We present a global distribution of surface methane (CH₄) emission estimates for 2000–2012 derived using the CarbonTracker Europe-CH₄ (CTE-CH₄) data assimilation system. In CTE-CH₄, anthropogenic and biospheric CH₄ emissions are simultaneously estimated based on constraints of global atmospheric in situ CH₄ observations. The system was configured to either estimate only anthropogenic or biospheric sources per region, or to estimate both categories simultaneously. The latter increased the number of optimizable parameters from 62 to 78. In addition, the differences between two numerical schemes available to perform turbulent vertical mixing in the atmospheric transport model TM5 were examined. Together, the system configurations encompass important axes of uncertainty in inversions and allow us to examine the robustness of the flux estimates. The posterior emission estimates are further evaluated by comparing simulated atmospheric CH₄ to surface in situ observations, vertical profiles of CH₄ made by aircraft, remotely sensed dry-air total column-averaged mole fraction (XCH₄) from the Total Carbon Column Observing Network (TCCON), and XCH₄ from the Greenhouse gases Observing Satellite (GOSAT). The evaluation with non-assimilated observations shows that posterior XCH₄ is better matched with the retrievals when the vertical mixing scheme with faster interhemispheric exchange is used. Estimated posterior mean total global emissions during 2000–2012 are 516 ± 51 Tg CH₄ yr⁻¹, with an increase of 18 Tg CH₄ yr⁻¹ from 2000–2006 to 2007–2012. The increase is mainly driven by an increase in emissions from South American temperate, Asian temperate and Asian tropical TransCom regions. In addition, the increase is hardly sensitive to different model configurations ( < 2 Tg CH₄ yr⁻¹ difference), and much smaller than suggested by EDGAR v4.2 FT2010 inventory (33 Tg CH₄ yr⁻¹), which was used for prior anthropogenic emission estimates. The result is in good agreement with other published estimates from inverse modelling studies (16–20 Tg CH₄ yr⁻¹). However, this study could not conclusively separate a small trend in biospheric emissions (−5 to +6.9 Tg CH₄ yr⁻¹) from the much larger trend in anthropogenic emissions (15–27 Tg CH₄ yr⁻¹). Finally, we find that the global and North American CH₄ balance could be closed over this time period without the previously suggested need to strongly increase anthropogenic CH₄ emissions in the United States. With further developments, especially on the treatment of the atmospheric CH₄ sink, we expect the data assimilation system presented here will be able to contribute to the ongoing interpretation of changes in this important greenhouse gas budget.

The Mediterranean basin represents a hot spot area for short-term O3 distribution and anthropogenic contributions to it. This is why we analysed in this work the surface O3 variability observed at Mt. Cimone WMO/GAW global station (CMN, 44°12′ N, 10°42′ E, 2165 m a.s.l., Italy) from 1991 to 2011. The measurements performed at this mountain observatory represent the longest surface O3 record at a baseline site in the Mediterranean basin.Monthly O3 averages at CMN show a typical seasonal cycle characterised by a winter minimum and a spring – summer maxima. The shape of the mean annual variation of O3 is well comparable with those observed at other four baseline sites in the Alps and in the Mediterranean region: Jungfraujoch – Swiss Alps, Sonnblick – Austrian Alps, Mt. Krvavec– Slovenia and Giordan Lightouse – Island of Gozo, Malta. In general, O3 levels at CMN show higher values during warm months, which is likely to be related both to vertical transport of polluted air-masses at regional and continental scales and to enhanced photochemistry.Here, we also investigate the influence of specific atmospheric processes (i.e. the occurrence of heat-waves, North Atlantic Oscillation, thermal transport of air-masses from the regional PBL and stratospheric intrusions) in affecting O3 variability at CMN.Overall, a significant positive (95% confidence level) linear trend in monthly O3 mole fraction was observed over the period 1991–2011 (0.21 ± 0.10 nmol/molyr−1) while no trend (-0.02 ± 0.12 nmol/molyr−1) was detected for the 1996–2011, when measurements were carried out by an homogeneous experimental set-up. On a seasonal basis, a positive trend has been observed for 1996–2011 (0.34 ± 0.32 nmol/molyr−1) only for spring. Significant decreases of the seasonal O3 growth-rates have been detected at CMN during 1991–2011 from winter to spring and only for summer during 1996–2011

The concentration of ozone at the Earth's surface is measured at many locations across the globe for the purposes of air quality monitoring and atmospheric chemistry research. We have brought together all publicly available surface ozone observations from online databases from the modern era to build a consistent data set for the evaluation of chemical transport and chemistry-climate (Earth System) models for projects such as the Chemistry-Climate Model Initiative and Aer-Chem-MIP. From a total data set of approximately 6600 sites and 500 million hourly observations from 1971–2015, approximately 2200 sites and 200 million hourly observations pass screening as high-quality sites in regionally representative locations that are appropriate for use in global model evaluation. There is generally good data volume since the start of air quality monitoring networks in 1990 through 2013. Ozone observations are biased heavily toward North America and Europe with sparse coverage over the rest of the globe. This data set is made available for the purposes of model evaluation as a set of gridded metrics intended to describe the distribution of ozone concentrations on monthly and annual timescales. Metrics include the moments of the distribution, percentiles, maximum daily 8-hour average (MDA8), sum of means over 35 ppb (daily maximum 8-h; SOMO35), accumulated ozone exposure above a threshold of 40 ppbv (AOT40), and metrics related to air quality regulatory thresholds. Gridded data sets are stored as netCDF-4 files and are available to download from the British Atmospheric Data Centre (doi:10.5285/08fbe63d-fa6d-4a7a-b952-5932e3ab0452). We provide recommendations to the ozone measurement community regarding improving metadata reporting to simplify ongoing and future efforts in working with ozone data from disparate networks in a consistent manner.

The northern wetland methane emission estimates have large uncertainties. Inversion models are a qualified method to estimate the methane fluxes and emissions in northern latitudes but when atmospheric observations are sparse, the models are only as good as their a priori estimates. Thus, improving a priori estimates is a competent way to reduce uncertainties and enhance emission estimates in the sparsely sampled regions. Here, we use a novel way to integrate remote sensing soil freeze/thaw (F/T) status from SMOS satellite to better capture the seasonality of methane emissions in the northern high latitude. The SMOS F/T data provide daily information of soil freezing state in the northern latitudes, and in this study, the data is used to define the cold season in the high latitudes and, thus, improve our knowledge of the seasonal cycle of biospheric methane fluxes. The SMOS F/T data is implemented to LPX-Bern DYPTOP model estimates and the modified fluxes are used as a biospheric a priori in the inversion model CarbonTracker Europe-CH${}_4$. The implementation of the SMOS F/T soil state is shown to be beneficial in improving the inversion model’s cold season biospheric flux estimates. Our results show that cold season biospheric CH${}_4$ emissions in northern high latitudes are approximately 0.60 Tg lower than previously estimated, which corresponds to 17% reduction in the cold season biospheric emissions. This reduction is partly compensated by increased anthropogenic emissions in the same area (0.23 Tg), and the results also indicates that the anthropogenic emissions could have even larger contribution in cold season than estimated here.