Distributed Modified Bowen Ratio method for surface layer fluxes of reactive and non-reactive trace gases

Modified Bowen ratio technique was used in a horizontally distributed form to determine turbulent fluxes of CO2, H2O, O3, NO and NO2 over a semi-natural grassland site in North-Eastern Germany. The applicability of the distributed variation of the Modified Bowen Ratio technique was proven prior to the calculation of trace gas fluxes. Turbulent NO fluxes were compared to fluxes up-scaled from laboratory measurements of biogenic NO emission from soil samples, which have been taken at the field site. The NO fluxes up-scaled from laboratory measurements were slightly larger than the fluxes observed in the field. However, both NO fluxes agreed within a factor of two. Under suitable night time conditions, we performed a detailed comparison of turbulent fluxes of CO2 and O3 with fluxes derived by the boundary layer budget technique. While there was agreement between these fluxes in a general sense, specific deviations were observed. They could be attributed to different footprint sizes of both methods and to in situ chemistry within the nocturnal boundary layer.

Research highlights▶ Horizontally separated proxy measurement in MBR technique feasible. ▶ Field and laboratory derived NO fluxes comparable. ▶ Vertical flux divergence critical for intercomparison of different methods.