Atmospheric Pseudohalogen Chemistry

David John Lary

Accepted by: Atmospheric Chemistry and Physics Discussions Reference: Vol. 4, pp 5381-5405, 16-9-2004

Hydrogen cyanide is not usually considered in atmospheric chemical models. The paper presents three reasons why hydrogen cyanide is likely to be signiscant for atmospheric chemistry. Firstly, HCN is a product and marker of biomass burning. Secondly, it is also likely that lightning is producing HCN, and as HCN is sparingly soluble it could be a usell long-lived “smoking gun” marker of lightning activity. Thirdly, the chemical decomposition of HCN leads to the production of small amounts of the cyanide (0and NCO radicals. The NCO radical can be photolyzed in the visible portion of the spectrum yielding nitrogen atoms (N). The production of nitrogen atoms is significant as it leads to the titration of total nitrogen from the atmosphere via N+N->N2, where N2 is molecular nitrogen. , 1..

This manuscript was prepared for Atmos. Chem. Phys. (Discuss.) with version 7.0 of the egu L5TS class egu.cls. Date: September 14,2004 ACP-LOGO

Atmospheric Pseudohalogen Chemistry

D. J. 'Global Modelling and Assimilation Office, NASA Goddard Space Flight Center ([email protected]) 'GEST at the University of Maryland Baltimore County, MD, USA ([email protected]) 3Unilever Cambridge Centre, Department of Chemistry, University of Cambridge, England ([email protected])

Abstract. There are at least three reasons why hydrogen 1E-01 1 1E-010 1E-009 cyanide is likely to be significant for atmospheric chemistry. 10 The first is well known, HCN is a product and marker of biomass burning. However, if a detailed ion chemistry of lightning is considered then it is almost certain than in addition to lightning producing KOzrit also produces HO, and HCN. Unlike NO, and HO,, HCN is long-lived and could therefore be a useful marker of lightning activity. Observa- n^ tional evidence is considered to support this view. Thirdly, -E 100 the chemical decomposition of HCN leads to the produc- n tion of small amounts of CN and NCO. NCO can be photolyzed in the visible portion of the spectrum yielding N atoms. The production of N atoms is significant as it leads to the titration of nitrogen from the atmosphere via N+N-+S*. Normally the only modelled source of N atoms is NO photolysis which happens largely in the UV Schumann-Runge 1000 $+ 1000 bands. However, NCO photolysis occurs in the visible and 1E-011 1E-010 1E-009 1E-008 1E-007 so could be involved in titration of atmospheric nitrogen in HCN v.m.r. the lower stratosphere and troposphere. HCN emission in- ventories are worthy of attention. The CN and NCO radicals Fig. 1. All HCN observations made by the Atmospheric Trace have been termed pseudohalogens since the 1920s. They are Molecule Spectroscopy Experiment (ATMOS) on the missions strongly bound, univalent, radicals with an extensive and var- ATLAS-I (1992), ATLAS-:! (1993), and .4TL4S-3 (19%) shorn ied chemistry. The products of the atmospheric oxidation of together with a typical mid-latitude NO, profile. The ATklOS data is publically available from the web site http:~/remus.jpl.nasa.gov/. HCN are NO, CO and 03.N+CH( and N+CH30H are found to be important sources of HCN. Including the pseudohalogen chemistry gives a small increase in ozone and total reactive nitrogen (NO,).

1 Introduction halogen radicals were first recognized as a potential threat to ozone. In like manner, there may be other radicals which play sincethe discovery of the Antarctic Ozone hole by F~~ a r6le in ozone photochemistry. There are many natural and et d.(1%) the importance of halos., in deknnin- anthropogenic sources of compounds containing CN which ing the concentrations of atmospheric Ozone has been can be released into the atmosphere. Many CN reactions are demonsmted. However, it wras in the mid I sr;rb that the shady considered when stud56ng combustion chemistry and interstellar clouds. This paper considers their importance in Correspondence lo: D. J. Lay ([email protected]) our okvn atmosphere.

