Meredith G Hastings

Brown University · Institute at Brown for Environment and Society

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. T...

Soils contribute 15%–75% of total atmospheric nitrogen oxide (NOx) emissions in agricultural regions during the growing season. However, the impacts of cropland fertilizer management on spatially heterogeneous, temporally episodic NOx emission patterns are highly uncertain. We examine the effects of liquid slurry dairy manure application practices...

The oxygen-stable isotope mass-independent composition (Δ(17O) = δ(17O) – 0.52×δ(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 alway...

Oxygen stable isotopes (i.e., ¹⁶O, ¹⁷O, ¹⁸O) of nitrite (NO2⁻) are useful for investigating chemical processes and sources contributing to this important environmental contaminant and nutrient. However, it remains difficult to quantify the oxygen isotope compositions of NO2⁻ due to the lack of internationally recognized NO2⁻ reference materials wit...

Atmospheric nitrate and sulfate are major inorganic particulate matter components that impact human and ecosystem health and air quality. Over the last several decades, emissions of the precursor gases, nitrogen oxides (NOx = NO + NO2) and sulfur dioxide (SO2), have dramatically decreased in the US in response to federal regulations. However, the r...

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 (NH3(g)) and particulate ammonium (p‐NH4⁺) due to uncertainties in the...

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...

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 cyclin...

The northeastern US represents a mostly urban corridor impacted by high population and fossil fuel combustion emission density. This has led to historically degraded air quality and acid rain that has been a focus of regulatory-driven emissions reductions. Detailing the chemistry of atmospheric nitrate formation is critical for improving the model...

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(15N)) to investigate atmospheric nitrate spatiotemporal trends in the northeastern US from sa...

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...

Geosciences remain one of the least diverse fields. Efforts to diversify the discipline need to address the role of hostile and exclusionary work and learning environments. A workplace climate survey distributed to five professional organizations illustrates varied experiences of earth and space scientists over a 12‐month period (pre‐COVID). A majo...

Narragansett Bay, the largest estuary in the northeastern U.S., 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 (NH3) and particulate ammonium (NH4+) due to uncertainties i...

The family of atmospheric oxides of nitrogen, NOy (e.g., nitrogen oxides (NOx) + nitric acid (HNO3) + nitrous acid (HONO) + peroxyacetyl nitrate (PAN) + particulate nitrate (pNO3-) + other), have an influential role in atmospheric chemistry, climate, and the environment. The nitrogen (δ15N) and oxygen (δ18O and Δ17O) stable isotopes of NOy are nove...

The NOAA/NASA Fire Influence on Regional to Global Environments and Air Quality (FIREX‐AQ) experiment was a multi‐agency, inter‐disciplinary research effort to: (a) obtain detailed measurements of trace gas and aerosol emissions from wildfires and prescribed fires using aircraft, satellites and ground‐based instruments, (b) make extensive suborbita...

Plain Language Summary Atmospheric nitrate can deposit into the oceans, potentially impacting the nitrogen cycle and primary productivity of the surface oceans. Thus, investigating nitrate sources and production pathways in the marine atmospheric boundary layer (MABL) is of great significance to ocean and atmosphere research. Here, we collected atm...

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 cyclin...

The northeastern US represents a mostly urban corridor impacted by high population density, high emissions density and degraded air quality and acid rain that has been a focus of regulatory-driven emissions reductions. Detailing the chemistry of atmospheric nitrate formation is critical for improving model representation of atmospheric chemistry an...

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(15N)) to investigate atmospheric nitrate spatiotemporal trends in the northeastern US from sam...

Atmospheric ammonia (NH3) is a critical component of our atmosphere that contributes to air quality degradation and reactive nitrogen deposition; however, our knowledge of NH3 in urban environments remains limited. Year-long ambient NH3 and related species were measured for concentrations and the nitrogen isotopic compositions (δ15N) of NH3 and par...

