Challenges in quantification of photocatalytic NO2 abatement effectiveness under real world exposure conditions illustrated by a case study.

Health risks due to NO2 exposure commonly exceed acceptable levels in modern societies. Among the measures to reduce such risks, photocatalytic materials present a promising technology. However, while the pollutant remediation of such materials has been extensively validated in laboratory studies, the performance under real world environmental exposure conditions is still subject to controversy. Indeed, a comparison of available in-situ monitoring studies manifests non-conclusive and highly scattered results regarding the photocatalytic effectiveness observed. The reasons for this behaviour must be carefully explored in order to prevent non-efficient photocatalytic applications from being put into practice on a larger scale. This paper presents a comprehensive large-scale study for assessing the photocatalytic NO2 remediation by active pavements in a street of Madrid (Spain), comprising different in-situ monitoring techniques. The discussion is enriched by relating the obtained results to those of other large-scale studies. The discrepancies between these results may be traced back to different circumstances, among them the distance between the active pavement and the pollutant concentration sampling inlet, as well as to significant site-specific and time-dependent variations of pollutant concentrations and climatic parameters. Under due consideration of these influences, for materials with relatively high initial effectiveness, it was concluded that in most such applications, the average NO2 removal effectiveness, if evaluated at a typical inlet height of Air Quality Stations (3 m), will not exceed a value of 4% (averaged over a sufficiently large number of measurement points in the area of application and a sustained amount of time, i.e. several months). When considering more realistic human exposure conditions (lower heights and daytime), it might be justified to assume somewhat higher average effectiveness.

Estimates of pedestrian exposure to atmospheric pollution using high-resolution modelling in a real traffic hot-spot.

Atmospheric pollution is a very relevant risk for the human health, in particular in urban environments, where most people lives and high levels of pollution are found. Population exposure is traditionally estimated through concentration recorded at air quality monitoring stations (AQMS) or modelled at a spatial resolution of the order of 1 km2. However, these methodologies have limitations in urban areas where strong gradients of concentration, even in the same street, exist. In addition, the movements of pedestrians make difficult to compute reliable estimates of pollutant concentration to which people are exposed to. In this context, the main objective of this study is to estimate the exposure of pedestrians to ambient nitrogen oxides (NOx) concentrations with high spatial resolution in a real urban traffic hot-spot under different methodologies. To achieve this objective, a novel methodology which combines high-resolution NOx concentrations from computational fluid dynamic (CFD) simulations with the pedestrian flows obtained by pedestrian mobility microsimulations is applied to an urban area of Madrid, Spain. High-resolution maps show pedestrian exposure peaks, at bus stops and crosswalks, that cannot be captured by the simpler methods based on spatial average concentration (SAC) or concentration measured in an AQMS. Total daily exposure obtained is 1.19 · 109 person s µg m-3, while SAC and AQMS concentration methods yielded 9-23% and 30-40% lower values. In conclusion, the proposed methodology allows to determine the areas with higher exposure in order to design local strategies to reduce the impact on human health. In addition, from a more general point of view, the total exposure in the studied area is better estimated by using spatial average concentration than through concentration recorded by AQMS. The assessment of the spatial representative of AQMS becomes necessary to use AQMS concentration to evaluate air quality and population exposure of an urban area.

NOx removal efficiency of urban photocatalytic pavements at pilot scale.

Photocatalytic technology implemented in construction materials is a promising solution to contribute to alleviate air quality issues found in big cities. Photocatalysis has been proved able to mineralise most harmful contaminants. However, important problems associated with monitoring the efficiency of these solutions under real conditions still remain, including the lack of affordable analytical tools to measure NOx concentrations with enough accuracy. In this work, two pilot scale demonstration platforms were built at two different locations to assess the photocatalytic NOX removal efficiency of ten selected materials exposed outdoors for AQmesh low-cost sensor PODs were used to measure ground-level to measure NO and NO2 concentrations during nearly one year. The pollutant removal efficiency of the materials was then calculated based on a comparison with simultaneously concentration measurements carried-out on reference, non-active materials. It was found that the NO2 removal efficiency presented large variations across the seasons, with maxima during the warmer months, while NO efficiencies were comparatively steadier. Statistical analysis delivered evidence that the efficiencies significantly depend on different meteorological variables (irradiance and relative humidity) besides NO, NO2 ambient concentrations. Lower efficiencies were observed for higher concentration levels and vice versa. The influence of water vapour could be related to two different effects: a short-term contribution by the instantaneous air humidity and a long-term component associated with the hygroscopic state of the material. The contribution of wind to the pollutant removal efficiencies was principally related to the humidity of air masses moving above the location and to the advection of pollutants from specific emission sources.

