scholarly journals Chemical ionization mass spectrometry (CIMS) may not measure all gas-phase sulfuric acid if base molecules are present

2010 ◽  
Vol 10 (12) ◽  
pp. 30539-30568
Author(s):  
T. Kurtén ◽  
T. Petäjä ◽  
J. Smith ◽  
I. K. Ortega ◽  
M. Sipilä ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Sulfuric Acid ◽  
Gas Phase ◽  
Chemical Ionization ◽  
Measurement Data ◽  
Ionization Mass Spectrometry ◽  
Chemical Ionization Mass Spectrometry ◽  
Ionization Mass ◽  
Proton Affinities ◽  
Reaction Thermodynamics

Abstract. The state-of-the art method for measuring atmospheric gas-phase sulfuric acid is chemical ionization mass spectrometry (CIMS) based on nitrate reagent ions. Using computed proton affinities and reaction thermodynamics for the relevant charging reactions, we show that in the presence of strong bases such as amines, which tend to cluster with the sulfuric acid molecules, a significant fraction of the total gas-phase sulfuric acid may not be measured by a CIMS instrument. If this is the case, this effect has to be taken into account in the interpretation of atmospheric sulfuric acid measurement data, as well as in intercomparison of different CIMS instruments, which likely have different susceptibilities to amine-sulfuric acid clustering.

scholarly journals The effect of H<sub>2</sub>SO<sub>4</sub> – amine clustering on chemical ionization mass spectrometry (CIMS) measurements of gas-phase sulfuric acid

2011 ◽  
Vol 11 (6) ◽  
pp. 3007-3019 ◽  
Author(s):  
T. Kurtén ◽  
T. Petäjä ◽  
J. Smith ◽  
I. K. Ortega ◽  
M. Sipilä ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Sulfuric Acid ◽  
Gas Phase ◽  
Chemical Ionization ◽  
Measurement Data ◽  
Ionization Mass Spectrometry ◽  
Chemical Ionization Mass Spectrometry ◽  
Ionization Mass ◽  
Computational Data ◽  
Ionization Methods

Abstract. The state-of-the art method for measuring atmospheric gas-phase sulfuric acid is chemical ionization mass spectrometry (CIMS) based on nitrate reagent ions. We have assessed the possible effect of the sulfuric acid molecules clustering with base molecules on CIMS measurements using computational chemistry. From the computational data, three conclusions can be drawn. First, a significant fraction of the gas-phase sulfuric acid molecules are very likely clustered with amines if the amine concentration is around or above a few ppt. Second, some fraction of these acid-amine clusters may not be charged by the CIMS instrument, though the most reliable computational methods employed predict this fraction to be small; on the order of ten percent or less. Third, the amine molecules will evaporate practically immediately after charging, thus evading detection. These effects may need to be taken into account in the interpretation of atmospheric measurement data obtained using chemical ionization methods. The purpose of this study is not to criticize the CIMS method, but to help understand the implications of the measured results.

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