Techniques for quantifying gaseous HOCl using atmospheric pressure ionization mass spectrometry

Abstract

HOCl is speculated to be an important intermediate in mid-latitude marine boundary layer chemistry and at high latitudes in spring-time when surface-level depletion occurs. However, techniques do not currently O 3 exist to measure HOCl in the troposphere. We demonstrate that atmospheric pressure ionization mass spectrometry (API-MS) is a highly sensitive and selective technique which has promise for HOCl measurements both in laboratory systems and in Ðeld studies. While HOCl can be measured as the adduct with air as the chemical ionization (CI) reagent gas, the intensity of this adduct is (HOCl AE O 2 )s ensitive to the presence of acids and to the amount of water vapor, complicating its use for quantitative measurements. However, the addition of bromoform vapor to the corona discharge region forms bromide ions that attach to HOCl and allow its detection via the (HOCl AE Br)~adduct. The ionÈmolecule chemistry associated with the use of air or bromoform as the CI reagent gas is discussed, with particular emphasis on the e †ects of relative humidity and gas phase acid concentrations. HOCl is quantiÐed by measuring the amount of formed by its heterogeneous reaction with condensed-phase Detection limits are D3 parts per Cl 2 HCl/H 2 O. billion (ppb) using air as the CI reagent gas and D0.9 ppb using bromoform. The atmospheric implications of this work are discussed.

Airborne Observations of Reactive Inorganic Chlorine and Bromine Species in the Exhaust of Coal‐Fired Power Plants

“…Br 2 was calibrated using a permeation device (96 ng/min, KIN‐TEK) whose output was verified by gravimetric analysis. HOCl was calibrated following the protocol described by Foster et al (). HCl was calibrated using microinjections of methanol solutions of known HCl concentrations (Sigma‐Aldrich), as described by Lee et al ().…”

Flight Deployment of a High‐Resolution Time‐of‐Flight Chemical Ionization Mass Spectrometer: Observations of Reactive Halogen and Nitrogen Oxide Species

“…Sensitivities to Cl 2 and SO 2 were determined using compressed gas standards (10.1 ppm ± 5% SO 2 in N 2 , Scott-Marin; 7.5 ppm ± 5% Cl 2 in N 2 , Praxair). HOCl was calibrated by quantitatively converting to Cl 2 following the protocol described by Foster et al (1999). Generating standards for HBr, BrNO 2 , HOBr, and BrCl is not trivial (Barnett, 1988;Caloz et al, 1998;Foster et al, 2001;Orlando & Burkholder, 1995).…”

“…The activation of surface-bound chloride by N 2 O 5 resulting in elevated levels of ClNO 2 in moderately polluted nighttime atmospheres both near and far from coastal regions (Mielke et al, 2011;Osthoff et al, 2008;Riedel et al, 2012Riedel et al, , 2013Thornton et al, 2010;Young et al, 2012) underscores a pathway by which RHS influence the transport and transformation of oxidants and NO x (Riedel et al, 2014;Sarwar et al, 2014;Wang et al, 2016). The measurement of subsets of these RHS using iodide-adduct ionization (Faxon et al, 2015;Huey et al, 1995;Kercher et al, 2009;Liao et al, 2011Liao et al, , 2014McNeill et al, 2006;Neuman et al, 2010;Osthoff et al, 2008;Riedel et al, 2012Riedel et al, , 2013Roberts et al, 2008Roberts et al, , 2010Thornton & Abbatt, 2005) and other ionization methods (Finley & Saltzman, 2006;Foster et al, 1999;Huey et al, 1995;Jurkat et al, 2010;Lawler et al, 2011;Marcy et al, 2005;Spicer et al, 1998) is well established. The technique described herein simultaneously measures HCl, HOCl, ClNO 2 , Cl 2 , BrNO 2 , Br 2 , and BrCl, along with their stable isotopologues that provide additional constraints to their identification.…”

HOCl and Cl<sub>2</sub> observations in marine air

“…HOCl and Cl 2 were detected using chemical ionization tandem mass spectrometry (CIMS-MS) via formation of a Br − adduct (Foster et al, 1999). The mass spectrometer was a Thermo Finnigan TSQ Quantum.…”

“…This reactor converted the HOCl to Cl 2 while letting Cl 2 pass. After the reactor, the flow was routed to the instrument inlet, and the increase in Cl 2 signal was attributed to a molar equivalent loss of HOCl in the reactor as a result of Reaction (R5) (Foster et al, 1999). This "HOCl as Cl 2 " signal was converted into an HOCl mixing ratio using the instrument sensitivity to Cl 2 , based on the Cl 2 permeation tube.…”