Information processing in the cortex depends on the integration of bottom-up and top-down signals through recurrent microcircuits spanning layers. Although the canonical microcircuit provides a framework for this integration, how these interactions are implemented at synapse resolution remains unclear. Here, we use large-volume electron microscopy reconstructions of mouse primary visual cortex to map the intralaminar and interlaminar connectivity of intratelencephalic (IT) neurons in layers 2/3 and 5. We find that layer 2/3 IT neurons formed a depth-dependent gradient of recurrent connectivity, with superficial (L2) and deeper (L3) neurons potentially forming two channels associated with top-down and bottom-up processing, respectively. These channels are preserved across layers via cell-type-specific pathways involving distinct L5 IT types, rather than collapsing into a single integrative pool. Moreover, each channel is regulated by a largely separate cohort of inhibitory interneurons, stabilizing recurrent excitation while limiting crosstalk. Together, these results reveal parallel, cell-type-specific processing streams embedded within the canonical circuit.

Biomass burning is a major global source of atmospheric ammonia (NH3), significantly influencing air quality, aerosol formation, and nitrogen cycling. Nitrogen isotope composition (delta 15N) of NH3 has been proposed as a powerful tool for source apportionment, yet values for several emission sources remain poorly constrained. This study presents the first field-based delta 15N of total reduced inorganic nitrogen (NH x = NH3 + pNH4) measurements from fresh and aged biomass-burning plumes, collected during the Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) campaign in the western United States during summer 2019. The NH x concentrations were strongly correlated with carbon monoxide (CO) and fine particulate matter (PM2.5), reflecting elevated emissions during smoldering conditions. The delta 15N(NH x ) ranged from -9.1 parts per thousand to 2.1 parts per thousand (x +/- sigma: -3.3 +/- 2.9 parts per thousand; n = 16). Using a Keeling plot approach, we derived a representative biomass-burning delta 15N(NH3) value of -4.7 +/- 1.3 parts per thousand, that integrates measurements across the sampled biomass burning events, while also accounting for background NH x influences. This field-based isotopic signature is clearly distinct from agricultural and vehicular sources and substantially lower than the +12 parts per thousand value commonly assumed for biomass burning in delta 15N-based source apportionment studies. Overall, this work improves our ability to track NH3 emissions using novel isotopic constraints. Field-based nitrogen isotope measurements of ammonia emissions from biomass burning reveal distinct isotopic signatures, enabling improved source apportionment and nitrogen cycling insights.

In 1949, Donald Hebb proposed that neuronal assemblies with temporally specific patterns of activity form the building blocks of perception, cognition, and behavior. Finding the structural underpinning of such assemblies has been technically challenging due to a lack of large-scale structure-activity maps. Here, we combine in vivo optical physiology with postmortem electron microscopy (EM) in the same tissue volume. Using higher-order correlations in fluorescence traces, we extract neuronal assemblies. Physiologically, we show that these assemblies respond more reliably to repeated natural movies than size-matched control ensembles and decode such stimuli more accurately. Structurally, we find that over a quarter of the pyramidal neurons do not participate in any assembly and are significantly less integrated into the connectome than those that do. We do not observe a marked increase in the strength of monosynaptic excitatory connections between neurons sharing assembly assignment, but instead find significantly stronger indirect inhibitory connections targeting cells in other assemblies. These results show that assemblies can serve as functional units of perception and suggest they may be structurally delineated by mutual inhibition.

Despite significant progress in characterizing neocortical cell types, a complete understanding of the synaptic connections of individual excitatory cells remains elusive. This study investigates the connectivity of mouse visual cortex thick tufted layer 5 pyramidal cells, also known as extratelencephalic neurons (L5-ETns), using a 1 mm3 publicly available electron microscopy dataset. The analysis reveals that, in their immediate vicinity, L5-ETns primarily establish connections with a group of inhibitory cell types, which, in turn, specifically target the L5-ETns back. The most common excitatory targets of L5-ETns are layer 5 intertelencephalic neurons (L5-ITns) and layer 6 (L6) pyramidal cells, whereas synapses with other L5-ETns are less common. When L5-ETns extend their axons to other cortical regions, they tend to connect more with excitatory cells. Our results highlight a circuit motif where a subclass of excitatory cells forms a subcircuit with specific inhibitory cell types. This is achieved using a publicly available, automated approach for synapse recognition and automated cell typing, offering a framework for exploring the connectivity of other neuron types.