0 European Geosciences Union 2004 .- ’..

2 Lary: Atmospheric Pseudohalogen Chemistry

1.1 Properties known as manioc, mandioc, or yuca) were used by primitive peoples to produce HCN for poison darts and arrows. HCN HCN (also called formonitrilej is a highly volatile, colorless, is produced by other plants, bacteria and fungi. and extremely poisonous liquid (boiling point 26°C freez- In addition, aliphatic-amines are produced from animal ing point -14°C). A solution of hydrogen cyanide in water husbandry and ma>- be a source of HCN (Schade and is called hydrocyanic acid, or prussic acid. It was discov- Crutzen, 1995). Schade and Crutzen (1995) measured the ered in 1782 by the Swedish chemist, Carl Wilhelm Scheele, emissions of \rolatile aliphatic amines and ammonia pro- who prepared it from the pigment Prussian blue (Britannia, duced by the manure of beef cattle, dairy cows, swine, lay- 2003). ing hens and horses in livestock buildings. The amine emissions consisted almost exclusively of the three methylamines 1.2 Observations and correlated with those of ammonia. Schade and Crutzen (1995) showed possible reaction pathways for atmospheric It is surprising that HCN is so often overlooked as it has been methylamines. These included the speculative but possible observed on numerous occasions over the last two decades production of HCN. (Yokelson et al., 2003; Singh et al., 2W; Zhao et al., 2002; There are many anthropogenic sources of compounds con- Rinsland et al., 2001, 2000; Zhao et al., 2OOO; Rinsland taining CN which can be released into the atmosphere. et al., 1999; Bradshaw et al., 1998; Rinsland et al., 1998a,b; Cyanides are used in a variety of chemical processes includ- Schneider et al., 1997; Mahieu et al., 19%’; Rinsland et al., ing fumigation, case hardening of iron and steel, electroplat- 1996; Notholt et al., 1995; Mahieu et al., 1995; Toon et al., ing and in the concentration of ores. Hydrogen cyanide is 1992b,a; Kopp, 1990; Jaramillo et al., 1989, Zander, 1988; a highly volatile and extremely poisonous gas that is used Carli and Park, 1988; Jaramillo et al., 1988; Abbas et al., in fumigation, ore concentration, and various other indus- 1987; Smith and Rinsland, 1985; Coffey et al., 1981). Re- trial processes. Cyanogen, or o?talonitrile, (CN)2, is also cently it has sometimes been considered as an ‘interference’ used as a chemical intermediate and a fumigant- Hydrogen for NO, observations, for example, Bradshaw et al. (1%); cyanide is used to prepare polyacrylonitrile fibres (known Thompson et al. (1997); Miner et al. (1997). However, re- by the generic name of acrylic) synthetic rubber, plastics, garding it as an ‘interference’ overlooks its potential impor- and in gas masers to produce a wavelength of 3.34 mm tance in atmospheric chemistry, part~cularlyas Cicerone and (Britanniw2003). Acrylic fibres are spun from polymers Zellner (1983) deduced that HCN has a very long residence consisting of at least 85% by weight of acrylonitrile units time against rainout produced from ethylene oxide and hydrocyanic acid. Figure 1 shows all the HCN observations made by the Hydrogen cyanide is a combustion product which is a hu- Atmospheric Trace Molecule Spectroscopy Experiment (AT- man hazard during domestic and industrial fires. Some cat- MOS) on the missions ATLAS-], ATLAS-2, and ATLAS-3 alj-tic converters in bad repr can produce large amounts of (Rinsland et al., lmb,19%) together {vith a typical mid- Hydrogen cyanide. Hydrogen cyanide is produced in large latitude NO, profile. In the upper troposphere and lower quantities for laboratory and commercial use by three prin- stratosphere the HCN abundance is comparable to the YO, cipal methods: Treatment of sodium cyanide with sulphuric present and should not be neglected. It is tantalizing that acid, CatalJtic oxidation of a methane-ammonia mixture, and some of the tropical vertical profiles seem to have a large decomposition of formamide (HCOKH2). peak in HCN close to the tropopause which may be prodwed We suggest that it is timely to compile HCN emission in- by lightning in regions of strong convective activity. ventories. It is interesting to note that the atmospheric measurements 1.3 Likely Sources of HCN reported by Zander (1988) gave a mixing ratio for HCN in the Southern Hemisphere which was approximately HCN is produced by biomass burning (Lobert et al., 1990; 5% higher than that for the Northern Hemisphere. This may Hurst et al., 1%; Yokelson et al., 1997b. Holzinger et al., be due to biomass burning. It seems that in addition to HCN 1999, Rinsland et al., 1999,2000, Barber et al., 2003; Li being a marker of biomass burning it is also a marker for et al., 2003; Singh et al., 2003; Yokelson et al., 2003) since lightning. nitrogen in plant material is mostly present as amino acids and upon combustion this nitrogen is emitted as a variety of 1.4 HCN, HO, and Lightning compounds including “3, NO, NO2, N20, organic nitriles and nitrates (Holzinger et al., 1999, Yokelson et al., 1997a; Emissions from CN radicals are occasionally observed from Lee and Atkins, 1994; Hurst et al., 1994b,a; Kuhlbusch et al., lightning disturbed air (Cicerone and Zellner, 1983). In the 1991). There are many naturally occumng substances yield- atmosphere of Jupiter HCN is present with a concentration of ing cyanide in their seeds, such as the pit of the wild cherry. It about 2 ppbv and is thought to be produced by lightning in usually occurs in combination with plant sugars. The tuber- the convective regions of Jupiter’s atmosphere (Britannia, ous edible plant of the spurge family called cassava (also 2003; Borucki et al., 1988, 1991). On Titan HCN is also

