Abstract. The PAES (French acronym for synoptic scale atmospheric pollution) network focuses on the chemical composition (ozone, CO, NOx/y and aerosols) of the lower troposphere (0–3000 m). Its high-altitude surface stations located in different mountainous areas in France complete the low-altitude rural MERA stations (the French contribution to the european program EMEP, European Monitoring and Evaluation Program). They are representative of pollution at the scale of the French territory because they are away from any major source of pollution. This study deals with ozone observations between 2001 and 2004 at 11 stations from PAES and MERA, in addition to 16 elevated stations located in mountainous areas of Switzerland, Germany, Austria, Italy and Spain. The set of stations covers a range of altitudes between 115 and 3550 m. The comparison between recent ozone mixing ratios to those of the last decade at Pic du Midi (2877 m), as well as trends calculated over 14-year data series at three high-altitude sites in the Alps (Jungfraujoch, Sonnblick and Zugspitze) reveal that ozone is still increasing but at a slower rate than in the 1980s and 1990s. The 2001–2004 mean levels of ozone from surface stations capture the ozone stratification revealed by climatological profiles from the airborne observation system MOZAIC (Measurement of OZone and water vapour by Airbus In-service airCraft) and from ozone soundings above Payerne (Switzerland). In particular all data evidence a clear transition at about 1000–1200 m a.s.l. between a sharp gradient below (of the order of +30 ppb/km) and a gentler gradient (+3 ppb/km) above. The same altitude (1200 m) is also found to be a threshold regarding how well the ozone levels at the surface stations agree with the free-tropospheric reference (MOZAIC or soundings). Below the departure can be as large as 40%, but suddenly drops within 15% above. For stations above 2000 m, the departure is even less than 8%. Ozone variability also reveals a clear transition between boundary-layer and free-tropospheric regimes around 1000 m a.s.l. Below, diurnal photochemistry accounts for about the third of the variability in summer, but less than 20% above – and at all levels in winter – where ozone variability is mostly due to day-to-day changes (linked to weather conditions or synoptic transport). In summary, the altitude range 1000–1200 m clearly turns out in our study to be an upper limit below which specific surface effects dominate the ozone content. Monthly-mean ozone mixing-ratios show at all levels a minimum in winter and the classical summer broad maximum in spring and summer – which is actually the superposition of the tropospheric spring maximum (April–May) and regional pollution episodes linked to persistent anticyclonic conditions that may occur from June to September. To complement this classical result it is shown that summer maxima are associated with considerably more variability than the spring maximum. This ensemble of findings support the relevance of mountain station networks such as PAES for the long-term observation of free-tropospheric ozone over Europe.

Abstract. The PAES (French acronym for synoptic scale atmospheric pollution) network focuses on the chemical composition (ozone, CO, NOx/y and aerosols) of the lower troposphere (0–3000 m). Its high-altitude surface stations located in different mountainous areas in France complete the low-altitude rural MERA stations (the French contribution to the european program EMEP, European Monitoring and Evaluation Program). They are representative of pollution at the scale of the French territory because they are away from any major source of pollution. This study deals with ozone observations between 2001 and 2004 at 11 stations from PAES and MERA, in addition to 16 elevated stations located in mountainous areas of Switzerland, Germany, Austria, Italy and Spain. The set of stations covers a range of altitudes between 115 and 3550 m. The comparison between recent ozone mixing ratios with those of the last decade found in the literature for two high-elevation sites (Pic du Midi, 2877 m and Jungfraujoch, 3580 m) leads to a trend that has slowed down compared to old trends but remains positive. This could be attribuable to the reduction of ozone precursors at European scale, that however do not compensate an ozone increase at the global scale. Averaged levels of ozone increase with elevation in good agreement with data provided by the airborne observation system MOZAIC (Measurement of OZone and water vapour by Airbus In-service airCraft), showing a highly stratified ozone field in the lower troposphere, with a transition at about 1000 m asl between a sharp gradient (30 ppb/km) below but a gentler gradient (3 ppb/km) above. Ozone variability also reveals a clear transition between boundary-layer and free-tropospheric regimes at the same altitude. Below, diurnal photochemistry accounts for about the third of the variability in summer, but less than 20% above – and at all levels in winter – where ozone variability is mostly due to day-to-day changes (linked to weather conditions or synoptic transport). Monthly-mean ozone mixing-ratios show at all levels a minimum in winter and the classical summer broad maximum in spring and summer – which is actually the superposition of the tropospheric spring maximum (April–May) and regional pollution episodes linked to persistent anticyclonic conditions that may occur from June to September. To complement this classical result it is shown that summer maxima are associated with considerably more variability than the spring maximum. This ensemble of findings support the relevance of mountain station networks such as PAES for the long-term observation of free-tropospheric ozone over Europe.

