135 results on '"FONG NGAN, SO"'
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2. Factors of COVID-19 Vaccine Perception among Transport Drivers in Singapore: A Cross-Sectional Pilot Study
- Author
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Huizi Lim, Evelyn, primary, Fong, Ngan Phoon, additional, and Pang, Junxiong, additional
- Published
- 2023
- Full Text
- View/download PDF
3. EPIDEMIOLOGY OF NONCOMMUNICABLE DISEASES
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Venkataraman, Kavita, primary and Fong, Ngan Phoon, additional
- Published
- 2019
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4. The Use of Small Uncrewed Aircraft System Observations in Meteorological and Dispersion Modeling
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Fong Ngan, Christopher P. Loughner, Sonny Zinn, Mark Cohen, Temple R. Lee, Edward Dumas, Travis J. Schuyler, C. Bruce Baker, Joseph Maloney, David Hotz, and George Mathews
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Atmospheric Science - Abstract
A series of meteorological measurements with a small Uncrewed Aircraft System (sUAS) was collected at Oliver Springs Airport, Tennessee. The sUAS provides a unique observing system capable of obtaining vertical profiles of meteorological data within the lowest few hundred meters of the boundary layer. The measurements benefit simulated plume predictions by providing more accurate meteorological data to a dispersion model. The sUAS profiles can be used directly to drive HYSPLIT dispersion simulations. When using sUAS data covering a small domain near a release and meteorological model fields covering a larger domain, simulated pollutants may be artificially increased or decreased near the domain boundary due to inconsistencies in the wind fields between the two meteorological inputs. Numerical experiments using the Weather Research and Forecasting (WRF) model with observational nudging reveal that incorporating sUAS data improves simulated wind fields and can significantly affect mixing characteristics of the boundary layer, especially during the morning transition period of the planetary boundary layer. We conducted HYSPLIT dispersion simulations for hypothetical releases for three case study periods using WRF meteorological fields with and without assimilating sUAS measurements. The comparison of dispersion results on 15 and 16 December 2021 shows that using sUAS observational nudging is more significant under weak synoptic conditions than strong influences from regional weather. Very different dispersion results were introduced by the meteorological fields used. The observational nudging produced not just a sUAS-nudged wind flow but also adjusted meteorological fields that further impacted the mixing calculation in HYSPLIT.
- Published
- 2023
5. Estimation of power plant SO2 emissions using HYSPLIT dispersion model and airborne observations with plume rise ensemble runs
- Author
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Tianfeng Chai, Xinrong Ren, Fong Ngan, Mark Cohen, and Alice Crawford
- Abstract
SO2 mixing ratio measurements were made by a research aircraft close to three power plants in North Carolina on March 26, 2019. An ensemble of dispersion simulations with HYSPLIT model v5.2.0 are carried out using a total of 15 heat release parameters ranging from 10 MW to 150 MW for the Briggs plume rise calculation to quantify some of the modeling uncertainties related to this phenomena. For each heat release value, a total of 72 independent HYSPLIT Lagrangian model runs with unit hourly emissions from the three point sources are made to form a transfer coefficient matrix (TCM) with the airborne observations. The TCMs can be decoupled into six segments where the observations of each segment are only influenced by a single power plant in its morning or afternoon operation. Prior to estimating the power plant emissions, the simulation performance is first evaluated with the correlation coefficients between the observations and the model prediction with constant unit-emission in its morning or afternoon operations. The segment influenced by the afternoon operations of Belews Creek power plant has negative correlation coefficients for all the plume rise options and is excluded from the emission estimate when the “optimal” member is selected based on the correlation coefficient. For the other segments, the plume rise runs with the highest correlation coefficients are selected for the emission estimates using the HYSPLIT inverse modeling system. In the TCM-based inverse modeling, the emission estimates are obtained by minimizing a cost function which measures the difference between logarithmic predicted and observed mixing ratios but also takes model uncertainties into account. A cost function normalization scheme is adopted to avoid spurious emission solutions when using logarithmic concentration differences following Chai et al. (2018). The source estimation results of the three power plants with the morning and afternoon flight segments are compared with the Continuous Emissions Monitoring Systems (CEMS) data. Overestimations are found for all the segments before considering the background SO2 mixing ratios. Both constant background mixing ratios and several segment-specific background values are tested in the HYSPLIT inverse modeling. The estimation results by assuming the 25th percentile observed SO2 mixing ratio inside each of the five segments agree well with the CEMS data, with relative errors as 18 %, -12 %, 3 %, 93.5 %, and -4 %. After emission estimations are performed for all the plume rise runs, least root mean square error (RMSE) between the predicted and observed mixing ratios are calculated to select a different set of “optimal” plume rise runs which have the least RMSEs. Identical plume rise runs are chosen as the “optimal” members for Roxboro and Belews Creek morning segments, but different members for the other segments yield smaller RMSEs than the previous correlation-based “optimal” members. It is also no longer necessary to exclude the Belews Creek afternoon segment that has negative correlation between predictions and observations. The RMSE-based “optimal” runs result in a much better agreement with the CEMS data for the previous severely overestimated segment and do not deteriorate much for the other segments, with relative errors as 18 %, -18 %, 3 %, -9 %, and 27 % for the five segments, and 2 % for Belews Creek afternoon segment. While the RMSE-based “optimal” plume rise runs appear to agree better with the observations than the correlation-based “optimal” runs when they are different, significant differences exist in the area where observations are missing.
- Published
- 2023
6. Rehabilitation Outcomes After Inpatient Rehabilitation for Lower Extremity Amputations in Patients With Diabetes
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Venkataraman, Kavita, Fong, Ngan Phoon, Chan, Kin Ming, Tan, Boon Yeow, Menon, Edward, Ee, Chye Hua, Lee, Kok Keng, and Koh, Gerald Choon-Huat
- Published
- 2016
- Full Text
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7. Evaluating the Effects of Capacity Building Initiatives and Primary Care Networks in Singapore: Outcome Harvesting of System Changes to Chronic Disease Care Delivery
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Chen, Andrew Teik Hong, primary, Koh, Gerald Choon-Huat, additional, Fong, Ngan Phoon, additional, Lim, Jeremy Fung Yen, additional, and Hildon, Zoe Jane-Lara, additional
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- 2023
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8. Meteorological Modeling Using the WRF-ARW Model for Grand Bay Intensive Studies of Atmospheric Mercury
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Fong Ngan, Mark Cohen, Winston Luke, Xinrong Ren, and Roland Draxler
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WRF ,mercury ,nudging ,reanalysis data ,Grand Bay ,Meteorology. Climatology ,QC851-999 - Abstract
Measurements at the Grand Bay National Estuarine Research Reserve support a range of research activities aimed at improving the understanding of the atmospheric fate and transport of mercury. Routine monitoring was enhanced by two intensive measurement periods conducted at the site in summer 2010 and spring 2011. Detailed meteorological data are required to properly represent the weather conditions, to determine the transport and dispersion of plumes and to understand the wet and dry deposition of mercury. To describe the mesoscale features that might influence future plume calculations for mercury episodes during the Grand Bay Intensive campaigns, fine-resolution meteorological simulations using the Weather Research and Forecasting (WRF) model were conducted with various initialization and nudging configurations. The WRF simulations with nudging generated reasonable results in comparison with conventional observations in the region and measurements obtained at the Grand Bay site, including surface and sounding data. The grid nudging, together with observational nudging, had a positive effect on wind prediction. However, the nudging of mass fields (temperature and moisture) led to overestimates of precipitation, which may introduce significant inaccuracies if the data were to be used for subsequent atmospheric mercury modeling. The regional flow prediction was also influenced by the reanalysis data used to initialize the WRF simulations. Even with observational nudging, the summer case simulation results in the fine resolution domain inherited features of the reanalysis data, resulting in different regional wind patterns. By contrast, the spring intensive period showed less influence from the reanalysis data.
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- 2015
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9. Factors and Trade-Offs With Rehabilitation Effectiveness and Efficiency in Newly Disabled Older Persons
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Chow, Patsy, Chen, Cynthia, Cheong, Angela, Fong, Ngan Phoon, Chan, Kin Ming, Tan, Boon Yeow, Menon, Edward, Ee, Chye Hua, Lee, Kok Keng, Koh, David, and Koh, Gerald C.
