We really appreciate the interest and comments regarding our manuscript. We hope we address all the lingering issues in this reply. This also gives us the opportunity of publishing an update on our dataset that will complete the original manuscript (see Table 1). We have followed the author pattern in our answers: I-Gas sampling procedure, 2-Reported gas concentrations results, 3-General remarks, 4-Conclusions. (c) 2007 Elsevier B.V. All rights reserved.