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Air Quality Research and Contract Reports: Photochemical Modeling

Reports related to photochemical modeling of air quality written by contractors for the Texas Commission on Environmental Quality.

Reports from Air Quality Research and Contract Projects related to photochemical modeling are posted here as PDF files (Help with PDF) unless otherwise specified. Some reports have companion data files in various formats.

For comments and questions regarding these reports, please e-mail us at, put "Air Quality Photochemical Modeling Contract Report Inquiry" in the subject line, and include the web address of the report PDF file in the e-mail text or attache the original report PDF file.

Evaluation of NOx Emission Inventory Bias Using 2013 Aircraft Observations - Many researchers have claimed that the NOx emissions used in regional photochemical modeling over-estimates NOx emissions, particularly from mobile sources, but modeling conducted by Texas has found reasonably good agreement between modeled and observed concentrations. This work by Ramboll Environ extends the comparison to three-dimensions using aircraft observations to see whether the favorable comparison extends through the mixed layer. (July 2017)

Fire Impact Modeling with CAMx - Ramboll Environ has created a fire impact tool for CAMx that can track wildfire and agricultural burning emissions, and assess the potential impact of these emissions upon pollutant concentrations in Texas cities. (July 2017)

Daily Near Real-time Ozone Modeling: Phase 4 (December 2016), Phase 3 (January 2016), Phase 2 (January 2015), and Phase 1 (November 2013) - These reports, provided by Ramboll Environ, describe meteorological and photochemical grid modeling that was performed during the summer of 2013 - 2016. This modeling was used to test different proposed improvements in the photochemical grid modeling, and to evaluate them on a rapid time scale. By evaluating daily model runs, model improvements could be tested quickly and frequently.

CMAQ Modeling Archive for Exceptional Events Analyses - This report, provided by University of Houston, documents photochemical modeling of April-October 2012, 2013, and 2014 performed using the US EPA CMAQ model under two scenarios: with and without biomass burning emissions (wild fires and controlled burns). Modeling methods, inputs and results are discussed in the report. Model predictions are archived at the University of Houston and are available for evaluating the impact of fires on air quality in Texas. (August 2016)

Updated Boundary Conditions for CAMx Modeling - This report, provided by Ramboll Environ, ​​​​​documents the study to provide TCEQ with updated boundary conditions for the CAMx regional modeling. The contractor added iodine chemistry to the latest version (v10-01) of the Goddard Earth Observing System Chemistry (GEOS-Chem) global model. The standard chemical mechanism in this version includes bromine and chlorine but lacks iodine chemistry. The GEOS-Chem model was run with iodine emissions and chemistry included for a base year (2012) and a future year (2017).​ (July 2016)

Improved Halogen Chemistry for CAMx Modeling - This report, provided by Ramboll Environ, ​​​​​documents the improvement of both speed and accuracy in modeling ozone transported into Texas from the Gulf of Mexico by: 1) implementing a condensed halogen mechanism; and 2) implementing an in-line emissions algorithm that incorporates recent findings on the feedback between ozone deposition to ocean waters and emission flux of iodine​. (May 2016)

Improved OSAT, APCA and PSAT Algorithms for CAMx - This report, provided by Environ, documents the modifications to improve the accuracy of the ozone source apportionment in two ways: 1) by keeping track of the source(s) of O3 removed by reaction with NO to form NO2 and subsequently returned as O3 when the NO2 is destroyed by photolysis; 2) by keeping track of so-called “NOx recycling” when NOx is converted to a different form of oxidized nitrogen, such as NHO3, and later converted back to NOx. (August 2015)

Three-Dimensional Performance Comparison of CAMx and CMAQ Using the 2013 DISCOVER-AQ Field Study Data Base - This report, provided by Environ, describes modeling of several days during the DISCOVER-AQ Houston-area field study using both the Comprehensive Air Quality Model with Extensions (CAMx) and the Community Model for Air Quality (CMAQ). Outputs from the two models are compared against each other and against surface and aircraft-sampled ambient concentration data. (August 2015)

