Using 13N as tracer in heterogeneous atmospheric chemistry experiments

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 N-13 enables laboratory experiments pertaining to the atmospheric chemistry of nitrogen oxides to be performed at extremely low concentrations, ambient humidity and pressure. N-13 was produced through O-16(p,alpha)N-13 reaction in a gas target in continuous mode, and transported as (NO)-N-13 in a carrier gas to the chemistry laboratory through a 70 m long capillary. Several gas-phase and surface chemical routines allowed converting (NO)-N-13 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 NO2 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 N-13-labelled HNO3 with sea-salt particles was studied using an aerosol flow reactor.