Meteorologisches Observatorium Hohenpeißenberg, www.dwd.de/mohp
Sulfuric acid is a key components in new particle formation in the atmosphere.
Nucleation rate and the number concentration of freshly nucleated particles are both
observed to strongly depend on sulfuric acid concentration (Kerminen et al., 2010,
Paasonen et al., 2010).
The only available technique to measure sulfuric acid in atmosphere (some 105–107
molecules/cm³) is Chemical Ionization Mass Spectrometry (CIMS) (Fig. 1).
Fig. 1: Scheme of a CIMS instrument ((Berresheim et al., 2000)
H2SO4 measurement by CIMS needs indirect calibration, generally, photolysis of
water vapor is used to produce OH radicals, which are then titrated by excess SO2 to
yield H2SO4 (Eisele and Tanner, 1993). Table 1 gives typical uncertainties of
calibration, OH measurement and H2SO4 measurements.
Table 1: 2-sigma uncertainties for CIMS measurements
Chemical artifacts in photolysis and titration zone in ambient air calibration:
Between photolysis, titration, and the addition of an OH-scavenger (rear injector)
(several 10 ms each) OH and HO2 radicals are not in equilibrium and inter-conversion
with artifact OH loss or H2SO4 formation may occur –> Periods short (<50ms),
chemical model for corrections (typically 10%)
Artifacts due to matrix effects using synthetic air flow tube calibrators:
Conditions in titration, flow tube and ion-molecule reaction zone are different from
ambient air and ion-molecule cluster formation (acid ions with water and neutral acids
and other polar compounds) is suppressed which might result in different instrument
sensitivity for ambient air matrix and synthetic air matrix -> occasional changes in
CIMS sensitivity in ambient air are observed and are not understood
Chemical artifacts in ambient air measurements – same as above
Matrix effect in ambient air measurements:
Neutral molecule clusters of H2SO4 with polar molecules (water, acids, ammonia,
amines,…) may form (Kurten et al., 2010). Depending on the clusters, the ionization
reaction with nitrate-ion clusters in the ion-molecule reaction zone might be
suppressed. Accordingly, cluster bound H2SO4 is (depending on the clusters) not
quantitatively detected – but: CIMS is for measurement of non-clustered H2SO4, yet,
the question remains which form of H2SO4 prevails in the atmosphere
Production of artifact H2SO4 in the CIMS system:
Impurities in the used process gases, e.g. t/c-2-pentene in propane, might react with
ambient ozone and produce Criegee radicals which then can form H2SO4 from
ambient SO2. Another issue is impurities in the nitric acid added to the sheath gas.
Malfunction of valves and flow controllers, plugged injectors … are other sources of
problems which are often hard to detect –> multiple problems hard to resolve
Sulfuric Acid Measurements by CIMS – Uncertainties and Consistency between Various Data Sets
C. PLASS-DÜLMER1, T. ELSTE1, P. PAASONEN2, and T. PETÄJÄ2
1Hohenpeissenberg Meteorological Observatory, Deutscher Wetterdienst, Germany, and 2Department of Physics, University of Helsinki, Finland
To check for consistency between different data sets, the calculated H2SO4 from
balance equations (assuming stationary state) can be compared to the measured data:
d/dt [H2SO4] = kOH [OH] [SO2] – CS [H2SO4] => [H2SO4] = kOH [OH] [SO2] / CS
This approach compares measured H2SO4 with calculated H2SO4 from OH measured
by the same CIMS, thus, uncertainties are substantially reduced. Data from the DWD-
CIMS from various campaigns and from different CIMS in Hyytiälä are compared.
Fig. 2: H2SO4 data obtained by the
DWD CIMS during EUCAARI
Sulfuric acid calculated from balance is generally lower than measured sulfuric acid
(Eisele and Tanner, 2003, Petäjä et al., 2009), on average by factors of 1-2, indicating
either an overestimation of the CS or a missing production pathway for sulfuric acid.
Fig. 4: Median diurnal cycles of k-UV=[H2SO4]meas / ([SO2] UV / CS) with UV=integrated irradiation 280-
320nm (left) and of k-OH-calc.=[H2SO4]meas / ([OH]meas [SO2] / CS); CIMS by UHEL , MPI , DWD
Using the UV radiation instead of measured OH in k-UV (Fig. 4) allows to compare
H2SO4-meas with independently measured quantities. At noon-time, k-UV varies on
average between 6 10-7 and 1.7 10-6 m²/J, e.g. factor 2.5 between min and max (Forest
Fire data were excluded for contaminated conditions). The same comparison for k-
OH-calc yields 6 10-13(min) and 3 10-12cm³/(molec.s) (max), which is more variable
probably due to additional uncertainties in OH measurements.
• H2SO4 data sets are comparable (median, noon) by better than factor 2 (k-UV)
• other H2SO4 sources than OH + SO2 in the morning/evening (Criegee+SO2 ?)
• overestimation of condensation sink? (H2SO4+H2O+… clusters / accomodation)
ACKNOWLEDGEMENTS
We wish to thank many contributors at DWD, UHEL, Melpitz (IFT), San Pietro Capofiume (CNR), and
NCAR for support, data provision and cooperation. Financial support was given by the EUCAARI project.