CAMx Speed Improvements - This report, provided by Environ, documents the project to improve the CAMx run speed. The areas of the model most needing speed improvements are first identified, and modifications are made to the CAMx code, OMP parallelization, and compiler flags, addressing the highest priority speed improvements. It also identify other areas for improvement in follow-on work. (July 2015)

Simulation of the Stratospheric Contribution to Surface Ozone - This report, provided by Environ, describes development and evaluation of new boundary conditions for the Comprehensive Air Quality Model with Extensions (CAMx) using the Goddard Earth Observation System global model with Chemistry (GEOS-Chem) with the optional Unified Chemistry Extension (UCX) option. Selecting the UCX option runs GEOS-Chem with full stratospheric chemistry and provides more realistic boundary condition concentrations for CAMx. (August 2015)

Ozone Depletion by Bromine and Iodine over the Gulf of Mexico - This report, provided by Environ, documents the addition of bromine chemistry into the iodine chemistry developed for CAMx and its impact on modeled background ozone over the Gulf of Mexico. A consistent halogen mechanism for chlorine, bromine, and iodine was developed and integrated with the CB6r2 ozone chemistry mechanism. The combined mechanism is referred to as CB6r2h. (November 2014)

Comprehensive Air Quality Model with extensions (CAMx) inputs to Community Model for Air Quality (CMAQ) Inputs Converter - This report, provided by Environ, documents the development of the CAMx2CMAQ converter which transforms emissions data, boundary and initial conditions data in CAMx input format to CMAQ netCDF input format. Meteorological data is not converted since meteorological output can be prepared for use in either model with existing software. Many researchers are interested in modeling Texas air quality. It is therefore important that they be provided the best possible input data with which to conduct this research. (CAMx2CMAQ User's Guide and source code) (August 2014)

Improving CAMx GREASD Plume-in-Grid Efficiency - Environ improved the physical and chemical evolution of large point source nitrogen oxides (NOx) plumes in the CAMx photochemical model that are too small to be resolved in the modeling grid. By using a Plume-in-Grid (PiG)-specific chemical mechanism limited to the inorganic chemical reactions in early NOx plumes, the computational efficiency was increased. Total CAMx run times were reduced 10-20% using the June 2006 episode. A bug fix corrected NOy conservation in the PiG mechanism, which artificially increased NOy by as much as 30% previously. Sensitivity tests showed the impact to be larger on course model grids, which is expected as PiG plumes dump to finer grids quickly. These improvements will be included in the next official release of CAMx version 6.1. (August 2013)

Foreign Contributions to Texas Ozone - This report, provided by Environ, documents the modeling project using GEOS-Chem global model to estimate the contribution of foreign anthropogenic sources to Texas ozone concentrations directly, and also to provide alternate boundary conditions from which TCEQ can conduct its own refined modeling to more accurately calculate the effects of foreign sources on Texas ozone. (August 2013)

Improving CAMx Performance in Simulating Ozone Transport from the Gulf of Mexico - This report, provided by Environ, documents the evaluation of three factors that could contribute to over-predicting ozone over the Gulf of Mexico: (1) Under-estimated dry deposition of ozone over water; (2) Over-estimated CAMx boundary conditions for ozone over the Gulf of Mexico and/or Atlantic Ocean, and (3) Chemical reactions of iodine that deplete ozone in the marine boundary layer and are not included in CAMx. (September 2012)

Improving the CAMx photochemical model and support programs with a focus on the Dallas-Fort Worth area - This report, provided by Environ, provides details on improving the vertical mixing algorithms in the CAMx pre-processor WRFCAMx, the nocturnal plume growth rates in the Plume-in-Grid sub-model, and temperature and pressure dependencies for specific photolysis rates. Model tests were conducted using the June 2006 modeling episode. (August 2012)

Improving the Representation of Vertical Mixing Processes in CAMx - This report, provided by Environ, provides details on the vertical mixing updates to the CAMx pre-processor WRFCAMx. Various boundary layer schemes in the WRF meteorological model were analyzed and considered for implementation into the WRFCAMx interface program. CAMx model sensitivity to revised vertical diffusivity (Kv) inputs was conducted and analyzed. (August 2011)