Use of insertable cardiac monitors for the detection of atrial fibrillation in patients with cryptogenic stroke in the United States is cost-effective.

Objectives: Atrial fibrillation (AF) is the most common arrhythmia and a major marker of ischemic stroke risk. Early detection is crucial and, once diagnosed, anticoagulation therapy can be initiated to reduce stroke risk. The aim of this study was to assess the cost-effectiveness of employing an insertable cardiac monitor (ICM), BIOMONITOR, for the detection of AF compared to standard of care (SoC) ECG and Holter monitoring in patients with cryptogenic stroke, that is, stroke of unknown origin and where paroxysmal, silent AF is suspected. Materials and methods: A Markov model was developed which consisted of five main health states reflecting the potential lifetime evolution of the AF disease: post cryptogenic stroke (index event), subsequent mild, moderate and severe stroke, and death. Sub-states were included to track a patient's AF diagnostic status and the use of antiplatelet or anticoagulant therapy. AF detection was assumed to result in a treatment switch from aspirin to anticoagulants, except among those with a history of major bleeding. Detection yield and accuracy, clinical actions and treatment effects were derived from the literature and validated by an expert clinician. All relevant costs from a US Medicare perspective were included. Results and conclusions: An ICM-based strategy was associated with a reduction of 37 secondary ischemic strokes per 1000 patients monitored compared with SoC. Total per-patient costs with an ICM were higher (US$90,052 vs. US$85,157) although stroke-related costs were reduced. The use of an ICM was associated with a base-case incremental cost-effectiveness ratio of US$18,487 per life year gained compared with SoC and US$25,098 per quality-adjusted life year gained, below established willingness-to-pay thresholds. The conclusions were found to be robust over a range of input values. From a US Medicare perspective the use of a BIOMONITOR ICM represents a cost-effective diagnostic strategy for patients with cryptogenic stroke and suspected AF.

Urban vegetation and particle air pollution: Experimental campaigns in a traffic hotspot.

This work presents the main results of two experimental campaigns carried out in summer and winter seasons in a complex pollution hotspot near a large park, El Retiro, in Madrid (Spain). These campaigns were aimed at understanding the microscale spatio-temporal variation of ambient concentration levels in areas with high pollution values to obtain data to validate models on the effect of urban trees on particulate matter concentrations. Two different measuring approaches have been used. The first one was static, with instruments continuously characterizing the meteorological variables and the particulate matter concentration outside and inside the park. During the summer campaign, the particulate matter concentration was clearly influenced by a Saharan dust outbreak during the period 23 June to 10 July 2016, when most of the particulate matter was in the fraction PM2.5-10. During the winter campaign, the mass concentrations were related to the meteorological conditions and the high atmospheric stability. The second approach was a dynamic case with mobile measurements by portable instruments. During the summer campaign, a DustTrak instrument was used to measure PM10 and PM2.5 in different transects close to and inside the park at different distances from the traffic lane. It was observed a decrease in the concentrations up to 25% at 20 m and 50% at 200 m. High PM10 values were linked to dust resuspension caused by recreational activities and to a Saharan dust outbreak. The highest PM values were measured at the Independencia square, an area with many bus stops and high traffic density. During the winter campaign, three microaethalometers were used for Black Carbon measurement. Both pollutants also showed a reduction in their concentrations when moving towards inside the park. For PM10 and PM2.5, reductions up to 50% were observed, while for BC this reduction was smaller, about 20%.

Unexpected increase in the oxidation capacity of the urban atmosphere of Madrid, Spain.

