The Evolution and Variability of Atmospheric Ozone Over Geological Time

ICARUS 39, 295--309 (1979)

The Evolution and Variability of Atmospheric Ozone over Geological Time

JOEL S. LEVINE Atmospheric Environmental Sciences Division, NASA Langley Research Center, Hampton, Virginia 23665

PAUL B. HAYS Department of Atmospheric and Oceanic Science, The University of Michigan, Ann Arbor, Michigan 48109

AND

JAMES C. G. WALKER Arecibo Observatory, National Astronomy and Ionosphere Center, Arecibo, Puerto Rico 00612

Received November 27, 1978; revised April 11, 1979

The rise of atmospheric O3 as a function of the evolution of 02 has been investigated using a one-dimensional steady-state photochemical model based on the chemistry and photochemistry of O~(O3, O, O(1D)), N~O, NOx(NO, NO2, HNO3), H20, and HOx(H, OH, HO2, H202) including the effect of vertical eddy transport on the species distribution. The total 03 column density was found to maximize for an 02 level of 10 -1 present atmospheric level (PAL) and exceeded the present total 03 column by about 40%. For that level of Oz, surface and tropospheric 03 densities exceeded those of the present atmosphere by about an order of magnitude. Surface and tropospheric OH densities of the paleoatmosphere exceeded those of the present atmosphere by orders of magnitude. We also found that in the Oz-deficient paleoatmosphere, N20 (even at present atmospheric levels) produces much less NOx than it does in the present atmosphere.

INTRODUCTION added the hydrogen species chemistry to By virtue of its very efficient shielding of the Chapman reactions in their study. More the Earth's surface from lethal solar ul- recently, Blake and Carver (1977) added the traviolet radiation, the evolution and nitrogen species chemistry (with the excep- natural variability of atmospheric ozone tion of nitrous oxide) to the hydrogen and (Oa) over geological time were important oxygen species chemistry in a study of the factors in biological evolution on our planet evolution of 03. Blake and Carver (1977) (Berkner and Marshall, 1965; Ratner and assumed photochemical equilibrium, i.e., Walker, 1972; and Walker, 1977). The ap- they did not include the effect of vertical pearance and evolution of 03 were strongly transport on species distribution in their coupled to the appearance and evolution of calculations. In the present study, we have molecular oxygen (02). The first investiga- included the chemistry of the oxygen, hy- tion of the evolution of 03 in the 02- drogen, and nitrogen species, plus the effect deficient paleoatmosphere was the qualita- of vertical transport on the distribution of tive treatment of Berkner and Marshall the calculated atmospheric species. The (1965). Next, Ratner and Walker (1972) present study is the first to include nitrous used a simple photochemical model--the oxide (N20) which is produced via dentrifi- four Chapman reactions for a pure 02 atmo- cation by soil bacteria (Bates and Hays, sphere, without transport--to investigate 1967; Crutzen, 1970; McElroy and McCon- the evolution of Oz. Hesstvedt et al. (1974) nell, 1971). The oxidation of NzO is the 295 0019-1035/79/080295-15 $02.00/0 Copyright © 1979 by Academic Press, Inc. All rights of reproduction in any form reserved. 296 LEVINE, HAYS, AND WALKER major source of the nitrogen oxides which atmosphere by Hart (1978). Walker con- control 03 levels in the present stratosphere cluded that the atmosphere formed via vol- (Crutzen, 1970). In addition, the present atile outgassing very early in the Earth's paper is the first to discuss the nitrogen and history and that the paleoatmosphere con- hydrogen species concentrations of the 02- tained about as much N2, H20, and CO2 as deficient paleoatmosphere and the variation the present atmosphere. Hart's computer of these species as 02 evolved to present simulation developed the following atmospheric levels. The oxygen, nitrogen, scenario: the 02 released from the photodis- and hydrogen reactions and rate constants sociation of H20 and from photosynthesis used in the present study are based on those (after the first 800 million years) chemically recommended in the recent NASA destroyed the CH4 and NHz in the paleoat- chlorofluoromethane-ozone assessment mosphere. By roughly 2 billion years ago, (Hudson, 1977). A description of the photo- all but the trace amounts of reduced gases chemical model used in this study is given had been removed from the atmosphere and in the appendix. at that point the atmosphere consisted primarily of N2 (about 96%). Hart's calcula- COMPOSITION AND STRUCTURE OF THE tions indicate that both CH4 and NH3 PALEOATMOSPHERE reached their present atmospheric levels One uncertainty in our study of the evo- about 2 billion years ago. The studies of lution of Oa as a function of evolving 02 Walker and Hart suggest that during the level concerns the composition and struc- evolution of O2 and 03 the chemical com- ture of the paleoatmosphere during the pe- position of the paleoatmosphere was similar riod that 02 rose from 10 -4 of its present to the composition of the present atmo- atmospheric level 00 -4 PAL) to its present sphere. Due to the assumed similarity (with atmospheric level (1 PAL). This uncertainty the exception of 02 and 03) in the composi- results in part from our lack of knowledge tion of the paleoatmosphere and the modern concerning the exact chronology for the atmosphere, we have adopted the 03 evolution of 02. For example, Berkner and photochemical and chemical reactions used Marshall (1965) have speculated that 02 rose in the current investigations of possible in- from 10 -3 PAL to its present level in the advertent depletion of 03 due to an- more recent past, over the last 600 million thropogenic activities (Hudson, 1977). The years, whereas Walker (1978) has sug- chemistry of CH4, NHa, COs, CO, and the gested that 02 rose rapidly from essentially chlorine species is not included in our calcu- zero to within a factor of 10 of its pres- lations. The photochemical and chemical ent atmospheric value as early as about 2 reactions used in our model are listed in Ta- billion years ago. For our photochemical bles I and II. calculations we need to know the approxi- To calculate the photodissociation rates mate concentrations of nitrogen (N2), water of the molecular species given in Table I, vapor (H20), carbon dioxide (CO2), and re- the solar spectrum between 110 and 735 nm duced species such as methane (CH4) and was divided into 174 spectral intervals, with ammonia (NH3) in the paleoatmosphere as molecular cross sections for each species 02 evolved from 10 -4 PAL to its present folded into these spectral intervals. The level. Our information concerning the solar flux data are from Ackerman (1971). chemical composition of the paleoatmo- The species absorption cross-section refer- sphere during the evolution of 02 is based on ences are also given in Table I. The calcula- two recent studies: a detailed review of the tions of the transmittance and rate of dis- available geological and paleontological sociation of molecular oxygen in the evidence by Walker (1977) and a computer Schumann-Runge band (19 spectral inter- simulation of the chemical evolution of the vals between 175 and 205 nm) are based on EVOLUTION OF OZONE 297

