96 research outputs found
Wintertime Spatial Distribution of Ammonia and its Emission Sources in the Great Salt Lake Region
Ammonium-containing aerosols are a major component of wintertime air pollution in many densely populated regions around the world. Especially in mountain basins, the formation of persistent cold-air pools (PCAPs) can enhance particulate matter with diameters less than 2.5 µm (PM2.5) to levels above air quality standards. Under these conditions, PM2.5 in the Great Salt Lake region of northern Utah has been shown to be primarily composed of ammonium nitrate; however, its formation processes and sources of its precursors are not fully understood. Hence, it is key to understanding the emission sources of its gas phase precursor, ammonia (NH3). To investigate the formation of ammonium nitrate, a suite of trace gases and aerosol composition were sampled from the NOAA Twin Otter aircraft during the Utah Winter Fine Particulate Study (UWFPS) in January and February 2017. NH3 was measured using a quantum cascade tunable infrared laser differential absorption spectrometer (QC-TILDAS), while aerosol composition, including particulate ammonium (pNH4), was measured with an aerosol mass spectrometer (AMS). The origin of the sampled air masses was investigated using the Stochastic Time-Inverted Lagrangian Transport (STILT) model and combined with an NH3 emission inventory to obtain model-predicted NHx (=NH3+pNH4) enhancements. Enhancements represent the increase in NH3 mixing ratios within the last 24 h due to emissions within the model footprint. Comparison of these NHx enhancements with measured NHx from the Twin Otter shows that modelled values are a factor of 1.6 to 4.4 lower for the three major valleys in the region. Among these, the underestimation is largest for Cache Valley, an area with intensive agricultural activities. We find that one explanation for the underestimation of wintertime emissions may be the seasonality factors applied to NH3 emissions from livestock. An investigation of inter-valley exchange revealed that transport of NH3 between major valleys was limited and PM2.5 in Salt Lake Valley (the most densely populated area in Utah) was not significantly impacted by NH3 from the agricultural areas in Cache Valley. We found that in Salt Lake Valley around two thirds of NHx originated within the valley, while about 30 % originated from mobile sources and 60 % from area source emissions in the region. For Cache Valley, a large fraction of NOx potentially leading to PM2.5 formation may not be locally emitted but mixed in from other counties
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Arctic marine secondary organic aerosol contributes significantly to summertime particle size distributions in the Canadian Arctic Archipelago
Summertime Arctic aerosol size distributions are strongly controlled by natural regional emissions. Within this context, we use a chemical transport model with sizeresolved aerosol microphysics (GEOS-Chem-TOMAS) to interpret measurements of aerosol size distributions from the Canadian Arctic Archipelago during the summer of 2016, as part of the "NETwork on Climate and Aerosols: Addressing key uncertainties in Remote Canadian Environments" (NETCARE) project. Our simulations suggest that condensation of secondary organic aerosol (SOA) from precursor vapors emitted in the Arctic and near Arctic marine (ice-free seawater) regions plays a key role in particle growth events that shape the aerosol size distributions observed at Alert (82.5° N, 62.3° W), Eureka (80.1° N, 86.4° W), and along a NETCARE ship track within the Archipelago. We refer to this SOA as Arctic marine SOA (AMSOA) to reflect the Arctic marine-based and likely biogenic sources for the precursors of the condensing organic vapors. AMSOA from a simulated flux (500 μgm-2 day-1, north of 50° N) of precursor vapors (with an assumed yield of unity) reduces the summertime particle size distribution model-observation mean fractional error 2- to 4-fold, relative to a simulation without this AMSOA. Particle growth due to the condensable organic vapor flux contributes strongly (30 %-50 %) to the simulated summertime-mean number of particles with diameters larger than 20 nm in the study region. This growth couples with ternary particle nucleation (sulfuric acid, ammonia, and water vapor) and biogenic sulfate condensation to account for more than 90% of this simulated particle number, which represents a strong biogenic influence. The simulated fit to summertime size-distribution observations is further improved at Eureka and for the ship track by scaling up the nucleation rate by a factor of 100 to account for other particle precursors such as gas-phase iodine and/or amines and/or fragmenting primary particles that could be missing from our simulations. Additionally, the fits to the observed size distributions and total aerosol number concentrations for particles larger than 4 nm improve with the assumption that the AMSOA contains semivolatile species: the model-observation mean fractional error is reduced 2- to 3-fold for the Alert and ship track size distributions. AMSOA accounts for about half of the simulated particle surface area and volume distributions in the summertime Canadian Arctic Archipelago, with climaterelevant simulated summertime pan-Arctic-mean top-of-theatmosphere aerosol direct (-0:04Wm-2) and cloud-albedo indirect (-0:4Wm-2) radiative effects, which due to uncertainties are viewed as an order of magnitude estimate. Future work should focus on further understanding summertime Arctic sources of AMSOA
Understanding the Sequence-Dependence of DNA Groove Dimensions: Implications for DNA Interactions
