Multi-model simulations of aerosol and ozone radiative forcing due to anthropogenic emission changes during the period 1990-2015

Over the past few decades, the geographical distribution of emissions of substances that alter the atmospheric energy balance has changed due to economic growth and air pollution regulations. Here, we show the resulting changes to aerosol and ozone abundances and their radiative forcing, using recently updated emission data for the period 1990-2015, as simulated by seven global atmospheric composition models. The models broadly reproduce large-scale changes in surface aerosol and ozone based on observations (e.g., -1 to -3%/yr in aerosols over 30 the US and Europe). The global mean radiative forcing due to ozone and aerosol changes over the 1990-2015 period increased by +0.17 ±0.08 Wm-2, with approximately 1/3 due to ozone. This increase is more strongly positive than that reported in IPCC AR5. The main reasons for the increased positive radiative forcing of aerosols over this period are the substantial reduction of global mean SO2 emissions, which is stronger in the new emission inventory compared to that used in the IPCC analysis, and higher black carbon emissions

On the impact of chemical boundary conditions on air quality modelling

In an attempt to improve air quality modelling at the regional scale, the sensitivity of the skills of the regional chemistry and transport model CHIMERE to chemical boundary conditions is assessed. Bridging the scales to reproduce the impact of long range transport on local air quality is an important focus of several ongoing European projects such as MACC (for short term forecasts) or CityZen (for mid-term trends). Three different global chemistry models can be used to drive the regional model (LMDzINCA, MOZART and CTM2). In this paper, we present an assessment of the performance of the model to all three sources of data using in-situ observations. The impacts of the temporal resolution (hourly, 6-hourly, daily or monthly) for both gaseous and aerosol species and the role of the selected components used as boundary conditions will be discussed

Clean air for future generations : a multi-model investigation of air quality projections

In order to investigate future air quality, the anthropogenic emissions scenarios developed in the framework of the Global Energy Assessment were implemented in six regional and global atmospheric chemistry transport models. Using decadal simulations and meteorological fields representative of the current (early 21st century) conditions we could isolate the impact of changes in anthropogenic emissions on the modelled concentrations of atmospheric pollutants. The strengths of the present work include: use of realistic emission scenarios (as opposed to sensitivity studies), similar in their design and development to IPCC projections, yet more appropriate for air pollution studies ; implementing a variety of chemistry transport models, including regional and global scale tools so that an ensemble representative of a range of scales could be derived, hence providing a better understanding of model uncertainty ; presenting the results in an "exposure-based" framework, with policy-relevant indicators specifically designed for health and ecosystem exposure assessment. The discussion includes a specific focus for Europe as well as a global overview. We find that, in Europe, O3 and PM10 concentrations decrease by 2030 compared to 2005 with a stronger improvement for the scenario including climate policy enforcement in addition to the current air quality legislation. However, for some models and scenarios a relative increase of O3 remains in areas saturated in nitrogen oxides. Nevertheless exposure indicators weighted by the population density or land use fraction unambiguously show the overall improvement in terms of total pollution cumulated over sensitive areas. The global simulations offer an interesting insight into the very different trajectories over developing countries as well as sensitivities studies on the impact of changing methane background concentrations

A joint modeling exercise designed to assess the respective impact of emission changes and meteorological variability on the observed air quality trends in major urban hotspots

With the growth of urban agglomerations, assessing the drivers of variability of air quality in and around the main anthropogenic emission hotspots has become a major societal concern as well as a scientific challenge. These drivers include emission changes and meteorological variability; both of them can be investigated by means of numerical modelling of trends over the past few years. A collaborative effort has been developed in the framework of the CityZen European project to address this question. Several chemistry and transport models (CTMs) are deployed in this activity: four regional models (BOLCHEM, CHIMERE, EMEP and EURAD) and three global models (CTM2, MOZART, and TM4). The period from 1998 to 2007 has been selected for the historic reconstruction. The focus for the present preliminary presentation is Europe. A consistent set of emissions is used by all partners (EMEP for the European domain and IPCC-AR5 beyond) while a variety of meteorological forcing is used to gain robustness in the ensemble spread amongst models. The results of this experiment will be investigated to address the following questions: Is the envelope of models able to reproduce the observed trends of the key chemical constituents? How the variability amongst models changes in time and space and what does it tell us about the processes driving the observed trends? Did chemical regimes and aerosol formation processes changed in selected hotspots? Answering the above questions will contribute to fulfil the ultimate goal of the present study: distinguish- ing the respective contribution of meteorological variability and emissions changes on air quality trends in major anthropogenic emissions hotspots

Air quality trends in European pollution hotspots : overview of CityZen multi-model hindcasts and projections

Understanding air quality distribution and evolution in the major European air pollution hotspots was one of the key objectives of the CityZen FP7 Project. Several initiatives were coordinated in the framework of the project to tackle this issue. The present communication proposes a specific focus on three of them. An assessment of air quality trends as reported by monitoring networks contributing to the AIRBASE repository was performed. A specific quality checking procedure was developed and applied so that time series statistical analysis could be performed to investigate trends of O3, NO2 and PM10 at the regional scale. In order to investigate the driving processes, a multi-model hindcast was setup, involving 6 modelling groups. The ability of the models to capture the trend reported in the observation-based assessment is discussed for the main regulated compounds. A special focus is devoted to the attribution of air quality variability to meteorological or anthropogenic factors. The hindcast is complemented by an air quality projection modelling initiative. Using the latest emission projections (from the Global Energy Assessment), the same multi-model ensemble performed multi-annual simulations corresponding to the 2030 decade. The projected air quality situation for several scenarios is discussed, both for raw air pollutant concentration and exposure proxies. Last, a specific discussion is devoted to the co-benefits of climate and air pollution policies

Extreme wet and dry conditions affected differently by greenhouse gases and aerosols

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Extratropical–Tropical Interaction Model Intercomparison Project (Etin-Mip): Protocol and Initial Results

International audienceThis article introduces the Extratropical–Tropical Interaction Model Intercomparison Project (ETIN-MIP), where a set of fully coupled model experiments are designed to examine the sources of longstanding tropical precipitation biases in climate models. In particular, we reduce insolation over three targeted latitudinal bands of persistent model biases: the southern extratropics, the southern tropics, and the northern extratropics. To address the effect of regional energy bias corrections on the mean distribution of tropical precipitation, such as the double intertropical convergence zone problem, we evaluate the quasi-equilibrium response of the climate system corresponding to a 50-yr period after the 100 years of prescribed energy perturbation. Initial results show that, despite a large intermodel spread in each perturbation experiment due to differences in ocean heat uptake response and climate feedbacks across models, the southern tropics is most efficient at driving a meridional shift of tropical precipitation. In contrast, the extratropical energy perturbations are effectively damped by anomalous heat uptake over the subpolar oceans, thereby inducing a smaller meridional shift of tropical precipitation compared with the tropical energy perturbations. The ETIN-MIP experiments allow us to investigate the global implications of regional energy bias corrections, providing a route to guide the practice of model development, with implications for understanding dynamical responses to anthropogenic climate change and geoengineering

Water vapour adjustments and responses differ between climate drivers

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