TABLE I PHOTOCHEMICAL REACTIONS

NO. Photochemical reaction References for (sec -~) cross sections

J1 O3 + hv(l10--175 nm) ~ O + OCD) Ackerman (1971); Watanabe (1958) J2 02 + hv(175-205 nm) ~ O + O Hudsoa and Mahle (1972) J3 02 + hz,(205-242 nm) ~ O + O Ackerman (1971); Hasson and Nicholls (1971) J4 Oa + hv(ll0-310nm) ---* O2(lAg) + OCD) Ackerman (1971); Inn and Tanaka (1953) J5 Oz + hv(310-360 nm) --> O2(~Ag) + O Ackerman (1971); Inn and Tanaka (1953); Griggs (1968) J6 03 + hv(360-735 nm) --* O3 + O Ackerman (1971); Inn and Tanaka (1953) J7 H20 + h~,(l10-200 nm) --~ OH + H Watanabe and Zelikoff (1953) J8 N20 + hv(l10-315 nm) --> Nz + O(~D) Bates and Hays (1967); Johnston and Selwyn (1975) J9 HNOa + h~(110-240 nm) --} H + NOa Johnston and Graham (1974); Schmidt, et al. (1974) Jl0 HNO3 + hJ,(240-325 nm) --> OH + NO2 Johnston and Graham (1974); Schmidt et al. (1974) Jll NO~ + hv(110-245 nm)--> NO + O(~D) Dixon (1940); Hall and Blacet (1952); Nakayama et al. (1959) J12 NO2 + hv(245-398 nm) --~ NO + O Dixon (1940); Hall and Blacet (1952); Nakayama et al. (1959) J13 H202 + hl,(110-370 nm) --> OH + OH Schiirgers and Welge (1968); Paukert and Johnston (1972) the data of Hudson and Mahle (1972). The tinuity equation, which combines the ef- Hudson and Mahle data include the values fects of both chemistry and vertical eddy of band oscillator strengths and rotational transport: Oz, nitrous oxide (N20), and the linewidths for the Schumann-Runge band odd nitrogen species (NOx), which we system from which the transmittance and define as the sum of nitric oxide (NO), nit- rate of dissociation of molecular oxygen as rogen dioxide (NOD, and nitric acid functions of temperature and oxygen col- (HNO3). The vertical distribution of the rap- umn density have been calculated. For all idly reacting atmospheric species (O, the photodissociation rates, the incident O(1D), H, OH, HO2, and H202) is deter- solar flux is attenuated by 02, Oa, H20, mined solely by chemistry, which for these COz, and CH4 absorption and is calculated species is considerably faster than trans- in 1-km altitude intervals between the sur- port. The production and loss terms for all face and 80 km. All of the photodissociation of the species are summarized in the Ap- calculations are diurnal averages for a pendix. The vertical distribution of the fol- specified latitude and solar declination lowing species are specified as input pa- based on the procedure of Rundel (1977). rameters: H20 (London and Park, 1974), Unless otherwise noted, all of the calcula- COs (Stewart and Hoffert, 1975), and CH4 tions in this paper are for a latitude of 30° (Wofsy, 1976; Liu and Donahue, 1974). and for a solar declination of 0° (equinoctial In the present atmosphere the H20 vapor conditions). mixing ratio above the tropopause is con- In the model, the following species pro- trolled by the tropopause temperature--the files are calculated using a time- so-called "cold trap." A tenfold increase in independent or steady-state species con- the H20 vapor mixing ratio above the 298 LEVINE, HAYS, AND WALKER

TABLE II CHEMICAL REACTIONS

No. Reaction Rate constant Reference (cm z sec -1 or cm ° sec -1)

1 O + 02+ M--* O3 + M 1.1 × 10 -a4 exp (510//) Huie et al. (1972) 2 O + Oa--* 202 1.9 × 10 -11 exp (-2300//) CIAP Monograph I (1974) 3 OCD) + Oz --~ 202 1.2 x 10 -1° Hudson (1977) 4 O(1D) + M--~O + M 2.0 x 10 -11 exp (107/10 Hudson (1977) 5 N20 + O(ID)--~ 2NO 5.5 × 10 -11 Hudson (1977) 6 N20 + O(ID) ~ Nz + O2 5.5 x 10 -u Hudson (1977) 7 NO + O + M~NO2+ M 1.55 x 10 -32 exp (584/10 Hudson (1977) 8 NO + Oa~NO2+ 02 2.1 × 10 -12 exp (- 1450/10 Hudson (1977) 9 NO2+ O--~O2+ NO 9.1 x 10 -lz Hudson (1977) 10 NO2 + 03 ~ NOa + 02 1.2 × 10 -13 exp (-2450/10 Hudson (1977) 11 NO + HOz~NO2+ OH 8 × 10 -12 Hudson (1977) 12 NO2+ OH+ M--,HNOz+ M 2.76 x 10 -13 exp (880//)/ (1.17 × 10 Is exp {222/T + [M]}) Hudson (1977) 13 HNO3 + OH ~ NO3 + H20 8 × 10 -14 Hudson (1977) 14 H20 + O(1D) --' 2OH 2.3 × 10 -l° Hudson (1977) 15 H + O2 + M--~ HO2+ M 2.1 × l0 -a2 exp (290/10 Hudson (1977) 16 H + Oa--~OH + 02 1.2 × 10 -1° exp (-560/10 Hudson (1977) 17 OH + O--~ H + 02 4.2 × 10 -11 Hudson (1977) 18 OH + Oa~ HO2 + 02 1.5 x l0 -12 exp (- 1000//) Hudson (1977) 19 OH + OH~H~O + O 1 × 10 -11 exp (-550/10 Hudson (1977) 20 HO2+ O--~OH + O2 3.5 x l0 -11 Hudson (1977) 21 HO2 + 03---' OH + 202 7.3 × l0 -14 exp (-1275/T) Hudson (1977) 22 HO2 + OH --~ H20 + 02 3 × 10 -11 Hudson (1977) 23 HO2 + HO2~ H202 + O2 2.5 × 10 -12 Hudson (1977) 24 H202 + OH --~ HO2 + H20 1 x 10 -11 exp (-750/10 Hudson (1977) 25 H202 + O--~ OH + HO2 2.75 × 10 -12 exp (-2125/T) Hudson (1977)

