Lỗ hổng ozone có làm nguy hại đến con người hay không ?


Tiến sĩ quốc gia TRẦN ĐÌNH SƠN
(PHÁP)

Theo Báo “Associated Press” đăng ngày 16 tháng 9 năm 2009, chính quyền Obama vừa tuyên bố : “Từ nay Mỹ, Gia Nã Đại và Mễ Tây Cơ sẽ chủ trương biến đổi “Nghị quyết Montreal” (Protocole de Montréal)  về việc bảo vệ lớp ozone thành một công cụ làm giảm các chất hydrofluoro-carbones (HFC). Các hóa chất này là những khí gây ra “hiệu ứng nhà kính” rất mạnh. Trong “Nghị quyết Montreal” với mục đích chống lại “lỗ hổng trong lớp ozone” và có hiệu lực kể từ năm 1989, các nước tham dự đã khuyến khích việc dùng HFC để thay thế CFC (chlorofluoro carbones) trong các máy lạnh, máy điều hòa không khí. Bởi vì chính các khí này (CFC) đã gây ra lỗ hổng ozone nên hiện nay không còn dùng nữa.

Các khí HFC tuy không phá hủy lớp ozone nhiều bằng CFC, nhưng chúng lại làm tăng hiệu ứng nhà kính : năng suất sưởi ấm toàn bộ của HFC lớn gấp 10.000 lần năng suất của khí carbonic  (CO2). Mặc dù thành phần của các khí HFC chỉ vào khoảng 2% trong tất cả các khí sưởi ấm bầu không khí, nhưng vì kể từ đây chúng sẽ được thông dụng nên đến nửa thế kỷ thứ 21 thành phần của chúng có thể sẽ tăng lên đến một phần ba. Vì lẽ đó mà chính quyền Obama cho rằng việc dùng HFC để thay thế CFC là một quyết định vô trách nhiệm.

Báo “Le Monde” đăng ngày 16-09-09 tỏ vẻ lo ngại vì còn chưa đầy ba tháng là đến hội nghị thượng đỉnh về hiện tượng sưởi ấm khí hậu ở Copenhague, sự thương nghị như vậy sẽ bị đình trệ. Tờ Gardian, đăng ngày 15-09-09 còn bi quan hơn, phỏng định rằng cuộc đàm phán sẽ bế tắc do sự bất đồng ý kiến giữa Mỹ và Âu châu.

Nhưng bây giờ chúng ta hãy gác lại một bên vấn đề sưởi ấm khí hậu và tập trung vào việc tìm nguyên nhân của lỗ hổng ozone. Câu chuyện này bắt đầu vào những năm 1980, các quan sát viên về khí tượng nhận thấy rằng mỗi năm sau mùa đông, lớp ozone ở trên thượng tần khí quyển của vùng Antarctique bị phá hủy rất nhiều. Trong suốt ba tháng mùa đông, vào khoảng 50% toàn bộ lượng ozone ở miền Nam cực biến mất và sự tổn thất về ozone có khi lên đến 90% nên được mệnh danh là lỗ hổng ozone. Lỗ hổng này được Joseph Farman, Brian Gardiner et Jonathan Shanklin thuộc nhóm “Quan sát vùng Antarctic của anh quốc” khám phá năm 1985.

Theo các chuyên gia (phần đông là các chuyên viên nghiên cứu về khí quyển, về lớp ozone hay thuộc các viện nghiên cứu về thời tiết của một số quốc gia) thì sự phá hủy lớp ozone là do các nguyên tử chlore hay brome của các halogéno-carbone như các chlorofluorocarbone (CFC). Nhưng điều rất ngạc nhiên là các halogéno-carbone này là những hóa chất rất bền (có đời sống trung bình vào khoảng một trăm năm), không làm hư hại môi trường và thường được dùng làm thuốc mê hay trong các máy làm lạnh, máy điều hòa không khí, trong các bình xịt hơi, hay để chửa lửa v.v.. Các chuyên gia nói trên cho rằng các phân tử CFC khi lên đến lớp thượng tần khí quyển (có độ cao từ 10 đến 40 km), sẽ bị phân hủy bởi các tia tử ngoại “có năng lượng rất lớn” để cho ra những nguyên tử chlore. Những nguyên tử này có thể phá hủy các phân tử ozone rồi chúng sẽ được điều chế trở lại nhờ những phản ứng khác tiếp theo. Thành thử một phân tử chlore có thể phá hủy đến 100.000 phân tử ozone. Lối giải thích này đã làm cho cả thế giới lo ngại và có lẽ vì vậy mà vỏn vẹn chỉ có hai năm, sau ngày khám phá ra lỗ hổng ozone ở Antarctic,  thì “Nghị Quyết Montreal” ra đời (1987). Tuy nhiên tôi nghĩ rằng những lý do mà các chuyên gia đưa ra để giải thích lỗ hổng trong lớp ozone hoàn toàn không hợp lý và không đúng sự thật.

Sau đây là vài khái niệm về quang hóa học: Trong hiện tượng quang phân là hiện tượng phân hủy các hóa chất bằng ánh sáng, các tia tử ngoại (tia UV) có năng lượng cao có thể bẻ gãy một liên kết có năng lượng thấp của các phân tử để cho ra các “gốc tự do” (radical libre hay free radical). Sau đó các “gốc tự do” này sẽ kết hợp lại với nhau hay tác động trên các các phân tử khác để tạo ra những phân tử hay những “gốc tự do” mới. Thí dụ, khi một tia tử ngoại (tia UV) do mặt trời phát ra đến trái đất và gặp một phân tử oxygen (O2) ở thượng tần khí quyển, nó sẽ bẻ gãy liên kết của O2 để cho ra 2 “gốc tự do” tức là nguyên tử oxygen (O2 → O + O). Hai nguyên tử này có khả năng phản ứng rất mạnh nên không thể ở lâu trong trạng thái tự do. Chúng sẽ kết hợp với nhau để hoàn lại phân tử oxygen (O + O → O2) hay phản ứng với phân tử oxygen để cho ra ozone (O + O2 → O3) (phản ứng này giải thích tại sao có ozone ở trong lớp thượng tần khí quyển). Khi nồng độ của ozone khá lớn, ozone sẽ bị tia UV phân hủy để cho ra một nguyên tử và một phân tử oxygen (O3 → O + O2).

Trong phòng thí nghiệm, phản ứng quang phân của oxygen có thể thực hiện bằng cách dùng một bóng đèn đựng khí iode (phát ra tia tử ngoại có làn sóng bằng 253,7 nm). Ta chỉ cần thắp một bóng đèn iode trong vài phút là ngửi thấy mùi hôi khó chịu của ozone. Các động cơ nổ của xe hơi, các máy điện trong kỷ nghệ phát ra nhiều tia chớp có chứa tia tử ngoại nên cũng tạo ra ozone. Các phản ứng quang phân xảy ra rất nhanh chóng trong khoảng một vài phần triệu giây và thời gian sống của các “gốc tự do” cũng rất ngắn, từ vài phần triệu giây đến vài phần mười giây.