Atmospheric oxidants such as ozone (O3), hydroxyl and nitrate radicals (OH and NO3) determine the ability of the urban atmosphere to process organic and inorganic pollutants, which have an impact on air quality, environmental health and climate. Madrid city has experienced an increase of 30-40% in ambient air O3 levels, along with a decrease of 20-40% in NO2, from 2007 to 2014. Using air pollution observations and a high-resolution air quality model, we find a large concentration increase of up to 70% and 90% in OH and NO3, respectively, in downtown Madrid (domain-wide average increase of 10% and 32% for OH and NO3, respectively). The results also show an 11% reduction in the nitric acid concentrations, leading to a remarkable denoxification of this urban atmosphere with implications for lower PM2.5 levels and nitrogen input into ecosystems. This study suggests that projected worldwide NOx emission reductions, following air quality standards, will lead to important changes in the oxidizing capacity of the atmosphere in and around large cities.

Evaluation of a CFD-based approach to estimate pollutant distribution within a real urban canopy by means of passive samplers.

The distribution of pollutants is spatially heterogeneous within urban streets making difficult to build a realistic concentration map. In this paper, a methodology based on computational fluid dynamic modeling with Reynolds-averaged Navier-Stokes approach is used to compute maps of concentration for a period of several weeks. The methodology is evaluated by comparing simulation results against experimental data from two different campaigns where a large number of passive samplers deployed in an area with heavy vehicular traffic in Madrid (Spain). The evaluation shows that the methodology is able to reproduce the general pattern of several-week averaged pollutant distribution in an urban area with heavy vehicular traffic, resolving the spatial variability up to a resolution of 1-2m. In addition, the model results fit satisfactorily the time evolution of the pollutant concentration measured at an air quality station deployed in the studied area. However, problems were detected close to zones with complex emissions patterns (tunnels, street forks, etc.), where the model compared poorly against passive sampler measurements. A preliminary assessment of the uncertainties induced in the numerical methodology due to consider NO2 as non-reactive pollutant under winter conditions indicates that it would be an acceptable approach for this particular case study. Overall, our analysis contributes to raise the confidence in that approached similar to the one presented in this study can be adopted for dealing with several aspects of the air quality management such as air quality assessment, optimization of the location of measurement stations, and the evaluation of air pollution reduction strategies.

Insights into the mechanism of sustained ventricular tachycardia after myocardial infarction in a closed chest porcine model using a multielectrode "basket" catheter.

INTRODUCTION: Accurate analysis of the arrhythmia substrate is important for successful radiofrequency ablation of sustained ventricular tachycardia (VT) after myocardial infarction (MI). METHODS AND RESULTS: A multielectrode "basket" catheter capable of endocardial recording and pacing was inserted percutaneously into the left ventricle of post-MI swine for analysis of the mechanism of sustained VT. Sustained VT was induced in 42 of 61 pigs that survived an acute MI produced by percutaneous transluminal coronary angioplasty balloon occlusion of the left anterior descending coronary artery and injection of agarose gel beads. A multielectrode "basket" catheter (Constellation) with 64 electrodes was inserted in 35 of these animals for analysis of the VT. Induced VT had a cycle length of 179 +/- 25 msec at control and 230 +/- 43 msec after administration of intravenous procainamide. Presystolic electrical activity was recorded from at least 1 of 32 bipolar pairs of electrodes at a mean 40.7 +/- 23.6 msec prior to QRS onset. Isolated mid-diastolic potentials were recorded in 26 of 35 animals. In 22 animals, there were multiple isolated potentials recorded from adjacent electrode pairs. Isochronal maps demonstrated that these potentials returned to the systolic site of origin. Resetting of sustained VT by single premature ventricular stimuli was observed in 6 of 12 animals. Entrainment with overdrive pacing was seen in 19 of 26 animals with induced VT. Concealed entrainment was observed in ten animals. The mean stimulus to QRS interval was 45 +/- 28 msec. Concealed entrainment was observed from adjacent electrode pairs with different stimulus to QRS intervals. CONCLUSION: These data suggest that sustained VT in this model is due to reentry with an excitable gap. A multielectrode "basket" catheter is useful for analyzing the zone of slow conduction participating in the tachycardia circuit. Such analysis may provide useful information to guide successful catheter ablation of sustained VT after MI.