Houston-Galveston-Brazoria Area Research Articles

Anthropogenic Source Contributions to Ozone Formation in the Greater Houston Area

The Houston-Galveston-Brazoria (HGB) area of Texas has historically experienced severe air pollution events with high concentrations of ozone (O3) during the summer season. This study evaluates the contribution of different anthropogenic sources to ozone formation in the HGB area. The Emission Processing System (EPS3) is used to process emission files in four different scenarios (Base case as including All emission sources (BC), All sources— Area sources (AMA), All sources—Point sources (AMP), and All sources— Mobile sources (AMM). These files are used as input in photochemical modeling with the Comprehensive Air Quality Model with Extensions (CAMx) to simulate ozone formation. The data is analyzed for daily maximum ozone concentrations and contribution of source categories at three air quality monitoring locations (La Porte Sylvan beach-C556, Houston Texas avenue-C411, and Texas city in Galveston-C683) for a study period of June 1-June 30, 2012. The contribution of the point sources to ozone formation is dominated at all three locations, followed by mobile sources and area sources on high ozone days. The relative contributions of point sources are 27.51% ± 3.53%, 21.45% ± 7.36%, and 30.30% ± 9.36%; and mobile sources are 18.27% ± 2.22%, 20.60% ± 6.89%, and 18.61% ± 7.43%; and area sources were 4.2% ± 1.65%, 5.21% ± 1.59%, and 3.72% ± 1.52% at C556, C411, and C683, respectively. These results demonstrate the importance of regulatory focus on controlling point and mobile source emissions for NAAQS attainment in the study region.

Influence of Cold Fronts on Variability of Daily Surface O3 over the Houston-Galveston-Brazoria Area in Texas USA during 2003–2016

We investigated the impacts of cold fronts on area-wide peak O3 and regional backgroundO3 mixing ratios on a daily scale over the Houston-Galveston-Brazoria (HGB) area of southeasternTexas during the O3 seasons (April–October) of 2003–2016. Back trajectories showed that an 18h timelag existed between arrival of cold fronts in the HGB area and onset of a predominately northerlyflow. Cold fronts showed increasing effects on both peak and background O3 over the HGB area.Compared to no front days, average peak O3 mixing ratios during the cold front 1st days, coldfront 2+ days, and post frontal days increased 0.7, 5.9, and 9.0 ppbv, respectively while averagebackground O3 increased 2.9, 6.8, and 8.6 ppbv, respectively. The change in wind direction fromsoutherly to northerly was the most important factor causing increasing O3 levels. Wind directionshifts caused variation of other meteorological factors (i.e., wind speed, precipitation, temperature,cloud cover, and relative humidity) and tended to overshadow their effects on O3 over the HGB area.On a long-term and large-scale view, cold fronts over the HGB area could be regarded as interruptionsin the cleansing effects of predominantly marine southerly flow from the Gulf of Mexico.

Air Quality Impact of Biomass Co-Firing with Coal at a Power Plant in the Greater Houston Area

The Houston-Galveston-Brazoria (HGB) area of Texas is a moderate nonattainment region for ozone, and has a history of severe summer ozone episodes. W. A. Parish power plant (WAP) located in the greater Houston area is the largest coal and natural gas based electricity generating unit (EGU) in Texas. Forest residue is an abundant renewable resource, and can be used to offset coal usage at EGUs. This study evaluates the impact of co-firing 5%, 10%, and 15% (energy-basis) of forest residue at WAP on the air quality of the HGB area. Photochemical modeling with Comprehensive Air Quality Model with Extensions (CAMx) was conducted to investigate the air quality at three air quality monitoring sites (C696, C53, C556) in the HGB area, under two source scenarios (all-sources, point + biogenic sources). Significant reduction of SO2 and O3 was observed for 10% and 15% co-firing ratios at monitoring station (C696) close to WAP. The maximum reduction of ozone observed for 15% co-firing is 4.7% and 6.3% for all-sources and point + biogenic sources scenarios respectively. The reduction in other criteria air pollutants is not significant at all locations. The overall results from this study indicate that biomass co-firing at WAP would not lead to a significant reduction in ozone concentrations in the region during periods of peak ozone.

