Prakash Karamchandani - Academia.edu (original) (raw)

Papers by Prakash Karamchandani

Air Pollution Modeling and Its Application XI, 1996

A non-linear three-dimensional grid model was used to derive source-receptor relationships, refer... more A non-linear three-dimensional grid model was used to derive source-receptor relationships, referred to as transfer coefficients, for visibility reducing species (such as sulfate) for 78 sources and 16 Class I receptors in the western United States for the calendar year 1992. The transfer coefficients will be used to assess the impact of changes in emissions on visibility at sensitive receptors, such as the Grand Canyon National Park. Uncertainties associated with model inputs and model formulation and assumptions lead to uncertainties in the derived transfer coefficients. This paper examines the uncertainties in the source-receptor relationships that are associated with grid resolution as well as the effect of assuming that levels of SO2 oxidants, such as H2O2, do not change when calculating transfer coefficients.

Atmospheric Environment. Part A. General Topics, 1992

Abstraet-A comprehensive acid deposition model was used to investigate the importance of nonpreci... more Abstraet-A comprehensive acid deposition model was used to investigate the importance of nonprecipitating stratus clouds for the production of ambient sulfate. A comparison of model estimates of ambient sulfate and SO2 concentrations with corresponding observations for an episode in the summer of 1988 showed that the model underestimated ambient sulfate concentrations and overestimated ambient SO 2 concentrations when non-precipitating stratus clouds were ignored in the model formulation. When the model was modified to include non-precipitating stratus clouds, a distinct improvement in model performance was obtained.

Journal of Geophysical Research, 2008

An existing plume-in-grid model for ozone and particulate matter, which provides an explicit trea... more An existing plume-in-grid model for ozone and particulate matter, which provides an explicit treatment of stack plumes embedded within a three-dimensional grid-based Eulerian air quality model, is extended to include a comprehensive treatment of mercury (Hg) processes. The model is applied to the continental United States to investigate the subgrid-scale effects associated with Hg emissions from large elevated point sources

Photochemical grid models, such as the Comprehensive Air quality Model with extensions (CAMx), ar... more Photochemical grid models, such as the Comprehensive Air quality Model with extensions (CAMx), are used to evaluate ozone impacts due to new emission sources since they account for non-linear ozone chemistry and processes such as transport and dispersion. However, applying such models for every proposed new source would impose an unnecessary burden that can be avoided by using an ozone screening method to determine whether more detailed evaluation is needed. An efficient and accurate screening methodology has been developed for evaluating ozone impacts of new sources in the New South Wales Greater Metropolitan Region (GMR) which includes the greater Sydney, Newcastle and Wollongong regions. The Level 1 Screening Procedure was developed based on high-order sensitivity analysis of CAMx simulations for the GMR. Prototypical new sources were introduced at five locations and the ozone plumes that formed downwind of each source analyzed. Ozone sensitivity to new emissions of NOx, VOCs and...

Atmospheric Environment (1967), 1987

The e&t of turbulent concentration fluctuations in the near-source region on fast, second-order a... more The e&t of turbulent concentration fluctuations in the near-source region on fast, second-order atmospheric reactions of the type A + i3 + C is investigated. The correlation term C>Cb is related to the concentration variance of emitted species A, c. The specific reactions studied are those pertaining to NO-O,-NO, chemistry. A locally one-dimensional finite element method (LODFEM) is used to solve the three-dimensional transport/chemistry equations.-By evaluating the differences in the photostationary-state parameter (i = k,CNoCo,/k, C,o,), the effect of the fluctuation term, CNo'Cb,, is shown to be substantial in the near-source region. The elTect initially increases with downwind distance, and then decreases as dilTusion and dissipation become dominant. Within the plume itself, the erects are smallest at the core of the plume and are most pronounced at the plume edges. The important dynamical parameters are the eddy diffusivity used for closure of the turbulent species transport equation and the dissipation of turbulent energy that controls the small-scale fluctuations. From a diurnal standpoint, the maximum effect is observed at around noontime, with minimal effects being observed in the early morning and late evening.

