Flow reactor and triple quadrupole mass spectrometer investigations of negative ion reactions involving nitric acid: Implications for atmospheric HNO3 detection by chemical ionization mass spectrometry

Abstract

Atmospheric nitric acid measurements by ACIMS (Active Chemical Ionization Mass Spectrometry) are based on ion-molecule reactions of CO3(H20) . and NO~(H20), with HNO 3. We have studied these reactions in the laboratory using a flow tube apparatus with mass spectrometric detection of reactant and product ions. Both product ion distributions and rate coefficients were measured. All reactions were investigated in an N2-buffer (1-3 hPa) at room temperature. The reaction rate coefficients of OH-, O2, 03, CO4, CO3, CO~H~O, NO3, and NO3H20 were measured relative to the known rate k = 3.0 x 10 -9 cm 3 s -1 for the reaction of O-with HNOa. The main product ion of the reaction of CO~HzO with HNO3 was found to be (CO3HNO3)-supporting a previous suggestion made on the basis of balloon-borne ACIMS measurements. For the reaction of bare COS with HNO3 three product ions were observed, namely NO 3, (NO3OH)-, and (CO3HNO3) -. The reaction rate coefficients for CO3H20 (1.7 x 10 -9 cm 3 s -j) and NO3H20 (1.6 x 10 -9 cm 3 s -l) were found to be close to the collision rate. The measured k values for bare CO3 (1.3 x 10 -9 cm 3 s -l) and NO3 (0.7 × 10 -9 cm 3 S -I) are somewhat smaller. The collisional dissociations of CO3(HzO) . , NO~(H/O), (n = 1, 2), (CO3HNO3)-and (NO3HNO3) -, occasionally influencing ACIMS measurements, were also studied. Fragment ion distributions were measured using a triple quadrupole mass spectrometer. The results showed that previous stratospheric nitric acid measurements were unimpaired from collisional dissociation processes whereas these processes played a major role during previous tropospheric measurements leading to an underestimation of nitric acid concentrations. Previous ACIMS HNO 3 detection was also affected by the conversion of CO3(H20), to NO3(H20)n due to ion source-produced neutral radicals. A novel ACIMS ion source was developed in order to avoid these problems and to improve the ACIMS method.

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

“…(Möhler and Arnold, 1991;Schneider et al, 1998). A recent study has reinvestigated this IMR and confirmed our rate coefficients (Guimbaud et al, 1998).…”

An experimental study of ion-induced nucleation using a drift tube ion mobility spectrometer/mass spectrometer and a cluster-differential mobility analyzer/Faraday cup electrometer

“…CO − 3 is also known to be formed in air by ion-molecule reactions involving CO 2 (Möhler & Arnold, 1991). In the present experiment, ultra-pure air supplied from a cylinder was used, but at least a few ppb of CO 2 is usually present.…”

The University of Bern Atmospheric Ion Model: Time‐dependent modeling of the ions in the mesosphere and lower thermosphere

“…CO 3 − forms clusters with H 2 O as well as with HNO 3 . The direct reactions with HNO 3 occur as well: (after Möhler and Arnold [1991]). Cl − forms clusters with H 2 O and HCl and reacts with HNO 3 to form NO 3 − .…”