Improving the Characterization of Pollution Transported into Texas - This report, provided by Harvard University, provides chemical boundary conditions for regional model simulations of U.S. air quality using the chemical transport model GEOS-Chem. The project calculated the chemical composition of the global atmosphere for two scenarios: (1) 2005-2006 meteorology with 2005-2006 emissions and (2) 2005-2006 meteorology with 2018 emissions. (April 2011)

Improving the Characterization of Pollution Transported into Texas Using OMI and TES Satellte and In Situ Data and HYSPLIT Back Trajectory Analyses - The Jet Propulsion Librartory (JPL) used ozone and NO2 measurements from the Tropospheric Emission Spectrometer (TES) and Ozone Monitoring Instrument (OMI) satellite-borne instruments together with in situ data and the Hybrid Single Particle Lagrangian Integrated Trajectory Model (Hy-SPLIT) to assess whether air parcels exhibiting enhanced ozone in the lower troposphere above Texas have moved within or outside of Texas. (April 2011)

Development, Evaluation and Testing of Version 6 of the Carbon Bond Chemical Mechanism (CB6) - This report, provided by Environ, documents the update of the carbon bond (CB) chemical mechanism for photochemical modeling applications from version CB05 to CB6. Compared to CB05, CB6 increases the number of chemical species from 51 to 77 and the number of reactions from 156 to 218. (September 2010)

Speed Improvements for EPS3 - This report, provided by Environ, documents the speed-up achieved with the latest Emissions Processing System v3 (EPS3). The entire process was examined for efficiency and various improvement techniques were implemented, with a significant speed-up of the oft-used merging and control tools. (July 2010)

Implementation of an Alternative Plume Rise Methodology in CAMx - This report, provided by Environ, documents a new plume rise algorithm for CAMx. The previous algorithm in CAMx did not allow the plume to release in more than one layer. Algorithms used in CMAQ and other air quality models were evaluated as possible replacements or options. Neither the existing schemes in CMAQ or CAMx was ideal in all conditions. Environ tested and ultimately chose this new algorithm for CAMx that eliminates discontinuities for various stability layer regimes and wind speeds. (June 2010)

Updated CAMx Boundary Conditions - This report, provided by Environ, documents the developement of new boundary conditions for the CAMx domain for the 2005 and 2006 Houston ozone episodes. The boundary conditions were extracted from CAMx runs on the RPO domain, which used boundary conditions from date-specific GEOS-Chem and date-specific MOZART. The GEOS-Chem results used in this study were specifically for 2005 and 2006 whereas previously monthly averaged 2002 results had been used. (July 2009)

Refining Hydrocarbon Oxidation Mechanisms via Isomeric Specific Radical Initiated Chemistry - This report, provided by Texas A&M University, documents the laboratory chemistry to perform measurements needed to improve the chemical mechanism used in the photochemical model CAMx itself. Dr. Simon North developed a new laboratory technique to measure the speed of radical oxidation of hydrocarbons (VOC). He then applied this technique to isoprene and measured individual rates of several reactions that are currently estimated in CAMx. In a future project, these individual reactions will be incorporated into CAMx. (December 2008)

CAMx Multiprocessing Capability for Computer Clusters Using the Message Passing Interface (MPI) Protocol - This report, provided by Environ, documents the implementation of MPI in CAMx. The MPI capablity in CAMx enables it to distribute a model application to multiple CPUs that share the computational load in integrating the model solution. (August 2008)

Higher-Order Decoupled Direct Method (HDDM) for Ozone Modeling Sensitivity Analyses and Code Refinements - This report, provided by Environ (Bonyoung Koo and Greg Yarwood) and Rice University (Dan Cohan), presents the results of their work on the HDDM method. Koo and Yarwood added refinements to the HDDM code in CAMx to help it run faster and more accurately, and Cohan performed an HDDM analysis on the June 2005 ozone episode. Cohan found that the ozone concentrations are very sensitive to photolysis, indicating a strong dependence on the placement of clouds. He also found that the sensitivity of ozone to VOC or NOx emission controls depends on weather. Two episode days showed strong NOx dependence, but one day showed strong VOC dependence in central Houston and strong NOx dependence further from the urban core. (August 2008)

