On the interaction of isotopic exchange processes with photochemical reactions in atmospheric oxides of nitrogen

Abstract

Gas‐phase isotopic exchange between NO and NO2 enriches the heavier 15N isotope in the more oxidized form. In the atmosphere the concentration of both gases, NO and NO2, is controlled during daytime by the Leighton relationship through the oxidation of NO with O3 and the photolytic reaction of NO2 to NO. For atmospheric concentrations (e.g., NOx, ∼10 ppb), isotopic exchange and photolytic reaction are very fast with characteristic time constants of a few minutes compared to other removing reactions of atmospheric NOx via OH radicals (daytime reaction) and O3 (nighttime reaction) with time constants of some hours and more. We have found from 15N/14N measurements of atmospheric NO2 and NOx at Jülich that both processes, isotopic exchange and photolytic reaction, interact and have an influence on the 15N/14N isotopic ratio. This interaction, together with seasonal variations of the NOx/O3 ratio at daytime and either complete oxidation of NO to NO2 or isotopic exchange between NO and NO2 at nighttime, explains the seasonal variation of the 15N/14N ratio of atmospheric NO2, which agrees with results from a simple model.

Isotopic composition of atmospheric nitrate in a tropical marine boundary layer

“…The only relationship that was noticeable between δ 15 N and its precursor molecules was a positive correlation with the NO 2 /NO x ratio (Fig. 1C), in contrast to the negative trend observed for polluted air masses with high NO x concentrations (19). A possible explanation would be a kinetic isotope effect between NO and NO 2 , but in the absence of a better constrained system, δ 15 N will not be further discussed because its interpretation will be too speculative.…”

“…1 shows a seasonal (19,(24)(25)(26), preventing any general hemispheric scale interpretations. We observed no common trend between δ 15 N and NO x concentrations.…”

Triple oxygen isotopes indicate urbanization affects sources of nitrate in wet and dry atmospheric deposition

“…The stable nitrogen and oxygen isotope compositions of nitrate have been suggested as potential tracers of the sources and fate of NO x in the environment (Elliott et al, 2009;Kendall et al, 2007;Freyer et al, 1993). Nitrogen isotopes (δ 15 N) of nitrate can potentially reflect those of NO x , but mass-dependent isotopic fractionations during the oxidation of NO x to nitrate can also alter the original δ 15 N value of NO x , thus complicating efforts to use δ 15 N values of nitrate for source partitioning (e.g., Michalski, 2015, 2016; (Alexander et al, 2009;Morin et al, 2008;Michalski et al, 2003;Tsunogai et al, , 2016 since direct emissions of nitrate during combustion are relatively small (Fraser et al, 1998).…”

Changing nitrogen deposition with low δ15N−NH4 + and δ15N−NO3 − values at the Experimental Lakes Area, northwestern Ontario, Canada

“…5), ranging from +63‰ to +82‰ in 2010-2012. Both deposition and throughfall from 1996 also exhibit the same seasonal trend (highest values in winter, lowest in mid-summer), as did TLW (Spoelstra 2004), Huntington Forest in Adirondack Park, New York (Campbell et al 2006), and mid-Appalachia, Pennsylvania and West Virginia (Williard et al 2001 There are many factors that have been shown to influence the isotopic composition of NO 3 − including, but not limited to, temperature, UV radiation (Freyer et al 1993), NO X source, storm track (Parker et al 2009), were about −3‰ to −1‰ (Fig. 6); very similar to the small amounts of NO 3 − released from forested catchments (Spoelstra et al 2001;Mayer et al 2002), but slightly higher than atmospheric deposition.…”

“…Atmospheric processes involving N species have also been inferred from the observed changes in stable isotope composition of N deposition including temperature (Freyer et al 1993), NO X source, storm track (Buda and DeWalle 2009), duration of rain event (Buda and DeWalle 2009), temporal separation from previous rain events (Heaton 1987), halogen chemistry (Altieri et al 2013), and atmospheric chemical reactions of NO 3 − precursors (Freyer et al 1993;Michalski et al 2012).…”