentration of thickly
coated BC-containing particles by turning on and off the laser in the LII-analyzer. For
this purpose, a optical particle counter (OPC, KC-01E, RION Co., Ltd.) was placed at
the outlet of the LII-analyzer. The sheath flow rates for first and second DMAs were
set to be 4 and 3 lpm, respectively. The diameter of fullerene particles as a proxy of
BC was selected to be 0.3 µm in Dmob by the first DMA. The diameter of coated
fullerene particles for this experiment was changed from 0.3 µm to 0.5 µm (coating
thickness 0 - 0.1 µm) classified by the second DMA.
Ambient Measurements
The sulfate mass concentrations for a sulfate particle analyzer (SO4SPA) (SPA, model
5020, Thermo Scientific, Inc.) were compared with the integrated values of the mass
spectral signals at m/z 48 (Q48) when the LII laser was turned off.
The flow rate of the
SPA is ~0.5 lpm. The ambient air was drawn from outside into SPA and LII-MS
through the PM2.5 cyclone (50% transmission for particles with Da of 2.5 µm,
URG-2000-30EH, URG Co.). Total flow rate of the sampling line for both instruments
was adjusted to 16.7 lpm by using an additional pump with the orifice flow regulator.
The average transmission efficiency weighted by an aerosol size distribution was
calculated to be 0.70 using the typical volume size distribution (0.15-1 µm) in urban
atmosphere which is given in Figure 4c.
Variability in the weighted transmission
efficiency was estimated to be ~1% by shifting the peak diameter (Da of ~0.4 µm) to
0.1-µm larger or smaller, indicating the small variations of the transmission efficiency
of the LII-analyzer with changes in the aerosol size distribution.
The atmospheric measurement was conducted for the period of 23-24 March, 2013.
The ambient air was sampled by the same way described earlier.
Uncertainties in
relation to quantifying the absolute mass concentrations have not been evaluated in this
study, which should be further investigated in future (Takegawa et al., manuscript in
preparation).
References
Moteki, N., and Y. Kondo (2007), Effects of mixing state on black carbon measurements
by laser-induced incandescence, Aerosol Sci. Technol., 41, 398-417.
Takegawa, N., T. Miyakawa, M. Watanabe, Y. Kondo, Y. Miyazaki, S. Han, Y. Zhao,
D. van Pinxteren, E. Bruggemann, T. Gnauk, H. Herrmann, R. Xiao, Z. Deng, M.
Hu, T. Zhu, and Y. Zhang (2009), Performance of an Aerodyne aerosol mass
spectrometer (AMS) during intensive campaigns in China in the summer of 2006,
Aerosol Sci. Technol., 43, 189-204.
Takegawa, N., T. Miyakawa, T. Nakamura, Y. Sameshima, M. Takei, Y. Kondo, and N.
Hirayama (2012), Evaluation of a New Particle Trap in a Laser Desorption Mass
Spectrometer for On-Line Measurement of Aerosol Composition, Aerosol Sci.
Technol., 46:4, 428-443.
Wang, X., R. Caldow, G. J. Sem, N. Hama, and H. Sakurai (2010), Evaluation of a
Condensation Particle Counter for Vehicle Emission Measurement: Experimental
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Figure S1 (a)
Figure S1 (b)
Figure S1 (c)
Figure S1 (d)
Figure S1 (e)
Figure S1.
Experimental setups for the laboratory evaluations for investigating (a)
transmission efficiency of the LII-analyzer, (b) instrumental responses of the LII-MS,
(c) vaporization of organics on the BC particle, (d) persistence of the non-light
absorbing particles externally mixed with the BC particles, (e) the effect of
non-core-shell BC. The thermodenuder and diffusion dryer have been used for
removing organic and water contents from the particle, respectively.
Figure S2
5000
Dmob =
200 nm
300 nm
400 nm
LII intensity (arb.)
4000
3000
2000
1000
0
5
10
15
20
Relative time (µs)
Figure S2.
Examples of LII signals from fullerene particles with Dmob of 200 (gray),
300 (dark gray), and 400 nm (black).
Low gain signals of 300- and 400-nm fullerene
particles at the PMT were converted high-gain-equivalent signals.