In this chapter, the overall methodology for addressing the three main tasks of the project is presented: (1) Projection of air quality for 2030 for the Nordic countries and selected cities, (2) Sector specific contribution to air quality in 2030 and health effects and related external costs, and (3) Evaluation of air quality monitoring in Nordic countries.
To address the analyses in (1) and (2), the regional scale air quality model (DEHM) and the urban scale air quality model (UBM) have been set up and applied, and to address health impacts and related external costs the integrated modelling system - EVA (Economic Valuation of Air Pollution) was used. A brief description of these model tools is provided below, followed by a description of the selection of cities and model boundaries. Aarhus University has developed all the models. Finally, a description of the methodologies for addressing task (3) is outlined.
2.1 Regional scale air quality modelling (DEHM)
The Danish Eulerian Hemispheric Model (DEHM) is a state-of-the-art, three-dimensional, atmospheric chemistry transport model (CTM) developed to study long-range transport of air pollution across the Northern Hemisphere. DEHM was originally developed in the early 1990s in the modelling group of ENVS in order to study atmospheric transport of sulphur-dioxide and sulphate into the Arctic (Christensen, 1997). The model has been modified, extended and up-dated continuously since then (Frohn et al., 2001; Brandt et al., 2012). The original simple sulphur-dioxide-sulphate chemistry has been replaced by a more comprehensive chemical scheme, including 80 chemical species, 9 primary particles and 158 chemical reactions. The DEHM model has also been used for studies of additional components, including POPs, mercury, pollen, CO2 and ultrafine particles.
The model includes descriptions of the atmospheric transport and mixing, the chemical processes as well as the removal by rain and the deposition/removal to land and water surfaces. Natural emissions of e.g. sea salt and biogenic VOCs are calculated on-line in the model, while anthropogenic emission input data are based on a number of international (e.g. EMEP) and national inventories. For Denmark the high-resolution (1 km x 1 km) emissions from the SPREAD model is applied (Plejdrup et al., 2021). The driving meteorological data are obtained from the Weather Research and Forecasting model (WRF, Skamarock et al., 2008), also run routinely at ENVS, or from the ECMWF Integrated Forecasting System (IFS,
http://dx.doi.org/10.21957/zw5j5zdz5).
The model domain covers most of the Northern Hemisphere, discretized on a polar stereographic projection true at 60°N, and includes a two-way nesting procedure with several nests, allowing for higher spatial resolution over selected areas. The setup is flexible and can change from study to study.
The most commonly applied setup includes three nested domains with higher resolution over Europe, Northern Europe and Denmark. Currently the finest resolution is 5.56 km x 5.56 km for a domain covering Denmark. The vertical discretization is defined on an irregular grid with 29 layers up to ~18 km. The thickness of the lowest layer is 15–25 m and varies with meteorological conditions.
The DEHM model has been developed and applied as a part of the Danish Air Quality Monitoring Programme (NOVANA) for more than 15 years – with focus both on chemical species important for human health (ozone, NO2, particles, etc.) and on deposition of reduced and oxidized nitrogen to marine and terrestrial eco-systems (Ellermann et al., 2022).
The model has also been applied for more than 30 years in the Arctic Monitoring and Assessment Programme (AMAP) in several assessments to study the atmospheric transport to and deposition within the Arctic of sulphur, sulphate, ozone, NOx, VOC’s, lead, Hg, Black Carbon, POPs and other components and is a reference model in AMAP.
The DEHM model has through the years been included in a number of international model intercomparison exercises together with similar state-of-the-art models from both Europe and North America (latest e.g. AQMEII phase 1 and 3) and for different areas (Europe, North America and Arctic).
DEHM is one of 11 European models of the EU-funded CAMS2-40 ‘Regional production’ (an extension of CAMS-50). CAMS2-40 is part of the Copernicus Atmosphere Monitoring Service (CAMS), providing air quality forecasts and analysis for Europe on a daily basis.
2.2 Urban scale air quality modelling (UBM)
The Urban Background Model (UBM) (Brandt et al., 2012; 2013a,b) is a high-resolution Gaussian plume-in-grid model for prediction of background concentrations with a 1 km x 1 km resolution. It is in its standard setup for Denmark, capable of calculating hourly values of 17 health related chemical components for a period covering 1979 to present. The emissions for this setup are obtained from the SPREAD model that provides spatially distributed national emissions from all sectors on a 1 km x 1 km grid for Denmark based on various geographic variables applied for the different emission sectors (Plejdrup et al., 2021).