tropopause requires a tropopause tempera- Another specified input parameter is the ture increase of 15°K (Visconti, 1977). It temperature profile of the paleoatmo- does not appear that the tropopause tem- sphere. Walker (1977) concluded that in the perature is strongly affected by even large absence of Oa, the paleoatmosphere had a variations in 03 (Manabe and Strickler, troposphere much like the present one and 1964). To determine the sensitivity of evolv- a more or less isothermal stratosphere and ing O3 to the choice of a H20 vapor profile, mesosphere. Following the procedure of we have performed calculations for the pre- Ratner and Walker (1972), we did not at- sent atmospheric H20 vapor mixing ratio tempt to evaluate temperature profiles in and for H20 vapor profiles equal to ~0 and the stratosphere and mesosphere as 02 and 10 times the present H20 vapor profile of Oa built up to present levels. Instead, we London and Park (1974). Since it is beyond used two limiting cases. We used the tem- the scope of this study to evaluate the eddy perature profile of the U.S. Standard Atmo- diffusion coefficient profile of the paleoat- sphere (midlatitude spring/fall temperature mosphere (there is some debate in the liter- profile) for oxygen levels equal to or greater ature concerning the eddy diffusion profile than l0 -I of the present atmospheric level in the present atmosphere), we have used (PAL) of 02 and a "primordial" tempera- the profile of McElroy et al. (1974) in all of ture profile for 02 levels less than 10 -1 PAL. the calculations presented here. The "primordial" temperature linearly de- EVOLUTION OF OZONE 299 creases from the tropopause (15 km) to the RESULTS mesopause (90 km), resulting in an almost The Evolution of 03 isothermal stratosphere. As noted by Ratner and Walker (1972), the effectiveness The vertical distribution of 03 as 02 of O3 absorption in producing a strato- evolved from 10 -4 to 1 PAL and for an 02 spheric temperature increase becomes level of 2 PAL for 30 ° latitude and equinoc- smaller as the 03 layer moves down to tial conditions is shown in Fig. 1. Berkner higher pressure levels and is negligibly and Marshall (1965) have suggested that small for O3 density profiles corresponding atmospheric 02 levels may have exceeded 1 to 02-< 10 -1 PAL. These changes in PAL before the present atmospheric level stratopause temperature affect only the was achieved. We see that as the O2 level high-altitude 03 profile. The effect of the increased from 10 -4 to 1 PAL, the height of two temperature profiles on the evolution of the O× peak moved from about 5 to about 25 total 03 will be discussed. km. Our calculations indicate that maxi- While we are fully aware of the lim- mum O× densities at the surface and through itations of one-dimensional photochemical the troposphere were achieved for an 02 models in trying to describe the three- level of 10 -1 PAL. We calculate surface and dimensional atmosphere, especially in light tropospheric 03 densities of about 5 × 1012 of the fact that the dominant atmospheric cm -3 for an 02 level of 10 -1 PAL compared motions are horizontal, not vertical, we be- to densities of about 5 × 1011 cm -3 in the lieve for the following reasons that a one- present atmosphere. dimensional model is an appropriate tool in The large surface and tropospheric 03 our study: (1) the chemical evolution of the densities (about 5 × 1012 cm -a) in the atmosphere can adequately be studied with paleoatmosphere found in this study were a one-dimensional photochemical model, not found in the previous studies. Ratner and (2) our lack of knowledge of motions and Walker (1972) reported maximum sur- and dynamics of the paleoatmosphere pre- face Oa densities of about 1 x 1012 cm -3 cludes a multidimensional study at the pres- based on their calculations using the Chap- ent time. man reactions. Hesstvedt et al. (1974) found

ALTITUDE kln 70

i 108 109 1O10 1011 1012 1013 [03] (crn-3)