Tóm lại, oxygen bị tia tử ngoại quang phân cho ra ozone và ozone bị quang phân thì hoàn lại oxygen. Nhờ vậy mà lượng oxygen trong bầu không khí gần như không thay đổi và không phụ thuộc vào thời gian chiếu của mặt trời, dù là hàng tỷ năm. Và khi nào có tia tử ngoại (của mặt trời) và còn oxygen là có ozone. Một mặt khác, mặc dù nồng độ của oxygen giảm xuống khi lên cao độ nhưng lượng oxygen ở thượng tần khí quyển củng đủ để hấp thụ phần lớn các tia UV từ mặt trời chiếu đến. Sự hấp thụ tia tử ngoại của oxygen lại còn hiệu quả hơn khi xuống gần mặt đất. Cho nên, sự hiện diện của ozone chỉ làm tăng sự phòng thủ của oxygen đối với tia tử ngoại : không có ozone, oxygen lâu ngày sẽ bị phá hủy vĩnh viễn bởi tia UV của mặt trời; nhưng không có oxygen thì lượng ozone nhỏ bé ở trên thượng tần khí quyển sẽ bị tiêu hủy trong khoảnh khắc. Vì vậy, sự khẳng định cho rằng lớp ozone đã che chở chúng ta khỏi bị tia tử ngoại làm hại là không đúng một cách hoàn toàn.

Một vài khái niệm về bầu khí quyển : Trong suốt mùa đông (tức là mùa hè ở bắc bán cầu), miền nam-cực của trái đất không nhận ánh sáng mặt trời. Việc chế tạo ozone bị gián đoạn. Do đó lớp ozone được tạo ra trước đây thu nhỏ lại, di chuyển đến vùng khác và luôn luôn thay đổi hình thể cũng như giống các đám mây trôi lơ lửng trên trời. Một lỗ hỗng trong lớp ozone ít nhiều rộng hẹp hiện ra vào mỗi mùa đông ở miền cực đạo. Nhưng hiện tượng này đã có như vậy từ hàng tỷ năm, mặc dù -theo như tôi biết- chưa ai để ý đến trước năm 1985. Tuy nhiên, lỗ hổng ozone này hoàn toàn vô hại vì là trong mùa đông, không có mặt trời để phát ra tia UV. Khi mùa xuân bắt đầu trở về miền cực đới, mặt trời hãy còn thấp ở chân trời. Các tia tử ngoại, trước khi chiếu đến mặt đất ở nam cực, phải xuyên qua lớp khí quyển của các vùng có vĩ tuyến nhỏ hơn (gần đường xích đạo) nên phần lớn bị oxygen ở các vùng này hấp thụ. Vì lẽ đó, lỗ hổng ozone ở miền Antarctic không thể được lấp đầy một cách nhanh chóng. Đó là lý do giải thích tại sao lỗ hổng ozone vẫn còn tồn tại sau mùa đông. Nhưng rồi mùa hè từ từ đến, mặt trời càng ngày càng lên cao trên bầu trời, ngày càng dài thêm, cường độ của luồng UV mỗi ngày mỗi mạnh và lỗ hổng ozone sẽ hoàn thành trở lại như xưa.

Ngày 18-8-2006, Tổ Chức Thời Tiết Quốc Tế (l’Organisation Météorologique Mondiale (OMM) và Chương Trình Liên hiệp Quốc về Môi Trường (Programme des Nations Unies pour l’Environnement (PNUE) đã đăng bản tường trình về sự biến chuyển của lượng ozone trong khí quyển do 250 chuyên gia trên thế giới thành lập. Trong đó có ghi rõ là “…trừ miền cực đạo ra, sự suy giảm của lượng ozone ở thượng tần khí quyển không còn nữa”. Hay “Năm 2002, lớp thượng tần khí quyển đuợc sưởi ấm một cách khác thường nên không còn thấy hiện tượng phá hủy ozone”. Hay “Trái lại ở miền Antarctic, từ 2004 đến 2005, một mùa đông băng giá đã làm cho lượng ozone xuống thấp”. Gần đây (16-09-2009), nhân “Ngày quốc tế nhằm phòng vệ lớp ozone” (Journée Internationale de la préservation de la couche d’ozone), hội Khí Tượng và Khoa Học Khí Quyển (l’Association Internationale de Météorologie et des Sciences Atmosphériques, IAMAS) đã thông báo rằng lượng ozone toàn bộ không thay đổi mà còn có thể tăng lên, đặc biệt là ở các vùng có vĩ tuyến trung bình.

Như vậy sự thăng giảm bề ngoài về sự phá hủy lớp ozone ở miền Nam cực vào mùa đông trước tiên là liên hệ với sự thay đổi của ánh nắng mặt trời.

Vai trò của CFC hay của HFC : Một câu hỏi được đặt ra là các hóa chất hologeno-carbone có gây thêm ảnh hưởng nào không ? Tôi nghĩ rằng không vì nhiều lý do :

–           Các phân tử CFC và HFC nặng hơn oxygen và nitrogen rất nhiều nên khó có thể bay lên đến thượng tần khí quyển với một nồng độ tạm đủ để thi đua với oxygen và ozone trong việc thu hút các tia tử ngoại.

–           Không ai hiểu tại sao các phân tử này (CFC và HFC) lại có thể bị quang phân bởi các tia UV khi không có mặt trời ?

–           Người ta cũng không hiểu tại sao các phân tử nặng và bền như CFC và HFC lại không bị quang phân ở thượng tần khí quyển, ngay trên đầu chúng ta, để tạo ra một lỗ hổng ozone tương tự mà phải du hành xa xôi đến miền Nam cực, nhưng lại không đến miền Bắc cực ?

–           Cuối cùng, các kết quả đo lường không có vẻ chứng tỏ rằng khi mùa hè trở lại, lượng ozone năm nay lại ít hơn các năm trước.

Nói tóm lại, sự khẳng định cho rằng lớp ozone đã che chở chúng ta tránh khỏi các tia tử ngoại là không đúng một cách hoàn toàn. Trong việc hấp thụ các tia UV, chính oxygen mới thật sự đóng vai trò chủ yếu. Lỗ hổng ozone hiện ra vào mùa đông chỉ là một hiện tượng thiên nhiên, xảy ra mỗi năm một lần, từ hàng tỷ năm nay. Lỗ hổng này không gây một nguy hại nào cho con người bởi vì lúc đó không có mặt trời ở miền cực đạo. Giả thuyết cho rằng việc phá hủy lớp ozone ở miền Nam cực là do các nguyên tử chlore của chlorofluorocarbone (CFC) hay của các hóa chất tương tự có lẽ là một sai lầm lớn và hoàn toàn phi lý. Do đó việc thay thế CFC bằng HFC không những không cần thiết mà còn gây hại bởi vì các HFC vẫn nổi tiếng là những chất có năng suất sưởi ấm bầu khí quyển lớn gấp 10.000 lần khí carbonic. Cho nên nếu sự suy luận trình bày ở trên không sai lệch thì sự thay thế CFC bằng HFC có lẽ nhằm phục vụ quyền lợi kinh tế và tài chánh cho một số công ty và kỷ nghệ gia, bởi vì bằng sáng chế của họ về các chất này đã (hoặc sắp) đến ngày hết hạn.

