The following is an excerpt from documents of NOAA/CMDL flask sampling

network which explain the flags (fff) put on the event data.

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*** CO2 data ***

     Explanation of data selection and definition of flags:



          Since samples are collected in pairs, the pair  

          difference is calculated, and samples with 

          a pair difference greater than 0.5 ppm are 

          flagged.  Through 1988 one or both members of a bad pair

          were sometimes retained if they fell within

	  +/- 3 sigma from a fitted curve.  From 1989 to

	  the present, both members of bad pairs have

	  been automatically rejected.  Retained and

	  rejected flasks are flagged as follows.

	  (NOTE: if either the first or second of these three characters is

	  not a period, the sample has been rejected.):



                         Flag         Description



     Retained     ... (3 periods)   good pair        

                                     (D <= 0.5 ppm)

                        ..H         high member of bad

                                    pair; retained

                        ..L         low member of bad

                                    pair; retained

                        ..S         single flask;    

                                    retained



     Rejected           .X.         rejected as not

                                    representative of 

                                    background 

                                    conditions (>3

                                    sigma from a fitted 

                                    curve)



                        +..         high member of bad

                                    pair; rejected

                        -..         low member of bad

                                    pair; rejected



                        R..         single flask;    

                                    rejected



                        *..         off scale or broken

                                    flask; rejected



                        N..         rejected due to  

                                    error in sampling 

                                    or analysis



                        T..         sample collected as

                                    part of a methods

                                    test; not used in

                                    data analysis



***** CH4 *****

     fff = a three-character flag indicating the results

           of our data selection process.



           An alphanumeric other than a period (.) in the FIRST

           column indicates samples with obvious problems during

           sample collection or analysis.



           An alphanumeric other than a period (.) in the SECOND

           column indicates samples which are believed to be

           non-background.



           An alphanumeric other than a period (.) in the THIRD

           column is a sample qualifier that is not presently used.





***** CO *****

     fff = a three-character flag indicating the results

           of our data selection process.



           An alphanumeric other than a period (.) in the FIRST

           column indicates samples with problems during

           sample collection or analysis.



           An alphanumeric other than a period (.) in the SECOND

           column indicates samples thought to represent non-

           background conditions.



           An alphanumeric other than a period (.) in the THIRD

           column is a sample qualifier that is not presently used.