Vapor Products Research Articles

Evaluation of Co/SSZ-13 Zeolite Catalysts Prepared by Solid-Phase Reaction for NO-SCR by Methane.

Co/SSZ‐13 zeolites were prepared by heating the finely dispersed mixture of NH4‐SSZ‐13 and different cobalt salts up to 550 °C. Investigations by thermogravimetry – differential scanning calorimetry – mass spectrometry provided new insight into details of the solid‐state reaction. Formation of Co carrying hydrate melt or volatile species was shown to proceed from chloride, nitrate, or acetylacetonate Co precursor salts upon thermal treatment. This phase change allows the transport of the Co species into the zeolite pores. The reaction of the NH4 + or H+ zeolite cations and the mobile Co precursors generates vapor or gas products, readily leaving the zeolite pores, and cobalt ions in lattice positions suggesting that solid‐state ion‐exchange is the prevailing process. The obtained catalysts are of good activity and N2 selectivity in the CH4/NO‐SCR reaction. The thermal treatment of acetate or formate salts give solid intermediates that are unable to get in contact and react with the cations in the zeolite micropores. These catalysts contain mainly Co‐oxide clusters located on the outer surface of the zeolite crystallites and have poor catalytic performance.

Interactions of PbCl2 capture and CdCl2 capture by kaolin in the high-temperature PbCl2-CdCl2-Kaolin reaction system

Using kaolin for capturing hazardous metals is an effective and promising technology. However, interactions of multiple-metals with kaolin are not been clearly understood. Interactions of PbCl2 capture and CdCl2 capture by kaolin in high-temperature PbCl2-CdCl2-Kaolin reaction system were investigated in a two-stage fixed bed at 800 °C. Capture efficiency considering kaolin dihydroxylation and Pb/Al or Cd/Al were used to evaluate capture performance of kaolin. The results showed that kaolin captured more PbCl2 or CdCl2 in the cases that kaolin captured PbCl2 and CdCl2 at the same time, kaolin captured CdCl2 after its first capture of PbCl2 and kaolin captured PbCl2 after its first capture of CdCl2 than in the case that kaolin only captured PbCl2 or kaolin only captured CdCl2. PbCl2 vapor promoted absorption of kaolin for CdCl2, and CdCl2 vapor also promoted adsorption of kaolin for PbCl2. Heavy metal capture effects were controlled by chemical kinetics due to small particle size of kaolin and short contract time between heavy metal chloride and kaolin. PbCl2 vapor or adsorption products on kaolin surface promoted capture effect of CdCl2 through inhibiting desorption rate of CdCl2. Adsorption products promoted eutectic melting of kaolin surface, and slightly melted kaolin surface exposed new layers with more active sites to continue reactions of kaolin with PbCl2 and CdCl2. Therefore, PbCl2 vapor in the gas flow promoted absorption of kaolin for CdCl2, and CdCl2 vapor also promoted adsorption of kaolin for PbCl2. The results can provide an important reference for Pb and Cd capture during MSW incineration.

The Association of Asthma, Sexual Identity, and Inhaled Substance Use among U.S. Adolescents.

Rationale: Minority sexual identity appears to confer asthma risks. Although associations between inhaled substances and asthma are established, these have not been examined among sexual minority youths. Given sexual minority adolescents' disproportionately high rates of substance use, research is needed to fill this important gap.Objectives: Using a representative sample of adolescents from the United States, we 1) examined associations among asthma, sexual identity, and inhaled substance use and tested 2a) whether sexual identity moderates relationships between asthma and inhaled substance use and 2b) whether inhaled substance use mediates associations between sexual identity and asthma.Methods: Data are from the 2015 and 2017 Youth Risk Behavior Surveillance Survey. Adolescents (n = 30,113) reported if they were ever diagnosed with asthma, current use of cigarettes, cigars and/or cigarillos, marijuana, and electronic vapor products and if they ever used inhalants or synthetic marijuana. We used logistic regression to examine associations between asthma, sexual identity, and inhaled substance use controlling for age, race or ethnicity, and body mass index percentile, stratified by sex.Results: Lesbian, gay, and bisexual respondents had higher relative risks for asthma than heterosexual youth. Sexual minority female youths had significantly higher relative risks than heterosexual female youths for use of every inhaled substance. There were few sexual identity differences in inhaled substance use among male youths. Inhaled substance use was significantly associated with higher risks for asthma. In general, associations between each individual inhaled substance and asthma did not differ between sexual minority and heterosexual youths. However, when all inhaled substances were added into the models concurrently, inhaled substance use appeared to mediate associations with asthma among lesbian and bisexual female youths, and partially mediated these associations among sexual minority male youths.Conclusions: Sexual identity and inhaled substance use appear to play important roles in asthma risk. However, these variables do not fully explain the risk, suggesting that other unmeasured variables (e.g., stress and victimization) may be implicated in risks for both inhaled substance use and asthma. It is important that clinicians providing care to adolescents ask about sexual identity and inhaled substance use. Effective approaches to reducing inhaled substance use among adolescents, especially sexual minorities, are needed.