- Published
- 2014
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10. Retrospective Air Quality Simulations of the TexAQS-II: Focused on Emissions Uncertainty
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DaeGyun Lee, Soontae Kim, Hyuncheol Kim, and Fong Ngan
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texaqs-ii ,emissions uncertainty ,houston ozone ,hrvoc ,cmaq ,Environmental technology. Sanitary engineering ,TD1-1066 ,Environmental sciences ,GE1-350 - Abstract
There are several studies on the effects of emissions of highly reactive volatile organic compounds (HRVOC) from the industrial sources in the Houston- Galveston-Brazoria (HGB) area on the high ozone events during the Texas Air Quality Study (TexAQS) in summer of 2000. They showed that the modeled atmosphere lacked reactivity to produce the observed high ozone event and suggested “imputation” of HRVOC emissions from the base inventory. Byun et al. (2007b) showed the imputed inventory leads to too high ethylene concentrations compared to the measurements at the chemical super sites but still too little aloft compared to the NOAA aircraft. The paper suggested that the lack of reactivity in the modeled Houston atmosphere must be corrected by targeted, and sometimes of episodic, increase of HRV OC emissions from the large sources such as flares in the Houston Ship Channel (HSC) distributed into the deeper level of the boundary layer. We performed retrospective meteorological and air quality modeling to achieve better air quality prediction of ozone by comparison with various chemical and meteorological measurements during the Texas Air Quality Study periods in August-September 2006 (TexA QS-II). After identifying several shortcomings of the forecast meteorological simulations and emissions inputs, we prepared new retrospective meteorological simulations and updated emissions inputs. We utilized assimilated MM5 inputs to achieve better meteorological simulations (detailed description of MM5 assimilation can be found in F. Ngan et al., 2012) and used them in this study for air quality simulations. Using the better predicted meteorological results, we focused on the emissions uncertainty in order to capture high peak ozone which occasionally happens in the HGB area. We described how the ozone predictions are affected by emissions uncertainty in the air quality simulations utilizing different emission inventories and adjustments.
- Published
- 2014
- Full Text
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11. Estimation of power plant SO2 emissions using HYSPLIT dispersion model and airborne observations with plume rise ensemble runs.
- Author
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Tianfeng Chai, Xinrong Ren, Fong Ngan, Cohen, Mark, and Crawford, Alice
- Abstract
SO
2 mixing ratio measurements were made by a research aircraft close to three power plants in North Carolina on March 26, 2019. An ensemble of dispersion simulations with HYSPLIT model v5.2.0 are carried out using a total of 15 heat release parameters ranging from 10 MW to 150 MW for the Briggs plume rise calculation to quantify the underlying modeling uncertainties. For each heat release value, a total of 72 independent HYSPLIT Lagrangian model runs with unit hourly emissions from the three point sources are made to form a transfer coefficient matrix (TCM) with the airborne observations. The TCMs can be decoupled into six segments where the observations of each segment are only influenced by a single power plant in its morning or afternoon operation. Prior to estimating the power plant emissions, the simulation performance is first evaluated with the correlation coefficients between the observations and the model prediction with constant unit-emission in its morning or afternoon operations. The segment influenced by the afternoon operations of Belews Creek power plant has negative correlation coefficients for all the plume rise options and is excluded from the emission estimate when the "optimal" member is selected based on the correlation coefficient. For the other segments, the plume rise runs with the highest correlation coefficients are selected for the emission estimates using the HYSPLIT inverse modeling system. In the TCM-based inverse modeling, the emission estimates are obtained by minimizing a cost function which measures the difference between logarithmic predicted and observed mixing ratios but also takes model uncertainties into account. A cost function normalization scheme is adopted to avoid spurious emission solutions when using logarithmic concentration differences following Chai et al. (2018). The source estimation results of the three power plants with the morning and afternoon flight segments are compared with the Continuous Emissions Monitoring Systems (CEMS) data. Overestimations are found for all the segments before considering the background SO2 mixing ratios. Both constant background mixing ratios and several segment-specific background values are tested in the HYSPLIT inverse modeling. The estimation results by assuming the 25th percentile observed SO2 mixing ratio inside each of the five segments agree well with the CEMS data, with relative errors as 18%, -12%, 3%, 93.5%, and -4%. After emission estimations are performed for all the plume rise runs, least root mean square errors (RMSEs) between the predicted and observed mixing ratios are calculated to select a different set of "optimal" plume rise runs which have the least RMSEs. Identical plume rise runs are chosen as the "optimal" members for Roxboro and Belews Creek morning segments, but different members for the other segments yield smaller RMSEs than the previous correlation-based "optimal" members. It is also no longer necessary to exclude the Belews Creek afternoon segment that has negative correlation between predictions and observations. The RMSE-based "optimal" runs result in a much better agreement with the CEMS data for the previous severely overestimated segment and do not deterioirate much for the other segments, with relative errors as 18%, -18%, 3%, - 9%, and 27% for the five segments, and 2% for Belews Creek afternoon segment. While the RMSE-based "optimal" plume rise runs appear to agree better with the observations than the correlation-based "optimal" runs when they are different, significant differences exist in the area where observations are missing. [ABSTRACT FROM AUTHOR]- Published
- 2023
- Full Text
- View/download PDF
12. Mercury Speciation at a Coastal Site in the Northern Gulf of Mexico: Results from the Grand Bay Intensive Studies in Summer 2010 and Spring 2011
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Xinrong Ren, Winston T. Luke, Paul Kelley, Mark Cohen, Fong Ngan, Richard Artz, Jake Walker, Steve Brooks, Christopher Moore, Phil Swartzendruber, Dieter Bauer, James Remeika, Anthony Hynes, Jack Dibb, John Rolison, Nishanth Krishnamurthy, William M. Landing, Arsineh Hecobian, Jeffery Shook, and L. Greg Huey
- Subjects
atmospheric mercury ,gaseous elemental mercury ,gaseous oxidized mercury ,particulate-bound mercury ,Gulf of Mexico ,principal component analysis ,HYSPLIT ,Meteorology. Climatology ,QC851-999 - Abstract
During two intensive studies in summer 2010 and spring 2011, measurements of mercury species including gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), and particulate-bound mercury (PBM), trace chemical species including O3, SO2, CO, NO, NOY, and black carbon, and meteorological parameters were made at an Atmospheric Mercury Network (AMNet) site at the Grand Bay National Estuarine Research Reserve (NERR) in Moss Point, Mississippi. Surface measurements indicate that the mean mercury concentrations were 1.42 ± 0.12 ng∙m−3 for GEM, 5.4 ± 10.2 pg∙m−3 for GOM, and 3.1 ± 1.9 pg∙m−3 for PBM during the summer 2010 intensive and 1.53 ± 0.11 ng∙m−3 for GEM, 5.3 ± 10.2 pg∙m−3 for GOM, and 5.7 ± 6.2 pg∙m−3 for PBM during the spring 2011 intensive. Elevated daytime GOM levels (>20 pg∙m−3) were observed on a few days in each study and were usually associated with either elevated O3 (>50 ppbv), BrO, and solar radiation or elevated SO2 (>a few ppbv) but lower O3 (~20–40 ppbv). This behavior suggests two potential sources of GOM: photochemical oxidation of GEM and direct emissions of GOM from nearby local sources. Lack of correlation between GOM and Beryllium-7 (7Be) suggests little influence on surface GOM from downward mixing of GOM from the upper troposphere. These data were analyzed using the HYSPLIT back trajectory model and principal component analysis in order to develop source-receptor relationships for mercury species in this coastal environment. Trajectory frequency analysis shows that high GOM events were generally associated with high frequencies of the trajectories passing through the areas with high mercury emissions, while low GOM levels were largely associated the trajectories passing through relatively clean areas. Principal component analysis also reveals two main factors: direct emission and photochemical processes that were clustered with high GOM and PBM. This study indicates that the receptor site, which is located in a coastal environment of the Gulf of Mexico, experienced impacts from mercury sources that are both local and regional in nature.
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- 2014
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13. Trends in Length of Stay, Functional Outcomes, and Discharge Destination Stratified by Disease Type for Inpatient Rehabilitation in Singapore Community Hospitals From 1996 to 2005
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Chen, Cynthia, Koh, Gerald Choon-Huat, Naidoo, Nasheen, Cheong, Angela, Fong, Ngan Phoon, Tan, Yaoyuan Vincent, Chan, Kin Ming, Tan, Boon Yeow, Menon, Edward, Ee, Chye Hua, Lee, Kok Keng, Ng, Yee Sien, Koh, David, Chia, Kee Seng, and Teo, Yik Ying
- Published
- 2013
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14. Colorectal Cancer Screening: The Effectiveness of Education on Its Barriers and Acceptability
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Foo, Aaron S. C., Thia, Joshua J. P., Ng, Zhi Peng, Fong, Ngan Phoon, and Koh, Gerald C. H.
