Review and integration of biosphere-atmosphere modelling of reactive trace gases and volatile aerosols

International audience

English. A full understanding of land-atmosphere exchange processes is a key to properly assess the air pollution and climate change impacts on humans and ecosystems as well as the link between climate change and air quality. Biogenic trace gas emissions used in air quality models are simplified and mostly based on the emission factors that are constitutively unable to integrate the impacts of climate change. Similarly, deposition of tropospheric pollutants in air quality models is simplified, and the effects of land-use changes on emissions and depositions are currently not well defined. We should therefore aim at better quantifying the contribution of terrestrial surfaces to atmospheric pollution and the global greenhouse gas balance. There is, however, at present no coherent model framework that can encompass the wide range of processes and their interactions that proceed in or near the canopy, and to a large extent govern the carbon and nitrogen land–atmosphere exchanges. In particular, this is true for those processes that operate on short timescales and involve reactive gases and aerosol particles. There is a need to identify major mechanisms and factors affecting the exchange of trace gases and volatile aerosols between the biosphere and the atmosphere and to improve methodologies currently used in accounting for emissions and deposition in landscape- and global-scale models. Moreover, a change in paradigm is needed to consider bidirectional exchanges rather than emission and deposition separately. Experts in biosphere–atmosphere exchange of trace gases and aerosols came together in Paris in September 2012 in order to integrate the most recent advances made in the field into a common modelling framework adapted for local-,regional- and global-scale models. The international workshop was jointly organized by the EU-COST 804 action, the EU-FP7 ‘Eclaire’ Integrated Project and the INRA and AgroParistech French research institutions. This book reports the major outcomes of the workshop in the form of four reviews based on four different compound types: (i) ammonia, (ii) ozone and nitrous oxides, (iii) volatile organic compounds and (iv) aerosols and acid gases given in the first part. The second part provides four synthesis chapters by compound type on recent research results, key challenges and shortcomings. The third part comprises four synthesis chapters on recent advances and key challenges on the components of a common modelling framework: (i) stomatal exchange and ecosystem functioning, (ii) surface and incanopy chemistry, (iii) within-canopy turbulence and (iv) soil and litter emissions. The final section consists of a conclusion which proposes a common conceptual modelling framework for reactive trace gases and volatile aerosols exchange in chemical transport model.