Donald E. Hagen

In Situ Observations of Air Traffic Emission Signatures in the North Atlantic Flight Corridor

Focussed aircraft measurements have been carried out over the eastern North Atlantic to search for signals of air traffic emissions in the flight corridor region. Observations include NO, NO2, HNO3, SO2, O3, H2O, total condensation nuclei (CN), and meteorological parameters. A flight pattern with constant-altitude north-south legs across the major North Atlantic air traffic tracks was flown. Signatures of air traffic emissions were clearly detected for NOx, SO2, and CN with peak concentrations of 2 ppbv, 0.25 ppbv, and 500 cm−3, respectively, exceeding background values by factors of 30 (NOx), 5 (SO2), and 3 (CN). The observed NOx, SO2, and CN peaks were attributed to aircraft plumes based on radar observations of the source air traffic and wind measurements. Major aircraft exhaust signatures are due to relatively fresh emissions, i.e., superpositions of 2 to 5 plumes with ages of about 15 min to 3 hs. The observed plume peak concentrations of NOx compare fairly well with concentrations computed with a Gaussian plume model using horizontal and vertical diffusivities as obtained by recent large-eddy simulations, measured vertical wind shear, and the corridor air traffic information. For the major emission signatures a mean CN/NOx abundance ratio of 300 cm−3ppbv−1 was measured corresponding to an emission index (EI) of about 1016 particles per 1 kg fuel burnt. This is higher than the expected soot particle EI of modern wide-bodied aircraft. For the most prominent plumes no increase of HNO3 concentrations exceeding variations of background values was observed. This indicates that only a small fraction of the emitted NOx is oxidized in the plumes within a timescale of about 3 hs for the conditions of the measurements.

Sources and chemistry of NOx in the upper troposphere over the United States

The origin of NOx in the upper troposphere over the central United States is examined using aircraft observations obtained during the SUCCESS campaign in April–May of 1996. Correlations between NOy (sum of NOx and its oxidation products) and CO at 8–12 km altitude indicate that NOx originates primarily from convective transport of polluted boundary layer air. Lightning and aircraft emissions appear to be only minor sources of NOx. Chemical steady state model calculations constrained by local observations of NO underestimate the measured NOx/NOy concentration ratio at 8–12 km altitude by a factor of two on average. The magnitude of the underestimate is correlated with concentrations of condensation nuclei, which we take as a proxy for the age of air in the upper troposphere. We conclude that the NOx/NOy ratio is maintained above chemical steady state by frequent convective injections of fresh NOx from the polluted boundary layer and by the long lifetime of NOx in the upper troposphere (5–10 days). In contrast to previous studies, we find no evidence for fast heterogeneous recycling from HNO3 to NOx in the upper troposphere.

Observation of upper tropospheric sulfur dioxide- and acetone-pollution: Potential implications for hydroxyl radicaland aerosol formation

Aircraft-based measurements of sulfur dioxide, acetone, carbon dioxide, and condensation nuclei (CN) were made over the north-eastern Atlantic at upper tropospheric altitudes, around 9000 m. On October 14, 1993, strong SO2- and acetone-pollution (both up to 3 ppbv) were observed, which were accompanied by a CO2-enhancement of up to 6 ppmv, and large CN-concentrations of up to about 1500 cm−3 (for radii ≥ 6 nm). CN, excess CO2, and to a lesser degree also acetone, were positively correlated with SO2. Air mass trajectory analyses indicate, that most of the air masses encountered by our aircraft originated from the polluted planetary boundary layer of the North-Eastern U. S. approximately 4–5 days prior to our measurements, and that polluted boundary layer air experienced fast vertical transport to the upper troposphere as well as horizontal transport across the Atlantic. From our data we conclude, that in the polluted air mass around 9000 m altitude HOx-formation, photochemical SO2-conversion to gaseous H2SO4, and eventually also CN-formation by homogeneous bimolecular (H2SO4-H2O) nucleation may have taken place with enhanced efficiency.

Near‐field measurements on contrail properties from fuels with different sulfur content

Microphysical properties of jet exhaust aerosol and contrails were studied in the near field of the emitting aircraft for different fuel sulfur contents. Measurements were performed behind two different aircraft (ATTAS test aircraft of type VFW 614 and Airbus A310-300) using fuels with sulfur contents of 6 ppm and 2700 ppm, respectively. At closest approach (plume age ‹ 1 s), the total number concentrations exceeded the measuring range of the condensation particle counter, i.e., N › 10 5 cm -3 . The concentration of the dry accumulation mode aerosol, i.e., predominantly soot particles, was not affected by the fuel sulfur content. At a plume age of 10 s, an increase in total number concentration (D p › 0.01 µm) by a factor of 3.5 in the high sulfur case compared to the low sulfur case was observed. The ultrafine condensation nuclei fraction (0.007 µm ‹ D p ‹ 0.018 µm) contributed at maximum 70% to the total aerosol in the plume while this fraction was much less outside the plume. The high fuel sulfur content also caused an increase in the typical number concentrations of contrail particles by about one third with respect to low sulfur fuel, while the effective diameter of the size distribution was lowered at a fuel sulfur independent ice water content. The major differences in accumulation mode aerosol and microphysical contrail properties between the used aircraft were an increased number concentration of both the accumulation mode aerosol and the contrail particles in the Airbus A310-300 plume relative to the ATTAS plume. Part of the difference in contrail particles may be caused by different ambient conditions, but the major differences are assumed to be caused by different engine and wake properties.

