A new method for using ¹⁸O to trace ozone deposition

Abstract

Isotopically labelled ozone ((18)O(3)) is an ideal tool to study the deposition of O(3) to plants and soil, but no studies have made use of it due to the technical difficulties in producing isotopically enriched ozone. For (18)O(3) to be used in fumigation experiments, it has to be purified and stored safely prior to fumigations, to ensure that the label is present predominantly in the form of O(3), and to make efficient use of isotopically highly enriched oxygen. We present a simple apparatus that allows for the safe generation, purification, storage, and release of (18)O(3). Following the purification and release of O(3), about half (by volume) of the (18)O is present in the form of O(3). This means that for a given release of (18)O(3) into the fumigation system, a roughly identical volume of (18)O(2) is released. However, the small volume of this concurrent (18)O(2) release (100 nmol mol(-1) in our experiment) results in only a minor shift of the much larger atmospheric oxygen pool, with no detectable consequence for the isotopic enrichment of either soil or plant materials. We demonstrate here the feasibility of using (18)O as an isotopic tracer in O(3) fumigations by exposing dry soil to 100 nmol mol(-1) (18)O(3) for periods ranging from 1 to 11 h. The (18)O tracer accumulation in soil samples is measured using gas chromatography/isotope ratio mass spectrometry (GC/IRMS), and the results show a linear increase in (18)O/(16)O isotope ratio over time, with significant differences detectable after 1 h of exposure. The apparatus is adapted for use with fumigation chambers sustaining flow rates of 1 m(3) min(-1) for up to 12 h, but simple modifications now allow larger quantities of O(3) to be stored and continuously released (e.g. for use with open-top chambers or FACE facilities).

Dry Deposition of Ozone Over Land: Processes, Measurement, and Modeling

“…Isotopic experiments in the laboratory and field may be able to pinpoint the primary sites of ozone surface reactions and thus improve understanding of ozone deposition pathways (Subke et al, ; Toet et al, ). Subke et al () present a method for adding 18 O into an electric discharge ozone generator and using a silica gel to separate 18 O ozone from 18 O O 2 .…”

“…Isotopic experiments in the laboratory and field may be able to pinpoint the primary sites of ozone surface reactions and thus improve understanding of ozone deposition pathways (Subke et al, ; Toet et al, ). Subke et al () present a method for adding 18 O into an electric discharge ozone generator and using a silica gel to separate 18 O ozone from 18 O O 2 . However, 18 O from the generated ozone leads to 18 O enriched water vapor as well as other gases (e.g., O 2 ) that do not necessarily remain on a surface, complicating estimates of deposited ozone (Toet et al, ).…”

A new stable isotope approach identifies the fate of ozone in plant–soil systems

“…Ozone was generated in a mixture of enriched oxygen (95% atom enrichment in 18 O) and helium by electrical discharge, and the effluent was flown over a cooled silica gel trap to absorb O 3 selectively before being circulated back into the O 3 generator. Following an O 3 ‐generation period of 10 min, the absorbed O 3 was released from the set‐up on a He carrier stream by careful warming of the silica gel trap (see Subke et al ., 2009 for a detailed description of the 18 O 3 generator). The high level of 18 O enrichment results in a δ 18 O value of over 450 000‰ for O 3 .…”

“…This method allowed the generation of O 3 : O 2 volume ratios of almost 50% (Subke et al ., 2009), a much higher value than generated using conventional O 3 generators, in which the majority of the labelled gas is introduced as O 2 , not O 3 , making identification of the origin of any label in the plant or soil uncertain. The concurrent release of 18 O 2 at 18 O 3 concentrations up to 100 nl l −1 O 3 in air in our system increased the δ 18 O value of the large atmospheric pool of O 2 by only 0.32‰.…”

Geração de ozônio isotopicamente marcado com átomo de oxigênio-18, (18O3), formando oxigênio-18 molecular singlete, 18O2 (1Δg), e modificações na 2'- desoxiguanosina

“…Proporcionando um maior volume de aproximadamente 6 mL, a mesma foi envolta em papel alumínio com a superfície reflexiva voltada para dentro da cubeta, assim obtemos um maior rendimento da emissão dos fótons. Esse sistema foi desenvolvido com a finalidade de gerar ozônio isotopicamente marcado a partir do 18 O 2 ( 3  g -), em um sistema fechado baseado em um sistema proposto por (Subke et. al., 2009).…”