Viết tại Saclay ngày 5 octobre 2009

Dr TRAN-DINH Son

Cố vấn khoa học của Nguyên tử lực cuộc Pháp

Adresse e-mail : trandinhs@yahoo.com

4 comments on “Lỗ hổng ozone có làm nguy hại đến con người hay không ?

  1. LE TROU D’OZONE REPRESENTE-T-IL VRAIMENT UN DANGER POUR L’HOMME ? MA REPONSE : NON !

    Selon l’Associated Press (AP) du 16 septembre 2009, “l’administration Obama a annoncé que, désormais, Etats-Unis, Canada et Mexique étaient favorables à la transformation du Protocole de Montréal sur la protection de la couche d’ozone, en outil de réduction des hydrofluorocarbones (HFC), qui sont parmi les plus puissants des gaz à effet de serre. Le Protocole de Montréal, destiné à lutter contre le trou dans la couche d’ozone, est entré en vigueur en 1989″… “Dans sa version actuelle, le protocole encourage le recours aux HFC dans les réfrigérateurs et appareils d’air conditionné comme produits de substitution pour remplacer les CFC (chlorofluorocarbones), ces gaz responsables du trou dans la couche d’ozone et dont l’utilisation a aujourd’hui quasiment disparu. S’ils ne détériorent pas autant la couche d’ozone, les HFC favorisent en revanche l’effet de serre : leur pouvoir de réchauffement global est plus de 10.000 fois supérieur à celui du très nocif dioxyde de carbone”… “Les HFC ne représentent qu’environ 2% des émissions de gaz responsables du réchauffement climatique. Mais ils sont désormais massivement utilisés, leur part risquant de constituer jusqu’à un tiers des gaz à effet de serre d’ici la moitié du XXIe siècle. Et ce à cause justement de leur promotion dans le traité sur l’ozone, promotion jugée “irresponsable” par l’administration Obama”.
    Ainsi a noté le Monde du 16-09-09, à moins de trois mois du sommet de Copenhague sur le réchauffement climatique, les négociations s’enlisent. Pire encore, selon The Guardian du mardi 15 septembre, elles seraient au point mort suite à un désaccord entre l’Europe et les Etats-Unis.
    Laissons pour l’instant de côté le problème de réchauffement climatique qui devra faire l’objet d’un autre débat et concentrons-nous sur l’origine du trou de la couche d’ozone. L’histoire a commencé par l’observation, dans les années 1980, d’une réduction massive, après chaque hiver, de la couche d’ozone présente au dessus de l’Antarctique, dans la stratosphère. Durant les trois mois d’hiver austral, environ 50% de la “colonne” totale d’ozone de cette région disparaît, et la perte d’ozone s’élève parfois jusqu’à 90%, d’où le nom du “trou d’ozone de l’Antarctique”. L’existence du trou d’ozone a été découverte en 1985 par Joseph Farman, Brian Gardiner et Jonathan Shanklin, du groupe British Antarctic Survey.
    D’après de nombreux spécialistes, pour la plupart experts en atmosphère ou chercheurs du comité de recherche sur l’Ozone, ou bien encore chercheurs des instituts de recherche météorologique de différents pays, la destruction de la couche d’ozone serait due essentiellement aux atomes de chlore ou de brome provenant des composés d’halogéno-carbones, comme par exemple le chlorofluorocarbone (CFC). Pourtant, ces produits, utilisés comme anesthésiques, réfrigérants, dans les aérosols, pour la fabrication de divers matériaux, ou lors de luttes contre le feu, étaient jusqu’ici décrits comme chimiquement inertes, stables (avec une durée de vie moyenne de 100 ans) et neutres pour l’environnement. Ces spécialistes ont imaginé que lorsque les molécules de CFC atteignaient la couche supérieure de l’atmosphère (la stratosphère, entre 10 à 40 km d’altitude), elles étaient décomposées par les rayons UV de “très haute énergie”, libérant ainsi des atomes de chlore susceptibles de détruire les molécules d’ozone et de se reformer ensuite par des réactions subséquentes, en conséquence de quoi un seul atome de chlore pouvait détruire jusqu’à 100.000 molécules d’ozone! Cette description inquiétante explique probablement en partie le bref délai qui s’est écoulé entre la découverte du trou d’ozone en Antarctique en 1985 et la signature du Protocole de Montréal en 1987.
    Les arguments avancés pour expliquer l’origine du trou de la couche d’ozone me semblent aberrants et peu convaincants, voire inexacts.

    Quelques notions de photochimie pour commencer : Lors d’une photolyse, les rayons UV d’énergie élevée peuvent casser les liaisons chimiques de faible énergie des molécules, et former des “radicaux libres”. Ces radicaux se recombinent ensuite ou réagissent sur d’autres molécules du voisinage pour former de nouvelles molécules ou d’autres radicaux (d’où le nom de “réactions radicalaires” donnés à ces processus). Par exemple, on sait que quand un rayon UV émis par le soleil arrive à la terre et rencontre une molécule d’oxygène de la couche stratosphérique, il casse sa liaison chimique pour donner deux atomes d’oxygène (O2 → O + O). Ces atomes d’oxygène, étant très réactifs, ne peuvent pas rester longtemps à l’état libre. Ils réagissent sur d’autres molécules d’oxygène pour donner de l’ozone (O + O2 → O3) (et c’est la raison de la présence d’ozone au-dessus de nos têtes) ou se recombinent pour reformer l’oxygène (O + O → O2). Quand la concentration d’ozone devient élevée, l’ozone est décomposé à son tour par les rayons UV pour régénérer un atome et une molécule d’oxygène (O3 → O + O2).
    En laboratoire, une telle photolyse, de l’oxygène par exemple, peut être réalisée grâce aux rayons UV d’une lampe à iode (émettant de la lumière à 253,7 nm de longueur d’onde). Il suffit d’allumer cette lampe pendant quelques minutes pour qu’on sente une odeur désagréable d’ozone. Hors des laboratoires, les étincelles émises par les moteurs de voitures ou les machines industrielles contiennent également des rayons UV, et donc produisent aussi de l’ozone. Les réactions de photolyse provoquées par les rayons UV sont très rapides, de l’ordre de la microseconde (mesurable en laboratoire, à l’aide d’éclairs très brefs mais puissants), et la durée de vie de la plupart des radicaux formés est également très courte, de quelques microsecondes à quelques centaines de millisecondes.
    En bref, l’oxygène photolysé par les rayons UV donne de l’ozone qui peut lui même être photolysé pour restituer de l’oxygène. Les deux réactions sont très rapides. Donc, tant qu’il y a des rayons UV (du soleil) et de l’oxygène, il y a de l’ozone, et la concentration d’oxygène atmosphérique reste donc pratiquement inchangée et indépendante du temps d’irradiation du soleil (des milliards d’années). D’autre part, bien que la concentration d’oxygène diminue à haute altitude, la quantité d’oxygène dans la couche stratosphérique reste suffisante pour capter la majeure partie des rayons UV émis par le soleil. Et la capture des rayons UV (par l’oxygène) est encore plus efficace à basse altitude. La présence de l’ozone ne permet que de renforcer la défense contre les rayons UV par l’oxygène: Sans ozone, l’oxygène serait détruit irréversiblement par le soleil, mais sans oxygène, la faible quantité d’ozone dans la couche stratosphérique serait détruite rapidement par le soleil. Par conséquence, l’affirmation selon laquelle la couche d’ozone nous protège des rayons UV du soleil n’est pas tout à fait juste.

