187 research outputs found
Characterisation and airborne deployment of a new counterflow virtual impactor inlet
A new counterflow virtual impactor (CVI) inlet is introduced with details of its design, laboratory characterisation tests and deployment on an aircraft during the 2011 Eastern Pacific Emitted Aerosol Cloud Experiment (E-PEACE). The CVI inlet addresses three key issues in previous designs; in particular, the inlet operates with: (i) negligible organic contamination; (ii) a significant sample flow rate to downstream instruments (âŒ15 l min^(â1)) that reduces the need for dilution; and (iii) a high level of accessibility to the probe interior for cleaning. Wind tunnel experiments characterised the cut size of sampled droplets and the particle size-dependent transmission efficiency in various parts of the probe. For a range of counter-flow rates and air velocities, the measured cut size was between 8.7â13.1 ÎŒm. The mean percentage error between cut size measurements and predictions from aerodynamic drag theory is 1.7%. The CVI was deployed on the Center for Interdisciplinary Remotely Piloted Aircraft Studies (CIRPAS) Twin Otter for thirty flights during E-PEACE to study aerosol-cloud-radiation interactions off the central coast of California in July and August 2011. Results are reported to assess the performance of the inlet including comparisons of particle number concentration downstream of the CVI and cloud drop number concentration measured by two independent aircraft probes. Measurements downstream of the CVI are also examined from one representative case flight coordinated with shipboard-emitted smoke that was intercepted in cloud by the Twin Otter
Is there an aerosol signature of chemical cloud processing?
The formation of sulfate and secondary organic aerosol mass in the aqueous
phase (aqSOA) of cloud and fog droplets can significantly contribute to
ambient aerosol mass. While tracer compounds give evidence that
aqueous-phase processing occurred, they do not reveal the extent to which
particle properties have been modified in terms of mass, chemical
composition, hygroscopicity, and oxidation state. We analyze data from
several field experiments and model studies for six air mass types (urban,
biogenic, marine, wild fire biomass burning, agricultural biomass burning,
and background air) using aerosol size and composition measurements for
particles 13â850 nm in diameter. We focus on the trends of changes in
mass, hygroscopicity parameter Îș, and oxygen-to-carbon (O â C) ratio
due to chemical cloud processing. We find that the modification of these
parameters upon cloud processing is most evident in urban, marine, and
biogenic air masses, i.e., air masses that are more polluted than very clean
air (background air) but cleaner than heavily polluted plumes as encountered
during biomass burning. Based on these trends, we suggest that the mass
ratio (Rtot) of the potential aerosol sulfate and aqSOA mass to the
initial aerosol mass can be used to predict whether chemical cloud
processing will be detectable. Scenarios in which this ratio exceeds RtotââŒâ0.5
are the most likely ones in which clouds can significantly
change aerosol parameters. It should be noted that the absolute value of Rtot
depends on the considered size range of particles. Rtot is
dominated by the addition of sulfate (Rsulf) in all scenarios due to
the more efficient conversion of SO2 to sulfate compared to aqSOA
formation from organic gases. As the formation processes of aqSOA are still
poorly understood, the estimate of RaqSOA is likely associated with
large uncertainties. Comparison to Rtot values as calculated for
ambient data at different locations validates the applicability of the
concept to predict a chemical cloud-processing signature in selected air masses.</p
Characterisation of the Putative Effector Interaction Site of the Regulatory HbpR Protein from Pseudomonas azelaica by Site-Directed Mutagenesis
Bacterial transcription activators of the XylR/DmpR subfamily exert their expression control via Ï54-dependent RNA polymerase upon stimulation by a chemical effector, typically an aromatic compound. Where the chemical effector interacts with the transcription regulator protein to achieve activation is still largely unknown. Here we focus on the HbpR protein from Pseudomonas azelaica, which is a member of the XylR/DmpR subfamily and responds to biaromatic effectors such as 2-hydroxybiphenyl. We use protein structure modeling to predict folding of the effector recognition domain of HbpR and molecular docking to identify the region where 2-hydroxybiphenyl may interact with HbpR. A large number of site-directed HbpR mutants of residues in- and outside the predicted interaction area was created and their potential to induce reporter gene expression in Escherichia coli from the cognate PC promoter upon activation with 2-hydroxybiphenyl was studied. Mutant proteins were purified to study their conformation. Critical residues for effector stimulation indeed grouped near the predicted area, some of which are conserved among XylR/DmpR subfamily members in spite of displaying different effector specificities. This suggests that they are important for the process of effector activation, but not necessarily for effector specificity recognition
Atmospheric oxidation in the presence of clouds during the Deep Convective Clouds and Chemistry (DC3) study
Deep convective clouds are critically important to the distribution of
atmospheric constituents throughout the troposphere but are difficult
environments to study. The Deep Convective Clouds and Chemistry (DC3) study
in 2012 provided the environment, platforms, and instrumentation to test
oxidation chemistry around deep convective clouds and their impacts downwind.
