Sensitivity of CO₂ and CH₄ Annual Cycles to Different Meteorological Variables at a Rural Site in Northern Spain

Table 5

Differences between average concentrations calculated with observations selected for thresholds and the annual cycle for nighttime observations. Availability of frequencies and number of days without observations (gaps) are also presented.

Type of test	Recirculation factor threshold	Availability (%)	Gap (days)	CO2 difference		CH4 difference
				ppm	%	ppm	%
Above	0.05	42.9	9	1.4	0.35	0.007	0.36
	0.10	25.9	57	2.2	0.55	0.010	0.51
	0.15	17.6	102	2.6	0.65	0.012	0.62
	0.20	12.7	137	3.1	0.77	0.015	0.76
	0.25	9.5	167	3.3	0.83	0.015	0.81
	0.30	7.5	188	3.8	0.96	0.017	0.92
Below	0.01	17.1	90	−2.2	−0.55	−0.010	−0.51
	0.02	30.1	39	−1.7	−0.41	−0.008	−0.42
	0.03	39.6	17	−1.5	−0.38	−0.007	−0.37
	0.04	47.2	9	−1.4	−0.35	−0.006	−0.33
	0.05	52.7	8	−1.2	−0.31	−0.005	−0.28
	0.06	57.6	7	−1.1	−0.28	−0.005	−0.26