Atmospheric Environment, 2015

h i g h l i g h t s New module to represent surface heterogeneous HONO formation in grid model. A... more h i g h l i g h t s New module to represent surface heterogeneous HONO formation in grid model. Addresses under-predictions of HONO concentrations by grid models. Model performance for HONO strongly dependent on performance for NO 2 and HNO 3. Modeled HONO:NO 2 and HONO:HNO 3 ratios compare well with observed ratios. Approach provides framework for future refinement based on scientific advances.

Atmospheric Pollution Research, 2010

The Community Multiscale Air Quality Model (CMAQ) is a comprehensive three-dimensional "one-atmos... more The Community Multiscale Air Quality Model (CMAQ) is a comprehensive three-dimensional "one-atmosphere" air quality model that is now routinely used to address urban, regional-scale and continental-scale multipollutant issues such as ozone, particulate matter, and air toxics. Several updates have been made to CMAQ by the scientific community to enhance its capabilities and to provide alternative science treatments of some of the relevant governing processes. The Advanced Modeling System for Transport, Emissions, Reactions and Deposition of Atmospheric Matter (AMSTERDAM) is one such adaptation of CMAQ that adds an Advanced Plume-in-grid Treatment (APT) for resolving sub-grid scale processes associated with emissions from elevated point sources. It also incorporates a state-of-the-science alternative treatment for aerosol processes based on the Model of Aerosol Dynamics, Reaction, Ionization and Dissolution (MADRID). AMSTERDAM is configured to provide flexibility to the model user in selecting options for the new science modules. This paper describes the parallelization of AMSTERDAM to make it a practical tool for plume-in-grid (PinG) treatment of a large number of point sources, and presents results from its application to the central and eastern United States for summer and winter periods in 2002. Over 150 coal-fired power plants in the domain with high emissions of sulfur dioxide (SO 2) and nitrogen oxides (NO X) were selected for PinG treatment in the CMAQ-MADRID-APT configuration of AMSTERDAM used for this application. Although both model configurations (grid-only and PinG) give similar model performance results (an aggregate measure of model skill), the results show significant differences between the two versions in the specific nature of the predicted spatial distribution of ozone and PM 2.5 concentrations. These differences can be important in determining source contributions to ambient concentrations. A companion paper examines the differences in the predicted contributions of hypothetical source regions from the two configurations of the model.

Science of The Total Environment, 2000

Previously, we developed and applied a regional atmospheric mercury model to a domain covering mo... more Previously, we developed and applied a regional atmospheric mercury model to a domain covering most of North America at a horizontal grid resolution of 100 km. The implication of using this coarse resolution is that point sources of mercury emissions are instantaneously spread over a grid volume of horizontal dimensions 100 x 100 km2 and a vertical dimension equal to the depth of the grid cell where the point source emissions are released. Since point sources comprise a significant majority of a regional mercury emissions inventory, it is important to understand what effect this artificial dilution may have on calculated mercury concentrations and deposition fluxes. To understand this effect, we conducted model simulations using a finer grid, embedded within the original coarse grid, over a sub-domain that includes over 50% of the largest mercury point sources in the north-eastern United States. The horizontal resolution of the fine grid is 20 km, i.e. it is five times smaller than that of the coarse grid. We compared short-term (daily) and long-term (annual) averaged mercury concentrations, and deposition (wet and dry) fluxes on the coarse and fine grids. As expected, the effect of grid resolution is more clearly seen in close proximity to point sources than at remote locations. For short-term averages near major point sources, the peak concentrations and dry deposition fluxes of mercury from the fine grid are almost a factor of two greater than the corresponding estimates from the coarse grid. At remote locations, however, the concentrations and dry deposition peaks estimated by the two model grid resolutions are more comparable. For total wet deposition of mercury, the distinction between the fine and the coarse grid model results is less significant, regardless of the location. This could be due to the redistribution of precipitation fields or the effect of mercury aqueous chemistry. The effect of grid resolution is more important when model estimates are averaged over short time periods, e.g. daily, as opposed to over long periods, e.g. seasonally and annually.

