Using¹³N as tracer in heterogeneous atmospheric chemistry experiments

Abstract

Current techniques aiming to study heterogeneous atmospheric chemistry under realistic conditions are often subject to restrictions caused by the low amount of processed material, the complex composition of gas and condensed phases and interference issues. The use of the short-lived tracer 13 N enables laboratory experiments pertaining to the atmospheric chemistry of nitrogen oxides to be performed at extremely low concentrations, ambient humidity and pressure. 13 N was produced through 16 O( p, α) 13 N reaction in a gas target in continuous mode, and transported as 13 NO in a carrier gas to the chemistry laboratory through a 70 m long capillary. Several gas-phase and surface chemical routines allowed converting 13 NO into other forms of oxidized nitrogen. Chemical separation and detection was achieved through chemically specific absorption reactions on the coatings of denuders, which additionally allowed separating gas-phase species from their particulate counterparts. In a first application, the reversible adsorption of NO 2 on a solid NaCl surface was investigated, from which an adsorption enthalpy of 28 kJ/mol was derived. As an example of a reaction with aerosol particles in gas suspension, the reaction of 13 N-labelled HNO 3 with sea-salt particles was studied using an aerosol flow reactor.

Uptake of HNO<sub>3</sub> to deliquescent sea-salt particles: a study using the short-lived radioactive isotope tracer <sup>13</sup>N

“…The narrow deposition pattern in each denuder has been well established (Ammann, 2001). It shows that the collection efficiency of the molecules is 100% on the denuders and on the filter.…”

“…The experimental techniques employed here are similar to those reported previously (Ammann, 2001;Kalberer et al, 1999). Nitrogen oxides labeled with the short-lived radioactive isotope 13 N are mixed with the aerosol particles in a flow reactor.…”

“…The concentration of each gaseous and particulate species is obtained by counting the number of decays of 13 N in each trap. The production of 13 N in the form of 13 NO has been described in detail elsewhere (Ammann, 2001). The experimental schematic to generate HNO 3 and the sea-salt particles is shown in Fig.…”

“…Under the present flow conditions, the characteristic time for this separation of HNO 3 from the aerosol is about 20 ms. The performance of this system has been demonstrated previously (Ammann, 2001). The HNO 3 uptake coefficient is derived from the concentration change of HNO 3 in the gas phase at the end of the flow tube when the aerosol was admitted to the flow tube, and from the concentration equivalent to HNO 3 taken up by the particles.…”

“…It shows that the collection efficiency of the molecules is 100% on the denuders and on the filter. This is checked by regularly measuring the amount of 13 N absorbed on each trap with a scanning counting system described in Ammann (2001) that provides a spatial distribution of 13 N along the denuders.…”