The Influence of Inflow Swirl on Cavitating and Mixing Processes in a Venturi Tube

A study of the mixing flows (Schmidt number = 103) in a cavitating Venturi tube that feature linear and swirling flows is presented in this paper. The Large Eddy Simulation (LES) turbulence model, the Schnerr–Sauer cavitation model, and the mixture multiphase model, as implemented in the commercial CFD ANSYS FLUENT 16.2, were employed. The main emphasis is spending on the influence of different inlet swirling ratios on the generation of cavitation and mixing behaviors in a Venturi tube. Four different inflow regimes were investigated for the Reynolds number Re = 19,044, 19,250, 19,622, 21,276: zero swirl, 15% swirl, 25% swirl and 50% swirl velocity relative to the transverse inflow velocity, respectively. The computed velocity and pressure profiles were shown in good agreement with the experiment data from the literature. The predicted results indicate that the imposed swirl flow moves the cavitation bubbles away from throat surfaces toward the throat axis. The rapid mixing between two volumetric components is promoted in the divergent section when the intense swirl is introduced. Additionally, the increase in the swirl ratio from 0.15 to 0.5 leads to a linear increase in the static pressure drop and a nonlinear increase in the vapor production. The reduction in the fluid viscosity ratio from μ2μ1=10 to μ2μ1=1 generates a high cavitation intensity in the throat of the Venturi tube. However, the changes in the pressure drop and vapor volume fraction are significantly small of pure water flow.

Magnetic solder to reduce porosity of solder joints formed in microgravity

Solder joints formed in microgravity are inferior to joints formed in Earth gravity. They are mechanically weaker and less electrically conductive due to voids forming in the joints when soldering in microgravity. Surface tension and lack of gravitational buoyancy combine to prevent flux and water vapors from escaping the molten solder in absence of gravity, resulting in more porous solder joints. Additionally, corrosive flux vapor products remain trapped in the voids causing further deterioration.Parabolic aircraft flight microgravity soldering data are presented, to compare the joint porosities of conventional nonmagnetic solders and new magnetic solders, to determine if the magnetic solder, when soldered in the presence of a magnetic field, would reduce porosity of solder joints formed in microgravity. Soldering irons were used to hand-solder resistor leads into PC board though-holes, for nonmagnetic and magnetic solders. Addition of 4 wt% and 6 wt% of iron microparticles to the solder pastes resulted in 24% and 28% reductions in the solder joint average cross-sectional porosity, respectively, relative to average nonmagnetic solder joint porosity. Joint porosity distributions were log-normal, so the Wilcoxon Rank Sum test for statistical significance was used to show these porosity reductions are statistically significant at α = 0.05. A fully-developed wire magnetic solder could enable in-space repair of electronics at the component level, giving space mission planners additional flexibility to eliminate some or all spare board-level electronics, and plan instead to perform electronics repairs at the component level. This could then reduce or eliminate required mass of these spare electronics boards.

Stable Self-Floating Reduced Graphene Oxide Hydrogel Membrane for High Rate of Solar Vapor Evaporation under 1 sun.

