The SO2 and DMS data contained in these files were obtained by gas chromatography - mass spectrometry using isotopically labelled internal standards added to the sampled air stream. Precision of these measurements is about 1 part-per-trillion by volume (pptv). The samples for SO2 and DMS were independent but were collected simultaneously. The concentration of each species is the value integrated over the sample period given. The data files have one line for each sample period in the following format: day of the year, start time of the sample in seconds past midnight, stop time of the sample in seconds past midnight, midpoint time of the sample in seconds past midnight, SO2 in pptv, DMS in pptv. Missing data are indicated by -99. The limit of detection is estimated to be 1 pptv for DMS and for SO2. The samples in which SO2 or DMS were not detected are indicated as -8. Flights 1-10 and 29-33 have a slightly different format. See the data file header for more information.