[1] Atmospheric concentrations of gaseous sulfuric acid (H 2 SO 4 ), methane sulfonic acid (MSA), and hydroxyl radicals (OH) were measured by chemical ionization mass spectrometry (CIMS) during the second New Particle Formation and Fate in the Coastal Environment (PARFORCE) campaign in June 1999 at Mace Head, Ireland. Overall median concentrations in marine background air were 1.5, 1.2, and 0.12 ϫ 10 6 cm Ϫ3 , respectively. H 2 SO 4 was also present at night indicating significant contributions from nonphotochemical sources. A strong correlation was found between daytime OH and H 2 SO 4 levels in clean marine air suggesting a fast local production of H 2 SO 4 from sulfur precursor gases. Steady state balance calculations of ambient H 2 SO 4 levels agreed with measured concentrations if either very low H 2 SO 4 sticking coefficients (0.02-0.03) or sources in addition to the SO 2 ϩ OH reaction were assumed. Overall, variations in ambient H 2 SO 4 levels showed no correlation with either the tidal cycle or ultrafine particle (UFP) concentrations. However, on particular days an anticorrelation between H 2 SO 4 and UFP levels was occasionally observed providing evidence for the contribution of H 2 SO 4 to new particle formation and/or particle growth. Gaseous MSA concentrations were inversely correlated with dew point temperature reflecting a highly sensitive gas-particle partitioning equilibrium of this compound. The present observations seriously question the general use of MSA as a conservative tracer to infer the relative production yield of H 2 SO 4 from dimethylsulfide (DMS) oxidation. MSA/H 2 SO 4 concentration ratios typically ranged between 0.06 and 1.0 in marine air at ground level. Measured diel OH profiles showed a significant deviation from concurrent variations of the ozone photolysis frequency. They also showed up to 1 order of magnitude lower values compared to OH concentrations calculated with a simple photochemical box model. These differences were most pronounced during particle nucleation events occurring on sunny days around noon and at low tide. The present results suggest that both the oxidation capacity and the particle formation potential in the coastal boundary layer were significantly affected by reactions of unknown compounds prevailing in this type of environment.

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...

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The fuel sulfur conversion efficiency ε behind the combustor of a JT9D-7A aircraft engine in flight has been simulated using an extended exhaust plume chemistry model. The model simulations start in the hightemperature intra-engine regime behind the combustor. The simulations show that the sulfur conversion efficiency is sensitively dependent on model assumptions like reaction rate constants and initial mixing ratios. Sensitivity studies to demonstrate the effect of the uncertainties and variabilities of these parameters on ε are presented. Among the rate constants k, the uncertainty of the reaction rate constant for SO 2 + OH + M → HSO 3 + M has the greatest effect on ε: The uncertainty of k(SO 2 + OH) results in an uncertainty range of 1.1% < ε < 6.2% for our simulation scenario, with a most probable value around 3.8%. The effect of the reaction SO 2 + O + M → SO 3 + M on ε is very small if the initial mixing ratio of O is smaller than that of OH. Among the initial mixing ratios, the variation of the initial OH mixing ratio OH 0 has the greatest effect on ε. For our simulation scenario, the uncertainty range of 5.7 ppmv < OH 0 < 14.7 ppmv (inferred from measurements) leads to an uncertainty range of 2.7% < ε < 5.0%. © 1999 Éditions scientifiques et médicales Elsevier SAS fuel sulfur conversion efficiency / aircraft engine / uncertainty / sensitivity study Zusammenfassung Modellsimulationen der Schwefel-Konversionseffizienz in einem Flugzeugtriebwerk: Abhängigkeit von Geschwindigkeitskonstanten und Anfangs-Mischungsverhältnissen. Die Treibstoffschwefel-Konversionseffizienz ε hinter der Brennkammer eines JT9D-7A-Triebwerkes unter Flugbedingungen wurde mit einem detaillierten Abgasfahnen-Chemiemodell simuliert. Als Referenzwert wurde eine Schwefelumwandlung von ε = 3.8% gefunden. Die berechnete Schwefelumwandlung hängt dabei ganz entscheidend von den Modellannahmen wie z.B. den Geschwindigkeitskonstanten und den Anfangskonzentrationen ab. Es werden Sensitivitätsstudien präsentiert, die den Einfluß dieser Parameter auf ε verdeutlichen sollen. Unter den Geschwindigkeitskonstanten k hat k(SO 2 + OH) den größten Einfluß auf ε: ihr Fehlerbereich führt zu einer Schwankungsbreite von ε zwischen 1.1 und 6.2% für unser Szenario. Der Effekt der Reaktion SO 2 + O ist dagegen eher klein, wenn das Mischungsverhältnis von O kleiner als das von OH ist. Unter den Anfangs-Mischungsverhältnissen hat die Variation des Mischungsverhältnisses von OH den größten Einfluß auf ε. Für unser Simulations-Szenario führt der Fehler bei der Bestimmung des anfänglichen OH-Wertes (OH liegt nach einer Abschätzung aus Messungen für dieses Szenario zwischen 5.7 und 14.7 ppmv) zu einem Bereich von 2.7% < ε < 5.0%.

