Assessment of key pollutant emissions under future scenarios of residential biomass combustion in Spain and Portugal

This study quantifies changes in residential emissions under near- and medium-term biomass-use scenarios, according to recent national policies and trends. Residential biomass combustion remains an important source of atmospheric pollution in southern Europe, despite its role in renewable heating and rural energy supply. Spain and Portugal provide an important case study because both countries combine marked climatic gradients, strong urban–rural contrasts, and persistent biomass use in inland and rural regions. This study evaluates projected changes in emissions of seven key air pollutants (PM₂.₅, PM₁₀, BC, CO, NOx, SOx and BaP) across Spain and Portugal under 18 scenarios, combining time horizon (2030 and 2040), which determine the technology mix (open fireplaces, conventional stoves, advanced/ecolabelled stoves and pellet boilers) and the biomass energy use estimate (low, medium, upper), as well as emission factor uncertainty. The study disaggregates biomass use to the regional level using a proxy-based spatial allocation method and projects regional trajectories for 2030 and 2040. Regional NUTS3 allocation was based on population and population growth, heating degree days, rurality and dwelling typology.

Results showed that technology mix is a key determinant of emission intensity, with open fireplaces and traditional stoves producing substantially higher emissions than advanced and modern pellet appliances. Under low-biomass use scenarios, the largest emission reductions are observed, particularly for particulate matter (PM₂.₅ and PM₁₀), black carbon (BC), and benzo[a]pyrene (BaP), which often decline by 30–90% depending on the region and year. Carbon monoxide (CO) and nitrogen oxides (NOx) also decrease substantially, while SOx shows more moderate and, in some Portuguese regions, slightly positive changes in 2030. Scenario sensitivity is pronounced: reductions weaken progressively from low to medium and highbiomass use, with some non-rural regions exhibiting smaller declines or occasional increases in CO and NOx. By 2040, emission reductions deepen across all pollutants and scenarios, often exceeding 70% for PM and BC in low-biomass cases. Portugal generally experiences larger reductions than Spain, particularly in northern regions. These findings demonstrate that effective air-quality policy and measures require technology-specific, spatially targeted mitigation.