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The oxygen isotope anomaly (Δ17O = δ17O - 0.52 × δ18O > 0) has proven to be a robust tool for probing photochemical cycling and atmospheric formation pathways of oxidized reactive nitrogen (NOy). Several studies have developed modeling techniques to implicitly model Δ17O of NOy molecules based on numerous assumptions that may not always be valid. Thus, these models may be oversimplified and limit our ability to compare model Δ17O values of NOy with observations. In this work, we introduce a novel method for explicitly tracking Δ17O transfer and propagation into NOy and odd oxygen (Ox), integrated into the Regional Atmospheric Chemistry Mechanism, version 2 (RACM2). Termed ICOIN-RACM2 (InCorporating Oxygen Isotopes of NOy in RACM2), this new model includes the addition of 55 new species and 729 replicate reactions to represent the propagation of Δ17O derived from O3 into NOy and Ox. Employing this mechanism within a box model, we simulate Δ17O for various NOy and Ox molecules for chamber experiments with varying initial nitrogen oxides (NOx = NO + NO2) and α -pinene conditions, revealing response shifts in Δ17O linked to distinct oxidant conditions. Furthermore, diel cycles are simulated under two summertime scenarios, representative of an urban and rural site, revealing pronounced Δ17O diurnal patterns for several NOy components and substantial Δ17O differences associated with pollution levels (urban vs. rural). Overall, the proposed mechanism offers the potential to assess NOy oxidation chemistry in chamber studies and air quality campaigns through Δ17O model comparisons against observations. The integration of this mechanism into a 3-D atmospheric chemistry transport model is expected to notably enhance our capacity to model and anticipate Δ17O across landscapes, consequently refining model representations of atmospheric chemistry and tropospheric oxidation capacity. [ABSTRACT FROM AUTHOR]

The oxygen-stable isotope mass-independent composition (Δ(17O) = d(17O) - 0.52×d(18O)) has proven to be a robust tool for probing photochemical cycling and atmospheric formation pathways of oxidized reactive nitrogen (NOy). Several studies have developed modeling techniques to implicitly model Δ(17O) based on numerous assumptions that may not always be valid. Thus, these models may be oversimplified and limit our ability to compare model Δ(17O) values of NOy with observations. In this work, we introduce a 5 novel method for explicit tracking of O3 transfer and propagation into NOy and odd oxygen (Ox), integrated into the Regional Atmospheric Chemistry Mechanism, version 2 (RACM2). Termed ICOIN-RACM2 (InCorporating Oxygen Isotopes of NOy in RACM2), this new model includes the addition of 55 new species and 727 replicate reactions to represent the oxygen isotopologues of NOy and Ox. Employing this mechanism within a box model, we simulate Δ(17O) for various NOy and Ox molecules for chamber experiments with varying initial nitrogen oxides (NOx = NO + NO2) and a-pinene conditions, revealing response shifts in Δ(17O) linked to distinct oxidant conditions. Furthermore, diel cycles are simulated under two summertime scenarios, representative of an urban and rural site, revealing pronounced Δ(17O) diurnal patterns for several NOy components and substantial Δ(17O) differences associated with pollution levels (urban vs. rural). Overall, the proposed mechanism offers the potential to assess NOy oxidation chemistry in chamber studies and air quality campaigns through Δ(17O) model comparisons against observations. The integration of this mechanism into a 3-D atmospheric chemistry transport model is expected to notably enhance our capacity to model and anticipate Δ(17O) across landscapes, consequently refining model representations of atmospheric chemistry and tropospheric oxidation capacity. [ABSTRACT FROM AUTHOR]

Hostile workplaces undermine efforts to make the ecological sciences more inclusive and welcoming. Survey responses by members of the Ecological Society of America (ESA) and subscribers to the ECOLOG‐L listserv provide a snapshot of a range of workplace experiences in ecology. The bottom line: identity matters. Although the majority of respondents reported positive workplace experiences (for instance, receiving mentorship), historically excluded groups – including scientists of color; women; lesbian, gay, bisexual, queer, pansexual, asexual, and other non‐heterosexual (LGBQPA+) individuals; and those who identify as disabled – on average were 1.5 times more likely to encounter negative workplace experiences (for instance, sexual harassment, interpersonal mistreatment, and insulting behaviors) as compared to their counterparts in the historical majority. Moreover, historically excluded groups were more likely to report opting out of professional opportunities, more likely to have considered leaving their institution, and twice as likely to consider a career change. We provide recommendations for professional associations, academic institutions, and other employers of ecologists to address interpersonal mistreatment through culture and policy changes. [ABSTRACT FROM AUTHOR]