    Un peu de météorologie ensuite : Pendant l’hiver austral (notre été), le pôle Sud ne reçoit plus de rayons solaires. La formation d’ozone est donc interrompue. En conséquence, il est parfaitement normal que la couche d’ozone formée auparavant au soleil se rétrécisse et se déplace vers d’autres régions, en changeant constamment de forme, tout comme par exemple les nuages dans le ciel. Un “trou” plus ou moins large, apparaît bien chaque hiver dans la couche d’ozone polaire. Mais il doit en être ainsi depuis des milliards d’années, même si à ma connaissance on ne l’a jamais mesuré avant les années 80 ! Et ce trou ne présente aucun danger puisque le soleil est ailleurs et n’envoie pas d’UV !! Au début du printemps austral, le soleil revient mais se trouve encore très bas dans le ciel (à l’horizontal). Les rayons UV, avant d’arriver au pôle Sud, doivent traverser la couche atmosphérique des régions de latitudes inférieures et sont absorbées en grande partie par l’oxygène de ces régions. Le trou de la couche d’ozone au dessus de l’Antarctique ne peut donc pas se reboucher immédiatement au début du printemps (du septembre au novembre) en raison de la faible intensité du flux UV. Au fur et à mesure que l’été s’approche, le soleil monte de plus en plus haut dans le ciel, les journées s’allongent, le flux d’UV devient plus intense et la couche d’ozone se reforme.
    D’ailleurs, dans le rapport d’évaluation sur l’évolution de l’ozone atmosphérique élaboré par 250 experts internationaux publié le 18 août 2006 par l’Organisation Météorologique Mondiale (OMM) et le Programme des Nations Unies pour l’Environnement (PNUE), on peut lire : “… en dehors des régions polaires, le taux d’ozone stratosphérique a cessé de diminuer”. Ou bien : “En 2002, un réchauffement inhabituel de la stratosphère avait enrayé le phénomène (de destruction d’ozone). Ou bien “A l’inverse, en Antarctique, en 2004-2005, un hiver particulièrement rigoureux avait occasionné une chute sévère de l’ozone”. Récemment, lors de la Journée Internationale de la préservation de la couche d’ozone, l’Association Internationale de Météorologie et des Sciences Atmosphériques (IAMAS) a rapporté (le 16 septembre 2009) que l’abondance globale d’ozone est stabilisée voire même augmentée en particulier sur les latitudes moyennes.
    Les fluctuations apparentes dans la destruction de la couche d’ozone au pôle Nord ou Sud en hiver, sont donc a priori liées d’abord aux variations d’ensoleillement.

    Le rôle du CFC ou des HFC : Les halogéno-carbones jouent-ils un rôle supplémentaire ? Je ne le pense pas, pour plusieurs raisons :
    – Les molécules de CFC ou d’HFC sont probablement trop lourdes en comparaison avec l’azote et l’oxygène pour monter jusqu’à la stratosphère en quantité suffisante pour entrer en compétition avec l’oxygène et l’ozone comme capteurs des UV.
    – On ne voit pas comment ces molécules pourraient être décomposées par les UV pendant l’hiver polaire, en absence du soleil.
    – Il est difficile de comprendre pourquoi ces molécules lourdes ne se décomposeraient pas aussi au dessus de nos latitudes pour créer le même phénomène de trou d’ozone, mais voyageraient jusqu’au pôle Sud (mais pas au pôle Nord) ?
    – Enfin les mesures actuelles n’ont pas l’air de montrer qu’une fois l’été revenu, l’ozone soit moins abondant.

    En résumé, l’affirmation selon laquelle la couche d’ozone nous protège des rayons UV du soleil n’est pas tout à fait juste : l’oxygène joue un rôle primordial dans la capture des UV! L’apparition du trou de la couche d’ozone en hiver est un phénomène naturel qui se répète tous les ans depuis des milliards d’années. Ce trou ne représente aucun danger pour l’homme car le soleil est absent du pôle pendant l’hiver local. Et quand le soleil revient au printemps, la couche d’ozone se reforme progressivement pour nous protéger. La théorie selon laquelle la destruction de la couche d’ozone au pôle Nord ou Sud en hiver est essentiellement due aux atomes de chlore provenant du chlorofluorocarbone (CFC) ou de ses dérivés est probablement inexacte et absurde. Le remplacement des CFC par des HFC (hydrofluorocarbones) n’est donc pas nécessaire. Ce remplacement pourrait même être néfaste puisque les HFC sont réputés avoir un pouvoir de réchauffement par effet de serre plus de 10.000 fois supérieur à celui du dioxyde de carbone (CO2). Sauf erreur dans les raisonnements exposés ci-dessus, on peut supposer que ce remplacement ne visait qu’à servir les intérêts des compagnies dont le brevet sur le CFC et ses dérivés allait venir bientôt à expiration.
    Bien que je sois actuellement Conseiller Scientifique au Commissariat à l’Energie Atomique (France), cet article a été écrit (le 05 octobre 2009) à ma propre initiative et n’engage que ma personne.

