TECHNOLOGIE 369 CHIMIA 44 (1990) Nr. II (November) Chimia 44 (1990) 369-371 ~'1Schwei=. Chemiker-Verband; ISSN 0009-4293 Nitrogen Oxide Emissions from Air Traffic Robert A. Egli* Rober! A. Eg/i: Born 1926 in Rheineck, Switzer- land. After completing his chemistry education at the HTL Winterthur (1948), he worked for 10years as a group leader in an organic synthesis laboratory for Ci/og AG in Schaffhausen, later as head of the Ahstract. About 153 million metric tons of aviation fuel were consumed in 1987, which analytical development laboratory, and in addition was ca. ]3% of the world's consumption of transportation fuel. Burning this fuel to this job. for 13 years quality control director of Ci/ag AG. From 1985 to 1989, he was responsible produced ca. 2.75 million tons of nitrogen oxides, calculated as N0 , using an average 2 for patents, library, and literature searches. He emission index £1 of 18 g N02 per kg fuel. 0.92 million tons of N02 was exhausted published 17 papers, mainly in the field of organic between 9 and 13 km, which is an especially endangered altitude range, estimated with an analytical chemistry. Since January 1990, Egli is £f of 15 g N02 per kg fuel. Air traffic is the main NO, source between 9 and 13 km. Since working as an independent consultant. For many the NO, background concentration at this altitude is low and the possible lifetime of an years, his special interests have been air pollution problems and climatology. admixture two orders of magnitude larger compared to the ground, these NO .•emissions can lead to an important increase of tropospheric ozone, which contributes to the g]obal greenhouse warming. Alternatively, NO, emitted in the lower stratosphere may con- tribute to stratospheric ozone depletion, especially at high latitudes. l. Nitrogen Oxides at Different Altitudes air traffic [4]. Catalytic converters for NO, ter vapour above 9 km by air traffic (see are not employed in jet engines because of Chapt.5). Nitrogen oxides emitted near the ground high working temperatures occurring there are removed from the atmosphere within and the high exhaust velocities. It should days mainly as nitric acid. This is also true be emphazised that according to Grassl [5] 3. Interactions of Nitrogen Oxides and for most of the 2-10 million tons N (6.5-33 ozone depletion above the northern hemi- Ozone million tons N02) per year from lightning sphere is about twice as high as calculated estimated by Crutzen and Muller [1]. Op- with chlorofluorocarbon (CFC) climate Anthropogenic nitrogen oxide emissions posed to that, NO, admixtures near 10 km models, which do not include nitrogen-ox- are responsible for increased tropospheric altitude, according to Fabian [2] [3], have a ide emissions from aviation. Staehelin and ozone [3] [6] [8] [9]. Ozone at that altitude, lifetime which is about 100 times longer Dutsch [6] also come to the conclusion that because of its infrared absorption, con- and, therefore, contribute more to the only half of the stratospheric ozone dep]e- tributes to the global greenhouse warming chemistry of the atmosphere. At 15 km, the tion can be explained by perturbations of [10]. concentration of NO, is about one order of photochemistry caused by CFCs. (They at- In the stratosphere, on the other hand, magnitude lower than at 25 km. Results of tribute the remaining half to changes in ozone is produced from oxygen by absorp- NO, measurements between 9 and ]3 km circulation.) Their measurements above tion of energetic UV radiation. At the same at different latitudes are not available. Arosa showed a 3 % ozone depletion 1966- time stratospheric ozone is catalytically de- The naturally produced stratospheric ni- 1987 between 10.5 and 22 km altitude (5% stroyed by NO, radicals. This results in a trogen oxides, 0.5-1.5 million tons N (1.6- over all altitudes above 10.5 km), that is in stationary state ozone concentration [1] [2] 5 million tons N02) per year according to the region disturbed by air traffic. (A [6] [10] [11]. Additional anthropogenic Crutzen and Miiller [1] are mainly formed planned supersonic air fleet of 600-1200 NO" and especially CFCs will decrease the from N20 above 20 km. Catalytic reaction planes at altitudes of 16-35 km would stationary state value. Stratospheric water cycles involving these nitric oxides are the cause an additional threat to the ozone vapour (via hydroxyl radicals) and other main sink for stratospheric ozone in the layer.) Depending on latitude and season, trace gases also contribute to ozone de- unperturbed atmosphere. the minimum heights for ozone depletion struction [1]. Stratospheric photochem- by NO, are between 10 and 18 km with istry is comprehensively described by lowest