- Published
- 2012
15. A Conservative Downscaling of Satellite-Detected Chemical Compositions: NO2 Column Densities of OMI, GOME-2, and CMAQ.
- Author
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Hyun Cheol Kim, Sang-Mi Lee, Tianfeng Chai, Fong Ngan, Li Pan, and Pius Lee
- Published
- 2018
- Full Text
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16. Effect of Duration, Participation Rate, and Supervision During Community Rehabilitation on Functional Outcomes in the First Poststroke Year in Singapore
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Koh, Gerald Choon-Huat, Saxena, Sanjiv K., Ng, Tze-Pin, Yong, David, and Fong, Ngan-Phoon
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- 2012
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17. Coupling of Important Physical Processes in the Planetary Boundary Layer between Meteorological and Chemistry Models for Regional to Continental Scale Air Quality Forecasting: An Overview
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Pius Lee and Fong Ngan
- Subjects
planetary boundary ,turbulent mixing ,air surface exchange ,dry deposition ,Meteorology. Climatology ,QC851-999 - Abstract
A consensus among many Air Quality (AQ) modelers is that planetary boundary layer processes are the most influential processes for surface concentrations of air pollutants. Due to the many uncertainties intrinsically embedded in the parameterization of these processes, parameter optimization is often employed to determine an optimal set or range of values of the sensitive parameters. In this review study, we focus on the two of the most important physical processes: turbulent mixing and dry deposition. An emphasis was put on surveying AQ models that have been proven to resolve meso-scale features and cover a large geographical area, such as large regional, continental, or trans-continental boundary extents. Five AQ models were selected. Four of the models were run in real-time operational forecasting settings for continental scale AQ. The models use various forms of level 2.5 closure algorithms to calculate turbulent mixing. Tuning and parameter optimization has been used to tailor these algorithms to better suit their AQ models which are typically comprised of a coupled chemistry and meteorology model. Longer forecasts and long lead-times are inevitably under increasing demand for these models. Land Surface Models that have the capability for soil moisture and temperature data assimilation will have an advantage to constrain the key variables that govern the partitioning of surface sensible and latent heat fluxes and thus attain the potential to perform better in longer forecasts than those models that do not have this capability. Dry deposition velocity is a very significant model parameter that governs a major surface exchange activity. An exploratory study has been conducted to see the upper bound of roughness length in the similarity equation for aerodynamic resistance.
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- 2011
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18. Chronic disease self-management competency and care satisfaction between users of public and private primary care in Singapore
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Ng, Jun Xuan, primary, Chia, Joshua Chin Howe, additional, Loo, Li Yang, additional, Lim, Zhi Kai, additional, Kho, Kangshi, additional, Chen, Cynthia, additional, and Fong, Ngan Phoon, additional
- Published
- 2021
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19. Ensemble PM 2.5 Forecasting During the 2018 Camp Fire Event Using the HYSPLIT Transport and Dispersion Model
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C. Ichoku, Daniel Tong, Shobha Kondragunta, Edward J. Hyer, Y. Li, Xiaoyang Zhang, Fong Ngan, Ariel F. Stein, Mark Cohen, and Ralph A. Kahn
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Atmospheric Science ,Geophysics ,Meteorology ,Space and Planetary Science ,Event (relativity) ,Dispersion (optics) ,Earth and Planetary Sciences (miscellaneous) ,HYSPLIT ,Environmental science ,Satellite ,Biomass burning ,Air quality index - Published
- 2020
20. Subseasonal Variability of Elevated Dust Concentrations Over South Florida
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Fong Ngan, Paquita Zuidema, S. Â. J. Kramer, and Benjamin Kirtman
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Atmospheric Science ,Geophysics ,Space and Planetary Science ,Earth and Planetary Sciences (miscellaneous) ,Environmental science ,Mineral dust ,Tropical cyclone ,Atmospheric sciences - Published
- 2020
21. Dispersion simulations using HYSPLIT for the Sagebrush Tracer Experiment
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Dennis Finn, Ariel F. Stein, Fong Ngan, and Richard M. Eckman
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Atmospheric Science ,010504 meteorology & atmospheric sciences ,Advection ,Planetary boundary layer ,010501 environmental sciences ,Atmospheric sciences ,01 natural sciences ,Wind speed ,Trace gas ,Weather Research and Forecasting Model ,TRACER ,Dispersion (optics) ,HYSPLIT ,Environmental science ,0105 earth and related environmental sciences ,General Environmental Science - Abstract
The Sagebrush experiment, led by NOAA's Field Research Division of the Air Resources Laboratory, consisted of five releases (intensive observation periods, or IOPs) of a chemically inert trace gas on five days in October 2013. All releases occurred in the afternoon under either near neutral stability conditions with high wind speeds or unstable conditions with low wind speeds. The sampling network for the tracer concentrations covered distances 200 m–3200 m from the release location and samples were obtained in 10-min averages. HYSPLIT, NOAA's transport and dispersion model, was used to simulate the spatial and temporal distribution of the tracer. The dispersion simulations were driven by WRF meteorological data with 27-km to 333-m grid spacing and using the inline and offline approaches as well as different planetary boundary layer schemes and a large-eddy simulation parameterization. Comparisons with measured wind speeds showed that none of the WRF PBL schemes or the large-eddy simulation parameterization was able to reproduce the rapid increase in high wind speeds observed during IOP3. The dispersion results were compared with the tracer measurements obtained during the experiment. The HYSPLIT dispersion simulations for IOP3, driven by the WRF data generated with various PBL schemes, showed greater concentration variability than the simulations performed for IOP5. The comparison between the inline and offline HYSPLIT simulations showed that the inline approach statistically outperformed the offline approach in three out of four IOPs because the tight coupling between the advection and dispersion processes implemented in the inline approach produced higher simulated concentrations close to the release location.
- Published
- 2018
22. Disparities in survival among elders with disabilities: possible implications for long-term care insurance
- Author
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Chen, Cynthia, primary, Lim, Jue Tao, additional, Chia, Ngee Choon, additional, Wang, Lijia, additional, Chong, Ming Zhe, additional, Cheong, Angela, additional, Fong, Ngan Phoon, additional, Tan, Boon Yeow, additional, Menon, Edward, additional, Ee, Chye Hua, additional, Lee, Kok Keng, additional, Chan, Kin Ming, additional, Ma, Stefan, additional, Tan, Kelvin Bryan, additional, and Koh, Gerald CH, additional
- Published
- 2020
- Full Text
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23. Trade-offs between effectiveness and efficiency in stroke rehabilitation
- Author
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Koh, Gerald Choon-Huat, Chen, Cynthia, Cheong, Angela, Choo, Tai Bee, Pui, Choi Kwok, Phoon, Fong Ngan, Ming, Chan Kin, Yeow, Tan Boon, Petrella, Robert, Thind, Amardeep, Koh, David, and Seng, Chia Kee
- Published
- 2012
- Full Text
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24. Facilitators and barriers of Hepatitis B screening and vaccination
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Tan, Si Heng Sharon, primary, Wang, DaoBo, additional, Tan, Win Jim, additional, Allameen, Nur Azizah, additional, and Fong, Ngan Phoon, additional
- Published
- 2020
- Full Text
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25. A Long-Term WRF Meteorological Archive for Dispersion Simulations: Application to Controlled Tracer Experiments
- Author
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Ariel F. Stein and Fong Ngan
- Subjects
Atmospheric Science ,010504 meteorology & atmospheric sciences ,Meteorology ,Planetary boundary layer ,010501 environmental sciences ,Atmospheric sciences ,01 natural sciences ,Term (time) ,symbols.namesake ,Weather Research and Forecasting Model ,TRACER ,symbols ,HYSPLIT ,Environmental science ,Dispersion (water waves) ,Trajectory (fluid mechanics) ,Lagrangian ,0105 earth and related environmental sciences - Abstract
A long-term archive of meteorological data using the Weather Research and Forecasting (WRF) Model was created to provide data that are compatible with the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) dispersion model and to serve as initial and boundary conditions for simulations at a finer resolution. On the basis of these WRF data, generated with a variety of planetary boundary layer (PBL) schemes and nudging options, the HYSPLIT model was run to simulate four controlled tracer experiments—the Cross Appalachian Tracer Experiment (CAPTEX), the Across North America Tracer Experiment (ANATEX), a 1980 release in Oklahoma City, Oklahoma (OKC80), and the Metropolitan Tracer Experiment (METREX)—covering different time periods with diverse durations, including a summer day, several days in autumn, three months during winter, and one full year, respectively. The evaluation of the WRF results utilizing conventional observations showed a similar statistical performance for the different PBL schemes. Given the limited information the meteorological evaluation alone can provide, the authors used the dispersion evaluation with measurements from multiple tracer experiments to gain further insight into the most appropriate WRF configuration to generate reasonable data for dispersion applications. The dispersion simulations that were based on WRF data generated equal or slightly better statistical performance than did those driven by the North American Regional Reanalysis (NARR) dataset. The statistical comparison showed a mixed impact for the dispersion results driven by the nonnudged and nudged WRF data. The main advantage of the WRF data is the availability of hourly meteorological data from 1980 to the present and the inclusion of additional variables that are relevant to atmospheric dispersion and are not available from NARR. This WRF dataset will be accessible online, providing additional capabilities for using different meteorological inputs and a variety of options to compute the HYSPLIT mixing parameters.