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Lary Atmospheric Pseudohalogen Chemistry

1E-Ell 1E-210 1E-OG9 1E-010 1E-039

i I I I *: A-I I 1E-011 4 IE 03E - I - 1E om

1M12 r "'T ' ' 1E-011 1E-Gl0 1E-OW 1 HCN (a)

Fig. 2. Scatter dia,pm of the HCN and NO, concentrations observed by ATMOS ATLAS3. Panel (a) shows all the available HCN and NO, observations made. Panel (b) is an enlargement showing just the high KO, and HCN concentrations which are probably associated with lightning (notice the log-log scale).

thought to be produced by lightning (Borucki et al., 1988). YO,. for high HCN concentrations. This corresponds to the It may well be that lightning is a significant source of HCN, air parcels that have probably recently encountered lightning. particularly due to its resistance to uptake by aqueous media. There is not a strong correlation for the lower HCN and NO, Lightning produces large scale ionisation in the atmo- concentrations as SO, and HCN are not in chemical equilib- sphere with temperatures of around 30,000 K produced rium. lvithin a few microseconds. Both the ionisation and high Thcrc arc several satellites which observe global lightning, temperatures are significant for atmospheric chemistry, and but these had not been launched at the time of the last AT- the full implications are usually completely overlooked, with MOS mission. However, for the six locations with HCN attention paid almost exclusively to NO,. Ionisation pro- concentrations greater than 0.7 ppbv visible satellite images duced by cosmic rays and precipitating particles is well show cloud cover as do the NCEP analyses (NCEP). Each of known to produce NO, and HO,(Brasseur and Solomon, the six locations were in a costal region or over land which is 198/). The ionisation associated with lightning is between where most lightning activity occurs. The vertical structure six and fifteen orders of magmtude greater than that associ- of the HCN profile may provide a good test for the hypothe- ated with cosmic rays (Boldi, 1992). It is therefore likely sis that HCN is produced by lightning. During thunderstorms that elevated HO, should be associated with lightning (Hill, we expect a 'C' shaped NO, profile (Pickering et al., 1998), 1992). This has been both calculated (Boldi, 1992) and and so should also expect a 'C' shaped HCN profile with en- hinted at by observations of elevated HO, in the vicinity of hanced HCN in the region between 5 and 14 km. convective outflow (Jaegle et al., 1999). Calculations suggest that there is a 56%increase in global lightning for every 1"C 1.5 Previous modelling work of warming (Pnce and Rind, 1994), so if there is a lightning source of HO, global warming could lead to a significant The only previous modelling studies of atmospheric HCN change in the oxidizing capacity of the atmosphere due to appear to be those of Cicerone and Zellner (1983); Brasseur lightning produced HO, alone. et al. (1985); Li et al. (2003);Singh et al. (2003) who consid- Equilibrium thermodynamic calculations (Boldi, 1992) ered the earth's current atmosphere and the studies of Zahnle show that for the conditions associated with a lightning strike (1986a.b) who presented a study ofthe likely HCN chemistry in the terrestrial atmosphere we would expect between 0.7 in the earth's early atmosphere. Cicerone and Zellner (1983) to 1 ppbv of HCN. If HCN is produced by lightning, then identified the major atmospheric losses of HCN. Li et al. in the surrounding air we would simultaneously expect ele- (2003) and Singh et al. (2003) showed that the main HCN vated concentrations of both KOz and NO,. This is exactly loss is due to oceanic uptake. what ATMOS observed (ATMOS). For example, around a This stud) expands the previous work by considering thousand observations of HCN were made during November many N, CN and NCO reactions which are kno\vn to be 1994 as part of ATLAS3 (ATMOS). Among these observa- important in flame chemistry. These reactions are consid- tions there were six anomalously high HCN observations of ered for conditions relevant to the current atmosphere. In- greater than 0.7 ppbv, for which elevated concentrations of cluding these reactions provides additional sources of HCN, both NO, and NO, were also observed. If one plots a scatter not included by Cicerone and Zellner (1983); Brasseur et al. diagram of the HCN against NO, concentrations (Figure 2). (1989, and some of which were not included by Zahnle we find that there is a strong correlation between HCN and (1%6a,b) either. HCN photolysis is shown to be a minor