    Dr TRAN-DINH Son
    Adresse e-mail : trandinhs@yahoo.com
    (Đây là nguyên bản tiếng Pháp)

  2. DOES THE HOLE OF OZONE REPRESENTE REALLY A DANGER FOR HUMANITY? MY ANSWER: NO!

    According to Associated Press (AP) of September 16th, 2009, “the Obama administration announced that, henceforth, the United States, Canada and Mexico were favourable to the elaboration of the Montreal Protocol on the protection of the ozone layer by reducing hydrofluorocarbons (HFC), which are among the most powerful of greenhouse gases. The Montreal Protocol, the purpose of which is intended to fight against the hole in the ozone layer, came into effect in 1989 ” … ” In its current version, the protocol encourages the use of HFCs in refrigerators and air-conditioners as substitute products, replacing CFC (chlorofluorocarbons), these gases, which are responsible for the hole in the ozone layer, have almost disappeared today. If HFCs do not damage so much the ozone layer as CFC, they, on the other hand, facilitate the greenhouse effect: their global power of reheating is about 10.000 times greater than that of harmful carbon dioxide “…”HFCs represent only approximately 2 % of the gases responsible for global warming. However nowadays they are used routinely, thus risking up to one third increase of the total concentration of greenhouse gases by the first half of the 21st century. It is for this reason that their promotion in the ozone treaty is considered “irresponsible” by the Obama administration”.
    So noted in the newspaper “Le Monde” (16-09-09), less than three months to the Copenhagen summit on global warming, the negotiations sink. Worse still, according to The Guardian (September 15th, 2009) they will be a deadlock between Europe and the United States.
    For the moment let us leave aside the problem of global warming which will have to be the object of another debate and concentrate on the origin of the hole of the ozone layer. The story began with the observation, in the 1980s, of a massive reduction of ozone, after each winter, in the stratosphere above Antarctica. During three months of southern winter, approximately 50 % of the total “column” of ozone of this region disappears, and the loss of ozone sometimes increases up to 90 %, thus giving rise to the use of the term “ozone hole”. The existence of the ozone hole was discovered in 1985 by Joseph Farman, Brian Gardiner and Jonathan Shanklin, of the British Antarctic Survey.
    For the greater part experts in atmospheric research and/or scientists of “The Committee of Research on the Ozone”, the destruction of the ozone layer is essentially due to the production of chlorine or bromine atoms resulting from halogeno-carbon compounds, e.g. chlorofluorocarbon (CFC). Nevertheless, these products, used as anaesthetics, coolers, in aerosols, and the manufacturing of various materials, or during fights against fire, were described up to now as chemically inert, stable (with an average life time of 100 years) and neutral for the environment. These specialists imagined that when the molecules of CFC reached the upper layer of the atmosphere (the stratosphere, between 10 and 40 km in height), they are decomposed by the “very high energy” UV radiation, so releasing chlorine atoms that destroy ozone molecules and then re-form by subsequent reactions; as a result of which a single chlorine atom could destroy up to 100.000 molecules of ozone! This disturbing description partially explains the brief deadline which occurred between the discovery of the ozone hole (in Antarctica) in 1985 and the signing of the Montreal Protocol in 1987.
    The arguments advanced to explain the origin of the hole in the ozone layer seem to me absurd, little convincing and even inaccurate.

    Some notions of photochemistry to begin: During a photolysis, the UV radiation of high energy can break weak chemical bonds in molecules, and form “free radicals”. These radicals recombine, then, or react with other molecules in the neighbourhood giving rise to the formation of new molecules and/or the other radicals. These processes are termed “free radical reactions”. For example, we know that when UV radiation emitted by the sun arrives at the earth and meets a molecule of oxygen in the stratosphere, it breaks its chemical bond to give two atoms of oxygen (O2 → O + O). These atoms of oxygen, being very reagent, cannot stay for long in a free state. They react with other molecules of oxygen to form ozone (O + O2 → O3) (and it is the reason of the presence of ozone above our heads) or recombines to reform oxygen (O + O → O2). When the concentration of ozone becomes high, it is decomposed in its turn by UV radiation to regenerate an atom and a molecule of oxygen (O3 → O + O2).
    In brief, the oxygen photolysed by UV radiation gives some ozone which can even be itself photolysed to restore some oxygen. Both reactions are very fast. Consequently, as long as there is UV radiation (from the sun) and some oxygen, there is some ozone, and the concentration of atmospheric oxygen thus remains practically unchanged and independent of the irradiation time of the sun (billions of years). On the other hand, although the concentration of oxygen decreases at high altitude, the quantity of oxygen in the stratosphere remains sufficient to pick up the major part of UV radiation emitted by the sun. Thus the capture of UV radiation by oxygen is even more effective at low altitudes. The presence of the ozone allows only to strengthen the defence against UV radiation by the oxygen: without ozone, the oxygen would be irreversibly decomposed by the sun, but without oxygen, the small quantity of ozone in the stratosphere would quickly be destroyed by the sun. Therefore, the assertion according to which the ozone layer protects us from UV radiation of the sun is not completely just.

    A little of meteorology then: During the southern winter (our summer), the South Pole receives no sunshine (i.e. UV radiation). The formation of ozone is thus interrupted. Therefore, it is perfectly normal that the ozone layer formed previously in the sun reduces and moves towards other regions, by changing constantly shape, like a massive cloud in the sky. A more or less large “hole”, appears every winter in the polar ozone layer. So it has to have been present for billions of years, even before it was discovered in the 1980s! This hole presents no danger because the sun is somewhere else and does not send UV!! At the beginning of the southern spring, the sun returns but is still very low in the sky, so UV light, before arriving to the South Pole, has to cross a large region of lower latitudes and is mainly absorbed by the oxygen in these regions. The ozone hole above Antarctica cannot thus refill immediately at the beginning of spring (from September to November) because of the weak intensity of the UV flux. As the summer approaches, the sun rises higher in the sky, days lengthen, the flux of UV becomes more intense and the ozone layer finally reforms.
    The visible fluctuations in the destruction of the ozone layer in the South Pole in winter are thus due a priori at first to the variations of periodic sunshine.

    The role of the CFC or the HFC: Do halogeno-carbons play a supplementary role? I do not think so, for several reasons:
    – Molecules of CFC or HFC are probably too heavy in comparison with nitrogen and oxygen to rise up into the stratosphere in sufficient concentrations to enter into competition with oxygen and ozone as absorbers of UV.
    – We do not see how these molecules could be decomposed by UV during the polar winter, in the absence of sunlight.
    – It is difficult to understand why these heavy molecules would not also decompose above our latitudes to create the same phenomenon as the ozone hole, but would travel only to the South Pole and not in the North Pole?
    – Finally the current measures do not seem to show that once summer has returned, the ozone is less plentiful than before.

