Observations and model calculations of jet aircraft exhaust products at cruise altitude and inferred initial OH emissions

Abstract

Abstract. Exhaust emissions of NO, HNO2, and HNO 3 in the near-field plume of two B747 jet airliners cruising in the upper troposphere were measured in situ using the research aircraft Falcon of the Deutsches Zentrum far Luft-und Raumfahrt. In addition, CO2 was measured providing exhaust plume dilution rates for the species. The observations were used to estimate the initial OH mixing ratio OHo and the initial NO2/NOx ratio (NO2/NOx)0 at the engine exit and the combustor exit by comparison with calculations using a plume chemistry box model. From the two different plume events, and using two different model simulation modes in each case, we inferred OH emission indices EI(OH) = 0.32-0.39 g (kg fuel) -• (OHo = 9.0-14.4 ppmv) and (NO2/NOx)0 = 0.12-0.17. Furthermore, our results indicate that the chemistry of the exhaust species during the short period between the combustion chamber exit and the engine exit must be considered with respect to the amount of OH at the engine exit plane because OH is already consumed to a great extent in this engine section because of conversion to HNO 2 and HNO3. For the engines discussed here the modeled OH concentration decreases by a factor of -350 between combustor exit and engine exit, leading to OH concentrations of 1-2 x 10 •2 molecules cm -3 (= 0.3-0.7 ppmv) at the engine exit. [1996] determined an upper limit for the OH concentration by measurements using a laser absorption technique behind a gas turbine engine in a test facility, and Hanisco et al. [1997] derived EI(HOx) from in situ measurements of HOx and NOy in exhaust plumes behind aircraft in the lower stratosphere for plume ages around 15 and 60 min. Here we present in-flight measurements of NO, HNO2, HNO3, CO2, and SO 2 in the exhaust plumes of two B747 cruising in the upper troposphere and use the data to infer the OH concentration and the NO2/ NOx ratio at the engine exit as well as the emission indices for NO x and SO2. Furthermore, H2SO 4 q-SO 3 formation via reaction of OH with SO 2 is estimated using the inferred OH. MeasurementsThe exhaust emissions of two B747-100 jet airliners were sampled on June 30, 1995, with the Falcon aircraft of the Table 3 lists details of the considered plume events including the measured maximum peak mixing ratios in total (X) and above background (AX), the background (ambient) mixing ratios Xa, and the ratios of the integrated emission abundances in the peaks (/•Xint//•x(CO2)int). The integration time is fitted to the peak width and amounts to ---30 s for both events, which is greater than the time responses of the instruments (see Table 2). Table 3 also shows the maximum emission mixing ratios and X' derived from the ratios of the integrated emission abundances above background of the respective species and CO2 in the plume:These mixing ratios X', obtained from the ratio of the integrals of the event peaks, and thus intended to eliminate the differences in time response of the employed instruments, are used Exhaust Plume Chemistry Box ModelThe applied aircraft exhaust plume...

Dimension of aircraft exhaust plumes at cruise conditions: effect of wake vortices

“…This resembles the typical range observed in the upper troposphere (Dürbeck and Gerz, 1996;Unterstrasser and Gierens, 2010a).…”

“…Primarily, the campaign aimed at probing contrails. In aircraft plumes of ages smaller than 3 min NO y is dominated by NO and NO 2 , and to a much lesser amount gas phase HONO and HNO 3 (Tremmel et al, 1998) from which only a small portion may be lost to the particulate phase at this early stage (Schäuble et al, 2009). For our purpose it may therefore be treated as passive tracer to a good approximation.…”

Airborne measurements of the nitric acid partitioning in persistent contrails

“…These early HNO 3 concentrations are determined by the NO x emission index and the engine exit plane concentration of the hydroxyl radical (OH) which acts as the primary oxidant. Arnold et al (1992) and Tremmel et al (1998) report the detection of gas phase HNO 3 in young aircraft exhaust plumes. Kärcher (1996) demonstrates by means of microphysical simulations that gaseous HNO 3 is efficiently transferred into plume aerosols and ice particles during contrail formation.…”

Chemical ionization mass spectrometric measurements of SO2 emissions from jet engines in flight and test chamber operations

“…Because SO3 is intermediate in the conversion of SO2 to H2SO4, the amount of sulfuric acid that can be produced in the exhaust plume is ultimately limited by the amount of OH radical available for reaction with SO2 [Brown et al, 1996a[Brown et al, , 1997[Brown et al, , 1996bTremmel et al, 1998]. However, SO2 also reacts with atomic oxygen within the engine combustors to form SO3 [Harris, 1990].…”