Concentrations and the stable isotopic composition of bulk aerosol nitrate (NO3⁻) 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 NO3⁻ in the equatorial Pacific. The δ¹⁵N‐NO3⁻ ranged from −14.5‰–0.5‰, with lowest values...

Plain Language Summary The atmospheric information contained in polar snow/ice nitrate (NO3⁻) is of great interest in paleoclimate research. The interpretation of NO3⁻ variability recorded in ice cores, however, remains challenging as atmospheric NO3⁻ can be lost from snow prior to ice formation. Here, we present 60‐year records of NO3⁻ and its iso...

Atmospheric ammonia (NH3) is a critical component of our atmosphere that contributes to air quality degradation and reactive nitrogen deposition; however, our knowledge of NH3 in urban environments remains limited. Year-long ambient NH3 and related species were measured for concentrations and the nitrogen isotopic compositions (δ15N) of NH3 and par...

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 atm...

Atmospheric samples and snowfall collected in coastal East Antarctica over two years are used to investigate the sources, production of atmospheric nitrate (NO3−) and its link with snowfall NO3− based upon the isotopic composition of NO3− (δ15N, δ18O, and Δ17O). Snowfall and the atmosphere show similar seasonal trends in concentrations and isotopic...

Geoscience remains one of the least diverse disciplines in Science, Technology, Engineering, Mathematics and Medicine (STEMM), with persistent underrepresentation of Black, Indigenous and other people of colour (BIPOC) and other minoritized groups, in the United States and other countries. The exclusion and limited recruitment, retention and succes...

Effects of human activities on atmospheric nitrate (NO3⁻) formation remain unclear, though the knowledge is critical for improving atmospheric chemistry models and acid deposition reduction strategies. A potentially useful way to explore this is to compare NO3⁻ oxidation processes in urban and rural atmospheres based upon the oxygen stable isotope...

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, it also results in highly polluted conditions that favor the heterogeneous formation of HONO from nitrogen oxides (NOx= NO + NO2) and nitr...

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° S, 81.9° W to 10.5° S, 152.0° W; October–December 2013) and measured for aerosol concentration and...

Sexual harassment in field settings brings unique challenges for prevention and response, as field research occurs outside “typical” workplaces, often in remote locations that create additional safety concerns and new team dynamics. We report on a project that has 1) trained field project participants to recognize, report, and confront sexual haras...

Coastal waters globally are increasingly impacted due to the anthropogenic loading of nitrogen (N) from the watershed. To assess dominant sources contributing to the eutrophication of the Little Narragansett Bay estuary in New England, we carried out an annual study of N loading from the Pawcatuck River. We conducted weekly monitoring of nutrients...

Atmospheric samples and surface seawater collected on a Chinese Antarctic Research Expedition (CHINARE) transect are used to investigate sources and production of nitrate (NO3−) in the atmosphere and its contribution to the surface NO3− pool in the ocean. Most atmospheric NO3− is concentrated on intermediate size particles, and much higher concentr...

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 i...

The budget of reactive nitrogen (Nr; oxidized and reduced inorganic and organic forms of nitrogen) has at least doubled since the preindustrial era due to human activities. There are significant detrimental effects of this excess Nr on many terrestrial and aquatic ecosystems, although less is known about the impact on the open ocean. Nr deposition...

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 ni...

To better understand snow chemistry in different environments across the Antarctic ice sheet, we investigated snow ions on a traverse from the coast to Dome A. Results show that the non-sea-salt (nss) fractions of K+, Mg2+, and Ca2+ are mainly from terrestrial particle mass and nssCl− is associated with HCl. Spatially, the non-sea-salt fractions of...

Stable isotopic composition of atmospheric nitrate (nitric acid (HNO3) + particulate nitrate (pNO3-)) provides a higher-order dimensional analysis of critical atmospheric components, enabling a process-level understanding of precursor emissions, oxidation chemistry, aerosol acidity, and depositional patterns. Current methods have not been evaluated...