- Published
- 2017
26. Weak-constraint inverse modeling using HYSPLIT-4 Lagrangian dispersion model and Cross-Appalachian Tracer Experiment (CAPTEX) observations – effect of including model uncertainties on source term estimation
- Author
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Tianfeng Chai, Fong Ngan, and Ariel F. Stein
- Subjects
Normalization (statistics) ,Inverse system ,010504 meteorology & atmospheric sciences ,Logarithm ,lcsh:QE1-996.5 ,General Medicine ,010502 geochemistry & geophysics ,01 natural sciences ,lcsh:Geology ,Data assimilation ,Approximation error ,HYSPLIT ,Range (statistics) ,Applied mathematics ,Spurious relationship ,0105 earth and related environmental sciences ,Mathematics - Abstract
A Hybrid Single-Particle Lagrangian Integrated Trajectory version 4 (HYSPLIT-4) inverse system that is based on variational data assimilation and a Lagrangian dispersion transfer coefficient matrix (TCM) is evaluated using the Cross-Appalachian Tracer Experiment (CAPTEX) data collected from six controlled releases. For simplicity, the initial tests are applied to release 2, for which the HYSPLIT has the best performance. Before introducing model uncertainty terms that will change with source estimates, the tests using concentration differences in the cost function result in severe underestimation, while those using logarithm concentration differences result in overestimation of the release rate. Adding model uncertainty terms improves results for both choices of the metric variables in the cost function. A cost function normalization scheme is later introduced to avoid spurious minimal source term solutions when using logarithm concentration differences. The scheme is effective in eliminating the spurious solutions and it also helps to improve the release estimates for both choices of the metric variables. The tests also show that calculating logarithm concentration differences generally yields better results than calculating concentration differences, and the estimates are more robust for a reasonable range of model uncertainty parameters. This is further confirmed with nine ensemble HYSPLIT runs in which meteorological fields were generated with varying planetary boundary layer (PBL) schemes. In addition, it is found that the emission estimate using a combined TCM by taking the average or median values of the nine TCMs is similar to the median of the nine estimates using each of the TCMs individually. The inverse system is then applied to the other CAPTEX releases with a fixed set of observational and model uncertainty parameters, and the largest relative error among the six releases is 53.3 %. At last, the system is tested for its capability to find a single source location as well as its source strength. In these tests, the location and strength that yield the best match between the predicted and the observed concentrations are considered as the inverse modeling results. The estimated release rates are mostly not as good as the cases in which the exact release locations are assumed known, but they are all within a factor of 3 for all six releases. However, the estimated location may have large errors.
- Published
- 2018
27. International challenge to model the long-range transport of radioxenon released from medical isotope production to six Comprehensive Nuclear-Test-Ban Treaty monitoring stations
- Author
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S. Generoso, Rich Britton, Blake Orr, Alice M. Crawford, Fong Ngan, Pieter De Meutter, L. G. Glascoe, Tianfeng Chai, Olivier Saunier, A.V. Davies, Denis Quélo, Andy Delcloo, Anne Philipp, Anne Mathieu, Martin Kalinowski, T.W. Bowyer, Donald D. Lucas, Jonathan Baré, Christian Maurer, Jolanta Kusmierczyk-Michulec, Ole Ross, Matthew Simpson, Susan Leadbetter, Petra Seibert, Yuichi Kijima, Pascal Achim, Paul W. Eslinger, Phil Vogt, Michael Schoeppner, Alain Malo, Ariel F. Stein, A. Ringbom, Bundesanstalt für Geowissenschaften und Rohstoffe (BGR), Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Institut de Radioprotection et de Sûreté Nucléaire (IRSN), NOAA Air Resources Laboratory (ARL), National Oceanic and Atmospheric Administration (NOAA), Institut Royal Météorologique de Belgique [Bruxelles] - Royal Meteorological Institute (IRM), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), and Institut Royal Météorologique de Belgique [Bruxelles] (IRM)
- Subjects
010504 meteorology & atmospheric sciences ,Meteorology ,International Cooperation ,Health, Toxicology and Mutagenesis ,010502 geochemistry & geophysics ,01 natural sciences ,Time frame ,Radiation Monitoring ,Comprehensive Nuclear-Test-Ban Treaty ,Range (statistics) ,Environmental Chemistry ,Production (economics) ,Waste Management and Disposal ,0105 earth and related environmental sciences ,[PHYS]Physics [physics] ,Comparability ,Australia ,Monitoring system ,Ranging ,General Medicine ,Grid ,Pollution ,Air Pollutants, Radioactive ,13. Climate action ,Environmental science ,Xenon Radioisotopes - Abstract
International audience; After performing a first multi-model exercise in 2015 a comprehensive and technically more demanding atmospheric transport modelling challenge was organized in 2016. Release data were provided by the Australian Nuclear Science and Technology Organization radiopharmaceutical facility in Sydney (Australia) for a one month period. Measured samples for the same time frame were gathered from six International Monitoring System stations in the Southern Hemisphere with distances to the source ranging between 680 (Melbourne) and about 17,000 km (Tristan da Cunha). Participants were prompted to work with unit emissions in pre-defined emission intervals (daily, half-daily, 3-hourly and hourly emission segment lengths) and in order to perform a blind test actual emission values were not provided to them. Despite the quite different settings of the two atmospheric transport modelling challenges there is common evidence that for long-range atmospheric transport using temporally highly resolved emissions and highly space-resolved meteorological input fields has no significant advantage compared to using lower resolved ones. As well an uncertainty of up to 20% in the daily stack emission data turns out to be acceptable for the purpose of a study like this. Model performance at individual stations is quite diverse depending largely on successfully capturing boundary layer processes. No single model-meteorology combination performs best for all stations. Moreover, the stations statistics do not depend on the distance between the source and the individual stations. Finally, it became more evident how future exercises need to be designed. Set-up parameters like the meteorological driver or the output grid resolution should be pre-scribed in order to enhance diversity as well as comparability among model runs.
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- 2018
28. Synoptic weather and surface ozone concentration in South Korea
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Changhan Bae, Soontae Kim, Jin-Ho Yoon, Hyun-cheol Kim, Fong Ngan, Byeong-Uk Kim, and Dasom Lee
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Atmospheric Science ,Ozone ,010504 meteorology & atmospheric sciences ,Climate change ,010501 environmental sciences ,High ozone ,Atmospheric sciences ,01 natural sciences ,chemistry.chemical_compound ,Surface ozone ,chemistry ,Environmental science ,Weather patterns ,Air quality index ,0105 earth and related environmental sciences ,General Environmental Science - Abstract
Seventeen years (2001–2017) of surface observations and spatial synoptic classification (SSC) data are used to analyze the characteristics of surface ozone concentration according to synoptic weather patterns. While weather conditions are known to play an important role in regional air quality, the extent to which synoptic weather patterns affect the production of high ground-level ozone concentrations has not yet been fully quantified. Using thermal characteristics and geographic origins, the SSC method classifies air masses into six types: dry polar (DP), dry moderate (DM), dry tropical (DT), moist polar (MP), moist moderate (MM), and moist tropical (MT). We link daily maximum 8-h ozone concentrations (MDA8 O3) from 306 monitoring sites to the closest SSC classifications at 17 airport sites and then analyze their association. We find that DM, DT, and MT are commonly associated with high ozone, whereas DT produces ozone with the greatest efficiency, especially high levels of concentration. This finding implies a potentially strong connection between surface ozone and climate change because the occurrence of DT weather has increased by more than three times over the past 50 years in South Korea. Sensitivity tests reveal that mean MDA8 ozone may increase by 3.5% (7.5%) as the DT frequency increases by 200% (300%). The impacts are larger for higher levels of concentration, with 31.7% (63.3%) or more prevalence of the >80 ppb range with the same increased DT frequency. We conclude that synoptic weather and its long-term trends play important roles in the increased surface ozone recently seen in South Korea.