Snow nitrate is vulnerable to photolytic loss that causes isotopic alteration, and thus its isotopes can potentially track the extent of snow nitrate photolysis and its impacts in environments where loss is significant. Large increases in δ15N‐NO3− below the snow surface have been attributed to photolysis and this behavior is generally consistent amongst theoretical as well as lab and field studies. Oxygen isotope ratios are thought to be influenced by photolysis as well as secondary condensed‐phase chemistry, but the competing effects have yet to be reconciled. Here we use a model that simulates nitrate burial, photolytic fractionation, and re‐oxidation in snow to quantitatively assess these processes with the aim of developing a consistent framework for interpreting the photolytic effects of the complete nitrate isotopic composition (δ15N, δ18O, and Δ17O). This study reveals that isotopic effects of nitrate photolysis and aqueous‐phase re‐oxidation chemistry are important sources of uncertainties in modeling δ18O‐NO3−. Plain Language Summary: Nitrate is a major ion species in Antarctic snow, and often measured in snow and ice cores. Accurate interpretation of ice core nitrate records, however, remains challenging mostly due to uncertainties associated with nitrate photolysis, especially in low snow accumulation sites. Consequently, both nitrogen and oxygen stable isotopes of nitrate are altered via photolysis, but can serve as a useful diagnostic of these processes. Compared to nitrogen isotopes, which have been characterized in detail by both model simulations and observations, oxygen isotopic effects of nitrate photolysis are far from understood. Here, we present a model incorporating processes of snow burial, photolytic loss, and re‐oxidation to quantitatively assess the changes in the full isotopic parameters (δ15N, δ18O, and Δ17O) over the course of snow nitrate burial in central Antarctica. Model simulations show that about 25%–30% of the photoproducts will be re‐oxidized to form secondary nitrate within the snow. Major uncertainty of our model predicted δ18O is largely associated with limited knowledge on oxygen isotopic fractionation during nitrate photolysis and reformation in snow grains. This model will help diagnose the processes of nitrate burial, photolytic fractionation, and re‐oxidation in snow and allow for better interpretation of these tracers in snow and ice. Key Points: We developed a model to quantify changes in NO3− isotopes based on burial, photolytic fractionation, and re‐oxidation in East Antarctic snowThe observed snow Δ17O profile is constrained by photolysis‐driven aqueous‐phase formation of secondary NO3− on the order of ∼25–30%Isotopic effects of NO3− photolysis and aqueous‐phase re‐oxidation chemistry are important sources of uncertainties in modeling δ18O [ABSTRACT FROM AUTHOR]

Despite significant precursor emission reductions in the US over recent decades, atmospheric nitrate deposition remains an important terrestrial stressor. Here, we utilized statistical air mass back trajectory analysis and nitrogen stable isotope deltas (δ (15 N)) to investigate atmospheric nitrate spatiotemporal trends in the northeastern US from samples collected at three US EPA Clean Air Status and Trends Network (CASTNET) sites from December 2016–2018. For the considered sites, similar seasonal patterns in nitric acid (HNO 3) and particulate nitrate (pNO 3) concentrations were observed with spatial differences attributed to nitrogen oxide (NO x) emission densities in source contributing regions that were typically ≤ 1000 km. Significant spatiotemporal δ (15 N) variabilities in HNO 3 and pNO 3 were observed with higher values during winter relative to summer, like previous reports from CASTNET samples collected in the early 2000s for our study region. In the early 2000s, δ (15 N) of atmospheric nitrate in the northeast US had been suggested to be driven by NO x emissions; however, we did not find significant spatiotemporal changes in the modeled NO x emissions by sector and fuel type or δ (15 N, NO x) for the source regions of the CASTNET sites. Instead, the seasonal and spatial differences in the observed δ (15 N) of atmospheric nitrate were driven by nitrate formation pathways (i.e., homogeneous reactions of NO 2 oxidation via hydroxyl radical or heterogeneous reactions of dinitrogen pentoxide on wetted aerosol surfaces) and their associated δ (15 N) fractionation. Under the field conditions of low NO x relative to O 3 concentrations and when δ (15 N, NO x) emission sources do not have significant variability, we demonstrate that δ (15 N) of atmospheric nitrate can be a robust tracer for diagnosing nitrate formation. [ABSTRACT FROM AUTHOR]