A data mining framework for environmental and geo-spatial data analysis

Mining geo-spatial data is an important task in many application domains, such as environmental science, geographic information science, and social networks. In this paper, we introduce a data mining framework, which includes pre-processing of environmental and geo-spatial data, geo-spatial data mining techniques, and visual analysis of environmental and geo-spatial data. In particular, we propose new density-based clustering algorithms to identify interesting distribution patterns from geo-spatial data, a change pattern discovery technique to detect dynamic change patterns within spatial clusters, and a post-processing technique to extract interesting patterns and useful knowledge from geo-spatial data. Our density-based clustering algorithms are based on the well-established density-based shared nearest neighbor clustering algorithm, which can find clusters of different shape, size, and densities in high-dimensional data. The post-processing analysis technique allows automatic screening of interesting spatial clusters. The change pattern discovery algorithm is able to detect and analyze dynamic patterns of changes within spatial clusters. This paper focuses on developing a framework integrating a sequence of data mining process including clustering algorithm, analysis technique and pattern changing discovery algorithm. In contrast to previous works in this area, our approaches can cluster and analyze dynamically evolved complex objects, i.e., polygons. We evaluate the effectiveness of our techniques through a challenging real case study involving ozone pollution events in the Houston–Galveston–Brazoria area. The experimental results show that our approaches can discover interesting patterns and useful information from geo-spatial air-quality data.

Photochemical model simulations of air quality for Houston–Galveston–Brazoria area and analysis of ozone–NO x –hydrocarbon sensitivity

As part of the State Implementation Plan for the Houston–Galveston–Brazoria (HGB) area which has been declared as a non-attainment area, it was required to assess the impacts of pollutant emissions, meteorological conditions, and initial and boundary conditions on air quality. In this study, photochemical model simulations using the Comprehensive Air Quality Model with extensions (CAMx) were conducted for three ozone episodes between May and October of 2006. The CAMx simulations compared fairly well with the hourly average concentrations of ozone measured at the monitoring sites, and the index of agreement (IOA) values for all the three ozone episodes were found greater than 0.65, which proved to be good for CAMx model performance. Both simulated and observed peak ozone concentrations were observed to occur between 12:00 and 15:00 h. The CAMx simulation results showed that there were 68 days where the maximum 8-h mean ozone concentrations exceeded the NAAQS of 75 ppb out of a total of 72 days simulated in the three ozone episodes. For all three episodes, ozone concentrations were highest during the third quarter of the day. The photochemical indicator ratios of hydrogen peroxide (H2O2) to nitric acid (HNO3) ([H2O2]/[HNO3]) showed the HGB area to be a nitrogen oxide (NO x )-sensitive regime for the episodes studied. This indicated that volatile organic compounds (VOCs) are plentiful, and NO x is the limiting precursor for ozone formation in the HGB area. The plentiful VOCs in this region are possibly produced from industries and refineries in the HGB area.

Prediction of surface ozone episodes using clusters based generalized linear mixed effects models in Houston–Galveston–Brazoria area, Texas

A two–stage strategy is proposed to predict regional peak ozone episodes in the Houston–Galveston–Brazoria (HGB) area of Texas, USA. With the forecasted meteorological information, ozone episodes can be predicted one day in advance. Three generalized linear mixed effects models (GLMMs) are built with air quality and meteorological data monitored at CAMS35, CAMS403 and CAMS1015; wind field data from 8 monitoring sites in HGB area are used to generate clusters which represent distinct weather patterns. Air quality and meteorological data during ozone seasons (Apr. 1st – Oct. 31st) from 2003 to 2005 are used to build site–specific prediction models. Data of ozone season from 2006 to 2007 are used to test these models. Compared to linear regression models (LM), generalized linear models (GLMs), multilayer perceptron (MLP) and support vector machine (SVM), GLMM which considers differences in ozone formation and diffusion in distinct weather patterns has the smallest fitting and prediction error on ozone exceedances and can detect the most number of exceedance days correctly.

Influence of Reactive Volatile Organic Compounds on Ozone Production in Houston-Galveston-Brazoria Area

Secondary pollutant ozone (O3) formation in a particular area is often influenced by various factors. Source of emissions is one of the factors. In south east Texas, Houston-Galveston-Brazoria (HGB) is a marginal non-attainment area for ozone (O3). A summer episode of May 28 to July 2, 2006 is simulated using Comprehensive Air Quality Model with extensions (CAMx). During this period O3 concentration in HGB often exceeds the National Ambient Air Quality Standards (NAAQS) 0.075 ppm of average 8 hour O3 concentration. HGB area has numerous point sources. Various studies found that some specific volatile organic compounds are very reactive in atmosphere. The objective of this study is to analyze the influence of volatile organic compounds present in point source emissions on the air quality of HGB area. For this purpose ozone sensitivity for HGB area is analyzed by the ratio of hydrogen peroxides (H2O2) to nitric acid (HNO3). HGB area is found NOx limited but reactive VOCs are found to be influential too. From (1-4 June, 2006) maximum O3 concentration was found on weekend, June 3. VOCs such as Acetaldehyde (ALD2), Formaldehyde (FORM) and Alkane (ETHA) showed good correlation with O3 concentrations on that day. In addition, Peroxyacetyl nitrate (PAN) formation was found correlated to higher ozone production. Criteria pollutant Sulfur dioxide (SO2) was found to influence the ALD2 and ETHA concentrations, and thus indirectly influenced O3 production.