Homogeneous nucleation rate measurements for water over a wide range of temperature and nucleation rate

An expansion cloud chamber was used to measure the homogeneous nucleation rate for water over a wide range of temperature from 230–290 K and nucleation rates of 1–106 drops cm−3 s−1. The comprehensive and extensive nature of this data allows a much more detailed comparison between theory and experiment than has previously been possible. The expansion chamber technique employs continuous pressure measurement and an adiabatic pulse of supersaturation to give the time history of supersaturation and temperature during the nucleation. The resulting drop concentration is determined using photographic techniques. The experimental observations are presented in tabular form and from them an empirical nucleation rate formula is determined: J=S2 exp[328.124−5.582 43T+0.030 365T2−5.0319E−5T3 −(999.814−4.100 87 T+3.010 84E−3 T2)ln−2S], where J is the nucleation rate in units of drops cm−3 s−1. S is the supersaturation ratio and T is the temperature in K.

The 5–6 December 1991 FIRE IFO II Jet Stream Cirrus Case Study: Possible Influences of Volcanic Aerosols

Abstract In presenting an overview of the cirrus clouds comprehensively studied by ground-based and airborne sensors from Coffeyville, Kansas, during the 5–6 December 1992 Project FIRE IFO II case study period, evidence is provided that volcanic aerosols from the June 1991 Pinatubo eruptions may have significantly influenced the formation and maintenance of the cirrus. Following the local appearance of a spur of stratospheric volcanic debris from the subtropics, a series of jet streaks subsequently conditioned the troposphere through tropopause foldings with sulfur-based particles that became effective cloud-forming nuclei in cirrus clouds. Aerosol and ozone measurements suggest a complicated history of stratospheric-tropospheric exchanges embedded within the upper-level flow, and cirrus cloud formation was noted to occur locally at the boundaries of stratospheric aerosol-enriched layers that became humidified through diffusion, precipitation, or advective processes. Apparent cirrus cloud alterations incl...

Linear inversion method to obtain aerosol size distributions from measurements with a differential mobility analyzer

The use of a differential mobility analyzer to perform aerosol size spectrum measurements requires an inversion method to go from the measured sensor responses to the desired size spectrum information. Here we present a linear inversion method that can be run on a microcomputer or a small minicomputer. It does not use some of the approximations made in the techniques currently available and hence gives better inversion accuracy. The method shows good immunity to both random and systematic experimental error. It is applied to numerous test case aerosols.

A FIELD SAMPLING OF JET EXHAUST AEROSOLS

ABSTRACT A mobile aerosol sampling facility was installed and operated on the NCAR (National Center for Atmospheric Research) Sabreliner high altitude research aircraft, for the purpose of sampling aerosols related to cirrus cloud phenomena. During this project the opportunity arose to do field sampling on jet exhaust aerosols, and these results are reported here. Aerosol properties sampled include concentration, size distribution, and hydration properties. The aerosol sampling facility features two electrostatic aerosol classifiers (EACs), in tandem, with a saturator in between. The saturator allows the aerosol to be equilibrated at 100% relative humidity between sizings with the EACs. The facility occupies about the space of two short equipment racks on the aircraft, and collects samples through a tube projecting through the aircraft skin. Exhaust samples were taken from Pratt and Whitney PT 6-42, JT 12A-8, and JT 15-D-4 engines, all burning Jet-A fuel. The results indicate that aerosol sampling offer...

Comparison of PM Emissions from a Commercial Jet Engine Burning Conventional, Biomass, and Fischer–Tropsch Fuels

Rising fuel costs, an increasing desire to enhance security of energy supply, and potential environmental benefits have driven research into alternative renewable fuels for commercial aviation applications. This paper reports the results of the first measurements of particulate matter (PM) emissions from a CFM56-7B commercial jet engine burning conventional and alternative biomass- and, Fischer-Tropsch (F-T)-based fuels. PM emissions reductions are observed with all fuels and blends when compared to the emissions from a reference conventional fuel, Jet A1, and are attributed to fuel properties associated with the fuels and blends studied. Although the alternative fuel candidates studied in this campaign offer the potential for large PM emissions reductions, with the exception of the 50% blend of F-T fuel, they do not meet current standards for aviation fuel and thus cannot be considered as certified replacement fuels. Over the ICAO Landing Takeoff Cycle, which is intended to simulate aircraft engine operations that affect local air quality, the overall PM number-based emissions for the 50% blend of F-T fuel were reduced by 34 ± 7%, and the mass-based emissions were reduced by 39 ± 7%.

Homogeneous condensation - Freezing nucleation rate measurements for small water droplets in an expansion cloud chamber

Abstract Experimental data on ice nucleation, presented in an earlier paper, are analyzed to yield information about the homogeneous nucleation rate of ice from supercooled liquid and the heights of energy barriers to that nucleation. The experiment consisted of using an expansion cloud chamber to nucleate from the vapor a cloud of supercooled pure water drops and the observation of the fraction of drops which subsequently froze. The analysis employed standard classical homogeneous nucleation theory. The data are used to extract the first experimental measurement (albeit indirect) of the activation energy for the transfer of a water molecule across the liquid-ice interface at temperatures near −40°C. The results provide further evidence that the local liquid structure becomes more icelike as the temperature is lowered.