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4 Lary: Atmospheric Pseudohalogen Chemistry loss for HCN.

Before systematically e'mining atmospheric CN, chemistry let us examine at least three reasons why we should consider atmospheric HCN chemistry.

2.1 Abundance

Figure 1 shows that in the upper troposphere and lower stratosphere the HCN abundance is comparable to the NO, present ca.n20, OH, HCHO. H~.HONO 2.2 Tracer

HCN is a long lived, low solubility (Cicerone and Zell- Fig. 3. The CN, NCO, HCN reaction scheme used in the model. ner, 1983) gas. If as it seems HCN is produced by lightning (Britannica, 2003; Cicerone and Zellner, 1983; Borucki et al., 1988, 1991) then it is not rained out it may well as (1992) for stiff systems of equations. Photolysis rates are cal- prove to be an effective tracer of lightning activity. Such a culated using full spherical geometry and multiple scattering marker could be extremely valuable to complement obsena- (Anderson, 1983; Laq and Pyle, 1991a.b. Meier et al., 1982; tions (Huntrieser et al., 1%; Kawakami et al., 1997; Hauf Nicolet et al., 1982) corrected after Becker et al. (2000). The et al., 1995). photolysis rate used for each time step is obtained by ten point Gaussian-Legendre integration (Press et al., 1992). In 2.3 N atom source this study the model described a total of 49 species includ- The main stratospheric sink of NO, is the reaction of N with ing CN, NCO and HCN. The model kinetic data is based NO on DeMore et al. (2ooo) with the cyanide reactions coming from a variety of sources. N+NO-N~+O(~P) (1) The eventual fate of most HCN released into the atmo- with the main source of N atoms generally accepted to be the sphere is NO. Since HCN has a long lifetime against rainout photolysis of NO (Cicerone and Zellner, lW),whereas NO, does not, HCN can be transported from the regions where it is emitted and XO+~~-+?:+O(~P)AS imml (3) slowly release NO, awaj- from the source regions. The net effect of HCN oxidation is summarized by the following re- However, the photolysis of NCO is also a source of N atoms. action sequence shown in Table 1. Therefore including HCN The rate of N production due to NCO photolysis is calculated to be faster than that due to NO photolysis below about 10 km. HCN + OH --+ H2O + CN NCO + hv - N+ CO X 5 342 nm CN+02--4NCO+O Consequently, when pseudohalogen chemistry is included in NCO + hv ------) N+CO the model there is a significant increase (more than an or- N+02 -NO+O der of magnitude) in the N atom concentration below 10 km 20 + 202 - 203 (Figure 4). 03+ hv - O('D) f02 O('D) + H20 - 20H 3 Atmospheric CN, chemistry Net : HCN +302 + 2hv - CO + 03+NO + OH Let us now consider the HCN chemistry depicted in Fig- ure 3 as simulated using the extensively validated AutoChem model (Lary et al.. 1995; Fisher and Lary, 1995; Lary, Table 1. HCN oxidation sequence. 19%;Lary et al., 2003). The model is explicit and uses the adaptive-timestep, error monitoring. Stoer and Bulirsch chemistry provides a small additional source of NO,, O3 (1980) time integration scheme designed by Press et al. and CO. If there is a heterogeneous conversion (oxidation)

