Browsing by Subject "ozone"
Now showing 1 - 5 of 5
Results Per Page
Sort Options
Item Investigations of Atmospheric and Plant Physiological Effects along an Urban-To-Rural Gradient in the Houston Metropolitan Area Comparing 2011 to 2012(2014-09-02) Gramann, JonathanThis project hypothesizes that changes in climate resulting from urbanization can serve as a proxy for the changes expected from climate change, and therefore, future climate change effects on the biosphere can be estimated by comparing urban trees to rural trees. To study this, an urban0to-rural gradient was set up starting near downtown Houston, TX, and extending north approximately 90 km. Three weather stations were erected along this gradient to continually monitor weather. Photosynthesis rates of oak trees near each weather station were measured on periodic field trips throughout the growing season. Comparisons of temperature, rainfall, carbon dioxide, and ozone concentrations indicate that urbanization is a possible but imperfect proxy for climate change. Considering only two years of photosynthesis measurements, the long term effects of climate change are difficult to distinguish from short term effects, such as rain, and seasonal term effects, such as drought. However, observations hold promise that further measurements may lead to more conclusive results.Item Lagrangian methods for climatological analysis of regional atmospheric transport with an emphasis on Texas ozone exceedances(Texas A&M University, 2004-11-15) Dexheimer, Darielle NicoleA quantitative climatology of atmospheric transport in Texas is developed using previously described Lagrangian trajectory methods (Rogers and Bowman, 2001; Bowman and Carrie, 2002). The trajectories are computed using winds from 1979-2001 from the National Center for Environmental Prediction (NCEP) Reanalysis Project data set. Probability distributions are created for particle transport using trajectories from urban areas, making six-hourly particle distributions available from four urban areas in Texas. These probability distributions represent a quantitative understanding of regional air transport. Time-dependent Green's functions are calculated given initial conditions such as urban areas weighted with respect to population. The Green's functions describe how air from urban areas is transported through the atmosphere as a function of time. Summertime backward Lagrangian trajectories initialized at 5 Texas Commission on Environmental Quality (TCEQ) monitoring stations are grouped according to the ozone value recorded at the station at the initialization time of the trajectory. The directions of the trajectories in each group are used to determine the relationship between the transport characteristics of the circulation over Texas and regional-scale observations of pollutants. Synoptic conditions occurring at the time of summertime ozone exceedances at the 5 TCEQ stations are investigated in order to resolve what conditions are likely to coincide with ozone exceedances.Item Source Contributions to VOC's to Ozone Formation in Southeast Texas Using a Source-oriented Air Quality Model(2011-08-08) Krishnan, AnupamaHouston-Galveston-Brazoria area is in severe non-attainment status for ozone compliance. Source-oriented mechanistic modeling was used to determine the major sources of VOCs that contributes to ozone formation during the Texas Air Quality Study (TexAQS) from August 16, 2000 to September 7, 2000. Environmental Protection Agency (EPA)?s Community Scale Air Quality Model (CMAQ) version 4.6 was used as a host model to include a revised Statewide Air Pollution Research Center (SAPRC99) photochemical mechanism with source-oriented extensions to track the contributions of Volatile Organic Compounds (VOCs) emissions from diesel engines, biogenic sources, highway gasoline vehicles, fuel combustion, off-highway gasoline engines, solvent utilization and petrochemical industries to ozone formation in the atmosphere. Source-oriented emissions needed to drive the model were generated using a revised Sparse Matrix Operator Kernel Emissions (SMOKE) model version 2.4. VOC/NOx ratios are found to be a critical factor in the formation of ozone. Highest ozone formation rates were observed for ratios from 5-15. The contributions of VOC to ozone formation were estimated based on the linear relationship between the rate of NO to NO2 conversion due to radicals generated from VOC oxidation and the rate of net ozone formation. Petroleum and other industrial sources are the largest anthropogenic sources in the urban Houston region and contribute to 45% of the ozone formation in the HGB area. Highway gasoline vehicles make contributions of approximately 28% to ozone formation. Wildfires contribute to as much 11% of ozone formation on days of high wildfire activity. The model results show that biogenic emissions account for a significant amount of ozone formation in the rural areas. Both highway and off-highway vehicles contribute significantly to ozone formation especially in the downwind region. Diesel vehicles do not contribute significantly to ozone formation due to their low VOC emissions.Item Source- and Age-Resolved Mechanistic Air Quality Models: Model Development and Application in Southeast Texas(2012-07-16) Zhang, HongliangOzone (O3) and particulate matter (PM) existing in the atmosphere have adverse effects to human and environment. Southeast Texas experiences high O3 and PM events due to special meteorological conditions and high emission rates of volatile organic compounds (VOCs) and nitrogen oxides (NOx). Quantitative knowledge of the contributions of different emissions