Households' daily mobility in France is characterized by the preponderance of the automobile. Passenger cars, mainly used by households but not only, are thus responsible for more than a half of fuel consumption in road transport (CGDD/SoES, July 2013) and more than a half of CO 2 emissions in the transport sector (SoES/CDC, December 2012). The main objective of this paper is thus to explain the modal choice of French households for their local daily trips, particularly the importance of the car, and to predict potential shifts from personal car to shared car. A multinomial logit model is estimated and reveals the particular importance of car equipment on modal choices and specifically on car use. Simulations by 2020 are thus conducted under three scenarios depending on the household's motorization (no car, one car, two cars or more) and per different mobility profiles. Personal car should remain the main mode of transportation by 2020 except if households have no car. In that case, modal shares would be more balanced, public transport would become the main transport mode and the shift to shared car would be at a maximum. Modal share of shared car could thus reach 16% for "exclusive motorists". A conditional logit model is also estimated and shows no particular importance of the means of transportation's costs in the modal choices. These results show that the increase in distances between 2010 and 2020 makes motorized modes more necessary. Thus, personal car and public transport should remain the main modes of transportation by 2020. Moreover, expected changes in costs and travel time by 2020 does not seem to have any effect on the deployment of shared car, its modal share being constant (in an average) between 2010 and 2020.

Abstract. Continuous CO measurements performed at 3 high-altitude stations in France are analyzed for the first time. Data are provided by the new PAES (Pollution Atmospherique à l'Echelle Synoptique) network since 2002 for the Puy de Dôme and 2004 for the Pic du Midi and the Donon. CO measurements of 5 another European stations have been analysed to put the PAES stations in an European perspective. The January 2002–April 2005 CO mean levels of surface stations capture the stratification revealed by climatological CO profiles from the airborne observation system MOZAIC (Measurement of OZone and water vapour by Airbus In-service Aircraft). The deviation between the free tropospheric reference MOZAIC and surface data above 2000 m is less than 10% and this deviation can be explained in term of spatial variability, as evidenced by MOPITT CO retrievals at 700 hPa. This suggests that, averaged at a seasonal time scale (4 months), surface data at stations above 2000 m are representative of background CO concentration. This paper focuses then on trends since the 1980s–1990s. The comparison between old (1982–1983) and recent CO mixing ratio (2005) at the Pic du Midi leads to a 10% decrease, consistent with the continuous data series at Zugspitze (ZSP) from 1991 to 2004. This decrease was found to be mainly due to a negative trend of January–April mean levels. The decrease in CO sources over France and Europe appears to be responsible for that trend. The stable values of June–September mean levels suggest that the summertime oxidizing capacity of the atmosphere related to OH radicals is important enough to counterbalance any CO inputs into the troposphere. Our study shows a recent change in CO evolution since 2000 over Western Europe, with a slowed down decrease in CO concentration. Studying specifically the interactions between CO, CH4 and OH turns out to be needed, however, to find definitive explanations to those observations.

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