Abstract. To estimate the impact of emissions by road, aircraft and ship traffic on ozone and OH in the present-day atmosphere six different atmospheric chemistry models have been used. Based on newly developed global emission inventories for road, ship and aircraft emission data sets each model performed sensitivity simulations reducing the emissions of each transport sector by 5%. The model results indicate that on global annual average lower tropospheric ozone responds most sensitive to ship emissions (50.6%±10.9% of the total traffic induced perturbation), followed by road (36.7%±9.3%) and aircraft exhausts (12.7%±2.9%), respectively. In the northern upper troposphere between 200–300 hPa at 30–60° N the maximum impact from road and ship are 93% and 73% of the maximum effect of aircraft, respectively. The latter is 0.185 ppbv for ozone (for the 5% case) or 3.69 ppbv when scaling to 100%. On the global average the impact of road even dominates in the UTLS-region. The sensitivity of ozone formation per NOx molecule emitted is highest for aircraft exhausts. The local maximum effect of the summed traffic emissions on the ozone column predicted by the models is 0.2 DU and occurs over the northern subtropical Atlantic extending to central Europe. Below 800 hPa both ozone and OH respond most sensitively to ship emissions in the marine lower troposphere over the Atlantic. Based on the 5% perturbation the effect on ozone can exceed 0.6% close to the marine surface (global zonal mean) which is 80% of the total traffic induced ozone perturbation. In the southern hemisphere ship emissions contribute relatively strongly to the total ozone perturbation by 60%–80% throughout the year. Methane lifetime changes against OH are affected strongest by ship emissions up to 0.21 (± 0.05)%, followed by road (0.08 (±0.01)%) and air traffic (0.05 (± 0.02)%). Based on the full scale ozone and methane perturbations positive radiative forcings were calculated for road emissions (7.3±6.2 mWm−2) and for aviation (2.9±2.3 mWm−2). Ship induced methane lifetime changes dominate over the ozone forcing and therefore lead to a net negative forcing (−25.5±13.2 mWm−2).

Abstract. Tropospheric NO 2 column retrievals from the Global Ozone Monitoring Experiment (GOME) satellite spectrometer are used to quantify the source strength and 3-D distribution of lightning produced nitrogen oxides (NO x =NO+NO 2 ). A sharp increase of NO 2 is observed at convective cloud tops with increasing cloud top height, consistent with a power-law behaviour with power 5±2. Convective production of clouds with the same cloud height are found to produce NO 2 with a ratio 1.6/1 for continents compared to oceans. This relation between cloud properties and NO 2 is used to construct a 10:30 local time global lightning NO 2 production map for 1997. An extensive statistical comparison is conducted to investigate the capability of the TM3 chemistry transport model to reproduce observed patterns of lightning NO 2 in time and space. This comparison uses the averaging kernel to relate modelled profiles of NO 2 to observed NO 2 columns. It exploits a masking scheme to minimise the interference of other NO x sources on the observed total columns. Simulations are performed with two lightning parameterizations, one relating convective preciptation (CP scheme) to lightning flash distributions, and the other relating the fifth power of the cloud top height (H5 scheme) to lightning distributions. The satellite-retrieved NO 2 fields show significant correlations with the simulated lightning contribution to the NO 2 concentrations for both parameterizations. Over tropical continents modelled lightning NO 2 shows remarkable quantitative agreement with observations. Over the oceans however, the two model lightning parameterizations overestimate the retrieved NO 2 attributed to lightning. Possible explanations for these overestimations are discussed. The ratio between satellite-retrieved NO 2 and modelled lightning NO 2 is used to rescale the original modelled lightning NO x production. Eight estimates of the lightning NO x production in 1997 are obtained from spatial and temporal correCorrespondence to: K. F. Boersma (boersma@knmi.nl) lation methods, from cloud-free and cloud-covered observations, and from two different lightning parameterizations. Accounting for a wide variety of random and possible systematic errors, we estimate the global NO x production from lightning to be in the range 1.1-6.4 Tg N in 1997.