Highly efficient vapor generation with considerable stability under natural solar irradiance is a promising technology for seawater desalination and wastewater purification. Here a broadband solar absorber of reduced graphene oxide hydrogel membrane (rGOHM), synthesized via an environmentally friendly one‐step hydrothermal reduction process, is demonstrated, which shows a high rate of solar vapor production and superior stability. The porous rGOHM containing more than 99.5% water within its small volume floats on the surface of water, exhibiting efficient solar absorption of ≈98% across 300–2500 nm, as well as sufficient water‐pumping pathways. The evaporation rate can be tuned by changing the water volume. By controlling the water volume, the self‐floating rGOHM can enable efficient interfacial solar vapor generation at a high rate of ≈2.33 kg m−2 h−1 under 1 sun, which is comparable to the rate generated by the evaporator with an extra insulator. In addition, the evaporation rate of rGOHM is only slightly affected at a high saltwater concentration (at least 15 wt%), and the rGOHM shows mechanical and physical stability. The superior evaporation performance combined with efficient eradication of wastewater contaminants, cost‐effectiveness, and straightforward fabrication process, makes this rGOHMs ideal for advanced high‐concentration seawater desalination and wastewater treatment technologies.

Validating HY-2A CMR precipitable water vapor using ground-based and shipborne GNSS observations

Abstract. The calibration microwave radiometer (CMR) on board the Haiyang-2A (HY-2A) satellite provides wet tropospheric delay correction for altimetry data, which can also contribute to the understanding of climate system and weather processes. The ground-based global navigation satellite system (GNSS) provides precise precipitable water vapor (PWV) with high temporal resolution and could be used for calibration and monitoring of the CMR data, and shipborne GNSS provides accurate PWV over open oceans, which can be directly compared with uncontaminated CMR data. In this study, the HY-2A CMR water vapor product is validated using ground-based GNSS observations of 100 International GNSS Service (IGS) stations along the global coastline and 56 d shipborne GNSS observations over the Indian Ocean. The processing strategy for GNSS data and CMR data is discussed in detail. Special efforts were made in the quality control and reconstruction of contaminated CMR data. The validation result shows that HY-2A CMR PWV agrees well with ground-based GNSS PWV with 2.67 mm as the root mean square (rms) within 100 km. Geographically, the rms is 1.12 mm in the polar region and 2.78 mm elsewhere. The PWV agreement between HY-2A and shipborne GNSS shows a significant correlation with the distance between the ship and the satellite footprint, with an rms of 1.57 mm for the distance threshold of 100 km. Ground-based GNSS and shipborne GNSS agree with HY-2A CMR well.

Refining MODIS NIR Atmospheric Water Vapor Retrieval Algorithm Using GPS-Derived Water Vapor Data

A new algorithm of retrieving atmospheric water vapor from MODIS near-infrared (IR) (NIR) data by using a regression fitting method based on Global Positioning System (GPS)-derived water vapor is developed in this work. The algorithm has been used to retrieve total column water vapor from Moderate Resolution Imaging Spectroradiometer (MODIS) satellites both Terra and Aqua under cloud-free conditions from solar radiation in the NIR channels. Water vapor data estimated from GPS observations recorded from 2003 to 2017 by the SuomiNet GPS network over the western North America are used as ground truth references. The GPS stations were classified into six subsets based on the surface types adopted from MCD12Q1 IGBP legend. The differences in surface types are considered in the regression fitting procedure, thus different regression functions are trained for different surface types. Thus, the wet bias in the operational MODIS water vapor products has been significantly reduced. Water vapor retrieved from each of the three absorption channels and the weighted water vapor of combined three absorption channels are analyzed. Validation shows that the weighted water vapor performs better than the single-channel results. Compared to the MODIS/Terra water vapor products, the RMSE has been reduced by 50.78% to 2.229 mm using the two-channel ratio transmittance method and has been reduced by 53.06% to 2.126 mm using the three-channel ratio transmittance method. Compared to the MODIS/Aqua water vapor products, the RMSE has been reduced by 45.54% to 2.423 mm using the two-channel ratio transmittance method and has been reduced by 45.34% to 2.432 mm using the three-channel ratio transmittance method.

Tobacco Product Use Among High School Students - Youth Risk Behavior Survey, United States, 2019.