- Published
- 2021
29. Functional outcomes in inpatient rehabilitative care of stroke patients: predictive factors and the effect of therapy intensity
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Saxena, Sanjiv K, Ng, TP, Yong, David, Fong, Ngan P, and Koh, Gerald
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- 2006
30. NOAA’s HYSPLIT Atmospheric Transport and Dispersion Modeling System
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Mark Cohen, Roland R. Draxler, Fong Ngan, Barbara J. B. Stunder, Glenn D. Rolph, and Ariel F. Stein
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Pollutant ,Atmospheric Science ,010504 meteorology & atmospheric sciences ,Meteorology ,010501 environmental sciences ,Atmospheric dispersion modeling ,Atmospheric sciences ,01 natural sciences ,Deposition (aerosol physics) ,TRACER ,Wild Fires ,HYSPLIT ,Environmental science ,Trajectory (fluid mechanics) ,0105 earth and related environmental sciences ,Volcanic ash - Abstract
The Hybrid Single-Particle Lagrangian Integrated Trajectory model (HYSPLIT), developed by NOAA’s Air Resources Laboratory, is one of the most widely used models for atmospheric trajectory and dispersion calculations. We present the model’s historical evolution over the last 30 years from simple hand-drawn back trajectories to very sophisticated computations of transport, mixing, chemical transformation, and deposition of pollutants and hazardous materials. We highlight recent applications of the HYSPLIT modeling system, including the simulation of atmospheric tracer release experiments, radionuclides, smoke originated from wild fires, volcanic ash, mercury, and wind-blown dust.
- Published
- 2015
31. Evaluation of modeled surface ozone biases as a function of cloud cover fraction
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Pius Lee, Li Pan, H. L. Yoo, Hyun-cheol Kim, Youhua Tang, and Fong Ngan
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Daytime ,Ozone ,Cloud cover ,Cloud fraction ,lcsh:QE1-996.5 ,Monitoring system ,Atmospheric sciences ,lcsh:Geology ,chemistry.chemical_compound ,Surface ozone ,chemistry ,Environmental science ,Moderate-resolution imaging spectroradiometer ,Air quality index - Abstract
A regional air-quality forecast system's model of surface ozone variability based on cloud coverage is evaluated using satellite-observed cloud fraction (CF) information and a surface air-quality monitoring system. We compared CF and daily maximum ozone from the National Oceanic and Atmospheric Administration's National Air Quality Forecast Capability (NOAA NAQFC) with CFs from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the U.S. Environmental Protection Agency's AirNow surface ozone measurements during May to October 2014. We found that observed surface ozone shows a clear (negative) correlation with the MODIS CFs, showing around 1 ppb decrease for 10% MODIS CF change over the Contiguous United States, while the correlation of modeled surface ozone with the model CFs is much weaker, showing only −0.5 ppb per 10% NAQFC CF change. Further, daytime CF differences between MODIS and NAQFC are correlated with modeled surface-ozone biases between AirNow and NAQFC, showing −1.05 ppb per 10% CF change, implying that spatial- and temporal-misplacement of the modeled cloud field might have biased modeled surface ozone-level. Current NAQFC cloud fields seem to be too bright compared to MODIS cloud fields (mean NAQFC CF = 0.38 and mean MODIS CF = 0.55), contributing up to 35% of surface-ozone bias in the current NAQFC system.
- Published
- 2015
32. Weak-constraint inverse modeling using HYSPLIT Lagrangian dispersion model and Cross Appalachian Tracer Experiment (CAPTEX) observations – Effect of including model uncertainties on source term estimation
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Tianfeng Chai, Ariel Stein, and Fong Ngan
- Abstract
A HYSPLIT inverse system that is based on variational data assimilation and a Lagrangian dispersion transfer coefficient matrix (TCM) is evaluated using the Cross Appalachian Tracer Experiment (CAPTEX) data collected from six controlled releases. For simplicity, the initial tests are applied to release 2 for which the HYSPLIT has the best performance. Before introducing model uncertainty terms, the tests using concentration differences in the cost function results in severe underestimation while those using logarithm concentrations differences results in overestimation of the release rate. Adding model uncertainty terms improves results for both choices of the metric variables in the cost function. A cost function normalization scheme is later introduced to avoid spurious minimal source term solutions when using logarithm concentration differences. The scheme is effective in eliminating the spurious solutions and it also helps to improve the release estimates for both choices of the metric variables. The tests also show that calculating logarithm concentration differences generally yield better results than calculating concentration differences and the estimates are more robust for a reasonable range of model uncertainty parameters. This is further confirmed with nine ensemble HYSPLIT runs in which meteorological fields were generated with varying planetary boundary layer (PBL) schemes. In addition, it is found that the emission estimate using a combined TCM by taking the average or median values of the nine TCMs is similar to the median of the nine estimates using each of the TCMs individually. The inverse system is then applied to the other CAPTEX releases with a fixed set of observational and model uncertainty parameters and the largest relative error among the six releases is 53.3 %. At last, the system is tested for its capability to find a single source location as well as its source strength. In these tests, the location and strength that yield the best match between the predicted and the observed concentrations are considered as the inverse modeling results. The estimated release rates are mostly not as good as the cases in which the exact release locations are assumed known, but they are all within a factor of 3 for all the six releases. However, the estimated location may have large errors.
- Published
- 2018
33. A Conservative Downscaling of Satellite-Detected Chemical Compositions: NO2 Column Densities of OMI, GOME-2, and CMAQ
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Pius Lee, Tianfeng Chai, Fong Ngan, Sang-Mi Lee, Hyun-cheol Kim, and Li Pan
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Ozone Monitoring Instrument ,Ozone ,010504 meteorology & atmospheric sciences ,Science ,OMI ,downscaling ,010501 environmental sciences ,Atmospheric sciences ,01 natural sciences ,NO2 column density ,chemistry.chemical_compound ,GOME-2 ,CMAQ ,chemistry ,Nadir ,General Earth and Planetary Sciences ,Environmental science ,Nitrogen dioxide ,Satellite ,Air quality index ,0105 earth and related environmental sciences ,Downscaling - Abstract
A conservative downscaling technique was applied when comparing nitrogen dioxide (NO2) column densities from space-borne observations and a fine-scale regional model. The conservative downscaling was designed to enhance the spatial resolution of satellite measurements by applying the fine-scale spatial structure from the model, with strict mass conservation at each satellite footprint pixel level. With the downscaling approach, NO2 column densities from the Ozone Monitoring Instrument (OMI; 13 × 24 km nadir footprint resolution) and the Global Ozone Monitoring Experiment-2 (GOME-2; 40 × 80 km) show excellent agreement with the Community Multiscale Air Quality (CMAQ; 4 × 4 km) NO2 column densities, with R = 0.96 for OMI and R = 0.97 for GOME-2. We further introduce an approach to reconstruct surface NO2 concentrations by combining satellite column densities and simulated surface-to-column ratios from the model. Compared with the Environmental Protection Agency’s (EPA) Air Quality System (AQS) surface observations, the reconstructed surface concentrations show a good agreement; R = 0.86 for both OMI and GOME-2. This study demonstrates that the conservative downscaling approach is a useful tool to compare coarse-scale satellites with fine-scale models or observations in urban areas for air quality and emissions studies. The reconstructed fine-scale surface concentration field could be used for future epidemiology and urbanization studies.