Atmos. Chem. Phys., oooO,0001-9,2004 Lary: Atmospheric Pseu&balogen Chemistry 5 of HCN then it may be more important than described here, 3.2 The cyanide radical, CN particularly in the upper troposphere. In the sunlit atmosphere CN is in photochemical equilibrium. 3.i iiCiu' CN has a very short lifetime because of the 1 ery fast reaction of CN with 02. The lifetime varies between about 10 ns and Figure 1 shows the observed HCN profiles from ATMOS. 60 ps. The calculated CN profile is shown in Figure 4. Cicerone and Zellner (1983) and Brasseur et al. (1985) \yere The most important production channel for CN in the able to reproduce the tropospheric portion of the profile but model km is not the stratospheric portion. They suggested that the discrepancy may be due to an inappropriate OH concentration HCN + OH - H2O + CN or HCN photolysis rate. The HCN photolysis rate calculated by assuming HCN has the same Weoncross-section as The reaction is slightly endothermic at 298 K, however, the HCI will be too fast as Herzberg and IMCS (1957) report a reverse reaction is not a significant source of HCN. In the up predissociation limit of 179 nm for HCN, which means that per atmosphere the reaction of HCN with O(lD) and HCN the HCN photolysis rate is very small. This is confirmed by photolysis each contribute a few percent to the overall pro- the calculations of Huebner et al. (1992). duction of CN. Another likely possibility for the discrepancy is in-situ at- HCN + O(lD) OH + CN mospheric production of HCN. Such production can occur by - several routes, most of which are very slow as they involve The main loss of CN at all altitudes in the model is the rapid the CN radical which is quickly removed by reaction with reaction of CN with 02which has two channels 02. For this reason, an effective production will probably not involve CN. Zahnle (1%) included the production of HCN CX + o2- NCO + o(3r) caused by the reaction of N with CH2 and CH3. Since CH2 is AHR = -173.4 kJ Mole-' produced mainly by Lymama CH4 photolj-sis, this source of branching ratio = 0.94 HCN will be small in the troposphere and stratosphere (these source are included in the model). The reaction of N with -CO+NO (14) CHI is the most important source of HCN in the model, and AHR = -455.6 kJ Mole-' has a noticeable effect on the calculated HCN concentration branching ratio = 0.06 above 25 km. It was not included by Cicerone and Zellner (1983); Brasseur et al. (1985); Zahnle (1986a,b). The rate The branching ratio quoted was determined by Schmatjko constant was measured by Takahashi (1972) at 298 K with and Wolfrum (1978). In the laboratory Basco (1%5) found N2 as the bth gas as 2.5~10-l~molecules-' cm3 s-l. that there was a production of ozone due to the first channel of this reaction in an excess of oxygen because it can be K+ CH4 -----t HCX + Hz + H (10) followed by Ocean uptake is the dominant sink for HCN (Singh et al., O(3P) 02 03 2003: Li et al., 2003). The main atmospheric loss of HCN is + x reaction with OH. Such a production of 03 does occur in the model to a very small extent, but it is only a small source of 03 as the CN HCN OH H20 CN + - + radicals are present in such small concentrations. In addition, If the HCI cross-section is used to calculate the HCN pho- the NO formed can then take part in catalytic destruction of tolysis rate as was done by Cicerone and Zellner (1983) and 03. Brasseur et al. (1985) then above 35 km photolysis is the Since CN is a pseudohalogen it might be expected tha most important loss of HCN. However, Herzbeg and Innes like the halogens, it could take part in the catalytic destruc- (1957) report a predissociation limit of 55900 cm-l, 179 nm. tion of ozone, for example This means that no photolysis would occur in the important UV window and HCN photolysis is very slow.

HCNfhv-H+CN XI179nm (11) There is also a minor loss due to reaction with O('P) and O('D) (Figure 4).