Science of The Total Environment, 2003

Mathematical modeling of the atmospheric fate and transport of mercury (Hg) was conducted using t... more Mathematical modeling of the atmospheric fate and transport of mercury (Hg) was conducted using three nested domains covering global, continental and regional scales with horizontal resolutions of approximately 1000, 100 and 20 km, respectively. Comparisons of modeling results with wet deposition fluxes show a coefficient of determination (r) of 0.45 for the continental simulation and 0.14 for the continentalyregional simulation. The poor correlation 2 obtained in the regional simulation results to a large extent from the fact that the model predicts an increasing gradient in Hg wet deposition from Minnesota to Pennsylvania, which is not observed in the monitoring network. The use of a finer spatial resolution (20 km) improves model performance in Minnesota and Wisconsin (upwind of major Hg emission sources) but degrades model performance in Pennsylvania (downwind of major Hg emission sources). We suggest the hypothesis that some key Hg chemical transformations are likely missing in current models of atmospheric Hg.

Journal of the Air & Waste Management Association, 1999

IMPLICATIONS The recent revisions to the National Ambient Air Quality Standards for PM will requi... more IMPLICATIONS The recent revisions to the National Ambient Air Quality Standards for PM will require the use of sophisticated models that can simulate the formation of secondary PM 2.5 to examine the effect of emission control strategies and field measurement studies to evaluate and improve these models. Some components of secondary PM 2.5 include sulfate and nitrate particles that can be formed from SO 2 and NO x emissions from a variety of sources, including coal-fired power plants. However, the chemistry governing particulate formation in power plant plumes can be significantly different from that in the background.

Journal of the Air & Waste Management Association, 1997

This paper describes the development and application of the Visibility and Haze in the Western At... more This paper describes the development and application of the Visibility and Haze in the Western Atmosphere (VISHWA) model to understand the source-receptor relationships that govern chemical species relevant to visibility degradation in the western United States. The model was developed as part of a project referred to as Visibility Assessment for Regional Emission Distributions (VARED), the objective of which is to estimate the contributions of various geographical regions, compounds, and emission sources to light scattering and absorption by particles on the Colorado Plateau. The VISHWA model is a modified version of a comprehensive Eulerian model, known as the Acid Deposition and Oxidant Model.1 The modifications were designed to obtain the computational efficiency required to simulate a one-year period at about 1/25th of real time, and at the same time incorporate mechanistic features relevant to realistic modeling of the fate and transport of visibility degrading species. The modifications included use of a condensed chemical mechanism; incorporation of reactions to simulate the formation of secondary organic particles; and use of a semi-Lagrangian advection scheme to preserve concentration peaks during advection. The model was evaluated with 1992 air quality data from Project MOHAVE (Measurements of Haze and Visual Effects) intensive experiments. An important conclusion of this evaluation is that aqueous-phase oxidation of SO2 to sulfate in nonprecipitating clouds makes a significant contribution to observed sulfate levels during winter as well as summer. Model estimates of ambient sulfate for the winter intensive were within a factor of 2 of the observations for 75% of the values. The corresponding statistic for the summer intensive was 90%. Model estimates of carbon were within a factor of 2 of the limited set of observations.

Journal of Geophysical Research, 2009

The export of reactive nitrogen (nitrogen oxides and their oxidation products, collectively refer... more The export of reactive nitrogen (nitrogen oxides and their oxidation products, collectively referred to as NO y) from coal-fired power plants in the U.S. to the rest of the world could have a significant global contribution to ozone. Traditional Eulerian gridded air quality models cannot characterize accurately the chemistry and transport of plumes from elevated point sources such as power plant stacks. A state-of-the-science plume-in-grid (PinG) air quality model, a reactive plume model embedded in an Eulerian gridded model, is used to estimate the export of NO y from 25 large coal-fired power plants in the U.S. (in terms of NO x and SO 2 emissions) in July 2001 to the global atmosphere. The PinG model used is the Community Multiscale Air Quality Model with Advanced Plume Treatment (CMAQ-APT). A benchmark simulation with only the gridded model, CMAQ, is also conducted for comparison purposes. The simulations with and without advanced plume treatment show differences in the calculated export of NO y from the 25 plants considered reflecting the effect of using a detailed and explicit treatment of plume transport and chemistry. The advanced plume treatment results in 31% greater simulated export of NO y compared to the purely grid-based modeling approach. The export efficiency of NO y (the fraction of NO y emitted that is exported) is predicted to be 21% without APT and 27% with APT. When considering only export through the eastern boundary across the Atlantic, CMAQ-APT predicts that the export efficiency is 24% and that 2% of NO y is exported as NO x , 49% as inorganic nitrate, and 25% as PAN. These results are in reasonably good agreement with an analysis reported in the literature of aircraft measurements over the North Atlantic.