- Published
- 2018
34. Disparities in survival for elders with disabilities: implication for long-term care insurance Disparities in survival for elders with disabilities
- Author
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Chen, Cynthia, primary, Lim, Jue Tao, additional, Chia, Ngee Choon, additional, Wang, Lijia, additional, Chong, Ming Zhe, additional, Cheong, Angela, additional, Fong, Ngan Phoon, additional, Tan, Boon Yeow, additional, Menon, Edward, additional, Ee, Chye Hua, additional, Lee, Kok Keng, additional, Chan, Kin Ming, additional, Ma, Stefan, additional, Tan, Kelvin Bryan, additional, and Koh, Gerald CH, additional
- Published
- 2019
- Full Text
- View/download PDF
35. Inline Coupling of WRF–HYSPLIT: Model Development and Evaluation Using Tracer Experiments
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Fong Ngan, Roland R. Draxler, and Ariel F. Stein
- Subjects
Atmospheric Science ,Meteorology ,Scale (ratio) ,Weather Research and Forecasting Model ,TRACER ,Dispersion (optics) ,HYSPLIT ,Environmental science ,Terrain ,Grid ,Trajectory (fluid mechanics) - Abstract
The Hybrid Single-Particle Lagrangian Integrated Trajectory model (HYSPLIT), a Lagrangian dispersion model, has been coupled (inline) to the the Weather Research and Forecasting (WRF) Model meteorological model in such a way that the HYSPLIT calculation is run as part of the WRF-ARW prediction calculation. This inline version of HYSPLIT takes advantage of the higher temporal frequency of WRF-ARW variables relative to what would be available for the offline approach. Furthermore, the dispersion calculation uses the same vertical coordinate system as WRF-ARW, resulting in a more consistent depiction of the state of the atmosphere and the dispersion simulation. Both inline and the offline HYSPLIT simulations were conducted for two tracer experiments at quite different model spatial resolutions: the Cross Appalachian Tracer Experiment (CAPTEX) in regional scale (at 9-km grid spacing) and the Atmospheric Studies in Complex Terrain (ASCOT) in finescale (at 333.3-m grid spacing). A comparison of the model with the measured values showed that the results of the two approaches were very similar for all six releases in CAPTEX. For the ASCOT experiments, the cumulative statistical score of the inline simulations was better than or equal to offline runs in four of five releases. Although the use of the inline approach did not provide any advantage over the offline method for the regional spatial scale and medium-range temporal scale represented by the CAPTEX experiment, the inline HYSPLIT was able to improve the simulation of the dispersion when compared with the offline version for the fine spatial and temporal resolutions over the complex-terrain area represented by ASCOT. The improvement of the inline over the offline calculation is attributed to the elimination of temporal and vertical interpolation of the meteorological data as compared with the offline version.
- Published
- 2015
36. Potential Use of Transport and Dispersion Model Ensembles for Forecasting Applications
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Tianfeng Chai, Roland R. Draxler, Fong Ngan, and Ariel F. Stein
- Subjects
Model output statistics ,Reduction (complexity) ,Atmospheric Science ,Mean squared error ,Meteorology ,Computer science ,Weather Research and Forecasting Model ,Trajectory ,HYSPLIT ,Statistical dispersion ,Measure (mathematics) ,Algorithm - Abstract
Using ensembles to improve the simulation of plume dispersion is becoming a more common practice. One of the biggest challenges in creating ensembles is developing the appropriate member selection process to get the most accurate results, quantify ensemble uncertainty, and use computing resources more efficiently by avoiding the use of redundant model information. In this work, two reduction techniques are tested: one that is independent of observations and is based on the exclusion of redundant members by using uncorrelation as a measure of distance among the members and a second one based on measured data, which minimizes the mean square error (MSE) of the average of all possible model combinations. These techniques are applied to a 24-member ensemble, created by varying the boundary layer parameterizations in the meteorological WRF Model and dispersion Hybrid Single-Particle Lagrangian Integrated Trajectory model (HYSPLIT) simulating six releases of the Cross-Appalachian Tracer Experiment (CAPTEX). Applying the first technique produced results statistically comparable to the full ensemble for four out of six releases, while the second technique shows a similar or superior performance for all cases. Furthermore, to mimic a forecast application, the first day of the tracer release is used to select the ensemble members and the subsequent days are utilized as a forecast proxy to evaluate their performance. The reduced ensembles chosen by applying the technique based on the minimization of the MSE statistically perform similarly to or better than the full ensemble for the forecasting time periods. This suggests that when observational data are available, the application of ensemble reduction techniques provides a potentially promising tool for improving the dispersion forecast.
- Published
- 2015
37. Meteorological Modeling Using the WRF-ARW Model for Grand Bay Intensive Studies of Atmospheric Mercury
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Roland R. Draxler, Xinrong Ren, Mark Cohen, Fong Ngan, and Winston T. Luke
- Subjects
Atmospheric Science ,geography ,mercury ,geography.geographical_feature_category ,Meteorology ,Global wind patterns ,WRF ,Mesoscale meteorology ,Estuary ,lcsh:QC851-999 ,Grand Bay ,Environmental Science (miscellaneous) ,Plume ,Depth sounding ,reanalysis data ,Climatology ,Weather Research and Forecasting Model ,nudging ,Environmental science ,lcsh:Meteorology. Climatology ,Precipitation ,Bay - Abstract
Measurements at the Grand Bay National Estuarine Research Reserve support a range of research activities aimed at improving the understanding of the atmospheric fate and transport of mercury. Routine monitoring was enhanced by two intensive measurement periods conducted at the site in summer 2010 and spring 2011. Detailed meteorological data are required to properly represent the weather conditions, to determine the transport and dispersion of plumes and to understand the wet and dry deposition of mercury. To describe the mesoscale features that might influence future plume calculations for mercury episodes during the Grand Bay Intensive campaigns, fine-resolution meteorological simulations using the Weather Research and Forecasting (WRF) model were conducted with various initialization and nudging configurations. The WRF simulations with nudging generated reasonable results in comparison with conventional observations in the region and measurements obtained at the Grand Bay site, including surface and sounding data. The grid nudging, together with observational nudging, had a positive effect on wind prediction. However, the nudging of mass fields (temperature and moisture) led to overestimates of precipitation, which may introduce significant inaccuracies if the data were to be used for subsequent atmospheric mercury modeling. The regional flow prediction was also influenced by the reanalysis data used to initialize the WRF simulations. Even with observational nudging, the summer case simulation results in the fine resolution domain inherited features of the reanalysis data, resulting in different regional wind patterns. By contrast, the spring intensive period showed less influence from the reanalysis data.
- Published
- 2015
38. Retrospective Air Quality Simulations of the TexAQS-II: Focused on Emissions Uncertainty
- Author
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Hyun-cheol Kim, Fong Ngan, Soontae Kim, and Dae-Gyun Lee
- Subjects
lcsh:GE1-350 ,High peak ,Atmospheric Science ,Ozone ,texaqs-ii ,cmaq ,Meteorology ,emissions uncertainty ,houston ozone ,hrvoc ,High ozone ,lcsh:TD1-1066 ,Atmosphere ,chemistry.chemical_compound ,chemistry ,MM5 ,Environmental science ,lcsh:Environmental technology. Sanitary engineering ,Air quality index ,lcsh:Environmental sciences ,General Environmental Science ,CMAQ - Abstract
There are several studies on the effects of emissions of highly reactive volatile organic compounds (HRVOC) from the industrial sources in the Houston- Galveston-Brazoria (HGB) area on the high ozone events during the Texas Air Quality Study (TexAQS) in summer of 2000. They showed that the modeled atmosphere lacked reactivity to produce the observed high ozone event and suggested “imputation” of HRVOC emissions from the base inventory. Byun et al. (2007b) showed the imputed inventory leads to too high ethylene concentrations compared to the measurements at the chemical super sites but still too little aloft compared to the NOAA aircraft. The paper suggested that the lack of reactivity in the modeled Houston atmosphere must be corrected by targeted, and sometimes of episodic, increase of HRV OC emissions from the large sources such as flares in the Houston Ship Channel (HSC) distributed into the deeper level of the boundary layer. We performed retrospective meteorological and air quality modeling to achieve better air quality prediction of ozone by comparison with various chemical and meteorological measurements during the Texas Air Quality Study periods in August-September 2006 (TexA QS-II). After identifying several shortcomings of the forecast meteorological simulations and emissions inputs, we prepared new retrospective meteorological simulations and updated emissions inputs. We utilized assimilated MM5 inputs to achieve better meteorological simulations (detailed description of MM5 assimilation can be found in F. Ngan et al., 2012) and used them in this study for air quality simulations. Using the better predicted meteorological results, we focused on the emissions uncertainty in order to capture high peak ozone which occasionally happens in the HGB area. We described how the ozone predictions are affected by emissions uncertainty in the air quality simulations utilizing different emission inventories and adjustments.