H202 and NO, NO 2, NOy, 03, SO2, and H20 were measured from an aircraft over the northeastern United States in August and September 1988. The data base consists of 13 flight missions; on 14 days during different meteorological conditions, 177 vertical profiles between about 100 and 3500 m were obtained. The mixing ratio of H202 varied from below the detection limit of 0.2 up to 5.9 parts per billion by volume (ppbv) and it was strongly dependent on altitude, indicating that processes controlling the H202 occurrence in the planetary boundary layer (PBL) were different from those in the free troposphere (FT). Average H20 2 mixing ratios varied between 0.20 and 1.30 ppbv in the PBL showing, in most cases, a decrease to the ground. High H202 values in the PBL were observed only when NO was below 1.5 ppbv. In more than 80% of the vertical profiles a pronounced maximum in the H202 mixing ratios (up to 2.3 ppbv) was observed at the top of the PBL. In the FT the H202 mixing ratio averaged over individual flights varied between 0.41 and 1.80 ppbv and was strongly correlated with the water vapor concentration, in agreement with a simple "low NOx case" photochemical model. The average SO2 mixing ratios were higher than the average H202 mixing ratios during all flights in the PBL and during most of the flights in the FT, indicating that the formation of sulfate in this region is oxidant limited for most of the time. zontal distribution of hydrogen peroxide to be made [e.g., Calvert et al., 1985; Heikes et al., 1987; Van Valin et al., 1987, 1990; Luria et al., 1989; Boatman et al., 1990; Daum et al., 1990; Gallagher et al., 1991]. The aircraft measurements and several other ground-based studies [Dollard et al., 1989; Sakugawa and Kaplan, 1989; Olszyna et al., 1988; Barth et al., 1989; Meagher et al., 1990; Jacob and Klockow, 1990; Claiborn and Aneja, 1991] revealed a high variability of hydrogen peroxide mixing ratios with a pronounced dependence on the season, latitude, altitude, and water vapor content of the air.The formation of hydrogen peroxide has been studied theoretically by Kleinman [1986]. His model calculations predict that under summer conditions the radical production rate over the United States is usually faster than the average NOx emission rate. Consequently, only a fraction of the radicals formed in the atmosphere can be removed by reactions with NO and NO2; the remainder are removed primarily by recombination reactions leading to peroxides. 1083

Distributions of organic hydroperoxides (ROOH), hydrogen peroxide (H2O2), other trace gases, and meteorological parameters were measured from an aircraft over the northeastern United States in August and September 1988. The data set consists of 13 flight missions on 14 days with 177 vertical profiles at altitudes between 100 and 3500 m. The mixing ratio of ROOH varied from below the detection limit of 0. 1 parts per billion by volume (ppbv) up to 3.14 ppbv, with generally higher average values in the free troposphere (FT) than in the planetary boundary layer (PBL). The average ratio of ROOH to the H2O2 mixing ratios was about 50 per cent. The ROOH mixing ratio was strongly correlated with H2O2, indicating similar production and loss mechanisms for ROOH and H2O2. The observed lower variability of the ROOH mixing ratios in comparison with that of H2O2 is probably due to a longer atmospheric residence time of ROOH. Combined with the lower ROOH mixing ratios, this longer residence time ind icates that the production and loss processes of ROOH are slower than those of H2O2. An ROOH formation rate of 56 ¤ 8 parts per trillion by volume ROOH/h per cent H2O was determined from the difference of ROOH mixing ratios between afternoon and morning flights on September 16. This formation rate is about twice as large as the rate predicted by a simple photochemical box model with methane chemistry, indicating that organic hydroperoxides other than CH3OOH may also be formed. The estimations of HO2 and RO2 concentrations in the free troposphere from H2O2, ROOH, and O3 formation rates were consistent

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