Narragansett Bay, the largest estuary in New England, is a heavily urbanized watershed impacted by deposition and runoff. Nutrient budgets and local policy rely on deposition data from a 1990 study that did not include any direct observations of dry deposition of gaseous ammonia (NH 3(g) ) and particulate ammonium (p‐NH 4 + ) due to uncertainties in their flux direction and measurement difficulty. Recent work has shown that wet deposition of ammonium (NH 4 + ) to the Bay has increased by a factor of 6 over the past three decades, leading to a 2.5‐fold increase in wet nitrogen (N) deposition. This documented increase in wet deposition of NH 4 + is concurrent with managed nutrient reductions in urbanized estuaries but has potentially increased the impacts of atmospheric N deposition, including the dry deposition of NH 3(g) and p‐NH 4 + . However, the lack of NH 3(g) and p‐NH 4 + measurements hinders our interpretation of this important N source. For the first time over Narragansett Bay, and to our knowledge over open water, dry (particulate and gas phase) total ammonia (NH x = NH 3(g) + p‐NH 4 + ) and the bidirectional NH 3(g) flux were quantified using a relaxed eddy accumulation sampling technique. We find that dry deposition of NH x comprises 9.6% of total (wet + dry) N deposition. During the fall season, the dominant flux direction for NH 3(g) is upward, which also has implications for urban air quality. We estimate that NH 3(g) emitted from the Bay to the atmosphere makes up to 10% of the local NH 3(g) emission budget for fall.

Nitrogen oxides, collectively referred to as NOx (NO + NO2), are an important component of atmospheric chemistry involved in the production and destruction of various oxidants that contribute to the oxidative capacity of the troposphere. The primary sink for NOx is atmospheric nitrate, which has an influence on climate and the biogeochemical cycling of reactive nitrogen. NOx sources and NOx-to-NO3- formation pathways remain poorly constrained in the remote marine boundary layer of the Southern Ocean, particularly outside of the more frequently sampled summer months. This study presents seasonally resolved measurements of the isotopic composition (δ15N, δ18O, and Δ17O) of atmospheric nitrate in coarse-mode (> 1 µm) aerosols, collected between South Africa and the sea ice edge in summer, winter, and spring. Similar latitudinal trends in δ15N–NO3- were observed in summer and spring, suggesting similar NOx sources. Based on δ15N–NO3-, the main NOx sources were likely a combination of lightning, biomass burning, and/or soil emissions at the low latitudes, as well as oceanic alkyl nitrates and snowpack emissions from continental Antarctica or the sea ice at the mid-latitudes and high latitudes, respectively. Snowpack emissions associated with photolysis were derived from both the Antarctic snowpack and snow on sea ice. A combination of natural NOx sources, likely transported from the lower-latitude Atlantic, contribute to the background-level NO3- observed in winter, with the potential for a stratospheric NO3- source evidenced by one sample of Antarctic origin. Greater values of δ18O–NO3- in spring and winter compared to summer suggest an increased influence of oxidation pathways that incorporate oxygen atoms from O3 into the end product NO3- (i.e. N2O5, DMS, and halogen oxides (XO)). Significant linear relationships between δ18O and Δ17O suggest isotopic mixing between H2O(v) and O3 in winter and isotopic mixing between H2O(v) and O3/XO in spring. The onset of sunlight in spring, coupled with large sea ice extent, can activate chlorine chemistry with the potential to increase peroxy radical concentrations, contributing to oxidant chemistry in the marine boundary layer. As a result, isotopic mixing with an additional third end-member (atmospheric O2) occurs in spring.

