scholarly journals Development of a chemical ionization mass spectrometry system for measurement of atmospheric OH radical

2020 ◽  
Author(s):  
Wei Pu ◽  
Zhouxing Zou ◽  
Weihao Wang ◽  
David Tanner ◽  
Zhe Wang ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Chemical Ionization ◽  
High Reactivity ◽  
Ion Source ◽  
Tropospheric Chemistry ◽  
Ionization Mass Spectrometry ◽  
Chemical Ionization Mass Spectrometry ◽  
Urban Site ◽  
Oh Radicals ◽  
Ionization Mass

Abstract. The hydroxyl radical (OH) is the most important oxidant in the atmosphere and plays a central role in tropospheric chemistry. Ambient OH is extremely difficult to measure because of its low concentration and high reactivity. We have developed and optimized a chemical ionization mass spectrometry (CIMS) system to measure OH based on ion-assisted mass spectrometry. A calibration unit was developed based on chemical actinometry to convert detected signals to OH concentration. Different types of ion sources (210Po and corona source) and scavenger gases (propane, C3F6, and NO2) were compared. Radioactive ion source (210Po foils) was chosen for lower detection limits, and propane was selected for high elimination efficiency and the negligible influence on the signal stability. The sensitivity of the CIMS instrument to OH radicals is influenced by the efficiencies of titration reaction, ion conversion, and ion transmission. Through adjusting their efficiencies by changing the flow rates and voltages, optimal sensitivity was determined. The background noise from OH interferences was reduced by adjusting the flow rate of scavenger gas. The CIMS system achieved a detection limit of ~ 0.15×106 molecules cm−3 (signal/noise = 2). The CIMS was then taken out to measure ambient OH radicals at an urban site in Hong Kong in April 2019. An obvious diurnal pattern of OH radicals was observed, with the highest concentration of ~ 6×106 molecules cm−3 at midday and the lowest concentration of ~ 0.25×106 molecules cm−3 at night, with an overall accuracy of about ±51 %. The results demonstrated the capability of our CIMS for OH measurements on clear days. The tests and results from our study provide a useful reference to other researchers who wish to develop and apply the CIMS technique to measure OH and other chemicals.

scholarly journals Atmospheric measurements of gas-phase HNO<sub>3</sub> and SO<sub>2</sub> using chemical ionization mass spectrometry during the MINATROC field campaign 2000 on Monte Cimone

2003 ◽  
Vol 3 (2) ◽  
pp. 417-436 ◽  
Author(s):  
M. Hanke ◽  
B. Umann ◽  
J. Uecker ◽  
F. Arnold ◽  
H. Bunz
Keyword(s):  
Mass Spectrometry ◽  
Gas Phase ◽  
Chemical Ionization ◽  
Mineral Dust ◽  
Tropospheric Chemistry ◽  
Ionization Mass Spectrometry ◽  
Chemical Ionization Mass Spectrometry ◽  
Ionization Mass ◽  
Atmospheric Measurements ◽  
Tropospheric Aerosol

Abstract. The EU-project MINATROC (MINeral dust And TROpospheric Chemistry) aims at enabling an estimation of the influence of mineral dust, a major, but to date largely ignored component of tropospheric aerosol, on tropospheric oxidant cycles. Within the scope of this project continuous atmospheric measurements of gas-phase HNO3 and SO2 were conducted in June and July 2000 at the CNR WMO station, situated on Monte Cimone (MTC) (44°11' N --10°42' E, 2165 m asl), Italy. African air transporting dust is occasionally advected over the Mediterranean Sea to the site, thus mineral aerosol emitted from Africa will encounter polluted air masses and provide ideal conditions to study their interactions. HNO3 and SO2 were measured with an improved CIMS (chemical ionization mass spectrometry) system for ground-based measurements that was developed and built at MPI-K Heidelberg. Since HNO3  is a very sticky compound special care was paid for the air-sampling and background-measurement system. Complete data sets could be obtained before, during and after major dust intrusions. For the first time these measurements might provide a strong observational indication of efficient uptake of gas-phase HNO3 by atmospheric mineral-dust aerosol particles.

scholarly journals Performance of a corona ion source for measurement of sulfuric acid by chemical ionization mass spectrometry

2011 ◽  
Vol 4 (3) ◽  
pp. 437-443 ◽  
Author(s):  
A. Kürten ◽  
L. Rondo ◽  
S. Ehrhart ◽  
J. Curtius
Keyword(s):  
Mass Spectrometry ◽  
Sulfuric Acid ◽  
Chemical Ionization ◽  
Ion Source ◽  
Ion Sources ◽  
Ionization Mass Spectrometry ◽  
Chemical Ionization Mass Spectrometry ◽  
Integration Time ◽  
Ionization Mass ◽  
H2so4 Concentration