HCN o(3~) H NCO + - + Clearly the important difference between the pseudo-halogen HCN + O('D) - OH + CN CN and halogens such as CI and Br, involved in stratospheric www.atmos-chem-phys.org/acp/OO00/0001/ Atmos. Chem. Phys., oooO,0001-9,2004 .-

6 Laq: Atmospheric Pseudohalogen Chemistry

% Contribution to loss of HCN N -- I 7

0 20 40 60 80 100 % conhibulion to loss of HCN

-2l

-27 t k4

3 6 9 12 15 18 21 3 6 9 i2 1; y8 21 (C) Local Sdar Time (hours) (4 Local Sdar Time (hours)

Fig. 4. Panel (a) shows the calculated contributions for the various loss terms of HCN. Panel (b) shows the effect on the nitrogen atom v.mr. when cyanide chemistry is included. The red line shows the calculation with pseudohalogen chemistry the blue line shows the calculation without pseudohalogen chemistry. Panels (c) and (d) show calculated diurnal cycles for CN and NCO.

ozone destruction, is the very marked difference in their re- The reaction CN + 03 is thermodynamically very favor- actions with 02. Chlorine and bromine form weakly bound able but its rate constant has not been determined. The NCO peroxides on reaction with 02 + 0 reaction to give CN as a product occurs in flames (Tsang, 1992). This reaction is endothermic at room temperature by C1+ 02+ M ++ ClOO + M (17) 173 KJ/Mde. So this reaction has not been included in the Br + O2 + M +-+ BrOO + M (18) reaction scheme. Consequently, with the current chemical which rapidly decompose to give back the halogen, whereas scheme the only way to convert the NCO formed by the re- CN reacts rapidly with 02, as we have mentioned pre\4ously action of CN \vith 03 back to CN is via HCN photolysis. CN+0~-+~CO+O Since HCN has a lifetime of about 5 months (Singh et al., 2003; Li et al., 2003) and HCN photolysis is extremely slow CN+02-CO+N0 this is not an effective loss of 03. Yielding primarilq. NCO and 0. If CI or Br atoms reacted The CN + 02 reaction has a second channel which pro- with 02 in a similar way to CN, there would be no omne duces CO + NO and so can either enhance the NO/N02 cat- loss. So the CN radical behaves in a crucially, very different alytic cycle, or enhance the production of odd oxygen if it manner to the halogens, preventing it from participating in is followed by the formation and photolysis of NO2. Unlike an efficient ozone loss cycle. the photolysis of YO2 or C10, the photolysis of NCO, does

