**********************************************************************
*** Atmospheric CO concentrations (ppbv)  derived from flask       ***
*** samples collected at Shetland Islands, Scotland                 ***
*** Source: L.P. Steele                                            ***
***              P.B. Krummel                                      ***  
***              R.L. Langenfelds                                  ***
***              Commonwealth Scientific,                          ***
***              and Industrial Research Organisation,             ***
***              Aspendale, Victoria,                              *** 
***              Australia  3195                                   ***                   
***                                                                ***   
*** February 2003                                                  ***
***                                                                ***
**********************************************************************

Year	Jan.	Feb.	Mar.	Apr.	May	Jun.	Jul.	Aug.	Sep.	Oct.	Nov.	Dec.	Ann. Ave.

1992												136.55	
1993	144.48	153.83	162.43	162.05	136.83	104.28	90.67	87.98	98.39	117.74	129.26	148.18	128.01
1994	163.8	163.89	172.36	167.41	139.31	111.51	96.16	104.87	119.84	127.17	132.43	142	136.73
1995	157.04	162.43	163.82	162.48	138.86	113.72	105	96.96	102.85	117.42	121.87	134.29	131.40
1996	154.74	160.27	159.59	153.44	133.91	115.75	101.29	94.5	105.02	119.94	128.26	141.47	130.68
1997	153.91	154.62	155.98	155.11	136.64	107.33	87.51	82.52	91.83	112.62	135.19	147.31	126.71
1998	155.54	159.57	164.38	166.68	146.74	117	104.48	119.88	151.79	171	159.67	155.97	147.73
1999	165.74	159.09	154.72	156.06	138.27	112.01	90.56	84.93	96.66	104.96	113.28	126.93	125.27
2000	136.36	140.99	147.11	144.51	126.84	103.29	86.05	88.2	95.3	96.36	106.57	124.59	116.35
2001	135.6	144.77	153.65	149.81	128.65	103.62	89.76	84.96	91.96	106.29	114.22	125.34	119.05


Monthly values, expressed in parts per billion by volume (ppbv), are linked to the gravimetrically derived 
scale of NOAA/CMDL using a single high-pressure cylinder standard with a CO mole fraction of 196 ppbv.  
Stability of the CSIRO scale and variations in instrument response are monitored with about 20 high 
pressure cylinder standards, with lifetimes of 4 to 10 or more years, spanning a CO range of 20 to 
400 ppbv.  Monthly values are calculated as the mean of the daily values from a smooth curve fit to 
the data using curve-fitting routines described by Thoning et al. 1989.  Annual values are the arithmetic 
means of the 12 monthly values.