Determining the magnitude and origins of nitrogen (N) deposition in the open ocean is vital for understanding how anthropogenic activities influence oceanic biogeochemical cycles. Excess N in the North Pacific Ocean (NPO) is suggested to reflect recent anthropogenic atmospheric deposition from the Asian continent, changes in nutrient dynamics due to marine N-fixation, and/or lateral transport of nutrients. We investigate the impact of anthropogenic and marine sources on reactive N deposition in the NPO, with a focus on ammonium (NH4+), an important bioavailable nutrient, using aerosol samples (n = 108) collected off the coast of China (Changdao Island). This study site is used as a proxy for continental emissions that can be exported and subsequently deposited to the ocean. The NH4+ concentration of aerosol samples varied seasonally (p < 0.05), with a higher average value in winter (2.8 +/- 1.1 mu g/m(3)) and spring (1.9 +/- 0.8 mu g/m(3)) compared to autumn (0.7 +/- 0.6 mu g/m(3)) and summer (1.4 +/- 0.4 mu g/m(3)). The isotopic composition of aerosol NH4+ varied seasonally, with higher averages in spring (13.3 +/- 7.9 parts per thousand) and summer (15.6 +/- 6.2 parts per thousand) compared to autumn (3.2 +/- 2.5 parts per thousand) and winter (3.8 +/- 11.4 parts per thousand). These seasonal patterns in the isotopic composition of NH4+ are investigated based on correlations of aerosol chemical species, seasonal shifts in transport patterns, partitioning of ammonia/ammonium between the gas and particle phase, and continental versus marine sources of ammonia. We find that anthropogenic activities, mainly agricultural practices (e.g., volatilization, fertilizer, animal husbandry), are the primary sources of NH4+ deposited to the NPO.

Atmospheric nitrate originates from the oxidation of nitrogen oxides (NOx=NO+NO2) and impacts both tropospheric chemistry and climate. NOx sources, cycling and NOx to nitrate formation pathways are poorly constrained in remote marine regions, especially the Southern Ocean, where pristine conditions serve as a useful proxy for the pre-industrial atmosphere. Here, we measured the isotopic composition (δ15N and δ18O) of atmospheric nitrate in coarse-mode (>1 µm) aerosols collected in the summertime marine boundary layer of the Atlantic Southern Ocean from 34.5 to 70∘ S and across the northern edge of the Weddell Sea. The δ15N–NO3- decreased with latitude from −2.7 ‰ to −42.9 ‰. The decline in δ15N with latitude is attributed to changes in the dominant NOx sources: lightning at the low latitudes, oceanic alkyl nitrates at the mid-latitudes and photolysis of nitrate in snow at the high latitudes. There is no evidence of any influence from anthropogenic NOx sources or equilibrium isotope fractionation. Using air mass back trajectories and an isotope mixing model, we calculate that oceanic alkyl nitrate emissions have a δ15N signature of -21.8±7.6 ‰. Given that measurements of alkyl nitrate contributions to remote nitrogen budgets are scarce, this may be a useful tracer for detecting their contribution in other oceanic regions. The δ18O–NO3- was always less than 70 ‰, indicating that daytime processes involving OH are the dominant NOx oxidation pathway during summer. Unusually low δ18O–NO3- values (less than 31 ‰) were observed at the western edge of the Weddell Sea. The air mass history of these samples indicates extensive interaction with sea-ice-covered ocean, which is known to enhance peroxy radical production. The observed low δ18O–NO3- is therefore attributed to increased exchange of NO with peroxy radicals, which have a low δ18O, relative to ozone, which has a high δ18O. This study reveals that the mid- and high-latitude surface ocean may serve as a more important NOx source than previously thought and that the ice-covered surface ocean impacts the reactive nitrogen budget as well as the oxidative capacity of the marine boundary layer.