- Published
- 2014
39. Modeling the fallout from stabilized nuclear clouds using the HYSPLIT atmospheric dispersion model
- Author
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Roland R. Draxler, Glenn D. Rolph, and Fong Ngan
- Subjects
Radioactive Fallout ,Meteorology ,Health, Toxicology and Mutagenesis ,Poison control ,HYSPLIT ,Radiation Monitoring ,Environmental Chemistry ,Nuclear fallout ,Deposition ,Weather ,Trajectory (fluid mechanics) ,Waste Management and Disposal ,Nuclear Warfare ,Air Movements ,Nuclear Weapons ,Dispersion modeling ,General Medicine ,Models, Theoretical ,Atmospheric dispersion modeling ,Pollution ,Plume ,Weather Research and Forecasting Model ,Environmental science ,Deposition (chemistry) ,Nevada - Abstract
The Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model, developed by the National Oceanic and Atmospheric Administration's Air Resources Laboratory, has been configured to simulate the dispersion and deposition of nuclear materials from a surface-based nuclear detonation using publicly available information on nuclear explosions. Much of the information was obtained from “The Effects of Nuclear Weapons” by Glasstone and Dolan (1977) . The model was evaluated against the measurements of nuclear fallout from six nuclear tests conducted between 1951 and 1957 at the Nevada Test Site using the global NCEP/NCAR Reanalysis Project (NNRP) and the Weather Research and Forecasting (WRF) meteorological data as input. The model was able to reproduce the general direction and deposition patterns using the coarse NNRP data with Figure of Merit in Space (FMS – the percent overlap between predicted and measured deposition patterns) scores in excess of 50% for four of six simulations for the smallest dose rate contour, with FMS scores declining for higher dose rate contours. When WRF meteorological data were used the FMS scores were 5–20% higher in five of the six simulations, especially at the higher dose rate contours. The one WRF simulation where the scores declined slightly (10–30%) was also the best scoring simulation when using the NNRP data. When compared with measurements of dose rate and time of arrival from the Town Data Base ( Thompson et al., 1994 ), similar results were found with the WRF simulations providing better results for four of six simulations. The overall result was that the different plume simulations using WRF data had more consistent performance than the plume simulations using NNRP data fields.
- Published
- 2014
- Full Text
- View/download PDF
40. Additional file 3: of Using peer review to distribute group work marks equitably between medical students
- Author
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Cook, Alex, Hartman, Mikael, Luo, Nan, Sng, Judy, Fong, Ngan, Lim, Wei, Chen, Mark, Wong, Mee, Natarajan Rajaraman, Lee, Jeannette, and Koh, Gerald
- Abstract
CHP 2014 Module Feedback Form. Form used to solicit feedback on the scoring system. (PDF 13 kb)
- Published
- 2017
- Full Text
- View/download PDF
41. Additional file 2: Figure S1. of Using peer review to distribute group work marks equitably between medical students
- Author
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Cook, Alex, Hartman, Mikael, Luo, Nan, Sng, Judy, Fong, Ngan, Lim, Wei, Chen, Mark, Wong, Mee, Natarajan Rajaraman, Lee, Jeannette, and Koh, Gerald
- Abstract
Each page represents one student, whose names have been replaced by Roman or Greek capitals. The index student referred in each page is indicated by the down arrow (â ) on the top row of letters. The upper chart indicates the marks the index student gave to each peer (black or colored circles), together with the average points awarded to that peer (grey bars). The lower chart indicates the marks each peer gives the index student (circles) and the average mark the index student received. Note: these marks are the raw marks prior to scaling. If any mark is more than 1.5 marks away from average, this is indicated by coloring the circle (orange for less, red for much [2.5] less, light blue for more, dark blue for much [2.5] more), increasing the shading on the bar, and adding an arrow. By maximizing the graph on screen and running through each page as a slide show, faculty can quickly assess for the presence of collusion between students. (PDF 140 kb)
- Published
- 2017
- Full Text
- View/download PDF
42. Mercury Speciation at a Coastal Site in the Northern Gulf of Mexico: Results from the Grand Bay Intensive Studies in Summer 2010 and Spring 2011
- Author
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Arsineh Hecobian, L. Gregory Huey, Winston T. Luke, Christopher W. Moore, Dieter Bauer, Fong Ngan, Richard S. Artz, Anthony J. Hynes, Jack E. Dibb, Mark Cohen, Phil Swartzendruber, Jake Walker, Xinrong Ren, John M. Rolison, Jeffery Shook, Paul Kelley, Steve Brooks, Nishanth P. Krishnamurthy, James Remeika, and William M. Landing
- Subjects
Atmospheric Science ,Daytime ,principal component analysis ,chemistry.chemical_element ,Atmospheric mercury ,HYSPLIT ,particulate-bound mercury ,Environmental Science (miscellaneous) ,lcsh:QC851-999 ,Troposphere ,gaseous oxidized mercury ,geography ,Gulf of Mexico ,geography.geographical_feature_category ,biology ,atmospheric mercury ,Estuary ,biology.organism_classification ,Moss ,Mercury (element) ,Oceanography ,chemistry ,gaseous elemental mercury ,Environmental science ,lcsh:Meteorology. Climatology ,Bay - Abstract
During two intensive studies in summer 2010 and spring 2011, measurements of mercury species including gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), and particulate-bound mercury (PBM), trace chemical species including O3, SO2, CO, NO, NOY, and black carbon, and meteorological parameters were made at an Atmospheric Mercury Network (AMNet) site at the Grand Bay National Estuarine Research Reserve (NERR) in Moss Point, Mississippi. Surface measurements indicate that the mean mercury concentrations were 1.42 ± 0.12 ng∙m−3 for GEM, 5.4 ± 10.2 pg∙m−3 for GOM, and 3.1 ± 1.9 pg∙m−3 for PBM during the summer 2010 intensive and 1.53 ± 0.11 ng∙m−3 for GEM, 5.3 ± 10.2 pg∙m−3 for GOM, and 5.7 ± 6.2 pg∙m−3 for PBM during the spring 2011 intensive. Elevated daytime GOM levels (>, 20 pg∙m−3) were observed on a few days in each study and were usually associated with either elevated O3 (>, 50 ppbv), BrO, and solar radiation or elevated SO2 (>, a few ppbv) but lower O3 (~20–40 ppbv). This behavior suggests two potential sources of GOM: photochemical oxidation of GEM and direct emissions of GOM from nearby local sources. Lack of correlation between GOM and Beryllium-7 (7Be) suggests little influence on surface GOM from downward mixing of GOM from the upper troposphere. These data were analyzed using the HYSPLIT back trajectory model and principal component analysis in order to develop source-receptor relationships for mercury species in this coastal environment. Trajectory frequency analysis shows that high GOM events were generally associated with high frequencies of the trajectories passing through the areas with high mercury emissions, while low GOM levels were largely associated the trajectories passing through relatively clean areas. Principal component analysis also reveals two main factors: direct emission and photochemical processes that were clustered with high GOM and PBM. This study indicates that the receptor site, which is located in a coastal environment of the Gulf of Mexico, experienced impacts from mercury sources that are both local and regional in nature.
- Published
- 2014
43. Supplementary material to 'Synoptic perspectives on pollutant transport patterns observed by satellites over East Asia: Case studies with a conceptual model'
- Author
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Hyun Cheol Kim, Soontae Kim, Seok-Woo Son, Pius Lee, Chun-Sil Jin, Eunhye Kim, Byeong-Uk Kim, Fong Ngan, Changhan Bae, Chang-Keun Song, and Ariel Stein
- Published
- 2016
44. Synoptic perspectives on pollutant transport patterns observed by satellites over East Asia: Case studies with a conceptual model
- Author
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Pius Lee, Hyun-cheol Kim, Changhan Bae, Chun-Sil Jin, Seok-Woo Son, Chang-Keun Song, Ariel F. Stein, Eunhye Kim, Soontae Kim, Byeong-Uk Kim, and Fong Ngan
- Subjects
Pollutant ,010504 meteorology & atmospheric sciences ,Air pollution ,Forcing (mathematics) ,010501 environmental sciences ,Atmospheric sciences ,medicine.disease_cause ,01 natural sciences ,Low-pressure area ,Siberian High ,Climatology ,Synoptic scale meteorology ,Cyclogenesis ,medicine ,Environmental science ,East Asia ,0105 earth and related environmental sciences - Abstract
We demonstrate that daily pollutant transport patterns in East Asia are visible from satellite images when inspected with corresponding synoptic weather analyses. Transport pathways of air pollutants in East Asia are investigated using satellite observations, surface weather charts, and chemical-transport model simulations. It is found that during cool season (fall to spring), pollutant transports in East Asia are largely determined by synoptic weather patterns associated with high pressure system over southern China, which is extended from the Siberia High, and low pressure system over Manchuria, which is initiated by Altai-Sayan cyclogenesis. Based on the relative location and strength of these weather systems, three types of synoptic weather patterns that may contribute to pollutants transport in East Asia, especially in China and Korea, are identified: i.e., (1) a strengthening of the Siberian High and its southeastward propagation; (2) a high-pressure system over southern China followed by a frontal passage associated with a northern low-pressure system; and (3) a stagnant high-pressure system over southern China. For all three patterns, the high-pressure system in southern China is essential for the development of regional air pollution, while frontal activities associated with low-pressure system provide a forcing mechanism to transport those pollutants eastward or southeastward. Observed and simulated surface PM distributions show good agreement in both aerosol optical depth and NO2 column density further implying that anthropogenic emissions also contribute to regional events of high surface PM concentrations. It is argued that the quasi-periodic migration of synoptic weather systems in East Asia works as an efficient pump of pollutants; i.e., regional air pollutions developed under high-pressure systems are transported downstream by low-pressure systems.