Retrospective Air Quality Simulations of the TexAQS-II: Focused on Emissions Uncertainty

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.

Overview of the SHARP campaign: Motivation, design, and major outcomes

AbstractThe Study of Houston Atmospheric Radical Precursors (SHARP) was a field campaign developed by the Houston Advanced Research Center on behalf of the Texas Environmental Research Consortium. SHARP capitalized on previous research associated with the Second Texas Air Quality Study and the development of the State Implementation Plan (SIP) for the Houston‐Galveston‐Brazoria (HGB) ozone nonattainment area. These earlier studies pointed to an apparent deficit in ozone production in the SIP attainment demonstration model despite the enhancement of simulated emissions of highly reactive volatile organic compounds in accordance with the findings of the original Texas Air Quality Study in 2000. The scientific hypothesis underlying the SHARP campaign was that there are significant undercounted primary and secondary sources of the radical precursors, formaldehyde, and nitrous acid, in both heavily industrialized and more typical urban areas of Houston. These sources, if properly taken into account, could increase the production of ozone in the SIP model and the simulated efficacy of control strategies designed to bring the HGB area into ozone attainment. This overview summarizes the precursor studies and motivations behind SHARP, as well as the overall experimental design and major findings of the 2009 field campaign. These findings include significant combustion sources of formaldehyde at levels greater than accounted for in current point source emission inventories; the underestimation of formaldehyde and nitrous acid emissions, as well as CO/NOx and NO2/NOx ratios, by mobile source models; and the enhancement of nitrous acid by atmospheric organic aerosol.

Magnitude, Decadal Changes, and Impact of Regional Background Ozone Transported into the Greater Houston, Texas, Area

Two independent analyses of the daily maximum 8 h average ozone concentrations measured during the high ozone season (May through October) at Continuous Ambient Monitoring Stations are used to quantify the regional background ozone transported into the Houston-Galveston-Brazoria (HGB) area. The dependence on wind direction is examined, and long-term trends are determined using measurements made between 1998 and 2012. Both analyses show that the regional background ozone has declined during periods of continental outflow: i.e., the conditions associated with most high ozone episodes in HGB. The changes in regional background ozone found for northeasterly and southeasterly flow are -0.50 ± 0.54 and -0.79 ± 0.65 (95% confidence limit) ppbv yr(-1), respectively, which correspond to decreases of ∼7-11 ppbv between 1998 and 2012. This finding is consistent with the summertime downward trend of -0.45 ppbv yr(-1) (range of sites: -0.87 to +0.07 ppbv yr(-1)) for ozone in the eastern U.S. between 1990 and 2010 reported by Cooper et al. and shows that changing background concentrations are at least partially responsible for the decreased surface ozone in the HGB area over the past decade. Baseline ozone concentrations in air flowing into Texas from the Gulf of Mexico have not changed significantly over this period.

Impacts of Emission Variability and Flare Combustion Efficiency on Ozone Formation in the Houston–Galveston–Brazoria Area

Recent studies in the Houston–Galveston–Brazoria (HGB) area of Texas have suggested that industrial flares exhibit high temporal emissions variability and that flare combustion efficiencies could vary with air and steam assist rates, particularly at lower flow rates, and when low heating value gases are combusted. This work examined the difference in ozone formation potential associated with accounting for temporal variability in flaring emissions, as opposed to assuming the same amount of mass was emitted at a constant, average flow rate. The temporal variability in flare emissions was found to lead to differences in ozone concentrations of as much as 27 ppb in the HGB area. This work also examined the potential ozone formation impacts of flare combustion efficiencies of less than 98–99%, applied to 25 flares throughout the HGB region. Deterioration in combustion efficiency (CE) was found to affect ozone concentrations by a few to more than 50 ppb, depending on the level of the assumed CE. While the ozone impacts associated with temporal variability in emissions typically lasted a few hours, consistent with the length of large flaring events, lowering of the CE significantly increased emissions and ozone concentrations over periods ranging from several hours to several days for some flare types. Thus, changes in CE may affect ozone concentrations for longer durations and over larger spatial extents than episodic emissions events.

