Background and anthropogenic influences on atmospheric CO2 concentrations measured at Pallas : comparison of two models for tracing air mass history

The FLEXTRA and SILAM models were utilized in estimating the influence regions (IR) for the measured CO 2 concentration ([CO 2 ]) at Pallas together with tracers for anthropogenic emissions.The models produced similar synoptic features and associated background [CO 2 ] with marine IR and elevated [CO 2 ] with continental IR, but there were also differences which affected the interpretation of measurements.The background, i.e. marine boundary layer (MBL) signal, was compared to the NOAA MBL reference.Both models performed well, with monthly mean deviations from the reference usually inside 1 ppm.The FLEXTRA MBL signal had some seasonality in the difference, however, only very few cases were associated with anthropogenic emissions.We used [CO] and fossil fuel [CO 2 ] simulations by the TM5 (CarbonTracker CT2011_oi) model as emission tracers.The model and [CO] captured well the timing of high [CO 2 ] in measurements.The anthropogenic influence was more pronounced in winter than in summer, and it had a large inter-annual variation.