The ozone column depletion over the western coast of South America has been previously explained, based on the existence of winds in the area of the depletion, which cause compression and thinning of the ozone layer. However, the presence of humidity and methane transported by these winds to the stratosphere where the ozone depletion is present gives evidence that these compounds also participate

in the depletion of the ozone layer. These two compounds, humidity and methane, are analysed during the ozone depletion of January, 1998. It is observed that when humidity presents fluctuations, ozone has fluctuations too. A maximum of humidity corresponds to a minimum of ozone, but there is a shift in altitude between them. This shift is observed in the stratosphere and upper troposphere and

corresponds to approximately 500 m. It is important to point out that during this event El Ni˜no was present and the sources of methane are the Amazon forest and the Pacific Ocean. The data for this study was obtained from NASA and HALOE

Da Silva, M. Luis

Gutiérrez, O. Luis

Morales, S. Luis

Torres, C. Arnaldo

English

Scientific Open-access Literature Archive and Repository

DOI 10.1393/ncc/i2005-10163-8IL NUOVO CIMENTO Vol. 29 C, N. 4 Luglio-Agosto 2006Presence of stratospheric humidity in the ozone column depletionon the west coast of South AmericaM. Luis Da Silva(1)(∗), S. Luis Morales(1)(2), O. Luis Gutie´rrez(1) andC. Arnaldo Torres(3)(1) Departamento de F´ısica, Universidad Tecnolo´gica Metropolitana - Av. J. P. Alessandri 1242Santiago, Chile(2) Departamento de Cs. Amb. y Recursos Naturales Ren., Universidad de ChileAv. Santa Rosa 11315, Santiago, Chile(3) Instituto Ignacio Domeyko, Universidad de Playa Ancha - Avda. Playa Ancha 850Valpara´ıso, Chile(ricevuto il 28 Luglio 2005; revisionato il 26 Gennaio 2006; approvato il 28 Gennaio 2006;pubblicato online l’1 Giugno 2006)Summary. — The ozone column depletion over the western coast of South Amer-ica has been previously explained, based on the existence of winds in the area of thedepletion, which cause compression and thinning of the ozone layer. However, thepresence of humidity and methane transported by these winds to the stratospherewhere the ozone depletion is present gives evidence that these compounds also par-ticipate in the depletion of the ozone layer. These two compounds, humidity andmethane, are analysed during the ozone depletion of January, 1998. It is observedthat when humidity presents fluctuations, ozone has fluctuations too. A maximumof humidity corresponds to a minimum of ozone, but there is a shift in altitudebetween them. This shift is observed in the stratosphere and upper troposphere andcorresponds to approximately 500 m. It is important to point out that during thisevent El Nin˜o was present and the sources of methane are the Amazon forest andthe Pacific Ocean. The data for this study was obtained from NASA and HALOE.PACS 92.70.-j – Global change.PACS 92.60.Vb – Radiative processes, solar radiation.PACS 93.30.Jg – Information related to geographical regions: South America.1. – IntroductionFor decades, depletion of the total ozone column over the West Coast of South Americahas been detected. These reductions in total ozone can be observed, especially during the(∗) E-mail: luis.dasilva@utem.clc© Societa` Italiana di Fisica 391392 L. DA SILVA, L. MORALES, L. GUTIE´RREZ and A. TORRESFig. 1. – Map of the distribution of stratospheric ozone that shows the depletion of total ozonecolumn on west side of South America, January 1st, 1998. EP/TOMS Total Ozone (1.0◦× 1.25◦).summer season of the Southern Hemisphere. The area of depletion extends from Ecuadorin the north to latitude 30◦S in Chile [1]. This depletion strip has its lowest total ozoneover the Andes Mountains Range and the width of the depletion strip is from the PacificOcean in the west to the eastern edge of the mountain range. An analysis of the velocityof the winds in this area has shown that there is a vertical component to the wind velocityfrom below up to the ozone layer, compressing it, thereby generating this depletion [2,3].However, it was recently determined that during the presence of this ozone depletionthere was also a high content of humidity present in the same zone. This fact has causedto be considered that if this humidity succeeds in reaching stratospheric regions, it cancause ozone destruction, collaborating in this way in the decline of stratospheric ozoneover the West Coast of South America. Observations of water vapour and ozone in thetropical upper troposphere over Juazeiro do Norte, Brazil (7.2◦S, 39.3◦W), show thatwhen there is an increase of humidity there is a decrease of ozone [4]. In addition, it hasbeen confirmed that for the last fifty years there has been an increase of stratospherichumidity, on the order of a 1%/y increase in stratospheric water vapour [5]. In thisstudy, two compounds that contribute to the stratospheric ozone depletion are analysed.One, the presence of increased amounts of stratospheric humidity over the West Coastof South America and, two, the presence of stratospheric methane in this region. Inparticular, the depletion that was present in January 1998 will be analysed using thedata provided by NASA and HALOE.PRESENCE OF STRATOSPHERIC HUMIDITY IN THE OZONE COLUMN DEPLETION 393Fig. 2. – Map of the distribution of stratospheric ozone that shows the depletion of total ozonecolumn on west side of South America, January 8th, 1998. EP/TOMS Total Ozone (1.0◦×1.25◦).2. – Data analysisDuring the summer of 1997/1998 in the Southern Hemisphere, a depletion of theozone column was present over the West Coast of South America. This event startedFig. 3. – Latitudinal cross-section of the total ozone column at 20◦ S, January 8th, 1998.394 L. DA SILVA, L. MORALES, L. GUTIE´RREZ and A. TORRESFig. 4. – Latitudinal cross-sections of humidity at 20◦ S, January 8th, 1998.on November 6th, 1997 and ended on March 11th, 1998. There were other events thatfollowed which extended further into 1998. Figures 1 and 2 show two situations of thefirst depletion event. Figure 1 shows the depletion on January 1st, 1998 and fig. 2 showsthe depletion on January 8th, 1998. These figures show how this depletion extends alongthe coast of South America, reaching as far as latitude 30◦S. Figure 1 also shows thatthis depletion is confined between the Pacific coast and mountainous chain of The Andes;in contrast, fig. 2 shows a wider strip of ozone depletion as it extends out over the PacificOcean. Shown in fig. 3 is a latitudinal cut of the ozone layer in the area of Arica (20◦S)between the longitudes 80◦W and 60◦W. This graph shows the minimum thickness ofthe layer whose value is 229 DU which is located over the mountain range. Towards theedges of this depletion, a rise in value of the ozone column, such as has been detectedin other studies. This analysis has been conducted at different latitudes and on differentdates of this event, maintaining the characteristics already indicated.In order to determine if there is humidity in the area of this ozone depletion, sev-eral latitudinal humidity graphs during this depletion event were analysed. In fig. 4, alatitudinal cut at 20◦S shows the presence of relative humidity of 40% to 300 mb. Inthis graph, it can be observed that, between 60◦W and 75◦W, there is a high relativehumidity value that reaches as high as 300 mb. This increase is presented as a “chim-ney” of humidity that coincides with the ozone depletion zone. This humidity chimneyis generated by the presence of vertical winds that occur in the zone because of the pres-ence of The Andes Mountain Range. In addition, the graph suggests that this humiditypenetrates the stratosphere. To confirm this suggestion, the data provided by HALOEfor January 8th, 1998 with 18.95◦S / 70.7◦W has been applied. In fig. 5 the humiditydata provided by HALOE between 12.76 km and 84 km of altitude is shown. Also infig. 5, ozone is present at different altitudes. It is observed that when humidity presentsfluctuations, ozone has fluctuations too. The graph of fig. 6 that belongs to Juazeiro doNorte, Brazil (7.2◦S, 39.3◦W), shows similar characteristics with respect to humidity andPRESENCE OF STRATOSPHERIC HUMIDITY IN THE OZONE COLUMN DEPLETION 395Fig. 5. – Satellite humidity and ozone measurements at 18.95◦S/70.7◦ W between 12.76 km and84 km (HALOE), January 8th, 1998.ozone in the upper troposphere but in this case it is clear that when there is a maximumamount of humidity, there is a minimum amount of ozone and vice versa. To be moreevident, the same behaviour in the data of ozone and humidity of HALOE given in thegraph of fig. 5, a graph of the derivate of concentration of compounds with respect tovertical direction. The results are presented in fig. 7. Now, it is possible in this graphto see how variation of humidity corresponds to variation in ozone. The correspondingFig. 6. – Humidity and ozone in the upper troposphere in Juazeiro do Norte, Brasil [4].396 L. DA SILVA, L. MORALES, L. GUTIE´RREZ and A. TORRESFig. 