Vehicle emissions have been identified as an important urban source of ammonia (NH3). However, there are large uncertainties regarding the contribution of vehicle emissions to urban NH3 budgets, as well as the role of NH3 in spatiotemporal fine particulate matter (PM2.5) formation and nitrogen (N) deposition patterns. The N stable isotopic composit...

There is a large variability in environmental conditions across the Antarctic ice sheet, and it is of significance to investigate the snow chemistry at as many locations as possible and over time, given that the ice sheet itself, and precipitation and deposition patterns and trends are changing. The China inland Antarctic traverse from coastal Zhon...

The geosciences are one of the least diverse disciplines in the United States, despite the field's relevance to livelihoods and local and global economies. Bias, discrimination, and harassment present serious hurdles to diversifying the field. These behaviors persist due to historical structures of exclusion, severe power imbalances, unique challen...

The stable isotopes of nitrogen in nitrate archived in polar ice have been interpreted as reflecting a shift in reactive nitrogen sources or changes in atmospheric chemical reactivity. Here, we present a novel concentration and isotopic record of nitrate (δ¹⁵N-NO3⁻) from a central Tibetan Plateau ice core over the last ~200 years. We find that nitr...

Abstract. Vehicle emissions have been identified as an important urban source of ammonia (NH₃). However, there are large uncertainties regarding the contribution of vehicle emissions to urban NH₃ budgets, as well as its role in spatiotemporal fine particulate matter (PM_2.5) formation and nitrogen (N) deposition patt...

New techniques have recently been developed and applied to capture reactive nitrogen species, including nitrogen oxides (NOx=NO+NO2), nitrous acid (HONO), nitric acid (HNO3), and particulate nitrate (pNO3-), for accurate measurement of their isotopic composition. Here, we report – for the first time – the isotopic composition of HONO from biomass b...

Abstract Nitrogen stable isotope composition (δ15N) of nitrate (NO3−) deposition can aid in source apportionment of its precursor emissions, nitrogen oxides (NOx), with implications in mitigation policy to address serious air pollution. However, potential δ15N fractionation during atmospheric NO3− formation may hinder accurate quantification of NOx...

Microbial processing of reactive nitrogen in stream sediments and connected aquifers can remove and transform nitrogen prior to its discharge into coastal waters, decreasing the likelihood of harmful algal blooms and low oxygen levels in estuaries. Canonical wisdom points to the decreased capacity of rivers to retain nitrogen as they flow toward th...

New techniques have recently been developed to capture reactive nitrogen species for accurate measurement of their isotopic composition. Reactive nitrogen species play important roles in atmospheric oxidation capacity (hydroxyl radical and ozone formation) and may have impacts on air quality and climate. Tracking reactive nitrogen species and their...

Nitrogen stable isotope analysis (δ15N) of particulate ammonium (NH4+) may provide additional constraints on this critical component of fine particulate matter; however, no previous collection method has been verified for its ability to accurately and precisely characterize δ15N(NH4+). This is a critical point due to the difficulty of quantitative...

Biochar has been promoted as a means to sequester C and improve soil quality. Biochar produced from agricultural waste streams and recycled as a soil amendment also provides a strategy for improved nutrient management in agricultural systems. The effects of biochar amendment on soil C and N cycling remain poorly constrained. This study aimed to exa...

Plain Language Summary In polar regions, there is great interest in using nitrate archived in snow/ice to reconstruct aspects of atmospheric composition and the influence of natural versus man‐made emissions. However, nitrate can be lost from the snowpack, such that the archived signals do not directly reflect atmospheric loading. Stable isotopes o...

Nitrogen (N) equilibrium isotope fractionation (15α) involving gaseous, dissolved, and solid phases of ammonia (NH3) and ammonium (NH4+) (e.g. NH3(g)- NH3(aq)-NH4+(aq)-NH4+(s)) represents a fundamental chemical process that has important implications for understanding the environmental dynamics involving NHx (NH3 + NH4+). However, recent literature...