Tobacco product use is the leading cause of preventable disease, disability, and death in the United States. This report used data from the 2019 Youth Risk Behavior Survey to assess the following among U.S. high school students: ever use of cigarettes and electronic vapor products, current use (≥1 day during the 30 days before the survey) of tobacco products, frequent use (≥20 days during the 30 days before the survey) among current users of tobacco products, trends in use over time, and usual source of electronic vapor products among current electronic vapor product users. In 2019, a total of 50.1% of U.S. high school students had ever used electronic vapor products, and 24.1% had ever tried cigarette smoking. Current electronic vapor product use was 32.7%, current cigarette smoking was 6.0%, current cigar smoking was 5.7%, and current smokeless tobacco use was 3.8%. Approximately 36.5% of students were current users of any tobacco product, and 8.2% were current users of two or more tobacco products. Frequent use among users of individual products was 32.6% for electronic vapor products, 28.5% for smokeless tobacco, 22.2% for cigarettes, and 18.4% for cigars. Among current electronic vapor product users who were aged ≤17 years, the most commonly reported source was borrowing them from someone else (42.8%). Significant decreases occurred in current cigarette smoking (1991: 27.5%; 2019: 6.0%), cigar smoking (1997: 22.0%; 2019: 5.7%), and smokeless tobacco use (2017: 5.5%; 2019: 3.8%). However, significant increases occurred in current electronic vapor product use (2015: 24.1%; 2019: 32.7%) and any tobacco product use (2017: 19.5%; 2019: 36.5%). Although current cigarette smoking, cigar smoking, and smokeless tobacco use has decreased among high school students, the increased prevalence of electronic vapor product use among youths is concerning. Continued surveillance for all tobacco product use is warranted for guiding and evaluating public health policy at the local, state, tribal, and national levels.

Validation of Sentinel-3 OLCI Integrated Water Vapor Products Using Regional GNSS Measurements in Crete, Greece

Water vapor is one of the essential variables in monitoring the Earth’s climate. The Ocean and Land Color Instrument (OLCI) on-board the Copernicus Sentinel-3 missions measures the Integrated Water Vapor (IWV) column over land and ocean surfaces. Post-launch calibration and validation of satellite measurements constitutes a key process in the operational phase of Earth observation satellites. This work presents the external and independent validation of OLCI-A IWV product using the regional network of continuously operating Global Navigation Satellite System (GNSS) comprised 10 stations distributed over the island of Crete in the eastern Mediterranean. The Sentinel-3A/-3B OLCI imagery that captures in a single scene the entire area of Crete has been examined. For each OLCI image, the IWV value of cloud-free pixels containing the GNSS stations have been derived and compared against simultaneous GNSS-derived measurements. The absolute as well as the relative bias between OLCI-A and OLCI-B IWV measurements have been determined. There is a good agreement between OLCI and GNSS with a bias of −0.57 mm ± 2.90 mm for OLCI(A) and +2.42 ± 3.41 mm for OLCI(B). The results of this regional validation activity are compared against other studies and the regular validation carried out at the Sentinel-3 Mission Performance Center. This work concludes that the accuracy of the OLCI IWV products is within its design requirements. The potential synergy between Sentinel-2 and Sentinel-3 IWV products is also discussed.

Electronic Vapor Product Use and Violence Victimization Among a Nationally Representative Sample of Adolescents

PurposeWe examined associations between electronic vapor product use (vaping) and violence victimization (adolescent relationship abuse (ARA), youth violence, bullying, and experiencing all three types of violence). MethodsData were drawn from the 2017 National Youth Risk Behavioral Survey. Logistic regression examined associations between vaping and violence victimization, adjusting for sex, age, race, identification as a sexual minority, and use of other substances. ResultsAfter adjusting for demographic characteristics, vaping was significantly and positively associated with ARA, youth violence, bullying, and experiencing all three types of violence (ARA: adjusted odds ratio (aOR) 3.0, 95% CI: 2.5–3.5; youth violence: aOR 3.0, CI: 2.4–3.6; bullying: aOR 1.5, CI: 1.4–1.7; all three types of violence: 10, CI: 6.3, 15.8). When use of other substances was added into the model, these associations attenuated, and, for bullying, lost significance. ConclusionsVaping is associated with increased violence victimization, particularly for youth experiencing ARA, youth violence, and polyvictimization. Further longitudinal studies are needed to determine directionality of these associations and guide prevention efforts.