Journal of Geophysical Research: Atmospheres, 2012

ABSTRACT Coal-fired electric power plants produce a large fraction of total U.S. NOx emissions, b... more ABSTRACT Coal-fired electric power plants produce a large fraction of total U.S. NOx emissions, but NOx from this sector has been declining in the last decade owing to installation of control technology. Nighttime aircraft intercepts of plumes from two different Texas power plants (Oklaunion near Wichita Falls and W. A. Parish near Houston) with different control technologies demonstrate the effect of these reductions on nighttime NOx oxidation rates. The analysis shows that the spatial extent of nighttime-emitted plumes to be quite limited and that mixing of highly concentrated plume NOx with ambient ozone is a determining factor for its nighttime oxidation. The plume from the uncontrolled plant had full titration of ozone through 74 km/2.4 h of downwind transport that suppressed nighttime oxidation of NO2 to higher oxides of nitrogen across the majority of the plume. The plume from the controlled plant did not have sufficient NOx to titrate background ozone, which led to rapid nighttime oxidation of NO2 during downwind transport. A plume model that includes horizontal mixing and nighttime chemistry reproduces the observed structures of the nitrogen species in the plumes from the two plants. The model shows that NOx controls not only reduce the emissions directly but also lead to an additional overnight NOx loss of 36–44% on average. The maximum reduction for 12 h of transport in darkness was 73%. The results imply that power plant NOx emissions controls may produce a larger than linear reduction in next-day, downwind ozone production following nighttime transport.

Fuel Processing Technology, 2004

A multiscale modeling system that consists of a global cycling model and a continental-scale mode... more A multiscale modeling system that consists of a global cycling model and a continental-scale model, TEAM, is applied to simulate the fate and transport of mercury over North America. The performance of the modeling system is shown to be satisfactory. TEAM is used to simulate three coal-fired power plant emission control scenarios that correspond to 47%, 30% and 16% reductions in mercury emissions from the 1999 base case. Changes in total mercury deposition are less than 10% over most of the United States. The latter two scenarios that include subcategorization of power plants by coal rank and stack temperature show little effect on mercury deposition compared to the first scenario.

Journal de Physique IV (Proceedings), 2003

ABSTRACT A multiscale modeling system that includes a global model and a nested continental model... more ABSTRACT A multiscale modeling system that includes a global model and a nested continental model is applied to simulate the global cycling of atmospheric mercury and its fate and transport over North America. The models show satisfactory performance with a coefficient of determination of 0.81 for mercury wet deposition over North America. The models are used to estimate source attribution of mercury deposition in the United States. On average, 73% of mercury deposited in the contiguous United States is calculated to originate from the global background.

Environmental Science & Technology, 1998

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Environmental Science & Technology, 2000

Environmental Fluid Mechanics, 2008

ABSTRACT Several air toxics are emitted from mobile sources on roadways and these emissions accou... more ABSTRACT Several air toxics are emitted from mobile sources on roadways and these emissions account for a significant fraction of the health risks to the population. In addition, health effect studies are now becoming more comprehensive and some account for the spatial heterogeneities of air pollutant concentration fields (as is the case near roadways). Standard models can simulate either the near-source concentration fields or the urban background, but no model can handle both spatial scales in the vicinity of roadways in a coherent and scientifically correct manner. Here, we present a model that provides such an integrated treatment by combining a grid-based air quality model of the urban background with a plume-in-grid representation of roadway emissions. The model is applied to simulate near-roadway concentrations due to emissions from a busy interstate highway in New York City. Qualitative comparisons with typical measured concentration profiles show that the model captures the observed features of toxic air pollutant concentrations near roadways.