Abstract. We present a computationally efficient approach to account for the non-linear chemistry occurring during the dispersion of ship exhaust plumes in a global 3-D model of atmospheric chemistry (GEOS-Chem). We use a plume-ingrid formulation where ship emissions age chemically for 5 h before being released in the global model grid. Besides reducing the original ship NO x emissions in GEOS-Chem, our approach also releases the secondary compounds ozone and HNO 3 , produced during the 5 h after the original emissions, into the model. We applied our improved method and also the widely used "instant dilution" approach to a 1-yr GEOS-Chem simulation of global tropospheric ozone-NO x -VOC-aerosol chemistry. We also ran simulations with the standard model (emitting 10 molecules O 3 and 1 molecule HNO 3 per ship NO x molecule), and a model without any ship emissions at all. The model without any ship emissions simulates up to 0.1 ppbv (or 50 %) lower NO x concentrations over the North Atlantic in July than our improved GEOS-Chem model. "Instant dilution" overestimates NO x concentrations by 0.1 ppbv (50 %) and ozone by 3-5 ppbv (10-25 %), compared to our improved model over this region. These conclusions are supported by comparing simulated and observed NO x and ozone concentrations in the lower troposphere over the Pacific Ocean. The comparisons show that the improved GEOS-Chem model simulates NO x concentrations in between the instant dilution model and the model without ship emissions, which results in lower O 3 conCorrespondence to: G. C. M. Vinken (g.c.m.vinken@tue.nl) centrations than the instant dilution model. The relative differences in simulated NO x and ozone between our improved approach and instant dilution are smallest over strongly polluted seas (e.g. North Sea), suggesting that accounting for inplume chemistry is most relevant for pristine marine areas.

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The age of air is a useful integrated quantity that represents transport processes. Most atmospheric models underestimate the age of air, especially when wind fields from data assimilation systems are used. Nonetheless data assimilation is necessary to provide realistic winds. The European Centre for Medium‐Range Weather Forecasts (ECMWF) uses different assimilation procedures with various forecast periods, where forecasting allows the model to recover from the non‐physical adjustments of the assimilation procedure. In this study we examine the impact of different assimilation procedures and forecast periods on ECWMF wind fields by performing simulations of the age of air. For all data sets the age of air is too young, and for the 45‐years re‐analysis data (ERA‐40) it is even anomalously young, which has to be attributed to the data assimilation procedure used in ERA‐40. Extending the forecast period partially remedies the low ages of air, but to an unsatisfactory degree.

Abstract. This is the second part of a rigorous model evaluation study involving five global Chemistry-Transport and two Chemistry-Climate Models operated by different groups in Europe. Simulated trace gas fields were interpolated to the exact times and positions of the observations to account for the actual weather conditions and hence for the specific histories of the sampled air masses. In this part of the study we focus on a detailed comparison with two selected campaigns, PEM-Tropics A and SONEX, contrasting the clean environment of the tropical Pacific with the more polluted North Atlantic region. The study highlights the different strengths and weaknesses of the models in accurately simulating key processes in the UT/LS region including stratosphere-troposphere-exchange, rapid convective transport, lightning emissions, radical chemistry and ozone production. Model simulated Radon, which was used as an idealized tracer for continental influence, was occasionally much better correlated with measured CO than simulated CO pointing towards deficiencies in the used biomass burning emission fields. The abundance and variability of HO x radicals is in general well represented in the models as inferred directly from the comparison with measured OH and HO 2 and indirectly from the comparison with hydrogen peroxide concentrations. Components of the NO y family such as PAN, HNO 3 and NO were found to compare less favorably. Interestingly, models showing good agreement with observations in the case of PEM-Tropics A often failed in the case Correspondence to: D. Brunner (dominik.brunner@env.ethz.ch) of SONEX and vice versa. A better description of NO x and NO y emissions, chemistry and sinks is thought to be key to future model improvements with respect to the representation of chemistry in the UT/LS region.

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