Abstract. The performance of an ion source based on corona discharge has been studied. This source is used for the detection of gaseous sulfuric acid by chemical ionization mass spectrometry (CIMS) through the reaction of NO3– ions with H2SO4. The ion source is operated under atmospheric pressure and its design is similar to the one of a radioactive (americium-241) ion source which has been used previously. The results show that the detection limit for the corona ion source is sufficiently good for most applications. For an integration time of 1 min it is ~6 × 104 molecule cm−3 of H2SO4. In addition, only a small cross-sensitivity to SO2 has been observed for concentrations as high as 1 ppmv in the sample gas. This low sensitivity to SO2 is achieved even without the addition of an OH scavenger. When comparing the new corona ion source with the americium ion source for the same provided H2SO4 concentration, both ion sources yield almost identical values. These features make the corona ion source investigated here favorable over the more commonly used radioactive ion sources for most applications where H2SO4 is measured by CIMS.

scholarly journals Aqueous-phase photooxidation of levoglucosan – a mechanistic study using Aerosol Time of Flight Chemical Ionization Mass Spectrometry (Aerosol-ToF-CIMS)

2014 ◽  
Vol 14 (7) ◽  
pp. 8819-8850 ◽  
Author(s):  
R. Zhao ◽  
E. L. Mungall ◽  
A. K. Y. Lee ◽  
D. Aljawhary ◽  
J. P. D. Abbatt
Keyword(s):  
Mass Spectrometry ◽  
Aqueous Phase ◽  
Chemical Ionization ◽  
Time Of Flight ◽  
Charge Ratio ◽  
Ionization Mass Spectrometry ◽  
Chemical Ionization Mass Spectrometry ◽  
Oh Radicals ◽  
Ionization Mass ◽  
Ambient Atmosphere

Abstract. Levoglucosan (LG) is a widely employed tracer for biomass burning (BB). Recent studies have shown that LG can react rapidly with hydroxyl (OH) radicals in the aqueous phase, despite many mass balance receptor models assuming it to be inert during atmospheric transport. In the current study, aqueous-phase photooxidation of LG by OH radicals was performed in the laboratory. The reaction kinetics and products were monitored by Aerosol Time of Flight Chemical Ionization Mass Spectrometry (Aerosol-ToF-CIMS). Approximately 50 reaction products were detected by the Aerosol-ToF-CIMS during the photooxidation experiments, representing one of the most detailed product studies yet performed. By following the evolution of mass defects of product peaks, unique trends of adding oxygen (+O) and removing hydrogen (−2H) were observed among the products detected, providing useful information to determine potential reaction mechanisms and sequences. As well, bond scission reactions take place, leading to reaction intermediates with lower carbon numbers. We introduce a data analysis framework where the average oxidation state (OSc) is plotted against a novel molecular property: double bond equivalence to carbon ratio (DBE / #C). The trajectory of LG photooxidation on this plot suggests formation of poly-carbonyl intermediates and their subsequent conversion to carboxylic acids as a general reaction trend. We also determined the rate constant of LG with OH radicals at room temperature to be 1.08 ± 0.16 × 109 M−1 s−1. By coupling an Aerosol Mass Spectrometer (AMS) to the system, we observed a rapid decay of the mass fraction of organic signals at mass-to-charge ratio 60 (f60), corresponding closely to the LG decay monitored by the Aerosol-ToF-CIMS. The trajectory of LG photooxidation on a f44–f60 correlation plot matched closely to literature field measurement data. This implies that aqueous-phase photooxidation might be partially contributing to aging of BB particles in the ambient atmosphere.

scholarly journals Performance of a corona ion source for measurement of sulfuric acid by chemical ionization mass spectrometry

2010 ◽  
Vol 3 (6) ◽  
pp. 5295-5312
Author(s):  
A. Kürten ◽  
L. Rondo ◽  
S. Ehrhart ◽  
J. Curtius
Keyword(s):  
Mass Spectrometry ◽  
Sulfuric Acid ◽  
Chemical Ionization ◽  
Ion Source ◽  
Ion Sources ◽  
Ionization Mass Spectrometry ◽  
Chemical Ionization Mass Spectrometry ◽  
Integration Time ◽  
Ionization Mass ◽  
H2so4 Concentration

Abstract. The performance of an ion source based on corona discharge has been studied. This source is used for the detection of gaseous sulfuric acid by chemical ionization mass spectrometry (CIMS) through the reaction of NO3– ions with H2SO4. The ion source is operated under atmospheric pressure and its design is similar to the one of a radioactive (Americium 241) ion source which has been used previously. Our results show that the detection limit for the corona ion source is sufficiently good for most applications. For an integration time of one minute it is ~6 × 104 molecules of H2SO4 per cm3. In addition, only a small cross-sensitivity to SO2 has been observed for concentrations as high as 1 ppmv in the sample gas. This low sensitivity to SO2 is achieved even without the addition of an OH scavenger. When comparing the new corona ion source with the americium ion source for the same provided H2SO4 concentration, both ion sources yield almost identical values. These features make the corona ion source investigated here favorable over the more commonly used radioactive ion sources for most applications where H2SO4 is measured by CIMS.

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