Emission estimates based on ambient N₂O concentrations measured at a 200m high tower in the Netherlands 1995–1997

Abstract

In the period 1995 to 1997 the N₂O concentration in ambient air at 200 m height was measured at the 200 m tower in Cabauw in the center of the Netherlands. These measurements were carried out simultaneously with CO₂ and CH₄ measurements. In this paper the time series for the different trace gas species are compared for the year 1995. This comparison shows the different nature of N₂O as compared to the two more abundant trace gases, methane (CH₄) and carbon dioxide (CO₂). The diffuse character of the main N₂O source in our region, the agricultural soils, in combination with the relatively poor resolution of the measurements as compared to the resolution of the CO₂ and CH₄ data, makes a detailed evaluation of the emissions impossible. Alternatively a simple calculation is proposed to evaluate the N₂O emission for a region up to about 200 km upwind of the measurement location. This calculation uses the sudden increase in concentration that is observed after the break-up of a nocturnal inversion layer. The results of 26 nights show an emission level of 31 ± 13 kton N/year. This level is lower compared to the emission level of 47.4 kton N/year that is reported for 1996 for the Netherlands using bottom up inventories.