Greenhouse gas observations from Cabauw Tall Tower (1992–2010)

A. T. Vermeulen, A. Hensen, M. E. Popa, W. C. M. van den Bulk, P. A. C. Jongejan
2010 Atmospheric Measurement Techniques Discussions  
Since 1992 semi-continuous in-situ observations of greenhouse gas concentrations have been performed at the tall tower of Cabauw (4.927 • E, 51.971 • N, −0.7 m a.s.l.). Through 1992 up to now, the measurement system has been gradually extended and improved in precision, starting with CO 2 and CH 4 concentrations from 200 m a.g.l. in 1992 to vertical gradients at 4 levels of the gases CO 2 , CH 4 , SF 6 , N 2 O, H 2 , CO and gradients at 2 levels for 222 Rn. In this paper the measurement systems
more » ... measurement systems and measurement results are described for the main greenhouse gases and CO, for the whole period. The automatic measurement system now provides half-hourly concentration gradients with a precision better than or close to the WMO recommendations. The observations at Cabauw show a complex pattern caused by the influence of sources and sinks from a large area around the tower with significant contributions of sources and sinks at distances up to 500-700 km. The concentration footprint area of Cabauw is one the most intensive and complex source areas of greenhouse gases in the world. Despite this, annual mean trends for the most important greenhouse gases, compatible with the values derived using the global network, can be reproduced from the measured concentrations at Cabauw over the entire measurement period, with a measured increase in the period 2000-2009 for CO 2 of 1.90 ± 0.1 ppm yr −1 , for CH 4 of 4.4 ± 0.6 ppb yr −1 , for N 2 O of 0.86 ± 0.04 ppb yr −1 , and for SF 6 of 0.27 ± 0.01 ppt yr −1 ; for CO no significant trend could be detected. The influences of strong local sources and sinks are reflected in the amplitude of the mean seasonal cycles observed at Cabauw, that are larger than the mean Northern Hemisphere average; Cabauw mean seasonal amplitude for CO 2 is 25-30 ppm (higher value for lower sampling levels). The observed CH 4 seasonal amplitude is 50-110 ppb. All gases
doi:10.5194/amtd-3-4169-2010 fatcat:irvcpmlytfa7vmhupecalwpu24