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Nitrogen dioxide (NO2) is a precursor of ozone (O3) and fine particulate matter (PM2.5) – two pollutants that are above regulatory guidelines in many cities. Bringing urban areas into compliance of these regulatory standards motivates an understanding of the distribution and sources of NO2 through observations and simulations. The TRACER-AQ campaign, conducted in Houston, TX in September 2021, provided a unique opportunity to compare observed NO2 columns from ground-, airborne-, and satellite-based spectrometers. In this study, we investigate how these observational datasets compare, and simulate column NO2 using WRF-CAMx with fine resolution (444 x 444 m2) comparable to the airborne column measurements. We find that observations from the GEOCAPE Airborne Simulator (GCAS) instrument were strongly correlated (r2=0.80) to observations from Pandora spectrometers with a negligible bias (NMB=0.1 %). Remote-sensing observations from the TROPOMI instrument were generally well correlated with Pandora observations (r2=0.73) with a negative bias (NMB=-22.8 %). We intercompare different versions of TROPOMI data and find similar correlations across three versions but slightly different biases (from -22.8 % in v2.4.0 to -18.2 % in the NASA MINDS product). Compared to Pandora observations, the WRF-CAMx simulation had reduced correlation (r2=0.34) and a low bias (-25.5 %) over the entire study region. We find particularly poor agreement between simulated NO2 columns and GCAS-observed NO2 columns in downtown Houston an area of high population and roadway densities. These findings point to a potential underestimate of vehicle NOX emissions in the WRF-CAMx simulation driven by the Texas state inventory; and further investigation is recommended. [ABSTRACT FROM AUTHOR]

Nitrogen dioxide (NO2) is a precursor of ozone (O3) and fine particulate matter (PM2.5) - two pollutants that are above regulatory guidelines in many cities. Bringing urban areas into compliance of these regulatory standards motivates an understanding of the distribution and sources of NO2 through observations and simulations. The TRACER-AQ campaign, conducted in Houston, TX in September 2021, provided a unique opportunity to compare observed NO2 columns from ground-, airborne-, and satellite-based spectrometers. In this study, we investigate how these observational datasets compare, and simulate column NO2 using WRF-CAMx with fine resolution (444 x 444 m2) comparable to the airborne column measurements. We find that observations from the GEOCAPE Airborne Simulator (GCAS) instrument were strongly correlated (r2=0.80) to observations from Pandora spectrometers with a negligible bias (NMB=0.1%). Remote-sensing observations from the TROPOMI instrument were generally well correlated with Pandora observations (r2=0.73) with a negative bias (NMB=-22.8%). We intercompare different versions of TROPOMI data and find similar correlations across three versions but slightly different biases (from -22.8% in v2.4.0 to -18.2% in the NASA MINDS product). Compared to Pandora observations, the WRF-CAMx simulation had reduced correlation (r2=0.34) and a low bias (-25.5%) over the entire study region. We find particularly poor agreement between simulated NO2 columns and GCAS-observed NO2 columns in downtown Houston an area of high population and roadway densities. These findings point to a potential underestimate of vehicle NOX emissions in the WRF-CAMx simulation driven by the Texas state inventory; and further investigation is recommended. [ABSTRACT FROM AUTHOR]

Polymer networks can have a range of desirable properties such as mechanical strength, wide compositional diversity between different materials, permanent porosity, convenient processability and broad solvent compatibility.sup.1,2. Designing polymer networks from the bottom up with new structural motifs and chemical compositions can be used to impart dynamic features such as malleability or self-healing, or to allow the material to respond to environmental stimuli.sup.3-8. However, many existing systems exhibit only one operational state that is defined by the material's composition and topology.sup.3-6; or their responsiveness may be irreversible.sup.7,9,10 and limited to a single network property.sup.11,12 (such as stiffness). Here we use cooperative self-assembly as a design principle to prepare a material that can be switched between two topological states. By using networks of polymer-linked metal-organic cages in which the cages change shape and size on irradiation, we can reversibly switch the network topology with ultraviolet or green light. This photoswitching produces coherent changes in several network properties at once, including branch functionality, junction fluctuations, defect tolerance, shear modulus, stress-relaxation behaviour and self-healing. Topology-switching materials could prove useful in fields such as soft robotics and photo-actuators as well as providing model systems for fundamental polymer physics studies.Using topology-switching metal-ligand cages to crosslink polymer networks produces gels whose chemical and mechanical properties can be radically and reversibly switched on irradiation., Author(s): Yuwei Gu [sup.1] , Eric A. Alt [sup.1] , Heng Wang [sup.2] , Xiaopeng Li [sup.2] , Adam P. Willard [sup.1] , Jeremiah A. Johnson [sup.1] Author Affiliations:(1) Department [...]

Background Recent advances in endovascular devices have allowed access and targeting of perivascular tissues of the peripheral circulation. The perivascular tissues of the cervical and cranial circulations have many important structures of clinical significance, yet the feasibility and safety of such an approach has not been demonstrated. Objective To evaluate the safety of a novel endovascular transmural approach to target the perivascular tissues of the common carotid artery in swine. Methods A micro- infusion device was positioned in the carotid arteries of three Yorkshire pigs (six carotid arteries in total), and each carotid artery was punctured 10 times in the same location to gain access to the perivascular tissues. Digital subtraction angiography was used to evaluate vessel injury or contrast extravasation. MRI and MR angiography were used to evaluate evidence of cerebral ischemia or vessel injury. Postmortem tissue analysis was performed to assess the level of extravascular hematoma and intravascular dissection. Results None of the tested carotid arteries showed evidence of vessel injury (dissection or perforation) or intravascular thrombosis. MRI performed after repeated puncture was negative for neck hematoma and brain ischemia. Post- mortem tissue analysis of the carotid arteries showed mild adventitial staining with blood, but without associated hematoma and without vessel dissection. Conclusion Repeated puncture of the carotid artery to gain access to the perivascular tissues using a novel endovascular transmural approach is safe in a swine model. This represents a novel approach to various tissues in close proximity to the cervical and cranial vasculature. [ABSTRACT FROM AUTHOR]