FIG. 1. The vertical distribution of Os as a function of atmospheric O~ level. 300 LEVINE, HAYS, AND WALKER maximum surface 03 densities of less than The evolution of the total O3 column 3 × l0 I° cm -3 for calculations assuming above the Earth's surface as a function of photochemical equilibrium (no transport) 02 level is shown in Fig. 2. The calculation and found maximum surface O3 of about of Berkner and Marshall (1965) is shown as 7 × 101~ cm -3 with the identical chemistry, the broken line curve 1, and our calculation but including vertical eddy transport. Blake for 30° latitude and equinoctial conditions is and Carver (1977), assuming photochemical shown as the solid line curve 2. The maxi- equilibrium in their study, reported maximum in total Os column for an 02 level of mum surface 03 densities of 2 × 10'" cm -3 10-' PAL, which is contrary to the Berkner for the present atmosphere and smaller sur- and Marshall results, was first pointed out face O8 levels for reduced Oz levels. The by Ratner and Walker and later confirmed enhanced surface and tropospheric 08 den- by Blake and Carver. The 03 maximum for sities calculated in our study are due in an Oz level of 10 -1 PAL resulted from the part to the inclusion of vertical eddy diffu- deeper penetration of solar ultraviolet radia- sion. The importance of vertical eddy tion responsible for the production of O via transport on the distribution of 08, particu- the photodissociation of 02. The enhanced larly below the 08 peak, has been discussed number of third bodies (M) at the lower al- by Nicolet (1975). The importance of verti- titude favored the more efficient formation cal eddy transport is also clearly seen in the of 03 via the three-body reaction: O + Oz + calculations of Hesstvedt et al. (1974). M ---> 03 + M. Solar radiation -<242 nm is Using identical chemical schemes, they re- responsible for the photolysis of 02 and the ported an increase in surface O8 of more production of O, and hence 03, via the than 2 orders of magnitude for an 02 level of three-body recombination, while solar radi- 10 -I PAL when vertical eddy transport was included in their calculations compared to 1020_ their photochemical equilibrium calculations (no transport). .z--1 1019 Of all tropospheric species, O8 comes closest to being naturally present at toxic I levels (Chameides and Walker, 1975). Many lO18 ii / varieties of plant life are extensively dam- OZONE aged when exposed to O8 concentrations COLUMN only two or three times greater than the DENSITY lO17 present average ambient concentrations. (cm-2) Chameides and Walker (1975) examined the 1016 possible variation of tropospheric O8 over geological time. They considered how changes in the CH4 production rate over 1015 geological time would affect the production of O8, and concluded that a tenfold increase 1014 in the CH4 production rate would cause a I. BERKNERAND MARSHALL (1965) fourfold increase in the tropospheric con- 2. 30° , EQUINOCTIAL centration of O8 for the present level of 02. 1013 l I L I , I ,. ,I Our calculations indicate much larger 10-6 10 "4 10 -2 1 102 tropospheric levels of Os than calculated by 02 LEVEL(P.A.L.) Chameides and Walker, corresponding to an Oz level of 10 -1 PAL. The toxic effects of FIG. 2. The total Oa column above the Earth's surface as a function of atmospheric 02 level: comparison these enhanced levels of tropospheric Os of results of Berkner and Marshall (1965) with the pres- may have had significant adverse effects on ent study. Curve 1 is from Berkner and Marshall; both animal and plant life. curve 2 is for 30 ° latitude, equinoctial conditions. EVOLUTION OF OZONE 301 ation < 1100 nm is responsible for the photo- 2 x 10 -5 sec-' for an O2 level of 10 -1 PAL lytic destruction of Oz. For an 02 level of to a value of about 7 x 10 -5 sec -1 for an 02 10 -1 PAL, the increased production of 03 level of 10 -4 PAL. The largest increase in resulting from the enhanced penetration of the 03 photodissociation rate constant was solar ultraviolet radiation is not accom- found for J4, where the surface value in- panied by a corresponding increase in the creased from about 5 × 10 -7 sec -1 for an Oz solar radiation responsible for the photoly- level of 10 -1 PAL to about 3 × 10 -z sec -1 tic loss of 03 and hence 03 maximized. For for an 02 level of 10 -4 PAL. The effect of O2 02 levels less than 10 -1 PAL, the photolytic and 03 for 02 levels ranging from 10 -4 to 2 destruction of Oz exceeded the production PAL on the vertical distribution of J4 can be of 03 via the photolysis of 02, and 03 de- seen in Fig. 4. creased with decreasing Oz level. For all of our 03 calculations, we have The deeper penetration of solar ul- assumed a zero flux of 03 into the surface. traviolet radiation in the Oz-deficient Any nonzero flux condition requires knowl- paleoatmosphere resulted in the efficient edge of the composition and the surface photolysis of 02 and Oz. The vertical profile chemistry at the Earth's surface, as well as of the photodissociation rate constant of J3 knowledge of the land vs water distribution (02:205-242 nm) for 02 levels ranging from of the early Earth. An identical zero flux 10 -4 to 2 PAL is shown in Fig. 3. We see assumption was made by Liu and Donahue that at 15 kin, the photolysis rate constant (1976) in their study of the 03 budget of the of Oz increased more than 6 orders of mag- Martian atmosphere (in which they calcu- nitude as Oz was decreased from 1 to 10 -4 lated 03 densities at the Martian surface not PAL. unlike those that we find for the Oz-deficient The photodissociation of 03 was divided paleoatmosphere). Liu and Donahue into three spectral intervals depending on showed that for the other extreme assump- the photolytic products, as shown in Table tion, i.e., if every 03 molecule striking the I: J4 (110-310 nm), J5 (310-360 nm), and J6 surface is lost to the surface, then the total (360-735 nm). The value of J6 was found to Oz column is only decreased by about 50%. be constant (about 1.8 × 10 -4 sec -1) at all Clearly, a surface flux value between the altitudes for all 02 levels. The surface value two extreme assumptions will result in less of J5 was found to increase from about than a 50% decrease in the total 03 column.

ALTITUDI km 60-- 300 . EQUINOCTIAL 5O

0 I 10-16 10-15 10-14 10-13 10-12 10-11 10-10 10~ PHOTODISSOCIATION RA1E OF 02. .13(205-242 nm) (sec-1)

FIG. 3. The vertical distribution of photodissociaUon rate constant of J3 (O~: 205-242 nm) as a function of atmospheric 02 level. 302 LEVINE, HAYS, AND WALKER

ALTITUDE, km

10-7 10-6 10-5 10-4 10-3 10-2 10-1 100 PHOTODISSOCIATION RATEOF 03, .14(110-310 nml (sec"11

FIG. 4. The vertical distribution of photodissociation rate constant of J4 (03:110-310 nm) as a function of atmospheric O2 level.

