Extensive trace gas measurement campaigns were performed in 2005 at the Swiss high‐altitude station Jungfraujoch, including measurements of ozone (O3), carbon monoxide (CO), nitrogen oxides (NOx = NO + NO2), the sum of reactive nitrogen species (NOy), peroxyacetylnitrate (PAN), formaldehyde (HCHO), oxygenated volatile organic compounds (OVOCs), volatile hydrocarbons (HCs), methane (CH4), and nitrous oxide (N2O). The air masses arriving at Jungfraujoch experience particular transport pathways and therefore are expected to have characteristic chemical signatures. These characteristics are often masked by mixing with European planetary boundary layer air. In order to address the influence of European emissions, a method to retrieve “background concentrations” based on backward trajectories and statistics was developed and applied to the trace gas observations at Jungfraujoch. This procedure is important to determine baseline values for subsequent assessment of surface air quality targets. Cluster analysis of backward trajectories for “background conditions” shows that the influence of long‐range transport is discernible in most of the clusters. Air masses tend to have lower background concentrations whenever transport conditions favor a higher amount of photochemical degradation (e.g., low latitude or no recent contact to emissions). The results of this study represent an alternative to aircraft measurements which are typically used to determine free tropospheric background conditions. They are valuable for comparison with numerical simulations and for policy making, and provide additional information about free tropospheric chemistry.

Abstract. Methods for the determination of ship fuel sulphur content and NO x emission factors based on remote measurements have been compared in the harbour of Rotterdam and compared to direct stack emission measurements on the ferry Stena Hollandica. The methods were selected based on a review of the available literature on ship emission measurements. They were either optical (LIDAR, Differential Optical Absorption Spectroscopy (DOAS), UV camera), combined with model-based estimates of fuel consumption, or based on the so called "sniffer" principle, where SO 2 or NO x emission factors are determined from simultaneous measurement of the increase of CO 2 and SO 2 or NO x concentrations in the plume of the ship compared to the background. The measurements were performed from stations at land, from a boat and from a helicopter. Mobile measurement platforms were found to have important advantages compared to the land-based ones because they allow optimizing the sampling conditions and sampling from ships on the open sea. Although optical methods can provide reliable results it was found that at the state of the art level, the "sniffer" approach is the most convenient technique for determining both SO 2 and NO x emission factors remotely. The average random error on the determination of SO 2 emission factors comparing two identical instrumental set-ups was 6 %. However, it was found that apparently minor differences in the instrumental characteristics, such as response time, could cause significant differences between the emission factors determined. Direct stack measurements showed that about 14 % of the fuel sulphur content was not emitted as SO 2 . This was supported by the remote measurements and is in agreement with the results of other field studies.

Abstract. Methods for the determination of ship fuel sulphur content and NOx emission factors from remote measurements have been compared in the harbour of Rotterdam and compared to direct stack emission measurements on the ferry Stena Hollandica. The methods were selected based on a review of the available literature on ship emission measurements. They were either optical (LIDAR, DOAS, UV camera), combined with model based estimates of fuel consumption, or based on the so called "sniffer" principle, where SO2 or NOx emission factors are determined from simultaneous measurement of the increase of CO2 and SO2 or NOx concentrations in the plume of the ship compared to the background. The measurements were performed from stations at land, from a boat, and from a helicopter. Mobile measurement platforms were found to have important advantages compared to the landbased ones because they allow to optimize the sampling conditions and to sample from ships on the open sea. Although optical methods can provide reliable results, it was found that at the state of the art, the "sniffer" approach is the most convenient technique for determining both SO2 and NOx emission factors remotely. The average random error on the determination of SO2 emission factors comparing two identical instrumental set-ups was 6%. However, it was found that apparently minor differences in the instrumental characteristics, such as response time, could cause significant differences between the emission factors determined. Direct stack measurements showed that about 14% of the fuel sulphur content was not emitted as SO2. This was supported by the remote measurements and is in agreement with the results of other field studies.

No abstract