An improvement in accuracy and spatiotemporal continuity of the MODIS precipitable water vapor product based on a data fusion approach

Precipitable water vapor (PWV) is among the key variables in the water and energy cycles, whereas current PWV products are limited by spatiotemporal discontinuity, low accuracy, and/or coarse spatial resolution. Based on two widely used global PWV products, i.e., satellite-based MODIS and reanalysis-based ERA5 products, here we propose a data fusion approach to generate PWV maps of spatiotemporal continuity and high resolution (0.01°, daily) for the Upper Brahmaputra River (UBR, referred to as the Yarlung Zangbo River in China) basin in the Tibetan Plateau (TP) during the monsoon period (May – September) from 2007 to 2013. Results show that the fused PWV estimates have good agreement with PWV estimates from nine GPS stations (i.e., correlation coefficient: 0.87–0.97, overall bias: −0.4–1.8 mm, and root-mean-square error: 1.1–2.0 mm), greatly improving the accuracy of the MODIS PWV product. The fused PWV maps of high spatial resolution provide detailed and reasonable spatial variations which are generally consistent with those from the MODIS estimates under confident clear conditions and ERA5. Mean monthly PWV estimates across the UBR basin vary from ~6 to ~12 mm during the study period, and for each month high PWV values are found along the UBR valley and at the basin outlet. The developed data fusion approach maximizes the potential of satellite and reanalysis-based PWV products for retrieving PWV and has the potential to be applied to other high-mountain regions. The generated PWV estimates for the UBR basin are valuable in understanding the water and energy cycles and in retrieving atmospheric and surface variables for the southern TP including the Himalaya.

A thermally-limited bubble growth model for the relaxation time of superheated fuels

We propose a novel approach to evaluate the relaxation time of vapor bubble growth in the context of the flash boiling of a superheated liquid. In alternative to the empirical correlation derived from superheated water experiments almost fifty years ago, the new model describes the thermally-dominated growth of vapor bubbles in terms that are dependent on the local Jakob number (the ratio of sensible heat to latent heat during phase change) and the number density of vapor bubbles. The model is tested by plugging the resulting relaxation time into the Homogenous Relaxation Model (HRM). Flash-boiling simulations carried out with HRM are compared with n-pentane (C5H12) injection and boil-off experiments conducted with a real-size, axial-hole, transparent gasoline injector discharging into a constant-pressure vessel. The long-distance microscopy images from the experiments, processed to derive the projected liquid volume (PLV) of the spray, provide a unique set of time-resolved validation data for direct fuel injection simulations. At conditions ranging from flaring to mild and minimal flash boiling, we show that switching to the new relaxation time improves the agreement with the measured PLV profiles with respect to the standard empirical model. Particularly at flaring conditions, the predicted increase in gas cooling caused by rapid vapor production is shown to be more consistent with the observed boil-off.

A Collaborative Community Approach to Address The Adolescent Vaping Epidemic

A new health crisis has emerged affecting our youth, the use of electronic cigarette devices. Based on data obtained by The University of Michigan, (Monitoring The Future), in 2017 the lifetime prevalence of vaping was at 40% for 12th graders, and 20% for 8th graders. Since then, the rates of use among youth ages 12 and above have reached alarming rates, increasing 10% among high school seniors this past year, and 2.6% among 8th graders, resulting in 1.3 million additional teens using nicotine vapor products in the past year …

Heater for Controlled Evaporation of Liquids for Personalized Drug Delivery to the Lungs

We examined the potential of thermal evaporation for the controlled production of aerosols for the administration of drugs to the lungs. A novel volumetric heater was designed and fabricated allowing better control of the heating power transferred to the solvent compared to conventional coil heaters that are commonly used in e-cigarettes. The whole silicon chip is used as a resistive heater. Therefore, we call this approach a volumetric heater. We demonstrate that the vapor production of the volumetric heater can be controlled over a wide dynamic range by varying the heater temperature. [2020-0105]

