The influence of residential wood combustion on the concentrations of PM2.5 in four Nordic cities

Kukkonen Jaakko1, Susana López-Aparicio2, David Segersson3, Camilla Geels4, Leena Kangas1, Mari 5 Kauhaniemi1, Androniki Maragkidou1, Anne Jensen4, Timo Assmuth5, Ari Karppinen1, Mikhail Sofiev1, Heidi Hellén1, Kari Riikonen1, Juha Nikmo1, Anu Kousa6, Jarkko V. Niemi6, Niko Karvosenoja5, Gabriela Sousa Santos2, Ingrid Sundvor7, Ulas Im4, Jesper H. Christensen4, Ole-Kenneth Nielsen4, Marlene S. Plejdrup4, Jacob Klenø Nøjgaard4, Gunnar Omstedt3, Camilla Andersson3, Bertil Forsberg8, Jørgen Brandt4 10 1 Finnish Meteorological Institute, Erik Palmenin aukio 1, P.O. Box 503, 00101, Helsinki, Finland 2 Norwegian Institute for Air Research, Instituttveien 18, P.O. Box 100, 2027 Kjeller, Norway 3 Swedish Meteorological and Hydrological Institute, SE-60176 Norrköping, Sweden 4 Aarhus University, Frederiksborgvej 399, 4000 Roskilde, Denmark 15 5 Finnish Environment Institute, Latokartanonkaari 11, FI-00790 Helsinki 6 Helsinki Region Environmental Services Authority, Ilmalantori 1, FI-00240 Helsinki 7 Institute of Transport Economics, Gaustadalléen 21, 0349 , Norway 8 Umeå University, 901 87 Umeå, Sweden

20 Correspondence: Jaakko Kukkonen ([email protected])

Abstract. Residential wood combustion (RWC) is an important contributor to air quality in numerous regions worldwide. This study is the first extensive evaluation of the influence of RWC on ambient air quality in several Nordic cities. We have analyzed the emissions and concentrations of PM2.5 in cities 25 within four Nordic countries: in the metropolitan areas of Copenhagen, Oslo and Helsinki, and in the city of Umeå. We have evaluated the emissions for the relevant urban source categories and modelled atmospheric dispersion on regional and urban scales. The emission inventories for RWC were based on local surveys, the amount of wood combusted, combustion technologies and other relevant factors. The accuracy of the predicted concentrations was evaluated based on urban concentration measurements. The 30 predicted annual average concentrations ranged spatially from 4 to 7 µg/m3 (2011), from 6 to 10 µg/m3 (2013), from 4 to more than 13 µg/m3 (2013) and from 9 to more than 13 µg/m3 (2014), in Umeå, Helsinki, Oslo and Copenhagen, respectively. The higher concentrations in Copenhagen were mainly caused by the relatively higher regionally and continentally transported background contributions. The annual average fractions of PM2.5 concentrations attributed to RWC within the considered urban regions 35 ranged spatially from 0 to 15 %, from 0 to 20 %, from 8 to 22 % and from 0 to 60 % in Helsinki, Copenhagen, Umeå and Oslo, respectively. In particular, the contributions of RWC in central Oslo were larger than 40 % as annual averages. In Oslo, wood combustion was used mainly for the heating of larger blocks of flats. On the contrary, in Helsinki, RWC was solely used in smaller detached houses. In Copenhagen and Helsinki, the highest fractions occurred outside the city centre in the suburban areas. In 40 Umeå, the highest fractions occurred both in the city centre and its surroundings.

1

1. Introduction The combustion of wood or other kinds of biomass for residential heating and cooking is a significant 45 source of atmospheric pollution, both in developed and developing countries (e.g., Patel et al., 2013; Sigsgaard et al., 2015; Butt et al., 2016). Biomass combustion and the combustion of residential solid fuels (RSF), such as wood crop residues, animal waste, coal and charcoal (Butt et al., 2016; Capistrano et al., 2017) have been found to contribute significantly to particulate matter emissions in numerous countries worldwide (e.g., Karagulian et al., 2015; Butt et al., 2016; Vicente and Alves, 2018; Im et al., 50 2019). In addition, such a combustion results in emissions of harmful or toxic gaseous pollutants, such as CO, CO2, NOx, heavy metals (i.e. Pb, Cu, Fe, Zn, and Hg, etc), polycycl