Atmos. Chem. Phys., oooO,0001-9,2004 www.atmos-chem-phys.org/acp/~~1/ Lay: Atmospheric Pseudohalogen Chemistry 7 not yield an oxygen atom ATIfOS, Data can be accessed from http:.':remus.jpl.nasagov. NCO + hv - K+ CO Barber, T. R., Lutes, C. C., Doom, Xi. R. J., Fuchsman, I? C., Tim- and so is not a source of odd oxygen. However, it is a source menga, H. j.,and Crouch, R. L., Aquatic ecoiogicai risks due to cyanide from biomass burning, Chemosphere, of N releases 50,343- atoms. 348,2003. 3.3 The NCO radical Basco, N.,Reaction of cyanogen radicals with oxygen, Proceed- ings of the Royal Socie? of Loncton Series a-Matkemztzcal and NCO is in photochemical equilibrium throughout the sunlit PhysicalScirnces, 283,302-, 1%5. Beclier, G., Gmss, J., XlcIGnna, D., and Xfuller, R., Stratospheric atmosphere. The lifetime varies from about 6 the seconds at photolysis fquencies: Impact of an improved numerical solu- surface down to about a second at 65 km. The calculated tion of the radiative transfer equation, J. Atmos. Chem., 37,217- NCO profile can be seen in Figure 4. By far the most impor- 229,2000. tant production of NCO is due to the fast reaction Boldi, R., A model of the ion chemistry of electrified convection, Tech. Rep. 23, Center for global change Science, MIT, Depart- ment of Earth, .4tmospheric and Planetary Sciences, 1992. The main loss of NCO in the model is Borucki, W., Giver, L., Mckay, C., Scattergood, T., and Parris, J., Lightning production of hydrocarbons and HCN on titan - labo- NCO + 02 -----* NO + CO1 (19) ratory measurements, ICARUS, 76,125-131,1988. Borucki, W.. Dyer, J., Phillips, J., and Pham, P, Venus or- In the upper atmosphere the reaction with O('P) also play Pioneer biter search for venusian lightning, J. (kuphys.Res., %, 1 1 033- a role. 11 043,1991. NCO + o(3r)- co + EO (20) Bradshaw, J., Sandholm, S., and Talbot, R., An update on reactive odd-nitpgen measurements made during recent NASA global tropospheric experiment programs, J. Geophys. Res., 103, 4 Condusions 19 129-19 148,1998. Brasseur, G. and Solomon, S., Aeronomy ofthe M&Ze Atmosphere In addition to NO, lightning it is suggested that it is also : Chemisg, and Physlcs of the Srrdosphere and Mesosphere, producing significant amounts of HCN and possibly HO,. Atmospheric Science Library, D Reidel Pub Co, second edn., HCN is a stable, long-lived, sparingly soluble molecule with 1987. a long residence time against rain-out Unlike NO,, HCN Brasseur, G., Zellner, R., Derudder, A., and Arijs, E., Is hydrogencyanide (HCN) a progenitor of acetonitrile (CHBCN)in the at- can act as a relatively inert 'marker' of lightning activity, and mosphere, Geophys. Res. Let?., /2, 1 17-120, 1985. proxy may thereby serve as a for the total amount of lightning Britannia, E., Enncydopaedra Arrtannicu Uitimate Reference Suite activity in the atmosphere. The vertical structure of HCN 2004DV19, Encyclopaedia Britannia, Inc., 2003. observed during thunderstorms may provide a good test for Carli, B. and Park, J., Simultaneous measurement of minor strato- the hypothesis that HCN is produced by lightning. spheric constituents with emission far-infrared spectroscopy, J. NCO photolysis enhances the N atom concentration, and Ciroph~.Res., 29,3851-3865, 1988. hence, enhances the rate of KO, loss due to the reaction of N Cicerone, R. and Zellner, R., The atmospheric chemistry of with NO. This additional source of N atoms is more impor- hydrogencyanide (HCN), J. Geophys. Res., 88,689-6%, 1983. tant than NO photolysis below 10 km. The NCO absorption Coffey, hi., Xfankin, W., and Cicerone, R., Spectroscopic detection cross-section does not appear to have been measured and is of stratospheric hydrogen cyanide, Science, 214,333-335.1981. one of the largest uncertainties in this study. Dehlore, W. B., Howard, C. J., Sander, S. P,Ravishankara, A. R., Golden, D. M., blb, C. E., Hampson, R. E Molina, M. J., and Acknowledgements. David Lay thanks J.A. Pyle, Zev Levin, Ralf Kurylo, M. J., Chemical kinetics and photochemical data for use Toumi, Colin Price and Dudley Shallcross for useful conversations. in stratospheric modeling, supplement to evaluation 12: Update It is a pleasure to acknowledge: NASA for a distinguished Goddard of key reactions, JPL Publ. 00-3, NASA JPL, 2000. Fellowship in Earth Science; The Royal Society for a Royal Society Farman, J. C., Gardiner, B. G., and Shanklin, J. D., Large losses of University Research Fellowship; The govemment of Israel for an total ozone in antarctica reveal seasonal CIO,!NO, interaction, Alon Fellowship; The NERC, EU, and FSA for research support. Nature, 3/5,207-210,1985. Fisher, M. and Lary, D., Lagrangian 4dimemional variational data assimilation of chemical-species, Q. J. R. Meteorol. Soc., i2I, References 1681-1704,1995. Hauf, T., Schulte, P, Alheit, R., and Schlager, H., Rapid vertical Abbas, M., Guo, J., Carli, B., h4encaraglia. E, Carlotti, M., and trace gas-transport by an isolated midlatitude thunderstorm, J. Nolt, I., Stratospheric distribution of HCN from far infrared ob- Geophys. Res., 100,22937-22 970, 1995. senfatiom,Geophys. Res. Lett., /4,531-534,1987. Herzberg, G. and hes, K. K., Ultraviolet absorption spectra of Anderson, D., The troposphere-stratosphere radiation-field at twi- HCN and DCN .l. the Alpha-5 and Beta-X systems, Cdian light - A spherical model, Planet. 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