861 research outputs found
Study of personal hygiene concepts for future manned missions Final report
Personal hygiene concepts for long-duration manned space fligh
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Latitudinal, vertical, and seasonal variations of C-1-C-4 alkyl nitrates in the troposphere over the Pacific Ocean during PEM-Tropics A and B: Oceanic and continental sources
We present concentration distributions of C1âC4 alkyl nitrates observed during the NASA airborne campaigns Pacific Exploratory Mission (PEM) âTropics A (SeptemberâOctober 1996) and PEMâTropics B (MarchâApril 1999). The total geographic range for PEMâTropics A was 45°Nâ72°S latitude and 153°Eâ75°W longitude, and for PEMâTropics B was 40°Nâ36°S latitude and 149°Eâ75°W longitude. The maximum altitude for these missions was 12 km. These experiments provide the most extensive set of tropospheric measurements collected to date over the tropical Pacific Ocean. We observed high methyl nitrate (MeONO2, CH3ONO2) mixing ratios (approximately 50 pptv) at low altitudes in a latitude band between 8°N to 13°S stretching across the equatorial Pacific, illustrating the oceanic source of MeONO2. This source may be associated with the highânutrient, lowâchlorophyll character of equatorial Pacific waters. We discuss MeONO2 and ethyl nitrate (EtONO2, C2H5ONO2), whose abundance is dominated by equatorial oceanic sources, 2âPropyl nitrate (2âPrONO2, 2âC3H7ONO2), which has significant oceanic and northern hemispheric (NH) sources associated with urban/industrial hydrocarbon emissions, and 2âbutyl nitrate (2âBuONO2 2âC4H8ONO2), which has mostly NH sources. PEMâTropics A and B resulted in remarkably similar equatorial mixing ratios. The excellent correlations between MeONO2 and the other alkyl nitrates in this region produced comparable correlation slopes between the two expeditions. By contrast, NH air masses influenced by urban/industrial emissions typically exhibited much lower MeONO2:EtONO2, MeONO2:2âPrONO2, and MeONO2:2âBuONO2 ratios. These relationships can be useful as a diagnostic of air mass origin. North of 10°N, the springtime PEMâTropics B mixing ratios of C2âC4 alkyl nitrates were manyâfold higher at lowâmid altitudes than for late summer PEMâTropics A, consistent with strong continental outflow of NMHC precursors during spring
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A biomass burning source of C1- C4alkyl nitrates
We report the first observations of the emission of five C1-C4alkyl nitrates (methyl-, ethyl-, n-propyl-, i-propyl-, and 2-butyl nitrate) from savanna burning. Average alkyl nitrate mixing ratios in the immediate vicinity of three bushfires in Northern Australia were 47-122 times higher than local background mixing ratios. These are the highest alkyl nitrate mixing ratios we have ever detected, with maximum mixing ratios exceeding 3 ppbv for methyl nitrate. Methyl nitrate dominated the alkyl nitrate emissions during the flaming stage of savanna burning, whereas C2-C4alkyl nitrates were mostly emitted during the smoldering stage. To explain the formation of alkyl nitrates from biomass burning, we propose a reaction mechanism involving the combination of reactive radicals at high temperature. Bearing in mind the uncertainties associated with extrapolating small data sets to much larger scales, alkyl nitrate emissions from global savanna burning are estimated to be on the order of 8 Gg/yr
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Distributions of brominated organic compounds in the troposphere and lower stratosphere
A comprehensive suite of brominated organic compounds was measured from whole air samples collected during the 1996 NASA Stratospheric Tracers of Atmospheric Transport aircraft campaign and the 1996 NASA Global Tropospheric Experiment Pacific Exploratory Mission-Tropics aircraft campaign. Measurements of individual species and total organic bromine were utilized to describe latitudinal and vertical distributions in the troposphere and lower stratosphere, fractional contributions to total organic bromine by individual species, fractional dissociation of the long-lived species relative to CFC-11, and the Ozone Depletion Potential of the halons and CH3Br. Spatial differences in the various organic brominated compounds were related to their respective sources and chemical lifetimes. The difference between tropospheric mixing ratios in the Northern and Southern Hemispheres for halons was approximately equivalent to their annual tropospheric growth rates, while the interhemispheric ratio of CH3Br was 1.18. The shorter-lived brominated organic species showed larger tropospheric mixing ratios in the tropics relative to midlatitudes, which may reflect marine biogenic sources. Significant vertical gradients in the troposphere were observed for the short-lived species with upper troposphere values 40-70% of the lower troposphere values. Much smaller vertical gradients (3-14%) were observed for CH3Br, and no significant vertical gradients were observed for the halons. Above the tropopause, the decrease in organic bromine compounds was found to have some seasonal and latitudinal differences. The combined losses of the individual compounds resulted in a loss of total organic bromine between the tropopause and 20 km of 38-40% in the tropics and 75-85% in midlatitudes. The fractional dissociation of the halons and CH3Br relative to CFC-11 showed latitudinal differences, with larger values in the tropics. Copyright 1999 by the American Geophysical Union
Reply to "Comment on 'Long-term atmospheric measurements of C1-C5 alkyl nitrates in the Pearl River Delta region of southeast China'"
Department of Civil and Environmental Engineerin
Ontological Expressivism
Ontological expressivism is the view that ontological existence claims express non-cognitive mental states. I develop a version of ontological expressivism that is modeled after Gibbardâs (2003) norm-expressivism. I argue that, when speakers assess whether, say, composite objects exist, they rely on assumptions with regard to what is required for composition to occur. These assumptions guide their assessment, similar to how norms may guide the assessment of normative propositions. Against this backdrop, I argue that âsome objects have partsâ, uttered in the context of an ontological disagreement, expresses a noncognitive disposition to assess the truth of propositions by using only rules of assessment according to which the proposition that some objects have parts is to be evaluated as true
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Troposheric Reactive Odd Nitrogen Over the South Pacific in Austral Springtime
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