Due to the many uncertainties associated Kz profile for all reduced levels of 02. These with the choice of a nonzero flux condition calculations indicate that the total 03 col- and the results of Liu and Donahue, we be- umn in the O2-deficient paleoatmosphere lieve that the choice of the zero flux is a was more sensitive to the NOx level than to reasonable one in our calculations. the HzO vapor level. However, as dis- We have also examined the sensitivity of cussed in the following section, N20 (even the total 03 column to variations in the as- at present atmospheric levels) was not an sumed model input parameters (NOx, H20, important source of NOx in the O2-deficient and Kz). For reduced levels of NO~ (one- paleoatmosphere. In addition, it appears tenth of the present atmospheric level), the that cosmic rays and solar proton events total 03 column was found to increase by were not important sources of NO~ in the 15, 30, and 100% for O3 levels of 10 -1, 10 -z, Oz-deficient paleoatmosphere (Blake and and 10 -3 PAL, respectively. For a reduced Carver, 1977). H20 vapor profile (one-tenth of the present Our calculations suggest the following atmospheric H20 vapor mixing ratio pro- scenario for the factors that controlled the file), the total 03 column was found to in- evolution of 03 in the O2-deficient paleoat- crease by 3, 5, and 40% for 02 levels of mosphere. For O3 levels ranging from 10 -4 10 -1, 10 -2, and 10 -~ PAL, respectively. For to 10 -2 PAL, the evolution of 03 was an enhanced H20 vapor profile (10× PAL), primarily controlled by HO~ chemistry. the total 03 column was found to decrease Once the 02 level reached 10 -1 PAL, N20 by 5, 25, and 50% for O2 levels of 10 -1, 10 -z, was no longer photolytically lost and be- and 10 -3 PAL, respectively. For an in- came a significant source of NOx. At this creased Kz profile [10 times the standard point, NO~ replaced HO~ as the major con- profile of McElroy et al. (1974)], the total 03 troller of the total 03 column. column was found to increase by about 25% for an 02 level of 10 -1 PAL. No significant The Evolution of Nitrogen and Hydrogen changes in the total 03 column were found Species for the 10 Kz profile for 02 levels less than In the present atmosphere, N20 is de- 10 -1 PAL. Similarly, no significant changes stroyed via photolysis yielding N2 + O(1D) in the total 03 column were found for a 1'0 and via oxidation by O(1D) yielding 2 NO. EVOLUTION OF OZONE 303

This production of NO is the dominant 70 source of stratospheric NOx. Our calcula- I~ 30° . EQUINOCTIAL tions indicate that for reduced levels of Oz 6C and corresponding O3 levels, the photolytic 5C destruction of N20 becomes extremely efficient below 20 km, thereby reducing the 4O main source of stratospheric NO~. The ALTITUDE, km combined effect of 02 and 03 levels on the 3O photodissociation rate of N20 (J8), which controls the photolytic destruction of N20, 20 at the expense of NO formation, can be seen in Fig. 5. The fact that the surface and 10 lower tropospheric values of J(N20) for an 0 O2 level of 10 -1 PAL are slightly less than I0-9 10-8 i0-7 i0"6 the values for an O2 level of 1 PAL results N20 MIXING RATIO from the fact that total atmospheric 03 maximizes for the 10 -1 PAL case. Inspec- FIG. 6. The vertical distribution of the NzO mixing ratio as a function of atmospheric 02 level. For all tion of Fig. 5 shows that in the present at- calculations the lower boundary mixing ratio was mosphere, the photodissociation rate con- 3.2 x 10 -7. stant of N20 is about 10 -r sec -1 at about 35 km. For an 02 level of 10 -1 PAL this same (3.2 × 10 -7) as the lower boundary for all of photodissociation rate constant is achieved the calculations shown in Fig. 6. Inspection at about 25 km, at about 15 km for an 02 of Fig. 6 shows that comparable N20 mix- level of 10 -2 PAL, and at the surface for an ing ratios (10 -8) are found above 55 km in 02 level of 10 -a PAL. The profile of N~O the present atmosphere and below 20 km mixing ratio for various 02 levels is shown for an 02 level of 10 -2 PAL. in Fig. 6. Due to our lack of knowledge con- This is the first study of the evolution of cerning the N20 surface mixing ratio ap- O3 to include N20, the main source of propriate for the primordial atmosphere, we stratospheric NOx, which is the dominant have used the present surface mixing ratio 03 destruction species in the present atmo-

ALTITUDE km 60 300 , EQUINOCTIAL

lO // lO; lO- o ,,. ,,,X,, ?lJ ,,, ,, 10-12 I0"II i0-I0 10-9 10-8 10-7 10-6 10-5 PHOTODISSOCIATIONRAll~ OF N20, J(N20) (sec -11

FIG. 5. The vertical distribution of the photodissociation rate constant of N20 (J8) as a function of atmospheric 02 level. 304 LEVINE, HAYS, AND WALKER sphere. In O2-deficient atmospheres, we found to decrease with decreasing 02 level. have found that N20 (even at present at- This is opposite from the effect we found mospheric mixing ratios) produces much for the hydrogen species (H, OH, and HO2) less NO~ than it does in the present atmo- where, at a given altitude, the number den- sphere. In addition, we found that NO~ was sity was found to increase with decreasing not an important 03 destruction species in O2 and 03 levels. O2-deficient atmospheres. We found that The efficient transmission of solar uv into the rapid photolytic destruction of N20 re- the lower stratosphere and troposphere, suited in negligible production of NOx via which results in the rapid photolytic loss of the oxidation of N20 which, in turn, rele- O3 and N20 [and production of O(1D)], at gated NO~ catalytic destruction of O3, per- the same time results in the extremely effi- haps the major Oa destruction process in the cient production of OH via the photolysis of present atmosphere (Johnston, 1975), to a H~O and the oxidation of H20 by O(1D). negligible role for reduced O~ levels. In past The combined effect of O~ and 03 on the studies N20 was neglected due to biological photodissociation rate constant of H=O (J7), considerations because it was assumed that which results in the photolytic production nitrogen fixation and the subsequent den- of OH, can be seen in Fig. 8. Inspection of trification of N20 by soil bacteria was not Fig. 8 shows that in the present atmo- important in the Earth's early history. sphere, the photodissociation rate constant Now, based on aeronomical considerations, of H20 is about 10 -9 sec -~ at about 45 km. we have found that N~O was not important For an 02 level of 10 -1 PAL, this photodis- in controlling early 03 levels, regardless of sociation rate constant is achieved at about the level of bacterial dentrification of N20. 30 kin, at about 17 km for an 02 level of The effects of the O2 and 03 levels on the about 10 -2 PAL, and at about 10 km for an vertical distribution of the odd nitrogen 02 level of 10 -3 PAL. The profile of OH species (NO + NO2 + HNO3) for the same resulting from the photolysis of H20 and surface mixing ratio (3.0 x 10 -9) are shown from the reaction of O(1D) with H20 for var- in Fig. 7. At a given altitude, the number ious O2 levels is shown in Fig. 9. Inspection density of the odd nitrogen species was of Fig. 9 shows that OH concentrations in

