Evaluation of a Particle Trap Laser Desorption Mass Spectrometer (PTLDMS) for the Quantification of Sulfate Aerosols
Y. Ozawa
1, 2 ,
N. Takeda 3 , T. Miyakawa
1, 4 ,
M. Takei 3 , N. Hirayama 3 , and N.
Takegawa 1, 5
1
Research Center for Advanced Science and Technology, The University of Tokyo,
Meguro, Tokyo, Japan.
2
Now at Department of Earth and Planetary Science, Graduate School of Science, The
University of Tokyo, Bunkyo, Tokyo, Japan (ozawa.yuya@eps.s.u-tokyo.ac.jp).
3
Fuji Electric, Co., Ltd., Hino, Tokyo, Japan.
4
Now at Department of Environmental Geochemical Cycle Research, Japan Agency for
Marine-Earth Science and Technology, Yokohama, Kanagawa, Japan.
5
Now at Graduate School of Science and Engineering, Tokyo Metropolitan University,
Hachioji, Tokyo, Japan.
Supplementary Material
S1. Correction for Multiple Charging
A method for multiply charged correction is described. The method is similar to
that described by Wang et al. (2010) and Takegawa and Sakurai (2011). The aerosol
flow passing through the DMA contain not only singly charged particles but also
multiply charged particles. The mass concentration of calibration particles may be
underestimated if we assume the particles are all singly charged. The population of
muliply charged particles needs to be experimentally evaluated.
The fraction of doubly charged particles (f 2 ) and triply charged particles (f3 ) was
calculated by using the method described in Wang et al. (2010) and Takegawa and
Sakurai (2011). The mass concentration determined from the CPC data (Mcal
CPC ) is
expressed as follows:
1
π
6
3
Mcal
CPC = ρNd1 (1 - f2 - f3 + f2
d32
d31
d3
+ f3 23 ) .
d1
(S1)
Where ρ is a particle density, N is the number concentration measured by the CPC, d1
is a particle diameter selected by DMA, d2 is the paricle diameter of doubly charged
particles, and d 3 is the particle diameter of triply cherged particles.
S2. KNO 3
The sensitivity for nitrate was measured under various Ttrap and Tcell conditions as
well as sulfate. Figure S1 shows the evolution of the m/z 30 ion currents for KNO 3
particles obtained at a Ttrap of ~550°C and Tcell values of 200 and 280°C. For KNO 3
particles, the overall shape of the m/z 30 signal significantly changed in the earlier time
period with increasing Tcell. The artifact signals were found be more pronounced for
KNO3 than for (NH4 )2SO4 particles.
Figure S2 shows the sensitivity experiment for KNO 3 . Although substantial
scatter was observed in the data, the dependence of the sensitivity on Tcell also
appeared to be more significant than the dependence on T trap for KNO 3. Higher T cell
conditions exhibited lower sensitivity for KNO 3 particles.Changes in the temporal
evolution of ion current and sensitivity depending on T cell were somewhat unexpected
results. These features may not be explained by adsorption of NO on the cell wall.
Further experiments are needed to investigate the mechanism.
2
3.0x10
-8
I30 (A)
2.0
2.0x10
-8
I30 (A)
m/z 30 ion current for KNO3
Tcell = 280°C
KNO3
Zero
Tcell = 200°C
KNO3
Zero
1.0
1.0
0.0
0
50
0.0
150
100
Elapsed time (s)
Figure S1. The evaluation of mass normalized m/z 30 ion current for KNO 3 particles
obtained at a Ttrap of ~550°C and T cell values of 200°C (blue and light blue lines, right
axis) and 280°C (red and orange lines, left axis).
4
-1
S30 of KNO3 (pC ng )
1.2x10
(b) Sensitivity for KNO3
Tcell = 280 °C
Tcell = 200 °C
1.0
0.8
0.6
360
400
440
480
520
560
600
Ttrap (•
°C)
Figure S2. Dependence of nitrate sensitivity versus Ttrap at various T cell values. The
error bars represent uncertainty originating from random error (2σ) of PT-LDMS (4%),
CPC (2%), and radiation thermometer (1%).
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S3. Effect of the Difference in Size Cut
The effects of the difference in the size cut between the PT-LDMS (approximately
PM 1 ) and SPA (PM 2.5 ) are described. Figure S3 shows an expample of volume size
distribution in urban air (quoted from Seinfeld and Pandis 2006), and that measured in
Tokyoin the spring of 2013 by a scanning mobility particle sizer (SMPS) and optical
particle counter (OPC; unpublished data), together with the transimission efficiencies
of the aerodynamic lens (Miyakawa et al. 2015) and the PM2.5 cyclone. We asumed
that the ambient particle density was 1.5 g cm -3 for calculating the vacuum
aerodynamic diameters. As a result, the uncertainty of size cut was estimated to be
−0.15 for ambient particles.
d va1
d va2 d va3
TEcyclone
1.0
3
0.6
0.4
0.2
0.0
dV/dlogDva (urban air)
0.8
10
Urban
TEADL
0.5
0.0
SMPS
5
6
7
8 9
2
3
0.1
4
5
OPC
5
Dva (µm)
6
7
8 9
2
3
4
dV/dlogDva (Tokyo)
TEADL • TEcyclone
1.0x10
0
1
Figure S3. An example of volume size distribution in urban air quoted from
Seinfeld and Pandis (2006) (dashed line) and that measured in Tokyo in the spring of
2013 (filed and open circles), transmission efficiency of the aerodynamic lens (TE ADL,
shaded line), and that of the PM2.5 cyclone (TEcyclone, solid line). The vacuum
aerodynamic diameters were calculated based on the assumption that the ambient
particle density was 1.5 g cm -3 . The curve of TEcyclone was drawn based on the
datasheet of URG-2000-30EH. The arrows indicate the vacuum aerodynamic
diameters of calibration (NH 4 )2 SO4 particles.
4
References
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