Concentrations and the stable isotopic composition of bulk aerosol nitrate (NO 3 − ) were quantified from two GEOTRACES cruises: (a) Alaska–Tahiti (GP15; n = 22) and (b) Peru–Tahiti (GP16; n = 17) to explore the hypothesis that a marine source influences aerosol NO 3 − in the equatorial Pacific. The δ 15 N‐NO 3 − ranged from −14.5‰–0.5‰, with lowest values furthest from the coast, primarily reflecting a shift in sources. The δ 18 O‐ and Δ 17 O‐NO 3 − were both relatively high (65.2‰–85.4‰ and 21.4‰–30.7‰, respectively) and decreased away from continental regions, reflecting a shift in the oxidants that influence the formation of NO 3 − . Transport modeling and co‐occurrence of low δ 15 N, δ 18 O and Δ 17 O provided evidence for an important influence of marine‐derived alkyl nitrates (RONO 2 ) on aerosol NO 3 − formation. Based on the Δ 17 O, we quantified that the contribution of RONO 2 to aerosol NO 3 − can be as high as 47.5% (range 7.5%–47.5%). We also estimate an average δ 15 N‐RONO 2 of −27.8‰ ± 23.3‰.

Ångström exponents (α) allow reconstruction of aerosol optical spectra over a broad range of wavelengths from measurements at two or more wavelengths. Hyperspectral measurements of atmospheric aerosols provide opportunities to probe measured spectra for information inaccessible from only a few wavelengths. Four sets of hyperspectral in situ aerosol optical coefficients (aerosol‐phase total extinction, σext, and absorption, σabs; liquid‐phase soluble absorption from methanol, σMeOH‐abs, and water, σDI‐abs, extracts) were measured from biomass burning aerosols (BBAs). Hyperspectral single scattering albedo (ω), calculated from σext and σabs, provide spectral resolution over a wide spectral range rare for this optical parameter. Observed spectral shifts between σabs and σMeOH‐abs/σDI‐abs argue in favor of measuring σabs rather than reconstructing it from liquid extracts. Logarithmically transformed spectra exhibited curvature better fit by second‐order polynomials than linear α. Mapping second order fit coefficients (a1, a2) revealed samples from a given fire tended to cluster together, that is, aerosol spectra from a given fire were similar to each other and somewhat distinct from others. Separation in (a1, a2) space for spectra with the same α suggest additional information in second‐order parameterization absent from the linear fit. Spectral features found in the fit residuals indicate more information in the measured spectra than captured by the fits. Above‐detection σMeOH‐abs at 0.7 μm suggests assuming all absorption at long visible wavelengths is BC to partition absorption between BC and brown carbon (BrC) overestimates BC and underestimates BrC across the spectral range. Hyperspectral measurements may eventually discriminate BBA among fires in different ecosystems under variable conditions.

Table S1: The starting and ending date, latitude (°S), and longitude(°E) are presented for each aerosol filter deployment.The wind speed (WS; m s⁻¹), atmospheric temperature (Atm T; °C), relative humidity (RH; %), and the number of daylight hours (hrs) were calculated as an average (Avg) over the duration of each filter deployment.For WS, Atm T and RH the standard deviations (SD) are also shown.Filter deployments are separated into early Summer (ES), Weddell Sea (WS) and late Summer (LS) depending on the location and time of sampling. Cruise

National monitoring networks have reported an increase in ammonium (NH4+) deposition, such that NH4+ now dominates inorganic nitrogen deposition across most of the United States. Atmospheric deposition of fixed nitrogen has significant environmental consequences, including acidification and eutrophication. Thus, understanding source contributions is critical for formulating policies to mitigate the effects of excess nitrogen in sensitive ecosystems. Here, we investigated sources of wet-deposited NH4+ (w-NH4+) in Providence, RI, U.S.A., a mid-sized coastal city at the head of Narragansett Bay. We utilized concentration measurements, nitrogen stable isotopes (815N), and air mass back trajectory analysis for precipitation events and intra-event samples collected between January-November 2018. There was a general lack of seasonality in 815N(w-NH4+). Air mass origin had a strong influence on [w-NH4+], but [w-NH4+] was not related to 815N(w-NH4+), suggesting the potential dominance of a single NH3 emission source type. An average 815N(w-NH4+) of -3.7 +/- 3.5 parts per thousand (n = 42) was measured for daily-based precipitation. This value is consistent with previous measurements in the U.S. over the past 40 years, indicating a similar source of NH3 across the U.S. likely derived from agricultural activities. Intra-event analysis from precipitation events collected throughout the year found frequent mid- and end-event [w-NH4+] peaks that were suggested to be related to in-cloud [w-NH4+] changes rather than changes in below-cloud scavenging due to a consistent corresponding shift in precipitation intensity. Large intra-event 815N(w-NH4+) variations as high as 15.9 parts per thousand were also observed. However, the cumulative mass-weighted 815N(w-NH4+) of the intra-event series tended to converge to a similar value (-4.8 +/- 1.3 parts per thousand; n = 6). Overall, our results indicate that long-range transport via in-cloud scavenging tended to play a stronger role in shaping w-NH4+ patterns compared to local emissions at our study site.

