Strengthening Cooperation on Air Pollution Impacts in the Arctic and Beyond

Air pollution has a wide variety of impacts, affecting human health, ecosystems, and climate both near the source and far away. Over the last 10 years the Task Force on Hemispheric Transport of Air Pollution (TF HTAP) under the United Nations Economic Commission for Europe (UNECE) Convention on Long- range Transboundary Air Pollution (CLRTAP) has worked with an international scientific network of experts from Europe, North America, and Asia to improve the understanding of the intercontinental transport of air pollution across the Northern Hemisphere, through systematic modelling intercomparisons, assessment of observational evidence and development of impact assessment methods. Although HTAP’s efforts cover the entire Northern Hemisphere, only some work has been performed to also evaluate impacts on the Arctic. The Arctic Monitoring and Assessment Program (AMAP) is the Working Group of the Arctic Council that is responsible for monitoring and assessing the status of the Arctic region with respect to pollution and climate change issues. Over the past 25 years, the AMAP monitoring programme has documented pollution levels and trends, pathways and processes, and effects on ecosystems and humans. The results of this monitoring effort have formed the basis for a series of AMAP assessments prepared by independent groups of scientific experts. These assessments cover a range of air pollution issues including Acidification and Arctic haze, Mercury and other trace metals, Persistent Organic Pollutants, and most recently Short-lived Climate Forcers (Black Carbon and Ozone, and Methane). These scientific outreach products and policy-makers summaries typically also propose actions to reduce associated threats and are specifically developed to inform decision-makers of the Arctic Council, governments and other relevant international fora. During the first day of a recent workshop, hosted by the IASS in Potsdam, Germany, the TF HTAP and AMAP explored opportunities to strengthen their cooperation on future scientific work to assess the (human) health, eco- system, and climate impacts of air pollution. Among the topics for enhanced collaboration are new modelling efforts to support evaluation of mitigation strategies for mer- cury, persistent organic pollutants, and short-lived climate pollutants (including black carbon and methane). This modelling work will also incorporate dedicated scenario studies for Arctic development and impact studies. By working together, HTAP and AMAP can provide better understanding of processes and uncertainties, as well as information to international bodies responsible for devel- oping policy measures to exploit the benefits of mitigation strategies in the Arctic and outside. The second and third day of the workshop were dedicated to evaluate methodologies to better quantify impacts of air pollution on human health, ecosystems (including crops) and climate. Presentations given by representatives of variety of communities, including CCMI (climate modelling communities); health impacts (overview of GBD, WHO efforts) and the emission scenario communities (e.g. GAINS as well as SSPs) were informing on the possibilities of exchanging information between the various efforts, and to promote the use of joint methods for the variety of assessments foreseen in the coming years. Further information on HTAP and meeting presentations are available via www.htap.org.JRC.D.5-Food Securit

Regional scale ozone data assimilation using an ensemble Kalman filter and the CHIMERE chemical transport model

International audienceAn ensemble Kalman filter (EnKF) has been coupled to the CHIMERE chemical transport model in order to assimilate ozone ground-based measurements on a regional scale. The number of ensembles is reduced to 20, which allows for future operational use of the system for air quality analysis and forecast. Observation sites of the European ozone monitoring network have been classified using criteria on ozone temporal variability, based on previous work by Flemming et al. (2005). This leads to the choice of specific subsets of suburban, rural and remote sites for data assimilation and for evaluation of the reference run and the assimilation system. For a 10-day experiment during an ozone pollution event over Western Europe, data assimilation allows for a significant improvement in ozone fields: the RMSE is reduced by about a third with respect to the reference run, and the hourly correlation coefficient is increased from 0.75 to 0.87. Several sensitivity tests focus on an a posteriori diagnostic estimation of errors associated with the background estimate and with the spatial representativeness of observations. A strong diurnal cycle of both these errors with an amplitude up to a factor of 2 is made evident. Therefore, the hourly ozone background error and the observation error variances are corrected online in separate assimilation experiments. These adjusted background and observational error variances provide a better uncertainty estimate, as verified by using statistics based on the reduced centered random variable. Over the studied 10-day period the overall EnKF performance over evaluation stations is found relatively unaffected by different formulations of observation and simulation errors, probably due to the large density of observation sites. From these sensitivity tests, an optimal configuration was chosen for an assimilation experiment extended over a three-month summer period. It shows a similarly good performance as the 10-day experiment

High resolution air quality simulation over Europe with the chemistry transport model CHIMERE

A high resolution air quality simulation (0.125° × 0.0625° horizontal resolution) performed over Europe for the year 2009 has been evaluated using both rural and urban background stations available over most of the domain. Using seasonal and yearly mean statistical indicators such as the correlation index, the fractional bias and the root mean squared error; we interpret objectively the performance of the simulation. Positive outcomes are: a very good reproduction of the daily variability at UB sites for O3 (R =0.73) as well as for NO2 (R =0.61); a very low bias calculated at UB stations for PM2.5 (FB = −6.4%) and PM10 concentrations (FB = −20.1%). Conversely, main weaknesses in model performance include: the underestimation of the NO2 daily maxima at UB site (FB = −53.6%); an overall underestimation of PM10 and PM2.5 concentrations observed over Eastern European countries (e.g. Poland); the overestimation of sulphates concentrations at spring time (FB = 53.7%); finally, over the year, total nitrate and ammonia concentrations are better reproduced than nitrate and ammonium aerosol phase compounds. Obtained results suggest that, in order to improve the model performances, efforts should focus on the improvement of the emission inventory quality for Eastern Europeans countries and the improvement of a specific parameterisation in the model to better account for the urban effect on meteorology and air pollutants concentrations.JRC.H.2-Air and Climat