BACKGROUND: The B-DNA major and minor groove dimensions are crucial for DNA-protein interactions. It has long been thought that the groove dimensions depend on the DNA sequence, however this relationship has remained elusive. Here, our aim is to elucidate how the DNA sequence intrinsically shapes the grooves. METHODOLOGY/PRINCIPAL FINDINGS: The present study is based on the analysis of datasets of free and protein-bound DNA crystal structures, and from a compilation of NMR (31)P chemical shifts measured on free DNA in solution on a broad range of representative sequences. The (31)P chemical shifts can be interpreted in terms of the BI↔BII backbone conformations and dynamics. The grooves width and depth of free and protein-bound DNA are found to be clearly related to the BI/BII backbone conformational states. The DNA propensity to undergo BI↔BII backbone transitions is highly sequence-dependent and can be quantified at the dinucleotide level. This dual relationship, between DNA sequence and backbone behavior on one hand, and backbone behavior and groove dimensions on the other hand, allows to decipher the link between DNA sequence and groove dimensions. It also firmly establishes that proteins take advantage of the intrinsic DNA groove properties. CONCLUSIONS/SIGNIFICANCE: The study provides a general framework explaining how the DNA sequence shapes the groove dimensions in free and protein-bound DNA, with far-reaching implications for DNA-protein indirect readout in both specific and non specific interactions
Structure of the NheA Component of the Nhe Toxin from Bacillus cereus: Implications for Function
The structure of NheA, a component of the Bacillus cereus Nhe tripartite toxin, has been solved at 2.05 Å resolution using selenomethionine multiple-wavelength anomalous dispersion (MAD). The structure shows it to have a fold that is similar to the Bacillus cereus Hbl-B and E. coli ClyA toxins, and it is therefore a member of the ClyA superfamily of α-helical pore forming toxins (α-PFTs), although its head domain is significantly enlarged compared with those of ClyA or Hbl-B. The hydrophobic β-hairpin structure that is a characteristic of these toxins is replaced by an amphipathic β-hairpin connected to the main structure via a β-latch that is reminiscent of a similar structure in the β-PFT Staphylococcus aureus α-hemolysin. Taken together these results suggest that, although it is a member of an archetypal α-PFT family of toxins, NheA may be capable of forming a β rather than an α pore
Arctic marine secondary organic aerosol contributes significantly to summertime particle size distributions in the Canadian Arctic Archipelago
Summertime Arctic aerosol size distributions are strongly controlled by
natural regional emissions. Within this context, we use a chemical transport
model with size-resolved aerosol microphysics (GEOS-Chem-TOMAS) to interpret
measurements of aerosol size distributions from the Canadian Arctic
Archipelago during the summer of 2016, as part of the “NETwork on Climate
and Aerosols: Addressing key uncertainties in Remote Canadian Environments”
(NETCARE) project. Our simulations suggest that condensation of secondary organic
aerosol (SOA) from precursor vapors emitted in the Arctic and near Arctic
marine (ice-free seawater) regions plays a key role in particle growth events
that shape the aerosol size distributions observed at Alert (82.5∘ N,
62.3∘ W), Eureka (80.1∘ N, 86.4∘ W), and
along a NETCARE ship track within the Archipelago. We refer to this SOA as
Arctic marine SOA (AMSOA) to reflect the Arctic marine-based and likely
biogenic sources for the precursors of the condensing organic vapors.
AMSOA from a simulated flux (500 µgm-2day-1, north of
50∘ N) of precursor vapors (with an assumed yield of unity) reduces the
summertime particle size distribution model–observation mean fractional
error 2- to 4-fold, relative to a simulation without this AMSOA. Particle
growth due to the condensable organic vapor flux contributes strongly
(30 %–50 %) to the simulated summertime-mean number of particles with
diameters larger than 20 nm in the study region. This growth couples with
ternary particle nucleation (sulfuric acid, ammonia, and water vapor) and
biogenic sulfate condensation to account for more than 90 % of this
simulated particle number, which represents a strong biogenic influence. The simulated fit to
summertime size-distribution observations is further improved at Eureka and
for the ship track by scaling up the nucleation rate by a factor of 100 to
account for other particle precursors such as gas-phase iodine and/or amines
and/or fragmenting primary particles that could be missing from our
simulations. Additionally, the fits to the observed size distributions and total
aerosol number concentrations for particles larger than 4 nm improve with
the assumption that the AMSOA contains semi-volatile species: the
model–observation mean fractional error is reduced 2- to 3-fold for the Alert and
ship track size distributions. AMSOA accounts for about half of the
simulated particle surface area and volume distributions in the summertime
Canadian Arctic Archipelago, with climate-relevant simulated summertime
pan-Arctic-mean top-of-the-atmosphere aerosol direct (−0.04 W m−2) and
cloud-albedo indirect (−0.4 W m−2) radiative effects, which due
to uncertainties are viewed as an order of magnitude estimate. Future work
should focus on further understanding summertime Arctic sources of AMSOA.</p
An odd oxygen framework for wintertime ammonium nitrate aerosol pollution in urban areas: NOx and VOC control as mitigation strategies
