Browsing by Subject "gas chromatography"
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Item Flux Measurements of Volatile Organic Compounds from an Urban Tower Platform(2011-08-08) Park, Chang HyounA tall tower flux measurement setup was established in metropolitan Houston, Texas, to measure trace gas fluxes from both anthropogenic and biogenic emission sources in the urban surface layer. We describe a new relaxed eddy accumulation system combined with a dual-channel gas chromatography - flame ionization detection used for volatile organic compound (VOC) flux measurements in the urban area, focusing on the results of selected anthropogenic VOCs, including benzene, toluene, ethylbenzene and xylenes (BTEX), and biogenic VOCs including isoprene and its oxidation products, methacrolein (MACR) and methyl vinyl ketone (MVK). We present diurnal variations of concentrations and fluxes of BTEX, and isoprene and its oxidation products during summer time (May 22 - July 22, 2008) and winter time (January 1 - February 28). The measured BTEX values exhibited diurnal cycles with a morning peak during weekdays related to rush-hour traffic and additional workday daytime flux maxima for toluene and xylenes in summer time. However, in winter time there was no additional workday daytime peaks due mainly to the different flux footprints between the two seasons. A comparison with different EPA National Emission Inventories (NEI) with our summer time flux data suggests potential underestimates in the NEI by a factor of 3 to 5. The mixing ratios and fluxes of isoprene, MACR and MVK were measured during the same time period in summer 2008. The presented results show that the isoprene was affected by both tail-pipe emission sources during the morning rush hours and biogenic emission sources in daytime. The observed daytime mixing ratios of isoprene were much lower than over forested areas, caused by a comparatively low density of isoprene emitters in the tower's footprint area. The average daytime isoprene flux agreed well with emission rates predicted by a temperature and light only emission model (Guenther et al., 1993). Our investigation of isoprene's oxidation products MACR and MVK showed that both anthropogenic and biogenic emission sources exist for MACR, while MVK was strongly dominated by a biogenic source, likely the isoprene oxidation between the emission and sampling points.Item Impact of Herbicides on Winter Canola (Brassica napus L.) Production and Fatty Acid Composition in South Texas(2013-01-16) Cogdill, Todd JosephCanola is a cool-season, oilseed crop grown throughout Europe, Canada, and the Northern Great Plains region of the United States. The expansion of canola production into new growing regions, such as the Southern Plains region, has resulted in new production challenges. The Southern Plains region cultivates canola as a winter annual compared to a spring annual for the Northern Great Plains and Canada. Given the difference in climate and weed spectrum, region-specific weed management systems need to be developed. Agronomic practices can affect seed oil content, protein content, and fatty acid composition, however the effect of herbicides on these and other characteristic of canola are unknown. Therefore, experiments were conducted in 2010 and 2011 to evaluate a broad spectrum of herbicides for potential use in South Texas canola production with respect to crop injury, effects on canola seed oil content, fatty acid composition, weed control, biomass yield, and forage quality. Visual crop injury at 42 DAE was unacceptable for saflufenacil at both 0.12 and 0.06 kg ai ha-1 and ethalfluralin at 1.05 kg ai ha-1. Trifluralin at 1.12 and 0.56 kg ai ha-1, S-metolachlor at 2.14 and 1.07 kg ai ha-1, pyroxasulfone at 0.24 and 0.12 kg ai ha-1, and pendimethalin at 0.8 kg ai ha-1 had lowest visual injury of all treatments. Fluroxypyr applied EPOST caused severe injury at both 0.21 and 0.11 kg ae ha-1. All other EPOST treatments did not cause any visible injury. Seed oil content was not affected by the herbicides evaluated. Fatty acid composition, specifically stearic acid, oleic acid, linolenic acid, and oleic to linolenic acid ratio, was affected by herbicide treatments. This research found that protoporphyrinogen oxidase (PPG oxidase) inhibitor herbicides, such as carfentrazone-ethyl and saflufenacil, negatively affect canola oil quality. Biomass yield was improved for all herbicide treatments except pendimethalin PRE when compared to the untreated plots. Crude protein content of canola forage was not affected by herbicide treatment. Digestible dry matter appeared to be reduced by treatments that included an EPOST application of sethoxydim. The research shows that pendimethalin and S-metolachlor may be suitable for canola production in South Texas based on low crop injury and effective weed control. Neither pendimethalin nor S-metolachlor is currently labeled for use in canola. The herbicides trifluralin, ethalfluralin, quizalofop P-ethyl, ethametsulfuron-methyl, sethoxydim, glyphosate, clethodim, and clopyralid are currently labeled for use in canola and were confirmed suitable for canola production in South Texas. Carfentrazone-ethyl is currently labeled for use in canola but the effects on oil quality should be considered.Item Improving the Flavor of Ground Beef by Selecting Trimmings from Specific Locations(2012-08-17) Harbison, Amanda 1989-We hypothesized that carcass subcutaneous fat location would affect sensory and quality traits. Five carcass fat sources were tested: brisket, chuck, plate, flank, and round. Ground beef was formulated using each fat source and extra-lean beef trim (>95% lean) to contain 80% lean trim and 20% fat trim. Patties (100 g) were evaluated for color, lipid oxidation, fatty acid composition and consumer evaluation. Flavor was analyzed using a Gas chromatography with mass spectrometry (GC/MS) on the headspace above a cooked (74 degrees C) patty in a heated (60 degrees C) 473 mL glass jar with a solid phase micro-extraction (SPME) fiber. Color, thiobarbituric acid reactive substance assay (TBARS), consumer sensory, and cook/freezer loss data showed no differences (P > 0.05) among carcass locations. Percentage stearic acid was lower (P = 0.044) in the brisket than in the chuck and flank. The brisket was higher in percentage cis-vaccenic acid (P = 0.016) and in the saturated fatty acid to monounsaturated fatty acid ratio (P = 0.018), and lower (P = 0.004) in the percentage of total saturated fatty acids than all other sources of subcutaneous fat. Butanedione was highest (P = 0.013) in the flank and plate fat. Brisket tended to be higher (P = 0.054) than flank, plate, and round in 1-octen-3-ol. Brisket was higher (P = 0.008) than chuck, flank, and round, but not different (P > 0.05) than plate in octanedione. Brisket was higher (P = 0.003) than all other sources for beefy aroma. Flank was higher (P = 0.047) than chuck and round for chemical aroma. Brisket was higher (P = 0.004) than all other sources except flank for floral aromas. Plate was higher (P = 0.029) than all other sources for heated oil aromas. For secondary aroma descriptor, round was higher (P < 0.001) than flank, plate, and chuck for dairy. While differences in some key fatty acids and aromatics existed among carcass locations, when the fat was diluted with a common lean source, fat source did not have a negative effect on sensory or quality traits. Therefore, formulating ground beef using subcutaneous fat from specific locations on a carcass may improve the beef aromatics without negatively affecting sensory or quality traits.