sources to O3 and PM is helpful to better understand their formation mechanisms and develop effective control strategies. Tagged reactive tracer techniques are developed and coupled into two chemical transport models (UCD/CIT model and CMAQ) to conduct source apportionment of O3, primary PM, secondary inorganic PM, and secondary organic aerosol (SOA) and aging distribution of elemental carbon (EC) and organic carbon (OC). Ozone (O3) and particulate matter (PM) existing in the atmosphere have adverse effects to human and environment. Southeast Texas experiences high O3 and PM events due to special meteorological conditions and high emission rates of volatile organic compounds (VOCs) and nitrogen oxides (NOx). Quantitative knowledge of the contributions of different emissions sources to O3 and PM is helpful to better understand their formation mechanisms and develop effective control strategies. Tagged reactive tracer techniques are developed and coupled into two chemical transport models (UCD/CIT model and CMAQ) to conduct source apportionment of O3, primary PM, secondary inorganic PM, and secondary organic aerosol (SOA) and aging distribution of elemental carbon (EC) and organic carbon (OC). Models successfully reproduce the concentrations of gas phase and PM phase species. Vehicles, natural gas, industries, and coal combustion are important O3 sources. Upwind sources have non-negligible influences (20-50%) on daytime O3, indicating that regional NOx emission controls are necessary to reduce O3 in Southeast Texas. EC is mainly from diesel engines while majority of primary OC is from internal combustion engines and industrial sources. Open burning, road dust, internal combustion engines and industries are the major sources of primary PM2.5. Wildfire dominates primary PM near fire locations. Over 80% of sulfate is produced in upwind areas and coal combustion contributes most. Ammonium ion is mainly from agriculture sources. The SOA peak values can be better predicted when the emissions are adjusted by a factor of 2. 20% of the total SOA is due to anthropogenic sources. Solvent and gasoline engines are the major sources. Oligomers from biogenic SOA account for 30-58% of the total SOA, indicating that long range transport is important. PAHs from anthropogenic sources can produce 4% of total anthropogenic SOA. Wild fire, vehicles, solvent and industries are the major sources. EC and OC emitted within 0-3 hours contribute approximately 70-90% in urban Houston and about 20-40% in rural areas. Significant diurnal variations in the relative contributions to EC are predicted. Fresh particles concentrations are high at morning and early evening. The concentrations of EC and OC that spend more than 9 hours in the air are low over land but almost accounts for 100% of the total EC and OC over the ocean.Item Trajectory Simulations of H2O, O3, and CO in the Upper Troposphere and Lower Stratosphere (UTLS)(2014-05-05) Wang, TaoThe purpose of this work is to simulate water vapor (H2O), ozone (O3), and carbon monoxide (CO) in the upper troposphere and lower stratosphere (UTLS) using a domain-filling, forward trajectory model. The influx of H2O to the UTLS is largely determined by the large-scale troposphere-to-stratosphere transport in the tropics, during which air is dehydrated across the cold tropical tropopause. In the domain-filling, forward trajectory model, trajectories are initialized in the upper troposphere, and the circulation is based on reanalysis wind fields. Along the trajectories, winds determine the pathways of parcels and temperature determines the H2O content through an idealized saturation calculation. Compared with the Aura Microwave Limb Sounder (MLS) measurements, this simple advection-condensation strategy yields reasonable results for H2O in the stratosphere in terms of both seasonal variability and vertical structures. The detailed global dehydration patterns are also revealed from this model and it improves our understanding of the H2O and its transport within the UTLS. Besides H2O, ozone (O3) and carbon monoxide (CO) are also important trace gases in the UTLS linked to circulation, transport and climate forcing (for O3). Combined with simple parameterization of chemical production and loss rates from the Whole Atmosphere Community Climate Model (WACCM), we also managed to simulate O3 and CO transport in the UTLS via this trajectory model. The trajectory modeled O3 and CO show good overall agreement with satellite observations from the MLS and the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) in terms of spatial structure and seasonal variability. The trajectory model results also agree well with the Eulerian WACCM simulations. Analysis of the simulated tracers shows that seasonal variations in tropical upwelling exerts strong influence on O3 and CO in the tropical lower stratosphere, and the coupled seasonal cycles provide a useful test of the transport simulations. Interannual variations in the tracers are also closely coupled to changes in upwelling, and the trajectory model can accurately capture and explain observed changes. This demonstrates the importance of variability in tropical upwelling in forcing chemical changes in the tropical UTLS. Trajectory modeling of O3 and CO can provide useful tests for simplified understanding of transport and chemical processes in the UTLS, and provide complementary information to the H2O simulations, which are primarily constrained by tropopause temperatures. This model is easy to use, easy to diagnose, and the Lagrangian perspective makes it exceptionally useful in studying transport processes within the UTLS.