Ozone and Cosmic Rays

The paper by Lu published in PRL in 2009 is being held up by part of the community to show that established theories of ozone depletion are totally wrong.  The paper actually accepts that Polar Stratospheric Clouds and halogens from CFCs and similar man-made chemicals are fundamental to Antarctic ozone depletion.  It however suggests that photochemistry does not trigger ozone depletion, and that depletion is instead generated by electrons from Cosmic Rays.  Unfortunately this paper suffers from fundamental flaws - it does not use all the available data and omits one critical observation.  Cosmic Ray data from South Pole is available back to 1964 according to the reference given in the paper (http://www.bartol.udel.edu/~pyle/bri_table.html) and ozone data from our site is available back to 1956.  CFC data is available for a similar period, so a multivariate analysis could have been conducted.  The paper selectively only uses data from 1990 to 2008, during which period the ozone hole has been on a plateau with minimum values being similar from one year to the next.  The paper argues that this is acceptable because the other variables (halogen concentration and ice amount) are roughly constant during this period and so any variation must be due to other causes (Cosmic Rays).  The theory requires that ozone amounts should begin to drop as soon as PSCs are present, however observations show that this is not the case and depletion does not start until PSCs are exposed to sunlight.  The Cosmic Ray hypothesis as presented is thus shown to be false.  This should have been picked up by the referees. 

Cosmic Rays can cause ozone depletion in the upper-most part of the ozone layer, which contains less than 10% of the total ozone column.  However, when the ozone hole is present over 60% of the total ozone is destroyed.  Much of the observed inter-annual variation in ozone depletion can be linked to ozone layer temperature and the consequent variation in volume of PSCs.  However, the photochemical theory does not exclude some variation being due to Cosmic Rays and this might be worth further investigation.