    In summary, the assertion according to which the ozone layer protects us from UV radiation from the sun is not completely just: the oxygen plays an essential role in the capture of UV! The appearance of the ozone hole in winter is a natural phenomenon which repeats itself every year since billions of years. This hole represents no danger for humanity because the sun is absent in the pole during the local winter. And when the sun comes back in spring, the ozone layer re-forms gradually to protect us. The theory, according to which the destruction of the ozone layer in the South Pole in winter is essentially due to the atoms of chlorine resulting from the chlorofluorocarbon (CFC), or from its derivatives, is probably inaccurate and absurd. The replacement of the CFC by HFC (hydrofluorocarbons) is not thus necessary. This replacement could even be fatal because HFC is considered to have a powerful influence on the greenhouse effect about 10.000 times greater than that of the carbon dioxide (CO2). Broadly speaking using the above argument, we can suppose that this replacement is aimed only to serve the interests of multinational companies where the CFC and its derivatives patents have since expired.
    Although I am actually a Scientific Consultant at the Atomic Energy Commission (France), this article was written on my own initiative and engages only my views

    Dr TRAN-DINH Son
    E-mail address: trandinhs@yahoo.com

  3. Discussion between Prof. D. W. and Trandinh Son

    Letter from Trandinh Son, (19 Oct 09)

    Dear Professor D. W., Director of Information of an International Commission on Ozone.
    Please find attached the article (in PDF) on my reflections and comments on the ozone hole for which I would like to ask you to forward to the experts in national and international Environmental Studies, in particular the World Meteorological Organization (WMO), the United Nations Environment Programme (UNEP), the International Association of Meteorology and the Atmospheric Sciences (IAMAS) and the Pierre Simon Laplace institute.
    To my opinion the “ozone hole” observed in Antarctica during the southern winter does not really represent danger for humanity. The replacement of the CFC by the HFC is not thus necessary, and it is maybe even fatal.
    I thank you beforehand.
    Sincerely Yours.

    Dr TRAN-DINH Son
    Scientific Consultant of the ATOMIC ENERGY COMISSION, FRANCE).
    E-mail address: trandinhs@yahoo.com

    Professor D. W’s answer, (19 Oct 09)
    Your writing reflects very little understanding of the atmosphere and certainly no knowledge of the many observations made in the lower and upper atmosphere, including those over Antarctica. As just an example, the atmosphere is controlled by transport processes below about 100 km not by molecular diffusion (did it occur. CFCs and their reaction products have been well measured in the stratosphere. So please, try learning something about the science before writing such garbage.

    Letter from Trandinh Son (20 Oct 09)
    Dear Professor D. W.,
    Thank you for your message. In my article there are several points and questions which I couldn’t understand. Therefore I would appreciate receiving your explanation:
    – Do you agree with me that the assertion according to which the ozone layer protects us from UV radiation from the sun is not completely just: the oxygen plays an essential role in the capture of UV? The presence of the ozone allows only strengthening the defence against UV radiation by the oxygen: without ozone, the oxygen would be irreversibly decomposed by the sun, but without oxygen, the small quantity of ozone in the stratosphere would quickly be destroyed by the sun.
    – Why wouldn’t CFCs, these heavy molecules, decompose above our latitudes to create the same phenomenon as the ozone hole, but travel only to the South Pole and not in the North Pole?
    – How could CFCs be decomposed by UV during the polar winter, in the absence of sunlight? If the atmosphere is controlled by transport processes below about 100 km not by molecular diffusion, why the ozone is not present in summer?
    – Do the current measures show that once summer has returned, the ozone is less plentiful than before?
    Could you please give me the reference about the CFCs and their reaction products which have been measured in the stratosphere.
    Thank you for your courtesy.
    2
    2
    Professor D. W’s answer, (21 Oct 09)
    Trandinh Son:
    In response to your questions:
    1. No, I do not agree. This is very elementary physics so I am surprised you have not looked at this more carefully. You need to carefully consider specific wavelengths. O2 is a strong absorber of UV but only below 240 nm. As a result, all of the solar radiation below 240 nm is absorbed in the upper stratosphere. Ozone absorbs at longer wavelengths and keeps the worst of the UV-B radiation (28-320 nm) from getting to the Earth’s surface where it is well documented to be harmful to human, animals, and plants. When ozone levels are reduced, more UV-B can penetrate to the Earth’s surface. It has been measured that this is exactly what occurs in the polar region during the “Ozone hole”. The rest of your argument makes no sense at all because of the wavelength differences at which different molecules absorb solar radiation.
    2. CFCs travel throughout the atmosphere (pole to pole), but once high enough in the stratosphere, where available UV solar radiation is sufficiently available (because they photolyze at wavelengths less than 260 nm), they will be photolyzed and then release their chlorine atoms that can then react with ozone. This has all been well substantiated through observations. We do get ozone hole behavior at the northern hemisphere pole, but the physics is not usually right in the northern hemisphere to get as large as a ozone decrease. You will need to read about the polar winter vortex and about polar stratospheric clouds (PSCs) to understand why the chlorine (and bromine from Halons) can be effective catalytic destroyers of ozone in the polar regions.
    3. Regarding mixing — It is not as I think, it is the facts — go look at any elemental atmospheric physics textbook! There is no ozone hole in the summer because of the strong mixing that occurs in the late spring, thus eliminating the effects of the polar winter vortex and the cold temperatures that form the PSCs.
    4. The CFCs are mostly destroyed at midlatitudes, leaving the reactive chlorine available to be transported to the poles. Again measurements clearly show this is what happens.
    5. The reduced levels of ozone during the ozone hole do lead to overall reduced levels in the hemisphere compared to the 1070s when there was no hole, but there are also catalytic reactions from the chlorine and bromine released from the CFCs and other halocarbons contributing to an overall decreased levels of ozone at every latitude and season compared to the period before levels of chlorine and bromine were sufficient to cause much ozone destruction.
    There are many references. I suggest you start with the WMO ozone assessments where the science community assesses the state of understanding of the science every fours or so. There are many references for the observations indicated in those reports. Go to the following websites to download the report Itself (it can take quite a while to download each chapter because the files are big) and the answers to 20 questions for the public about the ozone layer. Go to http://www.esrl.noaa.gov/csd/assessments/2006/ and to http://www.wmo.int/pages/prog/arep/gaw/ozone_2006/ozone_asst_report.html or you could also try http://ozone.unep.org/Assessment_Panels/SAP/Scientific_Assessment_2006/ (but as I said, it takes a long time to download these huge files so be patient).
    Who do you report to at the Atomic Energy Commission?
    Don

