High temporal resolution measurements of ozone precursors in a rural background station. A two-year study.

We present a very complete database of individual non-methane hydrocarbon (NMHC) measurements with high temporal resolution (hourly) in a rural background atmosphere. We show their use to characterize the biogenic NMHC as well as to identify the transport and impact of anthropogenic NMHC on rural areas. In January 2003 an automatic GC-FID analyzer of volatile organic compounds between 2 and 10 carbon atoms (C2-C10 VOCs) was placed in the centre of the Valderejo Natural Park in northern Iberia (42.87 degrees N, 3.22 degrees W), far away from important cities. The system operated continuously until December 2004. Data coverage was higher than 70% for a total of 59 VOC of both anthropogenic and biogenic origin, with detection limits in the range of pptv. Our results allow for the description of the behaviour of these compounds, in order to identify external impacts arriving to the sampling site which has been recognized to be highly representative of a rural background atmosphere. Biogenic VOC concentrations have been compared also with the calculated emissions, using Guenther's algorithm, and the discrepancies interpreted in terms of the different reactivity of such compounds.