ALTITUD[ km 70

40 i 30

20I

0 , , I , , I , ~ I 107 10s a09 x010 a0~l 101z [NOX]:[NO] +[NO2]+[HNO 3] (cm"31

FIG. 7. The vertical distribution of NO~(NO + NO2 + HNOa) as a function of atmospheric 02 level. For all calculations the lower boundary mixing ratio was 3.0 x 10 -9. EVOLUTION OF OZONE 305

ALTITUDE km 60- 50 300 , EQUINOCTIAL S

0 ..... I , , I , , I , , I , , I , , I 10-15 10-14 10"13 10-12 10-11 10-10 -1 10"9 10"8 PHOTODISSOCIATIONRATE OF H20, J(H20) (sec)

FIG. 8. The vertical distribution of the photodissociation rate constant of H20 (JT) as a function of atmospheric 02 level. the troposphere and lower stratosphere in- an almost identical percentage decrease (increased by about 4 orders of magnitude as crease) in 03 density beginning about 10 km the 02 level was reduced from 1 to 10 -4 above the 03 peak for all reduced 02 levels. PAL. The increase (decrease) in total 03 result- CONCLUSIONS ing from a decrease (increase) in the as- Some of the new findings of our investi- sumed HzO vapor profile previously dis- gation are: cussed is a direct consequence of decreased (increased) formation of OH via the photo- (1) Surface and tropospheric Oa densities lysis and oxidation of H20. The percentage of the paleoatmosphere exceeded those of increase (decrease) in OH density results in the present atmosphere by about a factor of

ALTITUDE km 70 300 , EQUINOCTIAL 6O

1O ,2 i0 )-4

0 l 10 ad lO6 lO7 lo8 lO9 [OH] (crn"3)

FIG. 9. The vertical distribution of OH as a function of atmospheric 02 level. 306 LEVINE, HAYS, AND WALKER

10. Our calculations indicate maximum sur- which was used to calculate the vertical dis- face and tropospheric 03 densities of about tribution of the transported species Oa, 5 × 10 ~2 cm -a for an 02 level of 10 -1 PAL, N20, and NOx is compared to surface Oz densities of 5 × 10 u cm -z in the present atmosphere. Od~,/Oz = Q,(nj) - L,(nj)Mf~, (1) (2) Surface and tropospheric OH den- where f~ is the volume mixing ratio of the ith sities of the paleoatmosphere exceeded species, qS, is the vertical flux (molecules those of the present atmosphere by several cm -z sec -1) of the/th species, Q~(nj) are the orders of magnitude. Maximum surface and chemical production terms and L~(nj)Mf~ are tropospheric OH densities approached 109 the chemical loss terms of the /th species. cm -z for an Oz level of 10 -a PAL, compared The volume mixing ratio f~ is related to n~, to surface and lower tropospheric OH den- the number density of the fth species (mole- sities of about 10 n cm -a in the present cules cm -a) by atmosphere. f~ = n~/M, (2) (3) In the O2-deficient paleoatmosphere, NzO (even at present atmospheric levels) where M is the total number density (mole- produces much less NOx than it does in the cules cm-3). present atmosphere. The vertical flux of the /th species ~b~ can (4) The evolution of 03 in the paleoat- be expressed as mosphere was controlled by the efficient 4,, = -KzM[(Of,/Oz)], (3) transmission of solar ultraviolet radiation through the lower stratosphere and tropo- where Kz is the vertical eddy diffusion coef- sphere. The enhanced level of ultraviolet ficient (cm 2 sec-l). Substituting Eq. (3) into radiation was responsible for the photolytic Eq. (1) we get destruction of 03 and NzO and the en- (OlOz)[K=M(Of~l Oz) ] hanced production of the hydrogen species. (5) The evolution of total 03 as a function = -Qi(ns) + Li(ns)Mfi. (4) of Oz level was fairly insensitive to the as- The vertical distribution of the rapidly sumed model input parameters (N20 level reacting atmospheric species O, O(ID), H, and temperature and H20 vapor profiles). OH, HO2, and H202 is determined solely by We also verified the results of the earlier chemistry, which, for these species, is con- studies of Ratner and Walker, and Blake siderably faster than transport. For these and Carver that Oz evolved to a greater species, we can neglect the transport terms level for a given 02 level than indicated by of the continuity equation [the left side of Berkner and Marshall; or alternatively, that Eq. (4)] and equate the chemical production 03 evolved earlier in the Earth's history to the chemical loss, and solve for the than suggested by Berkner and Marshall. species mixing ratio f using the photochem- The earlier rise of O3 in the history of 02 ical equilibrium assumption evolution undoubtedly had important impli- fi = Qi(nj)/Li(nj)M. (5) cations for biological evolution on our planet. The precise implications must wait N20 is produced by soil bacteria during until we have a better understanding of the dentrification. The main source of strato- exact chronology for the evolution of 02. spheric NO is the oxidation of N20 by O(1D) (Bates and Hays, 1967; Crutzen, 1970; APPENDIX: DESCRIPTION OF McElroy and McConnell, 1971). Assuming PHOTOCHEMICAL MODEL photochemical equilibrium, O(~D) is calculated by The form of the time-independent or steady-state species continuity equation [O(1D)] = J4[O3]/k4[m]. (6) EVOLUTION OF OZONE 307

