Comprehensive isotopic composition of atmospheric nitrate in the Atlantic Ocean boundary layer from 65°S to 79°N

Abstract

International audienceThe comprehensive isotopic composition of atmospheric nitrate (i.e., the simultaneous measurement of all its stable isotope ratios: 15N/14N, 17O/16O and 18O/16O) has been determined for aerosol samples collected in the marine boundary layer (MBL) over the Atlantic Ocean from 65°S (Weddell Sea) to 79°N (Svalbard), along a ship-borne latitudinal transect. In nonpolar areas, the δ 15N of nitrate mostly deriving from anthropogenically emitted NO x is found to be significantly different (from 0 to 6‰) from nitrate sampled in locations influenced by natural NO x sources (−4 ± 2)‰. The effects on δ 15N(NO3 −) of different NO x sources and nitrate removal processes associated with its atmospheric transport are discussed. Measurements of the oxygen isotope anomaly (Δ17O = δ 17O − 0.52 × δ 18O) of nitrate suggest that nocturnal processes involving the nitrate radical play a major role in terms of NO x sinks. Different Δ17O between aerosol size fractions indicate different proportions between nitrate formation pathways as a function of the size and composition of the particles. Extremely low δ 15N values (down to −40‰) are found in air masses exposed to snow-covered areas, showing that snowpack emissions of NO x from upwind regions can have a significant impact on the local surface budget of reactive nitrogen, in conjunction with interactions with active halogen chemistry. The implications of the results are discussed in light of the potential use of the stable isotopic composition of nitrate to infer atmospherically relevant information from nitrate preserved in ice cores

Isotopic composition of atmospheric nitrate in a tropical marine boundary layer

“…Although the models appeared to calculate a more pronounced seasonality than the observations, it is probably insignificant considering the large uncertainty. On the other hand, the identical concentrations predicted by both models strongly support the premise that the prevailing marine conditions at the CVAO are also valid for the air masses transported to this site, in agreement with recent studies (23,27), making our observed seasonal trends weakly sensitive to transport and air mass origin. The best concentration match between observations and model predictions was actually found for a nitrate lifetime of ca.…”

“…This technique uses Pseudomonas aureofaciens bacteria to convert nitrate to N 2 O, which is then analyzed for its isotopic composition after thermal decomposition to O 2 and N 2 in a gold tube (46). The analytical procedure used for this study is strictly identical to the description given by Morin et al (27). Isotopic analysis was performed on a Thermo Finnigan MAT253 (continuous flow mode) equipped with a gas-bench interface.…”

Sources of reactive nitrogen in marine aerosol over the Northwest Pacific Ocean in spring

“…5c and 5d). All the observed values of δ 15 N-NO 3 − fall within the previously reported atmospheric δ 15 N-NO 3 − ranges in land (Elliott et al, 2009;Fang et al, 2011;Felix and Elliott, 2014) and in marine boundary layer (Altieri et al, 2013;Gobel et al, 2013;Hastings et al, 2003;Morin et al, 2009;Savarino et al, 2013). The mass-weighted mean aerosol δ 15 N-NO 3 − in 2014 (+1.6‰ in the ECSs, -1.1‰ for dust aerosol and -2.6‰ for background aerosol sampled in the NWPO) were similar to those in 2015 (+1.9‰ in the ECSs, -3.8‰…”

Tracing the fate of atmospheric nitrate deposited onto a forest ecosystem in Eastern Asia using Δ<sup>17</sup>O

“…During the NO 2 oxidation to NO − 3 (atm), an additional oxygen atom is incorporated from various source molecules depending on the NO 2 oxidation channel (Michalski et al, 2003;Morin et al, 2008), which results in a characteristic 17 (Michalski et al, 2003;Michalski et al, 2004), Europe (Kaiser et al, 2007), and the Atlantic Ocean (Morin et al, 2009) at mid-latitudes, the correspondence further supports that 17 O and δ 18 O values of NO − 3 (atm) are determined by NO x oxidation channels that shift depending on the season and oxidant species; for example, shifts in oxidation chemistry (an increased importance of N 2 O 5 hydrolysis in winter) that vary with sunlight, temperature, and oxidant levels but not with NO x sources. The average 17 O of NO − 3 (atm) is substantially higher than values resulting from the reaction between OH and NO 2 (+17‰; Morin et al, 2009). Therefore, the reaction between OH and NO 2 cannot be the only channel from NO 2 to NO − 3 (atm), including that deposited in eastern Asia.…”