Boundary Conditions and Fire Emissions Modeling - This report, provided by Environ, describes in detail two related projects. First is the development of emissions inventories of biomass burning for the continental United States plus large portions of Canada and Mexico. Day-specific inventories for the 2005 and 2006 ozone seasons were developed using satellite-derived fire estimates, and a "typical" fire inventory was developed from inventories previously prepared by CenRAP. The Contractor also developed software to process the emissions and allocate emissions from major fires to elevated model layers. In the second part of this work, the Contractor used output from two global atmospheric models, MOZART and GEOS-Chem, to build boundary concentration files for the CENRAP continental scale modeling domain. The Contractor then ran the continental-scale model (incorporating the aforementioned fire emissions inventory) to create both base year and future year boundary conditions files for the TCEQ Eastern United States (EUS) modeling domain. The report includes performance evaluation of the resulting boundary conditions and recommendations on their use, along with recommendations for future work. (September 2008)

Lagrangian Modeling of Industrial Point-source Plumes in the Houston-Galveston Area - This report, provided by Noor Gillani and Yuling Wu of the University of Alabama at Huntsville, describes Lagrangian reactive plume modeling performed for the Harris-Galveston-Brazoria county area for August 28, 2000. The purpose of this modeling was to simulate the observed ozone and ozone precursors with a different type of model (other than a photochemical grid model which TCEQ uses in its regulatory ozone modeling). The report describes the modeling in detail, including the TexAQS 2000 data used to initialize the model's meteorological parameters. The report also provides an inferred point source emissions inventory for the industrial facilities in the greater Houston area. (March 2003)

Meteorological and Ozone Characteristics in the Houston Area from August 23 through September 1, 2000 - This report, from Sonoma Technology, Inc., provides a day-specific conceptual models of ozone formation in the Houston-Galveston-Brazoria area for each day of the Texas Air Quality Study. Each of these daily conceptual models provides a holistic picture of the processes leading to ozone formation (or lack thereof) throughout that day. Overall model performance for any day can then be assessed through comparing the modeled processes with the processes in that day's conceptual model. (August 2002)

Sensitivity Analyses of the September 8-11, 1993 Ozone Episode: Reports (1, 2, 3, 4) and Memo - Environ has prepared four reports and a technical memo describing a number of modeling analyses conducted for the September 8-11, 1993 episode. Environ first evaluated the use of Version 3 of CAMx, along with flexi-nesting and chlorine chemistry. Using these model enhancements, they then conducted sensitivity analyses to evaluate model performance under several hypothesized industrial VOC adjustments. Finally, future-case modeling was performed to assess the feasibility of trading the last 10% of industrial NOx reductions for VOC reductions. These analyses were conducted using the original SAIMM meteorology, and with MM5 and RAMS-generated meteorological inputs. The reports and memo are in PDF format. (May 2002)

An Investigation of CAMx Modeling Issues with Sensitivity Simulations for the September 6-11, 1993 Ozone Episode for Houston-Galveston Area - This report, from Sonoma Technology Inc., provides details on a project to isolate the causes of an area of ozone over prediction in the original modeling, assess the impact of cloud cover on CAMx ozone predictions, and determine if rapid ozone production events can be simulated with CAMx through a series of 12 sensitivity simulations. (August 2001)

Preliminary RAMS/CAMx Ozone Model Performance Results for the Houston Area and the September 6-11, 1993 COAST Episode - This memorandum, provided by Environ, describes the CAMx modeling performance evaluation done with the RAMS-based meteorological fields for the September 6-1,1 1993 Houston ozone episode. EPA performance criteria, including unpaired peak, bias, gross error, and time series are discussed. (January 2001)

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