Most of the N20 is simply photolyzed to N2 (10) are determined by species other than and O(1D). nitrogen and nitrogen-oxygen compounds. For the N20 continuity equation, the Unfortunately, such a simplification does chemical loss term L~(nj) in the general form not exist in the hydrogen chemistry. of the continuity equation in Eq. (4) has the In the case of the hydrogen species there form are many nonlinear terms of H, OH, HO2, and H2Oz, and they are not necessarily L,(nj) = {Js + (ks + kn)[O('D)]}. (7) smaller than the linear terms, although The only stratospheric chemical source some of them are small at particular for NO~ is the oxidation of N20. Further- heights. Hence it is very difficult to specify more, there are no stratospheric chemical concentration ratios which would be both sinks for NO~; all reactions simply involve simple and applicable to the entire strato- interconversions of species in the NO~ fam- sphere. Thus, the scheme used for the NOx ily. Tropospheric rainout of HNO3 is the family is not applicable for the hydrogen major atmospheric sink for NO~ resulting in species. However, in the stratosphere (and an NOx surface mixing ratio of about troposphere) H, OH, HO2, and HzO2 are in 3 x 10 -9, an order of magnitude smaller photochemical equilibrium (London and than the stratospheric mixing ratio of NO~. Park, 1974). The vertical profiles of H, OH, For the NO~ continuity equation, the chem- HOz, and H202 can be calculated by the ical production term Q~(nj) in the general simultaneous solution of Eqs. (12)-(15) as- form of the continuity equation in Eq. (4) suming photochemical equilibrium (London has the form and Park, 1974)

Q~(nj) = {2ks[O(~D)]} [N20]. (8) [H] = {k,8[O][OH] + JT[H20]}/ These facts result in a simplified approach {ka6[O3] + k,5[Oz][M]}, (12) to the calculation of the vertical profiles of NO, NO2, and HNO3, by far the dominant [HO2] = {kAO3][OH] species of NO~ within the stratosphere. The + k24[H202][OH] + klz[H][O2][M]}/ distribution of NO~ is determined using {k20[O] + k2,[O3] + kz2[OH] continuity Eq. (4). Next, NOx is divided + 2kz3[HO2] + kH[NO]}, (13) among NO, NOz, and HNOz by the ratios (Shimazaki and Ogawa, 1974; and Hudson, [OH] = ({Jr[H,O] + J~[H20,] 1977) + k,4[O('D)][H20]}/ ~'1 = [NO]/[NO2] ~ {J12 {k,a + k22[HO2]/[OH] + k23[HO2]Z/ + k9[O]}/{ks[Oz] + k,l[H02]}, (9) [OH] z + k13[HNOz]/[OH]}) ~/2, (14) rz = {[NO] + [NO2]}/[HNO3] ~ {(J9 + J~o) [H~O~] + k~3" [OH]}(1 + rO/k,2[OH][M]. (10) = kzs[HO2][HO2]/kz4[OH] + J13. (15) The vertical distribution of O required in Eqs. (9) and (10) is calculated assuming A continuity equation for stratospheric photochemical equilibrium and given by and mesospheric O3, including the effect of NOx and HOx species, can be written with [O] = {2(J, + Jz + J3)[O2] the following 03 chemical production + (J, + J5 + Jn)[O3] + J,2[NO2]}/ [Qi(nj)] and loss [L~(nj)] terms expressed as {k,[O2][M] + k2103] + kit[OH] (Nicolet, 1975) + k2o[HO2] + kg[SOz]}. (ll) Q,(nj) = k,[M][O2][O] (16) Note that the ratios given in Eqs. (9) and and 308 LEVINE, HAYS, AND WALKER

Li(nj) = {J4 + J~ + Jo + ks[O] Models and Related Experiments (G. Fiocco, Ed.), + ks[NO] + k,o[NO2] + kin[H] pp. 149-159. Reidel, Dordrecht. BATES, D. R., AND HAYS, P. B. (1967). Atmospheric + k,s[OH] + k21[HO2]}. (17) nitrous oxide. Planet. Space Sci. 15, 189-196. BERKNER, L. V., AND MARSHALL, L. C. (1965). On the For a given level of 02, a "first guess" origin and rise of oxygen concentration in the profile of Oz was calculated using the Earth's atmosphere. J. Atmos. Sci. 22, 225-261. Chapman scheme, identical to the proce- BLAKE, A. J., AND CARVER, J. H. (1977). The evolu- dure of Ratner and Walker (1972). The first tionary role of atmospheric ozone. J. Atmos. Sci. 34, guess Os profile was then used to calculate 720-728. CHAMEXDES, W., AND WALKER, J. C. G. (1975). Possi- the 13 photodissociation rates shown in ble variation of ozone in the troposphere during the Table I. Next, the profiles of N20 and NOx course of geologic time. Amer. J. Sci. 275, 737-752. (NO + NO2 + HNOz) were calculated via CRUTZEN, P. J. (1970). The influence of nitrogen the continuity equation, using a standard oxides on the atmospheric ozone content. Quart. J. tridiagonal solver, based on the Gaussian Roy. Meteorol. Soc. 96, 320-325. DIXON, J. K. (1940). The absorption coefficient of ni- elimination method without pivoting trogen dioxide in the visible spectrum. J. Chem. (Smith, 1965). The profiles of H, OH, HO2, Phys. 8, 157-160, and H202 were next calculated simulta- GRIGGS, M. (1968). Absorption coefficients of ozone in neously using the standard Newton- the ultraviolet and visible regions. J. Chem. Phys. Raphson method (Smith, 1965). Next, the 49, 857-859. HALL, T. C., AND BLACET, F. E. (1952). Separation of Os profile was recalculated via the con- the absorption spectra of NOz and NzO4 in the range tinuity equation, including the effect of ni- of 2400-5000 ~. J. Chem. Phys. 20, 1745-1749. trogen and hydrogen species. The new Oz HART, M. H. (1978). The evolution of the atmosphere profile was then used to recalculate the of the Earth. Icarus 33, 23-39. photodissociation rates and all of the HASSON, V., AND NICHOLLS, R. W. (1971). Absolute spectral absorption measurements on molecular species profiles. The iterative process con- oxygen from 2640-1920/~. 2. Continuum Measure- tinued until the convergence condition (a ments 2430-1920 /~. Proc. Phys. Soc. London At. change in 03 of less than 0.1% at all al- Molec. Phys. 4, 1789-1997. titudes on successive iterations) was HESSTVEDT, E., HENRIKSEN, S. E., AND HJARTAR- achieved. SON, H. (1974). On the development of an aerobic atmosphere. A model experiment. Geophysica Nor- vegica 31, 1-8. ACKNOWLEDGMENTS HUDSON, R. D. (1977). Chlorofluoromethanes and the It is a pleasure to acknowledge Ms. Kathryn A. Stratosphere. NASA Reference Publication 1010. Smith of the Langley Research Center for her impor- HUDSON, R. D., AND MAHLE, S. H. (1972). Photodis- tant contributions and expert support in the numerical sociation rates of molecular oxygen in the and computational aspects of this study. John E. mesosphere and lower thermosphere. J. Geophys. Hogge and John N. Shoosmith of Langley also assisted Res. 77, 2902-2914. on various numerical aspects of this investigation. HUIE, R. E., HERRON, J. T., AND DAVIS, D. D. (1972). Marvin R. Libson of Integrated Services, Inc. (ISI), Absolute rate constants for the reaction O + Oz + M Hampton, Virginia, was a continual source of many Oz + Mover the temperature range 200-346°K. J. enlightening discussions, and Fred M. Smith of Phys. Chem. 76, 2653-2658. Langley made most constructive comments in the pre- INN, E. C. Y., AND TANAKA, Y. (1953). Absorption paration of this manuscript. We would also like to ac- coefficients of ozone in the ultraviolet and visible knowledge the contributions of William R. Kuhn and regions. J. Opt. Soc. Amer. 43, 870-873. Herschel Weil (both of the University of Michigan), JOHNSTON, H. S. (1975). Global ozone balance in the Richard S. Stolarski (Goddard Space Flight Center), natural stratosphere. Rev. Geophys. Space Phys. and the continued support provided by Robert H. Tol- 13, 637-649. son and James D. Lawrence, Jr., of Langley during the JOHNSTON, H. S., AND GRAHAM, R. (1974). Photo- course of this study. chemistry of NOx and HNOx compounds. Canad. J. Chem. 52, 1415-1423. JOHNSTON, H. S., AND SELWYN, G. S. (1975). Cross REFERENCES sections for the absorption of near ultraviolet radia- ACKERMANN, M. (1971). Ultraviolet solar radiation re- tion by nitrous oxide (N20). Geophys. Res. Lett. 2, lated to mesospheric processes. In Mesospheric 549-551. EVOLUTION OF OZONE 309