Soil emissions represent ~25% of the global annual atmospheric budget of nitrogen oxides (NOx). The nitrogen isotopic composition of soil NOx emissions (δ¹⁵N-NOx) is potentially useful to track soil emission contributions to NOx budgets, yet its in situ variations with fertilizer management and meteorology are unknown. We quantify in situ δ¹⁵N-NOx...

In this study, we develop an alternative Fuel-based Oil and Gas inventory (FOG) of nitrogen oxides (NOx) from oil and gas production using publicly available fuel use records and emission factors reported in the literature. FOG is compared with the Environmental Protection Agency’s 2014 National Emissions Inventory (NEI) and with new top-down estim...

Antarctic ice core nitrate (NO3⁻) can provide a unique record of the atmospheric reactive nitrogen cycle. However, the factors influencing the deposition and preservation of NO3⁻ at the ice sheet surface must first be understood. Therefore, an intensive program of snow and atmospheric sampling was made on a traverse from the coast to the ice sheet...

Surface snow and atmospheric samples collected along a traverse from the coast to the ice sheet summit (Dome A) are used to investigate summertime atmospheric production of nitrate (NO3–) across East Antarctica. The strong relationship observed between δ¹⁵N and δ¹⁸O of nitrate in the surface snow suggests a large (lesser) extent of nitrate photolys...

Carbon accumulation in tropical secondary forests may be limited in part by nitrogen (N) availability, but changes in N during tropical forest succession have rarely been quantified. We explored N cycle dynamics across a chronosequence of secondary tropical forests in the Mata Atlântica of Bahia, Brazil in order to understand how quickly the N cycl...

The sources and chemistry of gaseous nitrous acid (HONO) in the environment are of great interest. HONO is a major source of atmospheric hydroxyl radical (OH), which greatly impacts air quality and climate. HONO is also a major indoor pollutant that threatens human health. However, the large uncertainty of HONO sources and chemistry hinders an accu...

The Antarctic ice core nitrate (NO3−) can provide a unique record of the atmospheric reactive nitrogen cycle. However, the factors influencing the deposition and preservation of NO3− at the ice sheet surface must first be understood. Therefore, an intensive program of snow sample collections was made on a traverse from the coast to the ice sheet su...

Pyrolysis is a viable option for the production of renewable energy and agricultural resources from diverted organic waste streams. This high temperature thermochemical process yields material with beneficial reuses, including bio-oil and biochar. Gaseous forms of carbon (C) and nitrogen (N) are also emitted during pyrolysis. The effluent mass emis...

Anthropogenic sources of reactive nitrogen have local and global impacts on air and water quality and detrimental effects on human and ecosystem health. This article uses the Nitrogen Footprint Tool (NFT) to determine the amount of nitrogen (N) released as a result of institutional consumption. The sectors accounted for include food (consumption an...

We review the mechanisms of deleterious nitrogen (N) deposition impacts on temperate forests, with a particular focus on trees and lichens. Elevated anthropogenic N deposition to forests has varied effects on individual organisms depending on characteristics both of the N inputs (form, timing, amount) and of the organisms (ecology, physiology) invo...

On-road vehicle nitrogen oxide (NOx) sources currently dominate U.S. anthropogenic emission budgets, yet vehicle NOx emissions have uncertain contributions to oxidized nitrogen (N) deposition patterns. Isotopic signatures serve as a potentially valuable observational tool to trace source contributions to NOx chemistry and N deposition, yet in-situ...

Nitrogen oxides (NOx = NO + NO2) are a family of atmospheric trace gases that have great impact on the environment. NOx concentrations directly influence the oxidizing capacity of the atmosphere through interactions with ozone and hydroxyl radicals. The main sink of NOx is the formation and deposition of nitric acid, a component of acid rain and a...