- Published
- 2016
45. Evaluation of Lagrangian Particle Dispersion Models with Measurements from Controlled Tracer Releases
- Author
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Thomas Nehrkorn, Janusz Eluszkiewicz, Ariel F. Stein, Jerome Brioude, Fong Ngan, J. D. Hegarty, Arlyn E. Andrews, Roland R. Draxler, and M. E. Mountain
- Subjects
Atmospheric Science ,symbols.namesake ,Meteorology ,TRACER ,Weather Research and Forecasting Model ,symbols ,HYSPLIT ,Statistical parameter ,Particle ,Environmental science ,Statistical dispersion ,Trajectory (fluid mechanics) ,Lagrangian - Abstract
Three widely used Lagrangian particle dispersion models (LPDMs)—the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT), Stochastic Time-Inverted Lagrangian Transport (STILT), and Flexible Particle (FLEXPART) models—are evaluated with measurements from the controlled tracer-release experiments Cross-Appalachian Tracer Experiment (CAPTEX) and Across North America Tracer Experiment (ANATEX). The LPDMs are run forward in time driven by identical meteorological inputs from the North American Regional Reanalysis (NARR) and several configurations of the Weather Research and Forecasting (WRF) model, and the simulations of tracer concentrations are evaluated against the measurements with a ranking procedure derived from the combination of four statistical parameters. The statistical evaluation reveals that all three LPDMs have comparable skill in simulating the tracer plumes when driven by the same meteorological inputs, indicating that the differences in their formulations play a secondary role. Simulations with HYSPLIT and STILT demonstrate the benefit of using customized hourly WRF fields with 10-km horizontal grid spacing over the use of 3-hourly NARR fields with 32-km horizontal grid spacing. All three LPDMs perform better when the WRF wind fields in the planetary boundary layer are nudged to NARR, with FLEXPART benefitting the most. Case studies indicate that the nudging corrects an overestimate in plume transport speed possibly caused by a positive bias in WRF wind speeds near the surface. All three LPDMs also benefit from the use of time-averaged velocity and convective mass flux fields generated by WRF, but the impact on HYSPLIT and STILT is much greater than on FLEXPART. STILT backward runs perform as well as their forward counterparts, demonstrating this model’s reversibility and its suitability for application to inverse flux estimates.
- Published
- 2013
46. A Study of Nocturnal Surface Wind Speed Overprediction by the WRF-ARW Model in Southeastern Texas
- Author
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Khalid Al-Wali, Hyun-cheol Kim, Fong Ngan, Pius Lee, and Bright Dornblaser
- Subjects
Troposphere ,Atmospheric Science ,Wind profile power law ,Meteorology ,Weather Research and Forecasting Model ,Wind shear ,Environmental science ,Sensible heat ,Pressure system ,Atmospheric sciences ,Air quality index ,Wind speed - Abstract
The overprediction of surface wind speed during nighttime by the Advanced Research core of the Weather Research and Forecasting (WRF-ARW) model was investigated for a period of the Second Texas Air Quality Study (28 May–3 July 2006). In coastal regions of southeastern Texas, the model had a significant increase of wind speed biases on the surface in the evening throughout the period, especially between 4 and 12 June. The synoptic pattern was a high pressure system centered over the Louisiana–Mississippi area that was subjected to a weak easterly–southeasterly flow in the lower troposphere. The weather conditions favorable for sea-breeze development brought a southerly–southwesterly onshore flow to the near-surface levels. In comparison with measurements, the downward sensible heat flux was overpredicted at night, which resulted in a warm bias in surface temperature. For the vertical wind profile on days with an evening wind bias, sea-breeze-driven nocturnal low-level jets (southerly–southwesterly) were present at around 300 m while another wind maximum was observed at higher levels (around 1.5–2 km), which were associated with a high pressure system centered on southeastern states. The vertical gradient of wind speed in the lowest 150 m was smoother in the model than it was in the observations; this could be attributed to excessive downward mixing. Sensitivities using different land surface and PBL parameterizations showed that the model's overprediction of nocturnal wind was still present despite improvements in the predictions of surface temperature and sensible heat flux.
- Published
- 2013
47. A numerical study of the dependence of long-range transport of CO to a mountain station in Taiwan on synoptic weather patterns during the Southeast Asia biomass-burning season
- Author
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Zhih Min Yang, Fong Ngan, Chang Feng Ou-Yang, and Fang Yi Cheng
- Subjects
Low-pressure area ,Atmospheric Science ,Range (biology) ,Weather Research and Forecasting Model ,Climatology ,Synoptic scale meteorology ,Environmental science ,Terrain ,Forcing (mathematics) ,Thermal low ,Atmospheric sciences ,Monsoon ,General Environmental Science - Abstract
This study is conducted to identify the synoptic weather patterns that are prone to cause high carbon monoxide (CO) concentrations observed at a mountain site, Lulin atmospheric background station (LABS), in Taiwan due to the biomass-burning activity in Southeast (SE) Asia. LABS is recognized as a clean background station. The study period targets the biomass-burning season (February to May) from 2007 to 2010. The synoptic weather patterns were classified using a two-stage clustering method with inputs from the Weather Research and Forecasting (WRF) meteorological model simulation result in a 27-km spatial grid. A 9-km resolution WRF modeling was performed additionally for 13 to 26 March 2007, when a high CO concentration reaching 500 ppb was observed at LABS. The simulation result indicates that not only the existence of the thermal forcing induced low pressure system formed in Indochina, but also the presence of the high terrain located in the northern part of SE Asia that further forced the uplift of the biomass-burning emissions. On the other hand, when the northeasterly monsoonal flow is strong enough and intruding into Indochina, this would hinder the development of the thermal low and weaken the upward movements, in turn preventing the transport of biomass-burning emissions from Indochina to the area of Taiwan. The simulation results also demonstrate that the location of the SE Asia high pressure system has a moderate effect on the particle dispersion path in the upper level.
- Published
- 2013
48. Caregivers: Do They Make a Difference to Patient Recovery in Subacute Stroke?
- Author
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Ong, Peck-Hoon, primary, Tai, Bee-Choo, additional, Wong, Wai-Pong, additional, Wee, Liang En, additional, Chen, Cynthia, additional, Cheong, Angela, additional, Fong, Ngan Phoon, additional, Chan, Kin Ming, additional, Tan, Boon Yeow, additional, Menon, Edward, additional, Lee, Kok Keng, additional, Ee, Chye Hua, additional, Petrella, Robert, additional, Thind, Amardeep, additional, and Koh, Gerald Choon-Huat, additional
- Published
- 2017
- Full Text
- View/download PDF
49. Using peer review to distribute group work marks equitably between medical students
- Author
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Cook, Alex R, primary, Hartman, Mikael, additional, Luo, Nan, additional, Sng, Judy, additional, Fong, Ngan Phoon, additional, Lim, Wei Yen, additional, Chen, Mark I-Cheng, additional, Wong, Mee Lian, additional, Rajaraman, Natarajan, additional, Lee, Jeannette Jen-Mai, additional, and Koh, Gerald Choon-Huat, additional
- Published
- 2017
- Full Text
- View/download PDF
50. Familial Clustering and Associated Risk Factors of Asymptomatic Hepatitis B Infection in Singapore
- Author
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Lau-Ting, Camay, Lee, James, and Fong, Ngan Phoon
- Published
- 1988
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