Classification of Weather Patterns and Associated Trajectories of High-Ozone Episodes in the Houston–Galveston–Brazoria Area during the 2005/06 TexAQS-II

Abstract The 850-hPa synoptic flow patterns over eastern Texas and adjacent states during the 2005/06 Second Texas Air Quality Studies (TexAQS-II) period were classified into six groups using a two-stage clustering method. This study identifies synoptic weather patterns that are conducive to creating high-ozone events and reveals potential emission source regions leading to ozone exceedances through backward trajectory analysis. Clusters with dominant southerly synoptic flows and higher average wind speeds (C1 and C2 clusters) were related to low mean daytime ozone levels. Easterly (C3) and northerly (C5) clusters showed a higher probability to exceed the 8-h ozone standard than the other clusters. The dry and sunny postfrontal days with weak northerly or easterly weather patterns were often associated with ozone exceedances in the Houston–Galveston–Brazoria (HGB) area during September 2006. The majority of backward trajectories on ozone episode days were from the east, which brought polluted air from the Houston Ship Channel resulting in high ozone in the southwestern part of the metropolitan area. The shifting trajectories of the C3 and C5 weather patterns were associated with surface wind turning from weak northerly to southeasterly/southerly because of the development of bay/sea breeze. Pollutants were shifting inside the metropolitan area and high ozone built up in the afternoon or early evening. A small portion of trajectories of C3 and C5 that caused high ozone passed over a short distance from the south of Houston, picking up emissions from the industries along the coast.

Extensive aerosol optical properties and aerosol mass related measurements during TRAMP/TexAQS 2006 – Implications for PM compliance and planning

Extensive aerosol optical properties, particle size distributions, and Aerodyne quadrupole aerosol mass spectrometer measurements collected during TRAMP/TexAQS 2006 were examined in light of collocated meteorological and chemical measurements. Much of the evident variability in the observed aerosol-related air quality is due to changing synoptic meteorological situations that direct emissions from various sources to the TRAMP site near the center of the Houston-Galveston-Brazoria (HGB) metropolitan area. In this study, five distinct long-term periods have been identified. During each of these periods, observed aerosol properties have implications that are of interest to environmental quality management agencies. During three of the periods, long range transport (LRT), both intra-continental and intercontinental, appears to have played an important role in producing the observed aerosol. During late August 2006, southerly winds brought super-micron Saharan dust and sea salt to the HGB area, adding mass to fine particulate matter (PM 2.5) measurements, but apparently not affecting secondary particle growth or gas-phase air pollution. A second type of LRT was associated with northerly winds in early September 2006 and with increased ozone and sub-micron particulate matter in the HGB area. Later in the study, LRT of emissions from wildfires appeared to increase the abundance of absorbing aerosols (and carbon monoxide and other chemical tracers) in the HGB area. However, the greatest impacts on Houston PM 2.5 air quality are caused by periods with low-wind-speed sea breeze circulation or winds that directly transport pollutants from major industrial areas, i.e., the Houston Ship Channel, into the city center.

Evaluation of air quality models for the simulation of a high ozone episode in the Houston metropolitan area

A high ozone event in the Houston–Galveston–Brazoria area was utilized to study the shortcomings of the current air quality models. To improve the baseline simulations with the Comprehensive Air quality Model with Extensions (CAMx) for developing the state implementation plan, the Texas Commission on Environmental Quality (TCEQ) imputed emissions of highly reactive volatile organic compounds (HRVOCs) by scaling the amount of fugitive emissions of olefins to co-emitted NO x from selected point sources, effectively multiplying by 3–12 times over the regular inventory values. In this paper, CAMx and the Community Multiscale Air Quality (CMAQ) model were used to determine if the imputed HRVOC emissions were consistent with the observed atmospheric conditions. With the base emissions, CMAQ and CAMx both with the Carbon-Bond 4 (CB-4) mechanism simulated similar ozone concentrations. But with the imputed HRVOC emissions, CMAQ predicted lower ozone peaks than CAMx in the vicinity and downwind of the Ship Channel and other highly HRVOC-rich areas. Based on analyses of sensitivity simulations of CMAQ with different emission inputs and vertical diffusion algorithms in the model, we found that the modeled atmosphere lacked reactivity to produce the observed high ozone event. Although the imputed HRVOC emissions improved ozone prediction at the surface sites, but the ethylene concentrations were not consistent with the measurements at the super sites (La Porte and Clinton) and by NOAA aircraft. Several sensitivity tests designed to provide additional radicals into the system and other research results suggested that the lack of reactivity may need to be corrected by targeted, and probably of episodic, increase of HRVOC emissions, from the sources in the Houston Ship Channel. Additional investigation of the ozone production efficiency for different chemical mechanisms is necessary to pinpoint the emissions uncertainty issues.

Air quality modeling for Houston–Galveston–Brazoria area

A coupled numerical model of the atmospheric thermo-hydrodynamics and pollutant photochemical transport is described. This model can be used to study the complex relationships between the chemical and thermo-hydrodynamic processes in the atmosphere of urban areas with an emphasis on photochemical ozone formation. Preliminary numerical results of ozone and other key chemical atmospheric pollutant concentrations and distribution across the Houston–Galveston–Brazoria area using virtual emission data from area and mobile sources are presented.