The nitrogen isotopic composition (δ¹⁵N) of NOx (NO + NO2) was measured during the fourth Fire Lab at Missoula Experiment (FLAME-4). The δ¹⁵N-NOx produced by burning a variety of biomass types ranged from -7 to +12‰ (vs. air N2). The variation in δ¹⁵N-NOx is primarily driven by variations in the biomass types burned (i.e. δ¹⁵N-biomass). In the labo...

The isotopic composition of nitrogen oxides (NOx = NO + NO2) hold potential to trace emissions sources, as well as chemistry in the atmosphere. Passive samplers that collect NOx and NO2 as nitrite could provide a simple and inexpensive means by which to collect samples in a variety of environments, and we report here on several methodological consi...

Nitrogen oxides (NOx = NO + NO2) have an important impact on the atmosphere and biosphere through controls on oxidant concentrations and the formation of nitric acid (e.g. acid rain). Anthropogenic emissions from fossil fuel combustion, land use change, and agriculture have altered the global nitrogen cycle since the beginning of the Industrial Rev...

As a major sink of atmospheric nitrogen oxides (NOx = NO + NO2), nitrate (NO3-) in polar snow can reflect the long-range transport of NOx and related species (e.g., PAN). On the other hand, because NO3- in snow can be photolyzed, potentially producing gas-phase NOx locally, NO3- in snow (and thus, ice) may reflect local processes. Here we investiga...

Significance Global models indicate that the human-derived nitrogen emissions that reach the ocean through atmospheric transport and deposition directly impact biology and the oceanic carbon dioxide (CO 2 ) sink. Here, we find that the organic nitrogen in marine aerosols derives predominantly from biological production in the surface ocean rather t...

We report observations of stable isotope ratios and ion concentrations from seasonal snowpack and summer bulk precipitation from remote alpine sites in the Southern Canadian Rocky Mountains. Spatial deposition patterns for sulfur (S) and δ34S-SO42- values indicate dominantly distant sources with little impact from local to regional pollution. Compa...

Snowpits along a traverse from coastal East Antarctica to the summit of the ice sheet (Dome Argus) are used to investigate the post-depositional processing of nitrate (NO3−) in snow. Seven snowpits from sites with accumulation rates between 24 and 172 kg m−2 a−1 were sampled to depths of 150 to 300 cm. At sites from the continental interior (low ac...

The Earth Science Women's Network (ESWN) aims to promote career development, build community, and facilitate professional collaborations for women across a variety of fields within the geosciences discipline. ESWN is a peer-mentoring network of women, with many early in their careers. ESWN started in 2002 as an initial group of six early-career wom...

Snowpits along a traverse from coastal East Antarctica to the summit of the ice sheet (Dome Argus) are used to investigate the post-depositional processing of nitrate in snow. Seven snowpits from sites with accumulation rates between 24 and 172 kg m−2 a−1 were sampled to depths of 150 to 300 cm. At sites from the continental interior (low accumulat...

There have been several measurements made of the nitrogen isotopic composition of gaseous NOx (NOx = NO + NO2) from various emission sources, utilizing a wide variety of methods to collect the NOx in solution as nitrate or nitrite. However, previous collection techniques have not been verified for complete or efficient capture of NOx such that the...

Summer deposition of sulfate and reactive nitrogen (mainly nitrate, and ammonium) to two alpine valleys in the Southern Canadian Rocky Mountains was investigated to constrain their major sources and evaluate physiographic influences on deposition. The effects of elevation, aspect, and air mass trajectory were evaluated using stable isotope composit...

Emissions of anthropogenic nitrogen (N) to the atmosphere have increased tenfold since preindustrial times, resulting in increased N deposition to terrestrial and coastal ecosystems. The sources of N deposition to the ocean, however, are poorly understood. Two years of event-based rainwater samples were collected on the island of Bermuda in the wes...