    Letter from Trandinh Son, (22 Oct 09)
    Dear Professor D. W.,
    In my article I didn’t want to use scientific details (for example about the wavelength of UV radiation to distinguish the photolysis of oxygen and ozone) because I am afraid that worries too many non expert readers. Now I am very please to see that you use them for discussion.
    I agree with you that O2 is a strong absorber of UV but only below 240 nm. As a result, all of the solar radiation below 240 nm is absorbed in the upper stratosphere. Ozone absorbs at longer wavelengths and keeps the worst of the UV-B radiation (28-320 nm) from getting to the Earth’s surface where it is well documented to be harmful to humans, Nevertheless, I hope you agree with me that the oxygen photolyzed by UV radiation gives rise to the formation of ozone and this reaction is very fast. This means that oxygen is an inexhaustible precursor of ozone and as long as there is UV radiation (from the sun) and some oxygen, there is always some ozone. Really I don’t worry very much about the destruction of ozone in the stratosphere above Antarctic in winter because when there are UV radiation (from the sun) and some oxygen, the ozone formation is immediate.
    – Therefore, I don’t understand why, on the one hand you said that “O2 is a strong absorber of UV below 240 nm and Ozone absorbs at longer wavelengths”, and on the other hand you don’t agree with me that the assertion (according to which the ozone layer protects us from UV radiation from the sun) is not completely just : oxygen plays an essential role in the capture of UV, the presence of the ozone allows only strengthening the defence against UV radiation by the oxygen and thus?
    – Without oxygen don’t you think that -i) the small quantity of ozone would be quickly destroyed by the sun? -ii) the UVs below 240 nm can arrive to the earth’s surface and they are more dangerous and more harmful to humans, animals, and plants than the UV-B radiation (280-320 nm)?
    Furthermore, You can read many alarmist statements in the New Report Projects Later Recovery of Ozone Layer on August 18, 2006 at Geneva (i.e. about twenty two years after the signing of the Montreal protocol) for example: “According to the “UNEP/WMO Scientific Assessment of Ozone Depletion: 2006” , the updated scientific understanding indicates that the ozone layer over the mid-latitudes (30° – 60° North and South) should recover by 2049, five years later than anticipated by the previous (2002) assessment. The ozone over the Antarctic should recover by 2065, 15 years later than once expected. Because of special conditions within the Antarctic vortex (a natural cyclone of super-cold, super-fast winds), the Antarctic ozone “hole” is expected to recur regularly for another two decades”.
    However you can find in a recent report published, only 3 years later, by the International Ozone Commission (IO3C) on the International Day for the Preservation of the Ozone Layer (16 September 2009) that “The Montreal protocol has been highly successful in reducing the emissions and atmospheric abundance of most ozone depleting substances. Ground-based and space-based measurements show that the stratospheric amounts of chlorine and bromine, the species most harmful to the ozone layer, are now in decline. Global ozone abundance has stabilized and even shows some signs of an increase, particularly over Northern mid-latitudes”.
    I don’t really understand why CFCs were replaced by HFCs for nearly 20 years since the Montreal Protocol came into effect, the amounts of chlorine and bromine, the species most harmful to the ozone layer, were not decreased until 2006 but they are suddenly in decline only three years later (in 2009). Thus, the recent observation (showing a stabilisation or even a slight increase of the global ozone abundance) clearly demonstrates that most of the theories, calculations and explanation (e.g. the Antarctic vortex, a natural cyclone of super-cold, super-fast winds, and the reactive chlorine being transported to the poles …) elaborated by many experts are not correct. The visible fluctuations in the destruction of the ozone layer in the South Pole in winter are simply due at first to the variations of periodic sunshine. I am sorry I don’t believe every thing they published on the Internet.
    Trandinh Son

    Professor D. W.’s answer, (22 Oct 09)
    At the poles you also have to consider the attenuation of the radiation — this results in very little production of ozone at the poles. Most of the ozone getting there is transported there from other regions. Therefore, the destruction mechanisms for ozone are extremely important. Also, ozone photolysis does not really destroy ozone because most of the oxygen atoms produced will just react with O2 again to form ozone. Meaningful ozone destruction occurs from catalytic mechanisms.
    On the second issue, the CFCs all have atmospheric lifetimes greater than 100 years, so the troposphere is a steady supplier of CFCs and thus chlorine to the stratosphere long after the Montreal Protocol and its amendments were put into place. That we are no longer seeing a decline in ozone exactly matches the theoretical explanation, but the recovery is slow because of the long lifetime of the CFCs. Please try reading more of the science.
    You act like the hundreds of scientists studying this issue are idiots and that you simplistic ideas, based on a huge lack of knowledge, are the truth. Wake up.
    Don

    Letter from Trandinh Son, (25 Oct 09)
    Dear Professor D. W.,
    I am very please you agree with me that the assertion according to which “the ozone layer protects us from UV radiation from the sun” is not completely just. Of course you don’t need say with me that “ozone photolysis does not really destroy ozone because most of the oxygen atoms produced will just react with O2 again to form ozone”. I have already repeated many times that “as long as there is UV radiation (from the sun) and some oxygen, there is some ozone”. However the inverse isn’t true because if there isn’t a great proportion of oxygen in the atmosphere (20%) to regenerate constantly ozone molecules in the stratosphere, the small amount of ozone (as well as the very small amount of oxygen produced by the photolysis of ozone) will be quickly dispersed all over the word and absorbed by plants, soil etc…
    When you said: “the CFCs are mostly destroyed at midlatitudes, leaving the reactive chlorine available to be transported to the poles”. I wonder if it isn’t your own idea. The chlorine atom is a radical very reactive. It reacts with many compounds for example non saturated hydrocarbons emitted from motor vehicles. How can this atom be transported for a very long distance to the pole without reacting with any compound in the atmosphere?
    Now I would like to discuss with you (or with any expert) about the crucial “theory” on which is based the Montreal Protocol in 1987. According to this theory, chlorine atoms destroy ozone molecules and reform by subsequent reactions (see below) thus “a single chlorine atom could destroy up to 100.000 molecules of ozone”:
    1) Cl + O3  ClO + O2
    2) ClO + O  Cl + O2
    3) O3 + O  2O2
    For this I have several remarks:
    1) First of all, as it can be stated, only in the reaction (1), one chlorine atom destroys one ozone molecule. The two others (reactions 2 and 3) involved globally the decomposition of one oxygen molecule but not that of ozone.
    2) All the above reactions give rise to the formation of oxygen, leading to the regeneration of ozone. As the concentration of chlorine atom is extremely low in the atmosphere, if one ozone molecule is destroyed by a chlorine atom, billions of ozone molecules will be formed by the sun.
    3) The great error of this theory is the unforgivable lack of the most important reaction between O and O2 and the reactions in which two chlorine or two oxygen atoms recombine:
    4) O + O2  O2
    5) Cl + Cl  Cl2
    6) O + O  O2
    4) As the concentrations of Cl radical and hence of ClO are very low in comparison with that of oxygen: –i) the reactions 2) (ClO + O  Cl + O2) and 5) (Cl + Cl  Cl2) have a negligible probability to take place in the atmosphere, -ii) chlorine atom can’t enter into competition with oxygen as captors of free atom oxygen (reactions 2 and 4).
    Furthermore, the sources of chlorine are not well established and measuring its precursors in a specific manner is difficult. And chlorine atom, being a very reactive radical, can involve in many reactions with other compounds. You can verify my assertion by doing the following experience:
    Introduce in a great hermetic quartz container: 1M oxygen + 1 or 2.10-3M ozone + 10-6M CFC + 10-6M CH4 + 10-6M butadiene + 10-6M C2H2 + 10-6M NO2 + 10-6M NO and some water vapour.
    You will see that when this container is irradiated by UV radiation, chlorine atom not only cannot destroy ozone but it will be absorbed by the other products. I don’t understand why amongst the experts, no one has noticed the absurdity of this theory? I am very please to see that you didn’t find anything wrong in my article. While all the experts say “the ozone layer protects us from UV radiation”, I say “this assertion is not completely correct. Oxygen plays a crucial role in the capture of UV and the presence of the ozone is simply to strengthen the defence against UV by the oxygen”. I explained for the first time that “the appearance of the ozone hole in winter is a natural phenomenon which repeats itself every year since billions of years. This hole represents no danger for humanity because the sun is absent in the pole during the local winter”.
    Now I demonstrate (as it was mentioned in my article) that the principal theory on which is based the Montreal Protocol and according to which “the destruction of the ozone layer in the South Pole in winter is essentially due to the chlorine atoms resulting from the photolysis of CFCs or its derivatives”, is inaccurate and absurd. This reinforces my conclusion (mentioned in the previous mail) that “most of the theories, calculations, predictions and explanations elaborated by many experts about the ozone hole are not correct”.
    Dear professor D. W., after some exchange of idea with you, I found that you didn’t take enough, if not any, critical attitude when you read a scientific paper. You believe every thing they reported like a student. You like using cutting words to hurt people (ex : try learning something about the science before writing such garbage; or You act like the hundreds of scientists studying this issue are idiots and that you simplistic ideas, based on a huge lack of knowledge, are the truth. Wake up). In my opinion, the most important quality of a good scientist during a discussion with the others is to be sure of him, to keep calm in any circumstances. What we need is to expose our reasons to convince the others but not to push insults. I am very polite with you as well as with everybody, so I am waiting for the reciprocity from you.
    Thank you very much
    Trandinh Son