7. – Derivate of concentrations of ozone and humidity with respect to altitude z for dataof HALOE.graphs are almost antisymmetric, except between 29 km and 37 km. An increment ofhumidity corresponds to an ozone depletion. Besides it is important to point out thatthe maximum of humidity is shifted in altitude with respect to the corresponding mini-mum of ozone. Maximum of humidity is always lower in altitude than the correspondingminimum of ozone. This shift is observed in the stratosphere and upper troposphere andit corresponds to approximately 500 m in the vertical direction.Fig. 8. – Satellite methane measurements at 18.95◦ S/70.7◦ W between 14.03 km and 80.40 km(HALOE), January 8th, 1998.PRESENCE OF STRATOSPHERIC HUMIDITY IN THE OZONE COLUMN DEPLETION 397The action of humidity is through a previous reaction with atomic oxygen in anexcited state which is produced through the decomposition of ozone by ultraviolet radia-tion. Humidity plus atomic oxygen generates OH and this, finally, interacts with ozone,destroying the ozone, as is indicated in the followings relations [6]:O3 + hν(λ ≤ 320 nm) → O(1D) + O2O(1D) + H20 → 2OHOH + O3 → HO2 + O2HO2 + O3 → OH + 2O2Analysing the presence of other components at a stratospheric level, methane is ob-served. In fig. 8, methane is shown in ppmv, present in the area of this analysis providedby HALOE. This graph shows CH4 between 14.03 km and 80.40 km of altitude at lat-itude 18.95◦S and longitude 70.7◦W. It is confirmed that methane, through a reactionwith the radical OH, generates humidity and this humidity contributes to the destructionof the ozone. In addition, it has been determined that for each molecule of methane thatoxidises 1.6–2.0 molecules of water vapour are obtained [7,8]. The origin of the methanein the stratosphere can be natural as much as anthropogenic.3. – Conclusion and commentsIt has been previously shown that the depletion of the ozone column over the WestCoast of South America is produced by the compression of the vertical winds that actupon the ozone layer. This analysis shows that there are other components that partic-ipate in the destruction of the ozone layer: stratospheric humidity and methane. Theaction of humidity upon ozone has been confirmed by measurements of ozone and hu-midity on site in other regions. With respect to methane, using measurements in thestratosphere, it has been determined that this contributes humidity after it oxidises andthat one molecule of CH4 produces 1.6 to 2.0 of H2O [7]. It can be established, by hypoth-esis, that these components are transported to the stratosphere by the same winds thatcompress the ozone layer. The existence of this phenomenon is caused by the presenceof The Andes Mountain Range, which serves as a barrier to the winds coming from thePacific Ocean as well as the Amazon Basin. But it shows that the presence of humidity inthe stratosphere affects the ozone: A humidity variation of 1% produces a change of 1.6ppbv of ozone. In addition, there is a shift, in a vertical direction, between the maximumof humidity and the corresponding minimum of ozone and vice versa. In addition thetopographic configuration and winds would give an explanation for high UV radiationin northern Chile and western Bolivia in this region. The sources of methane are theAmazon forest and the Pacific ocean. It is important to point out that this analyseddepletion occurred when El Nin˜o was present. It is not known to what extent El Nin˜ocontributes to the increase of humidity in the stratosphere in this region.REFERENCES[1] Earth Probe 1996-1999, Ozone-Aerosol Data & TOMS, NCEP/NCAR Reanalysis, GlobalAtmospheric Analysis, various year, National Centres for Environmental Prediction(Washington DC and National Center for Atmospheric Research, Version 7, 2000 April,Boulder, CO, USA).398 L. DA SILVA, L. MORALES, L. GUTIE´RREZ and A. TORRES[2] Zaratti F., Andrade M., Forno R. and Palenque E. R., Nuovo Cimento C, 22 (1999)145; and references cited therein.[3] Da Silva L., Nuovo Cimento C, 2 (2002) 35.[4] Vo¨mel H. et al., J. Geophys. Res. D, 14 (2002) 108-18-16.[5] Rosenlof K. H. et al., Geophys. Res. Lett., 28 (2001) 71195.[6] John H. Seinfeld and Spyros N. Padins, Atmospheric Chemistry and Physics (JohnWiley & Sons, Inc) 1998, pp. 171-173.[7] LeTexier H., Solomon S. and Garc´ıa R. R., Q. J. R. Meteorol. Soc., 114 (1988) 281.[8] Russell J. M. et al., J. Geophys., 98 (1993) D6 10.777.

Presence of stratospheric humidity in the ozone column depletion on the west coast of South America

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Presence of stratospheric humidity in the ozone column depletion on the west coast of South America

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