Hydrocarbon emissions from a modern commercial airliner

We report selected carbon species emission indices (EIs) for a Rolls Royce RB211-535-E4 turbofan engine that were acquired during the NASA EXperiment to Characterize Aircraft Volatile Aerosol and Trace-species Emissions (EXCAVATE). Conducted during winter 2002, the mission focused upon characterizing the exhaust constituents of the NASA Boeing 757 aircraft during ground-based operation. Carbon species concentrations were determined by chromatographic analyses of whole air samples collected 10 m behind the engine exit plane as engine power was varied from ground idle to about 60% of maximum rated thrust. Ambient air samples were also collected and analyzed to facilitate correction of calculated EIs for background concentrations. Results are consistent with previous observations and indicate that, on a relative basis, turbine engines emit considerable amounts of light hydrocarbon species at idle, but significantly lesser amounts at higher engine powers. © 2005 Elsevier Ltd. All rights reserved

Airborne observations of the tropospheric CO2 distribution and its controlling factors over the South Pacific Basin

Highly precise measurements of CO2 mixing ratios were recorded aboard both the NASA DC-8 and P3-B aircraft during the Pacific Exploratory Mission-Tropics conducted in August-October 1996. Data were obtained at altitudes ranging from 0.1 to 12 km over a large portion of the South Pacific Basin representing the most geographically extensive CO2 data set recorded in this region. These data along with CO2 surface measurements from the National Oceanic and Atmospheric Administration/Climate Monitoring and Diagnostics Laboratory (NOAA/CMDL) and the National Institute of Water and Atmospheric Research (NIWA) were examined to establish vertical and meridional gradients. The CO2 spatial distribution in the southern hemisphere appeared to be largely determined by interhemispheric transport as air masses with depleted CO2 levels characteristic of northern hemispheric air were frequently observed south of the Intertropical Convergence Zone. However, regional processes also played a role in modulating background concentrations. Comparisons of CO2 with other trace gases indicated that CO2 values were influenced by continental sources. Large scale plumes from biomass burning activities produced enhanced CO2 mixing ratios within the lower to midtroposphere over portions of the remote Pacific. An apparent CO2 source was observed in the NOAA/ CMDL surface data between 15° N and 15° S and in the lower altitude flight data between 8° N and 8.5° S with a zone of intensity from 6.5° N to 1° S. Inferred from these data is the presence of a Southern Ocean sink from south of 15° S having two distinct zones seasonally out of phase with one another. Copyright 1999 by the American Geophysical Union

Power-dependent speciation of volatile organic compounds in aircraft exhaust

As part of the third NASA Aircraft Particle Emissions Experiment (APEX-3, November 2005), whole air samples were collected to determine the emission rates of volatile organic compounds (VOCs) from aircraft equipped with three different gas-turbine engines (an Allison Engine 3007-A1E, a Pratt-Whitney 4158, and a Rolls-Royce RB211-535E4B). Samples were collected 1 m behind the engine exhaust plane of the engines while they were operated at powers ranging from idle up to 30% of maximum rated thrust.Exhaust emission indices (mass emitted per kilogram of fuel used) for CO and non-methane hydrocarbons (NMHCs) were calculated based on enhancements over background relative to CO 2. Emissions of all NMHCs were greatest at low power with values decreasing by an order of magnitude with increasing power. Previous studies have shown that scaling idle hydrocarbon emissions to formaldehyde or ethene (which are typically emitted at a ratio of 1-to-1 at idle) reduces variability amongst engine types. NMHC emissions were found to scale at low power, with alkenes contributing over 50% of measured NMHCs. However, as the power increases hydrocarbon emissions no longer scale to ethene, as the aromatics become the dominant species emitted. This may be due in part to a shift in combustion processes from thermal cracking (producing predominantly alkenes) to production of new molecules (producing proportionally more aromatics) as power increases. The formation of these aromatics is an intermediate step in the production of soot, which also increases with increasing power. The increase in aromatics relative to alkenes additionally results in a decrease in the hydroxyl radical reactivity and ozone formation potential of aircraft exhaust.Samples collected 30 m downwind of the engine were also analyzed for NMHCs and carbonyl compounds (acetone, 2-butanone and C 1-C 9 aldehydes). Formaldehyde was the predominant carbonyl emitted; however, the ratio of ethene-to-formaldehyde varied between the aircraft, possibly due to the sampling of transient emissions such as engine start-up and power changes. A large portion of the measured emissions (27-42% by mass) in the plume samples was made up of hazardous air pollutants (HAPs) with oxygenated compounds being most significant. © 2012

Chemical transport across the ITCZ in the central Pacific during an El Niño-Southern Oscillation cold phase event in March-April 1999

We examine interhemispheric transport processes that occurred over the central Pacific during the PEM-Tropics B mission (PTB) in March-April 1999 by correlating the observed distribution of chemical tracers with the prevailing and anomalous windfields. The Intertropical Convergence Zone (ITCZ) had a double structure during PTB, and interhemispheric mixing occurred in the equatorial region between ITCZ branches. The anomalously strong tropical easterly surface wind had a large northerly component across the equator in the central Pacific, causing transport of aged, polluted air into the Southern Hemisphere (SH) at altitudes below 4 km. Elevated concentrations of chemical tracers from the Northern Hemisphere (NH) measured south of the equator in the central Pacific during PTB may represent an upper limit because the coincidence of seasonal and cold phase ENSO conditions are optimum for this transport. Stronger and more consistent surface convergence between the northeasterly and southeasterly trade winds in the Southern Hemisphere (SH) resulted in more total convective activity in the SH branch of the ITCZ, at about 6° S. The middle troposphere between 4-7 km was a complex shear zone between prevailing northeasterly winds at low altitudes and southwesterly winds at higher altitudes. Persistent anomalous streamline patterns and the chemical tracer distribution show that during PTB most transport in the central Pacific was from SH to NH across the equator in the upper troposphere. Seasonal differences in source strength caused larger interhemispheric gradients of chemical tracers during PTB than during the complementary PEM-Tropics A mission in September-October 1996. Copyright 2001 by the American Geophysical Union

Nonmethane hydrocarbon measurements in the North Atlantic Flight Corridor during the Subsonic Assessment Ozone and Nitrogen Oxide Experiment

Mixing ratios of nonmethane hydrocarbons (NMHCs) were not enhanced in whole air samples collected within the North Atlantic Flight Corridor (NAFC) during the fall of 1997. The investigation was conducted aboard NASA's DC-8 research aircraft, as part of the Subsonic Assessment (SASS) Ozone and Nitrogen Oxide Experiment (SONEX). NMHC enhancements were not detected within the general organized tracking system of the NAFC, nor during two tail chases of the DC-8's own exhaust. Because positive evidence of aircraft emissions was demonstrated by enhancements in both nitrogen oxides and condensation nuclei during SONEX, the NMHC results suggest that the commercial air traffic fleet operating in the North Atlantic region does not contribute at all or contributes negligibly to NMHCs in the NAFC. Copyright 2000 by the American Geophysical Union