LIu, S. C., AND DONAHUE, T. M. (1974). The traviolet absorption by nitric acid vapor. Nature aeronomy of hydrogen in the atmosphere of the 238, 109. Earth. J. Atmos. Sci. 31, 1118-1136. SCHORGERS, M., AND WELGE, K. H. (1968). Absorp- LIU, S. C., AND DONAHUE, T. M. (1976). The regula- tion Koeffizient yon H202 Zwischen 1200 and 2000 tion of hydrogen and oxygen escape from Mars. ,~, Z. Naturforseh. A. 23, 1508-1510. Icarus 28, 23 i-246. SmMAZAKI, T., AND OGAWA, T. (1974). A theoretical LONDON, J., AND PARK, J. H. (1974). The interaction model of minor constituent distributions in the of ozone photochemistry and dynamics in the stratosphere including diurnal variations. J. stratosphere. A three-dimensional atmospheric Geophys. Res. 79, 3411-3423. model. Canad. J. Chem. 52, 1599-1609. SMITH, G. D. (1965). Numerical Solution of Partial MANABE, S., AND STRICKLER, R. F. (1964). Thermal Differential Equations. Oxford Univ. Press, London. equilibrium of the atmosphere with a convective ad- STEWART, R. W., AND HOFFERT, M. I. (1975). A justment. J. Atmos. Sci. 21, 361-385. chemical model of the troposphere and stratosphere. MCELROY, M. B., AND MCCONNELL, J. C. (1971). J. Atmos. Sci. 32, 195-210. Nitrous oxide: A natural source' of stratospheric The Natural Stratosphere of 1974. CIAP Monograph I. NO. J. Atmos. Sci. 28, 1095-1098. Final report prepared for the Climatic Impact As- MCELROY, M. B., WOFSY, S. C., PENNER, J. E., AND sessment Program, Dept. of Transportation, Wash- MCCONNELL, J. C. (1974). atmospheric ozone: Pos- ington, D.C. sible impact of stratospheric aviation. J. Atmos. Sci. U.S. Standard Atmosphere (1962). U.S. Government 31, 287-303. Printing Office, Washington, D.C. NAKAYAMA, T., KITAMURA, M. Y., AND WATANABE, VISCONTI, G. (1977). Hydrogen escape in the terrest- K. (1959). Ionization potential and absorption coeffi- rial atmosphere at low oxygen levels: A photochem- cients of nitrogen dioxide. J. Chem. Phys. 30, 1180-1186. ical model. J. Atmos. Sci. 34, 193-204. NICOLET, M. (1975). Stratospheric ozone: An intro- WALKER, J. C. G. (1977). Evolution of the Atmo- duction to its study. Rev. Geophys. Space Phys. 13, sphere. Macmillan Co., New York. 593-636. WALKER, J. C. G. (1978). The early history of oxygen PAUKERT, T. T., AND JOHNSTON, H. S. (1972). Spectra and ozone in the atmosphere. Pure Appl. Geophys. and kinetics of the hydroperoxyl free radical in the 117, 498-512. gas phase. J. Chem. Phys. 56, 2824-2838. WATANABE, K. (1958). Ultraviolet absorption pro- RATNER, N. I., AND WALKER, J. C. G. (1972). Atmo- cesses in the upper atmosphere. Advan. Geophys. 5, spheric ozone and the history of life. J. Atmos. Sci. 153-221. 29, 803-808. WATANABE, K., AND ZELIKOFF, M. (1953). Absorp- RUNDEL, D. R. (1977). Determination of diurnal aver- tion coefficients of water vapor in the vacuum ul- age photodissociation rates. J. Atmos. Sci. 34, 639- traviolet. J. Opt. Soc. Amer. 43, 753-755. 641. WOFSY. S. C. (1976). Interactions of CH4 and CO in SCHMIDT, S. G., AMME, R. C., MURCRAY, D. G., the Earth's atmosphere. Ann. Rev. Earth Planet. GOLDMAN, A., AND BONOMO, F. S. (1974). UI- Sci. 4, 441-469.