Measurements on the NASA DC-8 aircraft included those of the radicals
hydroxyl (OH) and hydroperoxyl (HO2), OH reactivity, and more than
100 other chemical species and atmospheric properties. OH, HO2, and
OH reactivity were compared to photochemical models, some with and some
without simplified heterogeneous chemistry, to test the understanding of
atmospheric oxidation as encoded in the model. In general, the agreement
between the observed and modeled OH, HO2, and OH reactivity was
within the combined uncertainties for the model without heterogeneous
chemistry and the model including heterogeneous chemistry with small OH and
HO2 uptake consistent with laboratory studies. This agreement is
generally independent of the altitude, ozone photolysis rate, nitric oxide
and ozone abundances, modeled OH reactivity, and aerosol and ice surface
area. For a sunrise to midday flight downwind of a nighttime mesoscale
convective system, the observed ozone increase is consistent with the
calculated ozone production rate. Even with some observed-to-modeled
discrepancies, these results provide evidence that a current
measurement-constrained photochemical model can simulate observed atmospheric
oxidation processes to within combined uncertainties, even around convective
clouds. For this DC3 study, reduction in the combined uncertainties would be
needed to confidently unmask errors or omissions in the model chemical
mechanism.</p
Evaluating WRF-GC v2.0 predictions of boundary layer height and vertical ozone profile during the 2021 TRACER-AQ campaign in Houston, Texas
The TRacking Aerosol Convection ExpeRiment â Air Quality (TRACER-AQ) campaign probed Houston air quality with a comprehensive suite of ground-based and airborne remote sensing measurements during the intensive operating period in September 2021. Two post-frontal high-ozone episodes (6â11 and 23â26 September) were recorded during the aforementioned period. In this study, we evaluated the simulation of the planetary boundary layer (PBL) height and the vertical ozone profile by a high-resolution (1.33âkm) 3-D photochemical model, the Weather Research and Forecasting (WRF)-driven
GEOS-Chem (WRF-GC). We evaluated the PBL heights with a ceilometer at the
coastal site La Porte and the airborne High Spectral Resolution Lidar 2
(HSRL-2) flying over urban Houston and adjacent waters. Compared with the
ceilometer at La Porte, the model captures the diurnal variations in the PBL heights with a very strong temporal correlation (R>0.7) and
±20â% biases. Compared with the airborne HSRL-2, the model exhibits a moderate to strong spatial correlation (R=0.26â0.68), with ±20â% biases during the noon and afternoon hours during ozone episodes. For landâwater differences in PBL heights, the water has shallower PBL heights compared to land. The model predicts larger landâwater differences than the observations because the model consistently underestimates the PBL heights over land compared to water. We evaluated vertical ozone distributions by comparing the model against vertical measurements from the TROPospheric OZone lidar (TROPOZ), the HSRL-2, and ozonesondes, as well as surface measurements at La Porte from a model 49i ozone analyzer and one Continuous Ambient Monitoring Station (CAMS). The model underestimates free-tropospheric ozone (2â3âkm aloft) by 9â%â22â% but overestimates near-ground ozone (<50âm aloft) by 6â%-39â% during the two ozone episodes. Boundary layer ozone (0.5â1âkm aloft) is underestimated by 1â%â11â% during 8â11 September but overestimated by 0â%â7â% during 23â26 September. Based on these evaluations, we identified two model limitations, namely the single-layer PBL representation and the free-tropospheric ozone underestimation. These limitations have implications for the predictivity of ozone's vertical mixing and distribution in other models.</p
Utilisation of an operative difficulty grading scale for laparoscopic cholecystectomy
Background
A reliable system for grading operative difficulty of laparoscopic cholecystectomy would standardise description of findings and reporting of outcomes. The aim of this study was to validate a difficulty grading system (Nassar scale), testing its applicability and consistency in two large prospective datasets.
Methods
Patient and disease-related variables and 30-day outcomes were identified in two prospective cholecystectomy databases: the multi-centre prospective cohort of 8820 patients from the recent CholeS Study and the single-surgeon series containing 4089 patients. Operative data and patient outcomes were correlated with Nassar operative difficultly scale, using Kendallâs tau for dichotomous variables, or JonckheereâTerpstra tests for continuous variables. A ROC curve analysis was performed, to quantify the predictive accuracy of the scale for each outcome, with continuous outcomes dichotomised, prior to analysis.
Results
A higher operative difficulty grade was consistently associated with worse outcomes for the patients in both the reference and CholeS cohorts. The median length of stay increased from 0 to 4 days, and the 30-day complication rate from 7.6 to 24.4% as the difficulty grade increased from 1 to 4/5 (both pâ<â0.001). In the CholeS cohort, a higher difficulty grade was found to be most strongly associated with conversion to open and 30-day mortality (AUROCâ=â0.903, 0.822, respectively). On multivariable analysis, the Nassar operative difficultly scale was found to be a significant independent predictor of operative duration, conversion to open surgery, 30-day complications and 30-day reintervention (all pâ<â0.001).
