Table 2. Separation of Data Sets Into Two Groups According To Whether the Seasonal Cycle is Below or Above 1% Significance Levela

Data	Below 1%	Above 1%
NOAA flask pre-1996	Alert (0.267)	Niwot Ridge
	Barrow (0.160)	Cape Matatula
	Mauna Loa (0.174)	South Pole
	Cape Grim (0.289)	
NOAA flask post-1996	Alert (0.062)*	Niwot Ridge
	Barrow (0.060)	Mauna Loa
	Cape Kumakahi (0.047)*	Cape Matatula
		Niwot Ridge
		South Pole
ALE 78–86		Mace Head
		Trinidad Head
	None	Ragged Point
		Cape Matatula
		Cape Grim
GAGE 85–96		Mace Head
		Trinidad Head
	None	Ragged Point
		Cape Matatula
		Cape Grim
AGAGE 93-03	Mace Head (0.022)*	Trinidad Head
	Cape Matatula (0.033)*	Ragged Point
	Cape Grim (0.024)*	
CATS	Barrow (0.004)*	Mauna Loa
	South Pole (0.007)*	Cape Matatula
		Niwot Ridge
RITS	Barrow (0.070)	Mauna Loa
	Niwot Ridge (0.182)	Cape Matatula
	South Pole (0.066)	
aThe standard deviations of measurement errors are given in brackets by frac1N sqrtsumlimitsj = 1/N sigmaj2. Units are ppb. Seven stations marked by asterisks are selected for detailed study.