altitudes in winter at high latitudes Crutzen and Muller [1] as well as by Staehe- 2. Possible Consequences of Air Traffic [7] [8]. Below this variable altitude limit lin and Dutsch [6]. Emissions at High Altitudes and in the troposphere, nitrogen oxides catalyse the photochemical ozone produc- The anthropogenic nitrogen oxide emis- tion. 4. Nitrogen Oxides and the Ozone-Hole sions above 9 km are of special concern It should also be mentioned that, above Theory regarding the g]obal climate. Between 9 ca. 9 km altitude, water vapour from ex- and 13 km, they are almost entirely from haust gases may influence the c1im'ate, es- According to the present state of knowl- pecially by forming condensation trails of edge [1] [3] [8] [11-13], a key reaction above cirrus ice crystals. Cirrus clouds contribute ca. 25 km is the photolytic formation of to the global greenhouse warming [7]. 1.25 halogen radicals from CFCs and other • Correspondence; Robert A. Egli kg of water vapour are produced from 1 kg halogenated hydrocarbons under the influ- Dip!. Chem. HTL Etzelstrasse 15 of fuel. This gives for 1987 a contribution ence of short wave solar UV radiation. The CH8200 Schafflmusen of 77 million metric tons of additional wa- most important halogen radicals are TECHNOLOGIE 370 CHIMIA 44 (1990) Nr.II(Novcmhcr) atomic chlorine and chlorine oxide. These Table. Fuel Consumption (in thousand metric tons) ing a questionable empirical formula given can catalytically destroy ozone, although Year All products _F_ue_ls _ by Bobick [21]. Kauanaugh assumes a de- they mainly react with CH4 and N02 to Transport (tot.) Aviation crease of the EI of II % till 2025 due to form HCI and CION02, respectively: ]971 2267822 7600] I 99462 improved engines. Furthermore, he men- 1977 2852555 976064 117246 tions that the mostly used engines PW- CI + CH4~HCI + CH) (I) ]985 2736676 I] 15875 141278 JT8D consumed in 1980 ca. 33% of the (2) 1987 2860100 1]80613 153218 global aviation fuel. CIO + N02~CION02 ]990 (]76500) Kinnison and Wuehh/es [22] give an Elof These substances slowly reach lower alti- 14 g NO, per kg at altitudes between 12 tudes. lated as N02 is resulting. For altitudes and 34 km for a US supersonic project. Crutzen and Arnold [11-13] identified above 9000 m, an emission index of 15 ± 3 Bula [23] from the Swiss Federal ('il,il the formation of polar stratospheric clouds g NO., per kg fuel is resulting. (At altitudes, Aviation Office assumes for 1988 en Elof as the main cause for the antarctic ozone no measured values are available.) The fol- 15.2 g per kg for LTO and an EJ of 19.6 g hole. These result from the freezing-out of lowing papers deal with emission indices: per kg as weighted average for the total nitric acid trihydrate crystals between 12 The US Environmental Protection amount of fuel burnt above Switzerland. and 22 km altitude at temperatures below Agency [18] calculated the emissions from Johnston et al. [24] used an EI of 40 g - 80°. On the particle surface three chlo- LTO up to 915 m for different types of NO, per kg fuel for current high-perfor- rine species: C12,HCIO, and CIONO are engines and planes based on the ICAO Ex- mance commercial aircraft, flying at about formed from the reaction of HCI and haust Emissions Data Bank sheets. From 12 km altitude (taken from a NASA re- CION02: that study, EI values for the LTO flight port). phase can be calculated. For the most im- HCI + CION02~CI2 + HNO) (3) portant civil engines, the average is ca. 15 g HCI + C10N02~HC10 + CIaNO (4) NO, per kg fuel. The decisive data for 7. Nitrogen-Oxide Emission Estimates flight altitudes above 915 m and for cruises above 9 km and in Total These molecules dissociate to form chlo- are missing like in the ICAO sheets. (A rine radicals at the end of the polar winter more recent edition of this compilation Calculated as N02 with an average under the influence of sunlight. They cata- was not available till March 1990.) weighted emission index EI of 18 g NO, lytically destroy ozone via CtO radicals Lecht et al. [17] calculated the height de- per kg fuel the total global NO, production with a rate depending on the square of the pendence of the emissions from the II en- from air traffic in 1987 is ca. 2.75 miJlion CIO concentration leading to the so-called gines mostly used in the FRG in 1984 metric tons (1990 probably about 3.2 mil- ozone hole and a temperature decrease in based on the ICAO Exhaust Emissions lion tons). With the EI valid above 9 km of the stratosphere. It is not clear, however, Data Bank sheets. The calculations rely on ca. IS g NO, per kg, the nitrogen-oxide how much anthropogenic NO, emissions several assumptions, so that experimental emission between 9 and 13 km is ca.