REFERENCESBerresheim et al., Int. J. Mass Spectrom., 202, (2000) 91. Boy et al., Atmos. Chem. Phys. 5, 863, 2005.
Eisele and Tanner, J. Geophys. Res. 98 (1993) 9001. Kerminen et al., Atmos. Chem. Phys., 10, 10829, 2010.
Kurten et al., Atmos. Chem. Phys. Disc., 10, 30539, 2010. Paasonen et al., Atmos. Chem. Phys., 10, 11223, 2010
Petäjä et al., Atmos. Chem. Phys., 9, 7435, 2009.
DW
D -
10
/20
10
Melpitz
random systematic total random systematic total
Calibration OH-meas.
Photonflux 184.9 nm 5% 15% 16% count statistics (30 s) 25% 25%
v (inlet-flow) 4% 6% 7% wind+chem+cal.factor 7% 16% 31%
[H2O] 3% 10% 10% total OH (30 s) 26% 16% 40%
s-H2O 3% 3% total OH (5 min) 11% 32%
wind ind. turbulence 5% 10% 11%
chemical artifacts 5% 10% 11% H2SO4
meas. Reproduc. 5-10% count statistics (30 s) 13% 13%
calibration factor 26% wind+cal.factor 5% 10% 31%
total H2SO4 (30 s) 13% 10% 33%
total H2SO4 (5 min) 6% 31%
Fig. 3: Sulfuric acid
concentration calculated
versus measured H2SO4 for
different CIMS instruments
in different campaigns.
Upper row by DWD-CIMS:
San Pietro Capofiume, Italy
Melpitz, Germany
Hohenpeissenberg
lower row all Hyytiälä by:
MPI-Heidelberg CIMS (Boy
et al., 2005)
UHEL-CIMS
NCAR-CIMS oper. by
UHEL (Petäjä et al., 2009)
y = 0.98x
R2 = 0.46
0.0E+00
5.0E+06
1.0E+07
1.5E+07
0.0E+00 5.0E+06 1.0E+07 1.5E+07
H2SO4-meas, molec/cm³
H2S
O4-
calc
, m
olec
/cm
³
QuestII_03-04/2003_MPI Heidelberg
1:1
y = 0.78x
R2 = 0.79
0.0E+00
2.0E+06
4.0E+06
6.0E+06
8.0E+06
0.0E+00 2.0E+06 4.0E+06 6.0E+06 8.0E+06
H2SO4-meas, molec/cm³
H2S
O4-
calc
, m
olec
/cm
³
HUMPPA_07-08/2010_UHEL
1:1
y = 0.48x
R2 = 0.75
0.0E+00
2.0E+06
4.0E+06
6.0E+06
8.0E+06
0.0E+00 2.0E+06 4.0E+06 6.0E+06 8.0E+06
H2SO4-meas, molec/cm³
H2S
O4-
calc
, m
olec
/cm
³
EUCAARI_03-06/2007_UHEL w NCAR
1:1
y = 0.77x
R2 = 0.87
0.0E+00
2.0E+07
4.0E+07
6.0E+07
0.0E+00 2.0E+07 4.0E+07 6.0E+07
H2SO4-meas, molec/cm³
H2S
O4-
calc
, mol
ec/c
m³
1:1
San Pietro Capofiume, June/July 2009
y = 0.73x
R2 = 0.87
0.0E+00
2.0E+07
4.0E+07
6.0E+07
0.0E+00 2.0E+07 4.0E+07 6.0E+07
H2SO4-meas, molec/cm³H
2SO
4-c
alc
, mol
ec/c
m³
1:1
Melpitz, May 2008
y = 0.66x
R2 = 0.64
0.0E+00
1.0E+07
2.0E+07
3.0E+07
4.0E+07
0.0E+00 1.0E+07 2.0E+07 3.0E+07 4.0E+07
H2SO4-meas, molec/cm³
H2S
O4-
calc
, m
olec
/cm
³
1:1
Hohenpeißenberg, 1998-99
1.0E+05
1.0E+06
1.0E+07
1.0E+08
01.01.07 01.01.08 01.01.09 01.01.10
sulp
hu
ric
aci
d, m
ole
c/cm
³ X
daily mean d(10-14:59)d(22-2:59) monthly meanm(10-14:59) m(22-2:59)
San Pietro Capofiume
Melpitz
1.0E-07
1.0E-06
1.0E-05
1.0E-04
0:00 2:00 4:00 6:00 8:00 10:00 12:00 14:00 16:00 18:00 20:00 22:00 0:00
med
ian
k-U
V,
m²/
J
EUC_03-4/07
EUC_05/07
EUC_06/07
Ffire_04-05/09
HUM_07-8/10
QuestII_03-4/03
QuestIV_04-5/05
HPB_01-7/08
SPC_07/09
Melpitz_05/09
1.0E-13
1.0E-12
1.0E-11
1.0E-10
0:00 2:00 4:00 6:00 8:00 10:00 12:00 14:00 16:00 18:00 20:00 22:00 0:00
med
ian
k-O
H-c
alc,
cm
³/(m
olec
s)
k(OH)=9.2e-13, DeMore et al., JPL, 1997