London wood burning project: air quality data collection

The 'London Wood Burning Project' was funded through the Defra Air Quality Grant Scheme 2021-22 and is led by London Borough of Camden and London Borough of Islington on behalf of 13 additional London boroughs. The overall aims of the project are to improve scientific understanding of the air quality effects of solid-fuel burning, including from different fuel and appliance types, to improve understanding of the health impact risk from these activities and to improve and enhance public awareness and engagement, with the long-term ambition to improve air quality and reduce health damage from solid-fuel burning in London.

Imperial College Projects Ltd was contracted to provide element 2, air quality data collection, via the expert services of the Environmental Research Group (ERG) at Imperial College London. The report linked here details the methodology, results, analysis and conclusions of the air quality data collection work.

Domestic wood and solid fuel burning is currently the second biggest source of PM_2.5 emissions in London and one of the main components of ambient PM_2.5 that can be influenced on a local level. This study investigated indoor, house adjacent, outdoor and city scale wood and solid fuel burning.

Burning was linked to PM_2.5 increases of ~175 µg m^-3 indoors, associated with fire lighting and refuelling. However, the contribution of stoves and fireplaces to indoor PM_2.5 was found to be lower than from cooking and cigarette smoking. Wood and solid fuel burning caused short-term peaks of up to 50 µg m^-3 outside homes, measured at ground level, typically up to a distance of ~10m from the chimney, again linked to fire lighting and refuelling.

Newer appliances, highly rated for efficiency and low emissions, may have advantages in terms of air quality compared with older appliances. However, emissions were detected from these also. Burning authorised and exempt fuels did not show benefits for indoor or outdoor air quality compared to burning seasoned wood in this study.

Wood and solid fuel burning particulate concentrations were calculated from portable micro-aethalometer measurements. Hotspots detected along two transects in north and south London agreed well with modelled emissions. Agreement between measurements and reported wood and solid fuel burning odour demonstrated that smell can be a reliable indicator of wood and solid fuel burning pollution.

Wood and solid fuel burning particulates contributed 8-9% of the total annual mean PM_2.5 at two urban background locations in London in 2022, both considered to be representative of the wider urban area. Over half was attributed to urban sources of wood and solid fuel burning within London with a slightly smaller contribution from wood and solid fuel burning in the regional background.

This study improves understanding of wood and solid fuel burning emissions and their role in the urban air quality landscape. Further observations and management are needed to enable progress towards meeting the WHO air quality guidelines 2021, especially for PM_2.5.