November, 2009

 1. The original ADS GCMS instruments at Mace Head and Cape Grim were retired
    in December 2004, and replced by new generation of improved GC-MS system.
    The new GC-MS cryogenic preconcentration system, which we called Medusa
    have been installed in five (Macehead, Trinidad Head, Barbados, Samoa, 
    and Cape Grim) AGAGE sites. This new Medus GC-MS system has much better 
    capability to measure most volatile and radiatively active perfluorinated 
    compounds.

 2. Please see "readme.scale" for calibration scale used for in-situ measuremnets 
    from AGAGE GC-MS Medusa instruments

 3. Most of GC-MS-Medusa data up to March 2009 are included in this update 

 4. Archived data are saved in the follwoing three folders
     (a) complete   -- all high frequency mesurements with pollution flags
                       (identified by "P" after reported mole fractions (ppt))  
     (b) monthly    -- monthly means of backgound values at 5 AGAGE sites
     (c) precisions -- instrument precision files 

 5. HFC-125 data are included as part of released compounds measured 
    by AGAGE GCMS-Medusa instrument in Nov. 2009. The following 18 compounds
    are available from AGAGE GC-MS Medusa instrument for public access
       CFC-113
       HCFC-22,  HCFC-141b, HCFC-142b
       HFC-125,  HFC-134a,  HFC-152a,  HFC-365mfc
       Halon-1211, Halon-1301 
       CH3Cl,    CH2Cl2,    CHCl3
       CH3CCl3,  CHClCCl2,  CCl2CCl2
       SF6,      SO2F2

 6. Please be aware both Medusa TCE (CHClCCl2), and PCE (CCl2CCl2) data
    have not been applied "blank correction". Those data are preliminary
    and will be updated later (after blank correction is applied).  

 7. It was found that there are offsets in Mace Head CHCl3 data between 
    GC-MD and GC-MS Medusa measurements. The reason is unknown and it's
    under investigation by instrument team.

=======
 In subdirectories "complete" and "precisions", there are five further
 subdirectories (macehead, trinidad, barbados, samoa, tasmania), one for
 each monitoring site. The data files are named according to the convention

    station_name-medusa_yyyy.typ (example, Barbados-medusa_2005.dat, and 
                                           Barbados-medusa_2005.pre)
 where 
    "station_name" indicates station name, such as 
       Macehead
       Trinidadhead
       Barbados
       Samoa
       Capegrim

    "medusa" indicates intrument (GC-MS-Medusa)
    
    "yyyy" inducates year (e.g. 2005)
    
    "typ" indicates date type, such as 
       dat -- for measured compounds in mole fraction
       pre -- for precision information of measured species
        

 I.
 For measured compounds in mole fraction, for example, "Macehead_medusa_2009.dat"
 The first 2 lines are headers, indicating the date of raw data file being created
 and time and reported species

 the first column, "YYYYMMDD", is date in year (YYYY), month (MM) and day (DD)
 The 2nd   column, "hh:mm",    is time in hour (hh), and minute (mm)
 the 3rd   column, "ABSDA",    is the day number since the first day of 
                                  ALE/GAGE/AGAGE program
 the 4th to last columns,  are mole fractions (ppt) of measured species.
            a flag "P" immediately following reported mole fraction indicates
            it's a pollution event (non-baseline) base on AGAGE's pollution
            identification algorithm. For those without "P" flag, they are
            determined to be baseline data.   

 II.
 For instrument precisions, for example, "Macehead-medusa_2009.pre"
 It was represented by daily standard deviation of individual calibration
 tank measurements divided by the mean of two surrounding (in time) measurements
 (time 100; units are in percent).
 
 the first column, "YYYYMMDD", indicates year (YYYY), month (MM) and day (DD)
 the 2nd   column, "Gday"    , is the day number since the first day of                                     
                                  ALE/GAGE/AGAGE program               
 For each compound, there are 2 columns used to indicate precisioninformation
      the 1st under "%s" column, is daily standard deviation in percent of the 
                     ratio of measured calibration tank values (as described
                     earlier). In general, the smaller this number the better
                     instrument precision.
      the 2nd column, under "n", indicates # of measurements to derive
                     standard deviation
          

=====
 In sub-directory, "monthly", monthly average of background (i.e. without
      "P" flag) values at each site are saved here.

 In monthly mean file (e.g. "Macehead_medusa.mon"), 
 the 1st column, "MM/YYYY", indicates month (MM) and year (YYYY) 
 the 2nd to 4th columns, are used to represent HFC-134a 
    where, 2nd column ("N")   indictes # of baseline measurements in this month
           3rd column ("VAL") indicates monthly mean value of baseline data
           4tn column ('SD")  indicates standard deviation of monthly mean 

 The same format as columns 2 to 4 are then repreated for all other reported species

 ====

 END