Wintertime ammonium nitrate aerosol pollution is a severe air quality issue affecting both developed and rapidly urbanizing regions from Europe to East Asia. In the US, it is acute in western basins subject to inversions that confine pollutants near the surface. Measurements and modeling of a wintertime pollution episode in Salt Lake City, Utah demonstrates that ammonium nitrate is closely related to photochemical ozone through a common parameter, total odd oxygen, Ox,total. We show that the traditional NOx‐VOC framework for evaluating ozone mitigation strategies also applies to ammonium nitrate. Despite being nitrate‐limited, ammonium nitrate aerosol pollution in Salt Lake City is responsive to VOC control and, counterintuitively, not initially responsive to NOx control. We demonstrate simultaneous nitrate limitation and NOx saturation and suggest this phenomenon may be general. This finding may identify an unrecognized control strategy to address a global public health issue in regions with severe winter aerosol pollution
A View from the Past Into our Collective Future: The Oncofertility Consortium Vision Statement
Today, male and female adult and pediatric cancer patients, individuals transitioning between gender identities, and other individuals facing health extending but fertility limiting treatments can look forward to a fertile future. This is, in part, due to the work of members associated with the Oncofertility Consortium. The Oncofertility Consortium is an international, interdisciplinary initiative originally designed to explore the urgent unmet need associated with the reproductive future of cancer survivors. As the strategies for fertility management were invented, developed or applied, the individuals for who the program offered hope, similarly expanded. As a community of practice, Consortium participants share information in an open and rapid manner to addresses the complex health care and quality-of-life issues of cancer, transgender and other patients. To ensure that the organization remains contemporary to the needs of the community, the field designed a fully inclusive mechanism for strategic planning and here present the findings of this process. This interprofessional network of medical specialists, scientists, and scholars in the law, medical ethics, religious studies and other disciplines associated with human interventions, explore the relationships between health, disease, survivorship, treatment, gender and reproductive longevity. The goals are to continually integrate the best science in the service of the needs of patients and build a community of care that is ready for the challenges of the field in the future
Overview paper: New insights into aerosol and climate in the Arctic
Motivated by the need to predict how the Arctic atmosphere will
change in a warming world, this article summarizes recent advances made by
the research consortium NETCARE (Network on Climate and Aerosols: Addressing
Key Uncertainties in Remote Canadian Environments) that contribute to our
fundamental understanding of Arctic aerosol particles as they relate to
climate forcing. The overall goal of NETCARE research has been to use an
interdisciplinary approach encompassing extensive field observations and a
range of chemical transport, earth system, and biogeochemical models. Several
major findings and advances have emerged from NETCARE since its formation in
2013. (1) Unexpectedly high summertime dimethyl sulfide (DMS) levels were
identified in ocean water (up to 75 nM) and the overlying atmosphere (up to
1 ppbv) in the Canadian Arctic Archipelago (CAA). Furthermore, melt ponds,
which are widely prevalent, were identified as an important DMS source (with
DMS concentrations of up to 6 nM and a potential contribution to atmospheric
DMS of 20 % in the study area). (2) Evidence of widespread particle
nucleation and growth in the marine boundary layer was found in the CAA in
the summertime, with these events observed on 41 % of days in a 2016
cruise. As well, at Alert, Nunavut, particles that are newly formed and grown
under conditions of minimal anthropogenic influence during the months of July
and August are estimated to contribute 20 % to 80 % of the 30–50 nm
particle number density. DMS-oxidation-driven nucleation is facilitated by
the presence of atmospheric ammonia arising from seabird-colony emissions,
and potentially also from coastal regions, tundra, and biomass burning. Via
accumulation of secondary organic aerosol (SOA), a significant fraction of the new
particles grow to sizes that are active in cloud droplet formation. Although
the gaseous precursors to Arctic marine SOA remain poorly defined, the
measured levels of common continental SOA precursors (isoprene and
monoterpenes) were low, whereas elevated mixing ratios of oxygenated volatile
organic compounds (OVOCs) were inferred to arise via processes involving the
sea surface microlayer. (3) The variability in the vertical distribution of
black carbon (BC) under both springtime Arctic haze and more pristine
summertime aerosol conditions was observed. Measured particle size
distributions and mixing states were used to constrain, for the first time,
calculations of aerosol–climate interactions under Arctic conditions.
Aircraft- and ground-based measurements were used to better establish the BC
source regions that supply the Arctic via long-range transport mechanisms,
with evidence for a dominant springtime contribution from eastern and
southern Asia to the middle troposphere, and a major contribution from
northern Asia to the surface. (4) Measurements of ice nucleating particles
(INPs) in the Arctic indicate that a major source of these particles is
mineral dust, likely derived from local sources in the summer and long-range
transport in the spring. In addition, INPs are abundant in the sea surface
microlayer in the Arctic, and possibly play a role in ice nucleation in the
atmosphere when mineral dust concentrations are low. (5) Amongst multiple
aerosol components, BC was observed to have the smallest effective deposition
velocities to high Arctic snow (0.03 cm s−1).</p
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