Conclusion
We have shown that an operative difficulty scale can standardise the description of operative findings by multiple grades of surgeons to facilitate audit, training assessment and research. It provides a tool for reporting operative findings, disease severity and technical difficulty and can be utilised in future research to reliably compare outcomes according to case mix and intra-operative difficulty
Phase II trial of Modified Vaccinia Ankara (MVA) virus expressing 5T4 and high dose Interleukin-2 (IL-2) in patients with metastatic renal cell carcinoma
<p>Abstract</p> <p>Background</p> <p>Interleukin-2 (IL-2) induces durable objective responses in a small cohort of patients with metastatic renal cell carcinoma (RCC) but the antigen(s) responsible for tumor rejection are not known. 5T4 is a non-secreted membrane glycoprotein expressed on clear cell and papillary RCCs. A modified vaccinia virus Ankara (MVA) encoding 5T4 was tested in combination with high-dose IL-2 to determine the safety, objective response rate and effect on humoral and cell-mediated immunity.</p> <p>Methods</p> <p>25 patients with metastatic RCC who qualified for IL-2 were eligible and received three immunizations every three weeks followed by IL-2 (600,000 IU/kg) after the second and third vaccinations. Blood was collected for analysis of humoral, effector and regulatory T cell responses.</p> <p>Results</p> <p>There were no serious vaccine-related adverse events. While no objective responses were observed, three patients (12%) were rendered disease-free after nephrectomy or resection of residual metastatic disease. Twelve patients (48%) had stable disease which was associated with improved median overall survival compared to patients with progressive disease (not reached vs. 28 months, p = 0.0261). All patients developed 5T4-specific antibody responses and 13 patients had an increase in 5T4-specific T cell responses. Although the baseline frequency of Tregs was elevated in all patients, those with stable disease showed a trend toward increased effector CD8+ T cells and a decrease in Tregs.</p> <p>Conclusion</p> <p><b>V</b>accination with MVA-5T4 did not improve objective response rates of IL-2 therapy but did result in stable disease associated with an increase in the ratio of 5T4-specific effector to regulatory T cells in selected patients.</p> <p>Trial registration number</p> <p>ISRCTN83977250</p
Frequent new particle formation over the high Arctic pack ice by enhanced iodine emissions
In the central Arctic Ocean the formation of clouds and their properties are sensitive to the availability of cloud condensation nuclei (CCN). The vapors responsible for new particle formation (NPF), potentially leading to CCN, have remained unidentified since the first aerosol measurements in 1991. Here, we report that all the observed NPF events from the Arctic Ocean 2018 expedition are driven by iodic acid with little contribution from sulfuric acid. Iodic acid largely explains the growth of ultrafine particles (UFP) in most events. The iodic acid concentration increases significantly from summer towards autumn, possibly linked to the ocean freeze-up and a seasonal rise in ozone. This leads to a one order of magnitude higher UFP concentration in autumn. Measurements of cloud residuals suggest that particles smaller than 30ânm in diameter can activate as CCN. Therefore, iodine NPF has the potential to influence cloud properties over the Arctic Ocean
Reconciling Assumptions in Bottom-Up and Top-Down Approaches for Estimating Aerosol Emission Rates From Wildland Fires Using Observations From FIREX-AQ
Accurate fire emissions inventories are crucial to predict the impacts of wildland fires on air quality and atmospheric composition. Two traditional approaches are widely used to calculate fire emissions: a satellite-based top-down approach and a fuels-based bottom-up approach. However, these methods often considerably disagree on the amount of particulate mass emitted from fires. Previously available observational datasets tended to be sparse, and lacked the statistics needed to resolve these methodological discrepancies. Here, we leverage the extensive and comprehensive airborne in situ and remote sensing measurements of smoke plumes from the recent Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) campaign to statistically assess the skill of the two traditional approaches. We use detailed campaign observations to calculate and compare emission rates at an exceptionally high-resolution using three separate approaches: top-down, bottom-up, and a novel approach based entirely on integrated airborne in situ measurements. We then compute the daily average of these high-resolution estimates and compare with estimates from lower resolution, global top-down and bottom-up inventories. We uncover strong, linear relationships between all of the high-resolution emission rate estimates in aggregate, however no single approach is capable of capturing the emission characteristics of every fire. Global inventory emission rate estimates exhibited weaker correlations with the high-resolution approaches and displayed evidence of systematic bias. The disparity between the low-resolution global inventories and the high-resolution approaches is likely caused by high levels of uncertainty in essential variables used in bottom-up inventories and imperfect assumptions in top-down inventories
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