To understand the brain we must relate neurons’ functional responses to the circuit architecture that shapes them. Here, we present a large functional connectomics dataset with dense calcium imaging of a millimeter scale volume. We recorded activity from approximately 75,000 neurons in primary visual cortex (VISp) and three higher visual areas (VISrl, VISal and VISlm) in an awake mouse viewing natural movies and synthetic stimuli. The functional data were co-registered with a volumetric electron microscopy (EM) reconstruction containing more than 200,000 cells and 0.5 billion synapses. Subsequent proofreading of a subset of neurons in this volume yielded reconstructions that include complete dendritic trees as well the local and inter-areal axonal projections that map up to thousands of cell-to-cell connections per neuron. Here, we release this dataset as an open-access resource to the scientific community including a set of tools that facilitate data retrieval and downstream analysis. In accompanying papers we describe our findings using the dataset to provide a comprehensive structural characterization of cortical cell types 1–3 and the most detailed synaptic level connectivity diagram of a cortical column to date 2 , uncovering unique cell-type specific inhibitory motifs that can be linked to gene expression data 4 . Functionally, we identify new computational principles of how information is integrated across visual space 5 , characterize novel types of neuronal invariances 6 and bring structure and function together to decipher a general principle that wires excitatory neurons within and across areas 7, 8 .

Abstract. Nitrous acid (HONO) is an important precursor to hydroxyl radical(OH) that determines atmospheric oxidative capacity and thus impacts climateand air quality. Wildfire is not only a major direct source of HONO, it alsoresults in highly polluted conditions that favor the heterogeneous formation ofHONO from nitrogen oxides (NOx= NO + NO2) and nitrate on bothground and particle surfaces. However, these processes remain poorlyconstrained. To quantitatively constrain the HONO budget under variousfire and/or smoke conditions, we combine a unique dataset of field concentrationsand isotopic ratios (15N / 14N and 18O / 16O) of NOxand HONO with an isotopic box model. Here we report the first isotopicevidence of secondary HONO production in near-ground wildfire plumes (over asample integration time of hours) and the subsequent quantification of therelative importance of each pathway to total HONO production. Mostimportantly, our results reveal that nitrate photolysis plays a minor role(<5 %) in HONO formation in daytime aged smoke, whileNO2-to-HONO heterogeneous conversion contributes 85 %–95 % to totalHONO production, followed by OH + NO (5 %–15 %). At nighttime, heterogeneousreduction of NO2 catalyzed by redox active species (e.g., iron oxideand/or quinone) is essential (≥ 75 %) for HONO production in additionto surface NO2 hydrolysis. Additionally, the 18O / 16O of HONOis used for the first time to constrain the NO-to-NO2 oxidationbranching ratio between ozone and peroxy radicals. Our approach provides anew and critical way to mechanistically constrain atmospheric chemistry and/or airquality models on a diurnal timescale.

