Shaheen R. Tonse

A preliminary synthesis of modeled climate change impacts on U.S. regional ozone concentrations.

This paper provides a synthesis of results that have emerged from recent modeling studies of the potential sensitivity of U.S. regional ozone (O3) concentrations to global climate change (ca. 2050). This research has been carried out under the auspices of an ongoing U.S. Environmental Protection Agency (EPA) assessment effort to increase scientific understanding of the multiple complex interactions among climate, emissions, atmospheric chemistry, and air quality. The ultimate goal is to enhance the ability of air quality managers to consider global change in their decisions through improved characterization of the potential effects of global change on air quality, including O3 The results discussed here are interim, representing the first phase of the EPA assessment. The aim in this first phase was to consider the effects of climate change alone on air quality, without accompanying changes in anthropogenic emissions of precursor pollutants. Across all of the modeling experiments carried out by the differe...

Extension and evaluation of sensitivity analysis capabilities in a photochemical model

The decoupled direct method in three dimensions (DDM-3D) provides an efficient and accurate approach for probing the sensitivity of atmospheric pollutant concentrations to various changes in photochemical model inputs. The implementation of DDM-3D for the widely used Community Multiscale Air Quality (CMAQ) model was updated to account for recent changes in the base model and to include additional chemical mechanisms and advection schemes. The capabilities of CMAQ-DDM-3D were extended to enable execution using multiple processors in parallel and the computation of sensitivities to chemical reaction rate constants. The resulting direct sensitivity modeling system was tested for statistical agreement with the traditional difference method for calculating sensitivities, considering a summer episode in a domain covering the continental United States. Sensitivities to domain-wide and sector specific emissions, initial/boundary conditions, and chemical reaction rates were compared and found to be in good correlation for both primary and secondary air pollutants. The scalability of CMAQ-DDM-3D to the number of processors used in parallel was also examined. Sensitivity calculations were found to scale in a similar way to the base model, where the benefit to model runtime of adding more processors diminished for simulations that used more than eight processors.

LABORATORY INVESTIGATION OF AN ULTRALOW NOx PREMIXED COMBUSTION CONCEPT FOR INDUSTRIAL BOILERS

A combustion concept to achieve ultralow emissions (NOx 2 ppm and CO 20 ppm) was tested on a 18 kW low-swirl burner (LSB). It is based on lean premixed combustion combined with flue gas recirculation (FGR) and partially reformed natural gas (PRNG). Flame stability and emissions were assessed as a function of , FGR, and PRNG. The results show that PRNG improves flame stability and reduces CO, with no impact on NOx at 0.8. A one-dimensional flame simulation satisfactorily predicted prompt NOx under lean conditions with high FGR. Two catalysts were tested in a prototype steam reformer, and the results were used to estimate reactor volume and steam requirements in a practical system. An advanced Sud Chemie catalyst displayed good conversion efficiency at relatively low temperatures and high space velocities, which indicates that the reformer can be small and will track load changes. Tests conducted on the LSB with FGR and 0.05 PRNG show that boilers using a LSB with PRNG and high FGR and close to stoichiometry can operate with low emissions and high efficiency.

The dependence of chemistry on the inlet equivalence ratio in vortex-flame interactions

The interaction of a vortex pair with a premixed flame serves as an important prototype for premixed turbulent combustion. In this study, we investigate the interaction of a counter-rotating vortex pair with an initially flat premixed methane flame. We focus on characterizing the mechanical nature of the flame-vortex interaction and on the features of the interaction strongly affected by fuel equivalence ratio. We compare computational solutions obtained using a time-dependent, two-dimensional adaptive low Mach number combustion algorithm that incorporates GRI-Mech 1.2 for the chemistry, thermodynamics and transport of the chemical species. We find that the circulation around the vortex scours gas from the preheat zone in front of the flame, making the interaction extremely sensitive to equivalence ratio. For nearly stoichiometric cases, the peak mole fraction of CH across the flame is relatively insensitive to the vortex whereas for richer flames we observe a substantial and rapid decline in the peak CH mole fraction, commencing early in the flame-vortex interaction. The peak concentration of HCO is found to correlate, in both space and time, with the peak heat release across a broad range of equivalence ratios. The model also predicts a measurable increase in C2H2 as a result of interaction with the vortex, and a marked increase in the low temperature chemistry activity.

A Seasonal Perspective on Regional Air Quality in CentralCalifornia - Phase 1

A Seasonal Perspective on Regional Air Quality in Central California – Phase 1 Final Report Prepared for: San Joaquin Valleywide Air Pollution Study Agency California Air Resources Board Contract 04-1CCOS With support from: California Energy Commission U.S. Department of Energy by Robert A. Harley Department of Civil and Environmental Engineering University of California, Berkeley, CA Nancy J. Brown, Shaheen R. Tonse, and Ling Jin Atmospheric Science Department Lawrence Berkeley National Laboratory, Berkeley, CA December 2006