Remotely Sensed Urban Surface Ecological Index (RSUSEI): An Analytical Framework for Assessing the Surface Ecological Status in Urban Environments

Urban Surface Ecological Status (USES) reflects the structure and function of an urban ecosystem. USES is influenced by the surface biophysical, biochemical, and biological properties. The assessment and modeling of USES is crucial for sustainability assessment in support of achieving sustainable development goals such as sustainable cities and communities. The objective of this study is to present a new analytical framework for assessing the USES. This analytical framework is centered on a new index, Remotely Sensed Urban Surface Ecological index (RSUSEI). In this study, RSUSEI is used to assess the USES of six selected cities in the U.S.A. To this end, Landsat 8 images, water vapor products, and the National Land Cover Database (NLCD) land cover and imperviousness datasets are downloaded for use. Firstly, Land Surface Temperature (LST), Wetness, Normalized Difference Vegetation Index (NDVI), and Normalized Difference Soil Index (NDSI) are derived by remote sensing methods. Then, RSUSEI is developed by the combination of NDVI, NDSI, Wetness, LST, and Impervious Surface Cover (ISC) with Principal Components Analysis (PCA). Next, the spatial variations of USES across the cities are evaluated and compared. Finally, the association degree of each parameter in the USES modeling is investigated. Results show that the spatial variability of LST, ISC, NDVI, NDSI, and Wetness is heterogeneous within and between cities. The mean (standard deviation) value of RSUSEI for Minneapolis, Dallas, Phoenix, Los Angeles, Chicago and Seattle yielded 0.58 (0.16), 0.54 (0.17), 0.47 (0.19), 0.63 (0.21), 0.50 (0.17), and 0.44 (0.19), respectively. For all the cities, PC1 included more than 93% of the surface information, which is contributed by greenness, moisture, dryness, heat, and imperviousness. The highest and lowest mean values of RSUSEI are found in “Developed, High intensity” (0.76) and “Developed, Open Space” (0.35) lands, respectively. The mean correlation coefficient between RSUSEI and LST, ISC, NDVI, NDSI, and Wetness, is 0.47, 0.97, −0.31, 0.17, and −0.27, respectively. The statistical significance of these correlations is confirmed at 95% confidence level. These results suggest that the association degree of ISC in USES modeling is the highest, despite the differences in land cover and biophysical characteristics in the cities. RSUSEI could be very useful in modeling and comparing USES across cities with different geographical, climatic, environmental, and biophysical conditions and can also be used for assessing urban sustainability over space and time.

A hybrid method for reconstructing the historical evolution of aerosol optical depth from sunshine duration measurements

Abstract. A novel method has been developed to estimate aerosol optical depth (AOD) from sunshine duration (SD) measurements under cloud-free conditions. It is a physically based method serving for the reconstruction of the historical evolution of AOD during the last century. In addition to sunshine duration data, it requires daily water vapor and ozone products as inputs taken from the ECMWF 20th century reanalysis ERA-20C, available at the global scale over the period 1900–2010. Surface synoptic cloud observations are used to identify cloud-free days. For 16 sites over Europe, the accuracy of the estimated daily AOD, and its seasonal variability, is similar to or better than those from two earlier methods when compared to AErosol RObotic NETwork measurements. In addition, it also improves the detection of the signal from massive aerosol events such as important volcanic eruptions (e.g., Arenal and Fernandina Island in 1968, El Chichón in 1982 and Pinatubo in 1992). Finally, the reconstructed AOD time series are in good agreement with the dimming/brightening phenomenon and also provide preliminary evidence of the early-brightening phenomenon.