Anthropogenic changes to nitrogen cycling have dramatically altered ecosystems across the globe, particularly in coastal estuaries where nitrogen limits primary production. The impacts of nitrogen pollution are especially evident in Narragansett Bay, RI, where eutrophication in the urbanized Providence River Estuary persists despite a > 50% decrease in wastewater nitrogen loading over the past two decades. Precipitation-derived nitrogen tends to be understudied and may be underestimated in contemporary budgets. Here, the magnitude and ecological impacts of precipitation-derived nitrogen in the Providence River Estuary were assessed by the following: relationships between precipitation, river discharge, and chlorophyll abundance; inorganic nitrogen concentration and isotopic composition of precipitation, surface runoff, and stormwater; and changes in stable nitrogen (δ15N) and carbon (δ13C) isotopes of macroalgae (Ulva spp.) after large precipitation events. Precipitation and chlorophyll concentration measured 5 days after the rain event exhibited a linear relationship. Furthermore, Ulva spp. experienced decreases in δ15N of 0.3–1‰ and increases in δ13C of 1–3‰ that peaked 5 days after precipitation events. These results are indicative of a direct impact of precipitation-derived nitrogen on nutrient dynamics, including summer phytoplankton blooms. However, the inorganic nitrogen concentrations of stormwater were approximately 240% higher than surface runoff, and the isotopic composition of stormwater discharge indicates that most precipitation-derived nitrate stems from terrestrial nitrogen and sewage rather than direct atmospheric deposition. The magnitude and spatial heterogeneity of precipitation-derived nitrogen remains uncertain, and further work is needed to understand how this nitrogen source will change in a wetter climate of the future.

Abstract. Nitrous acid (HONO) is an important precursor to hydroxyl radical (OH) that determines atmospheric oxidative capacity and thus impacts climate and air quality. Wildfire is not only a major direct source of HONO, but it also results in highly polluted conditions that favour heterogeneous formation of HONO from nitrogen oxides (NOx = NO + NO2) and nitrate on both ground and particle surfaces. However, these processes remain poorly constrained. To quantitatively constrain the HONO budget under various fire/smoke conditions, we combine a unique dataset of field concentrations and isotopic ratios (15N/14N and 18O/16O) of NOx and HONO, with an isotopic box model. Here we report the first isotopic evidence of secondary HONO production in near-ground wildfire plumes, and the subsequent quantification of relative importance of each pathway to total HONO production. Most importantly, our results reveal that nitrate photolysis plays a minor role (< 5 %) in HONO formation in daytime aged smoke, while photo-enhanced NO2-to-HONO heterogeneous conversion contributes 85–95 % to total HONO production, followed by OH+NO (5–15 %). In nighttime, heterogeneous reduction of NO2 catalysed by redox active species (e.g., iron oxide and/or quinone) is essential (≥ 75 %) for HONO production in addition to surface NO2 hydrolysis. Additionally, the 18O/16O of HONO is used for the first time to constrain the NO-to-NO2 oxidation branching ratio between ozone and peroxy radicals. Our approach provides a new and critical way to mechanistically constrain atmospheric chemistry/air quality models.

This study aims to better our collective understanding of the oxidative capacity and atmospheric chemistry over the equatorial Pacific. Bulk and size-segregated filter samples were collected during the GEOTRACES Eastern Tropical Pacific transect (4.1 degrees S, 81.9 degrees W to 10.5 degrees S, 152.0 degrees W; October-December 2013) and measured for aerosol concentration and complete isotopic composition of nitrate (delta N-15, delta O-18, Delta O-17 where Delta O-17 = delta O-17 - 0.52 x delta O-18). Combined size-segregated filters produced data similar to that found in bulk filter samples, and notably neither delta N-15 nor delta O-18 showed any trends based on aerosol size. Similar to other studies, NO3- is concentrated (>80%) in the coarse size fractions (>1.5 mu m). Bulk aerosol concentrations ranged from 6.6 to 89.8 nmol/m(3). The bulk delta N-15-, delta O-18-, and Delta O-17-nitrate ranged from -13.1 to -3.2%, 68.5 to 79.3%, and 23.5 to 28.4%, respectively. Higher delta N-15 values near the coast are best explained by the influence of continental sources; lower delta N-15 values far from the coast may be associated with chemical fractionation during long-range transport or an oceanic source. Both Delta O-17 and delta O-18 are interpreted using kinetic analysis and gas concentrations from a global atmospheric chemical transport model (GEOS-Chem), which showed that nitrate production in this environment is dominated by OH oxidation (60%) and RONO2 hydrolysis (15%). To best match the delta O-18 and Delta O-17 observations in this study, the terminal oxygen isotopic values for ozone must be higher than those suggested by available observations and/or halogen-mediated chemistry must be more important than the models currently suggest.