    Professor D. W.’s answer, (26 Oct 09)
    The fact is ozone does protects us from important levels of UV in the UV-B region!
    CFCs destruction my own idea?? — get a life — there are many measurements of chlorine at the poles. It gets transported there as longer-lived species — HCl and ClONO2 and then gets reconverted to short-lived Cl and ClO by reactions on the PSCs (well measured in chemistry laboratories AND in the atmosphere).
    Regarding the catalytic cycles, reaction 3 is not a reaction, it is the sum of reactions 1 and 2. Normally an oxygen atom would quickly produce an ozone (through reaction with O2), so if you destroy the oxygen atom it is the same as destroying an ozone. This is very basic understanding and has been well measured in chemistry laboratories.
    Reaction 4 (I assume you meant for in the produce ozone) is the ozone production reaction. We fully account for that reaction in the models.
    Reaction 5 is relatively unimportant because there are many more ozone molecules than chlorine atoms (this is basic chemical kinetics). Even when Cl2 forms and it does in small amounts outside of the polar vortex and larger amounts within the vortex, it photolyzes very easily at visible wavelengths.
    Reaction 6 is too slow to be important but does occur.
    All of these reactions are in our models of atmospheric chemistry.
    Your statement four just shows how little you understand about atmospheric chemistry. Outside of the ozone hole region, there is plenty of oxygen atoms available in the upper stratosphere and reactions 1 and 2 end up being important. In the ozone hole region, reaction 2 is not important because thereis not enough oxygen atoms at the pole, but the primary ozone destruction because the ClO reacts with another ClO to form a chlorine dimer that then photolyzes to produce Cl atoms that then react with ozone very quickly and produces a CLO again. The ozone hole ends because of the break up the vortex then allows the ClO to react with something else (usually NO2) to form something less reactive, like ClONO2.
    I base all of my comments on measurements in the atmosphere and in the laboratory, combined with my own modeling of the chemistry and physics of the atmosphere. A quartz container cannot be used to represent how the atmosphere works, that has been shown many times by very smart chemists. You will almost immediately get a series of reacions happening on the walls of the container that have nothing to do with how the atmosphere works.
    I have no indication you are even a scientist because you have so little understanding of the basics of how the atmosphere works, yet make claims that are totally unwarranted. A true scientist would actually look at the observational evidence and the state of the knowledge before making idiotic statements like CFCs are too heavy to be transported to the stratosphere. I make cutting statements because you are trying to argue that the Montreal Protocol is wrong without you even having the lowest freshman level understanding of how the atmosphere works. If you just wanted clarification, it would be one thing, but you are trying to argue that many hundreds of scientists are wrong in their understanding of atmospheric processes without you having done your homework to begin to even understand those processes and all of the observations that underly them.
    Don

    Letter from Trandinh Son, (27 Oct 09)
    Dear Professor D. W.,
    Of course, nobody denies that ozone protects us from UV-B but it can’t absorb all UV. Therefore the assertion that “the ozone layer protects us from UV radiation from the sun” is not correct. This is evident for everyone why don’t you accept it and alter your view point?
    It is surprising when you said “reaction 3 is not a reaction, it is the sum of reactions 1 and 2”. This reaction takes place independently in the absence or the presence of Cl or ClO and becomes efficient when the ozone concentration is relatively high (O2  O + O; O + O2  O3 and O + O3  2O2).
    You said “If you destroy one oxygen atom it is the same as destroying an ozone molecule”. This isn’t true because the ozone concentration very low in comparison with that of oxygen. If all ozone molecules are destroyed, the loss in oxygen molecules is still negligible.
    Presently we know that “the sources of chlorine are not well established and measuring its precursors in a specific manner is difficult”. There are many measurements of chlorine at the poles. This doesn’t prove that “chlorine atom was produced from the photolysis of CFCs at mid-latitudes and then transported for a very long distance to the poles”. HCl and ClONO2 can be synthesized by numerous reactions.
    The wall effect exercises only a little influence on radical reactions (which are very fast i.e. micro- to milliseconds, thus the radicals have no time to reach the walls by diffusion). It is only an excuse for someone who couldn’t prove that “one chlorine atom could destroy 100.000 ozone molecules”. If the results obtained from the experience I proposed previously were not in agreement which the theory (chlorine atoms resulting from CFCs destroy ozone), this means that the crucial theory (the destruction of the ozone layer is essentially due to the production of chlorine atom resulting from CFCs), on which is based the Montreal Protocol in 1987, is unfounded. A true scientist should know that a theory accepted (or a model elaborated) by many experts, doesn’t mean that it is correct.
    I don’t know how you and your experts conceive the atmospheric model. But one thing is certain: when the results and predictions taken from a model are very different from reality, hence this model is not good. We need to do an auto-critic and try to find the reasons why.
    You liked using cutting statements to hurt people and you continue to do it (in spite your arguments are not solid; you don’t have enough critical mind when reading a scientific paper). This is because you think you know everything and all the others are idiots, writing garbage. So I tried to offer a similar “gift” to you and I found that you were very unhappy. Now with your permission, I would like to stop the discussion with you here. I don’t want to continue it anymore.
    Thank you so much.
    Trandinh Son

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