Evaluation of Precipitable Water Vapor from Five Reanalysis Products with Ground-Based GNSS Observations

At present, the global reliability and accuracy of Precipitable Water Vapor (PWV) from different reanalysis products have not been comprehensively evaluated. In this study, PWV values derived by 268 Global Navigation Satellite Systems (GNSS) stations around the world covering the period from 2016 to 2018 are used to evaluate the accuracies of PWV values from five reanalysis products. The temporal and spatial evolution is not taken into account in this analysis, although the temporal and spatial evolution of atmospheric flows is one of the most important information elements available in numerical weather prediction products. The evaluation results present that five reanalysis products with PWV accuracy from high to low are in the order of the fifth generation of European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis (ERA5), ERA-Interim, Japanese 55-year Reanalysis (JRA-55), National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR), and NCEP/DOE (Department of Energy) according to root mean square error (RMSE), bias and correlation coefficient. The ERA5 has the smallest RMSE value of 1.84 mm, while NCEP/NCAR and NCEP/DOE have bigger RMSE values of 3.34 mm and 3.51 mm, respectively. The findings demonstrate that ERA5 and two NCEP reanalysis products have the best and worst performance, respectively, among five reanalysis products. The differences in the accuracy of the five reanalysis products are mainly attributed to the differences in the spatial resolution of reanalysis products. There are some large absolute biases greater than 4 mm between GNSS PWV values and the PWV values of five reanalysis products in the southwest of South America and western China due to the limit of terrains and fewer observations. The accuracies of five reanalysis products are compared in different climatic zones. The results indicate that the absolute accuracies of five reanalysis products are highest in the polar regions and lowest in the tropics. Furthermore, the effects of different seasons on the accuracies of five reanalysis products are also analyzed, which indicates that RMSE values of five reanalysis products in summer and in winter are the largest and the smallest in the temperate regions. Evaluation results from five reanalysis products can help us to learn more about the advantages and disadvantages of the five released water vapor products and promote their applications.

Cigarette and electronic vapor product use among high school students in Georgia, 2015-2018.

Adolescent use of electronic vapor products (EVP) is increasing; however, changes in EVP use in the context of cigarette smoking is less certain. We analyzed trends in EVP and cigarette use among high school students in the state of Georgia. We used self-reported EVP and cigarette use from the annual Georgia Student Health Survey 2.0 for 2015 to 2018 (N = 1,405,108). Users were categorized as exclusive EVP users, exclusive cigarette users, or dual users. We assessed current (≥1 day in past 30 days) use of EVPs, cigarettes, and dual users of both products, as well as number of days the products were used among current users. We compared current users, as well as number of days used, across adjacent years using tests for proportion and Wilcoxon t-tests, respectively. The proportion of current exclusive EVP users and dual users increased during 2017–2018 (4.2% to 6.9% and 1.6% to 3.7%, p < 0.001, respectively) after declining during 2015–2017, while the proportion of exclusive cigarette users declined during 2015–2018 (2.0% to 1.0%, p < 0.001). Similarly, the mean number of days of EVP use increased among exclusive EVP and dual users, and mean number of days of cigarette use increased among dual users during 2017–2018 (p < 0.001). These findings reinforce the importance of continued efforts to reduce all forms of tobacco products use among Georgia high school students.

Recent declines in global water vapor from MODIS products: Artifact or real trend?

Atmospheric water vapor plays a key role in the global water and energy cycles. Accurate estimation of water vapor and consistent representation of its spatial-temporal variation are critical to climate analysis and model validation. This study used ground observational data from global radiosonde and sunphotometer networks to evaluate MODIS (MODerate-resolution Imaging Spectroradiometer) precipitable water vapor (PWV) products for 2000–2017. The products included the thermal-infrared (TIR) (Collection 6, C006) and its updated version (Collection 061, C061), and near-infrared (NIR) products (C061). Our results demonstrated that compared to its earlier version subject to sensor crosstalk problem, the C061_TIR data showed improved accuracy in terms of bias, standard deviation, mean absolute error, root mean square error, and coefficient of determination, regression slope and intercept. Among the PWV products, C061_NIR data achieved the best overall performance in accuracy evaluation. The C061_NIR revealed the PWV had a multi-year average of 2.50 ± 0.08 cm for the globe, 2.03 ± 0.06 cm for continents, and 2.70 ± 0.09 cm for oceans in 2000–2017. The PWV values yielded an increasing rate of 0.015 cm/year for the globe, 0.010 cm/year for continents, and 0.017 cm/year for oceans. Nearly 98.95% of the globe showed an increasing trend, 80.74% of statistical significance, mainly distributed within and around the tropical zones. The findings should be valuable for understanding of global water and energy cycles.