Western European N2O emissions:: A top-down approach based on atmospheric observations

We present a 3 year record of continuous gas chromatographic nitrous oxide (N2O) observations performed at the urban station Heidelberg (Germany) together with weekly flask data from a remote continental site, Schauinsland (Black Forest, Germany), and two-weekly integrated data from the maritime background station Izana (Canary Islands). These data are supplemented by continuous atmospheric radon 222 observations. Mean rates of increase of N2O of 0.70-0.78 ppb yr(-1) were observed over the continent and in maritime background air (Izana). The well-mixed continental mixing ratio was found to be higher by only 1.1 ppb (Schauinsland) and 2.4 ppb (Heidelberg) than for maritime background air. Specially tailored data selection of the Heidelberg record allowed the changing influence of a regional N2O point source (adipic acid production, BASF AG) to be clearly identified. The radon (Rn-222) tracer method was applied to nighttime N2O observations at Heidelberg to estimate mean regional emissions, which changed from (161 +/- 32) mug N2O-N m(-2) h(-1) in 1996-1997 to (77 +/- 10) mug N2O-N m h(-1) in 1998 as a consequence of 90% emission reduction from BASF. An estimate of the continental N2O flux from southwestern Europe based on further selected Heidelberg data (only well-mixed, late afternoon situations) and observations from the Schauinsland station yielded mean N2O fluxes of (43 +/- 5) mug N2O-N m(-2) h(-1) and (42 +/- 4) mug N2O-N m(-2) h(-1) These results compare well with statistical emissions inventories, when taking into account possible systematic errors of the radon tracer method of 30-35%.