Ad description
A digital poster by Brighton & Hove City Council, seen in December 2025, included a graphic of a wood burning stove that was emitting smoke in the shape of an adult and child. Text in the ad stated “Harmful particle pollution near 4 city primary schools was 78% higher last winter compared with last summer […] Wood burners and open fires. The cosy killer”. Small text at the bottom of the ad stated “City sensor data comparing December 2024 to April 2025 with May 2025 to November 2025 at Middle Street, Elm Grove Primary, Adlington Primary and Saltdean Primary schools”.
Issue
The complainants, one of whom owned a chimney sweeping business, challenged whether the ad misleadingly implied the use of wood burners and open fires was the cause of the claimed increase in particle pollution.
Response
Brighton & Hove City Council said the ad was part of a campaign which was devised to raise awareness of the damaging impact of particulate matter (PM) pollution from domestic wood burning, including open fires and wood burners, in relation to public health, and its contribution to deaths. Using data from a city-wide network of air quality sensors, the ad also raised awareness of the increase in particle pollution during the ‘heating season’ – a period that ran from October until March or April – which they said was attributable to domestic burning. The heating season was meteorological and weather-dependent, rather than fixed by calendar seasons, and winter-like conditions and solid fuel burning could continue into early spring. The most recent data published by the Department for Environment, Food and Rural Affairs (Defra), from 2023, showed ‘domestic combustion’ – which included wood, solid smokeless fuels, coal, and fuels derived from waste such as coffee logs – was the second highest source of national PM2.5 emissions. Though it post-dated publication of the ad, they said a Defra consultation on solid fuel burning reiterated those findings.
They explained that in Brighton & Hove the dominant contributor to PM2.5 emissions in the area was domestic burning. The monitoring evidence they had gathered strongly indicated episodic increases in outdoor PM2.5 pollution were due to solid fuel burning, rather than other emissions sources. They observed no significant differences in PM2.5 levels at roadside or suburban detectors, which suggested year-round traffic emissions were not the reason for seasonally monitored PM2.5 peaks. PM emissions from road traffic had gradually dropped due to cleaner exhausts and more electric and hybrid vehicles. Winter ambient PM2.5 concentrations tended to peak late at night, long after traffic and vehicle movements had fallen, which suggested wood burning was the cause of the peak. Additionally, there were no motorways nor heavy industries, such as factories, near the city centre that produced PM2.5. Ships at nearby Shoreham Port used electric charging, and major airports and runways were at least 40 km from the city. Local power generation was principally from offshore wind, and gas fired power stations and domestic boilers did not emit PM2.5. International agricultural ammonia accounted for 12 out of 52 of the 24-hour exceedances of PM2.5 in the city, but those were mostly in April after the heating season. Remote sensors in the South Downs showed extremely low PM2.5, which suggested winter peaks came from local, urban activity. They said over the monitoring period 30 out of 52 daily PM2.5 exceedances were during the heating season, which strongly indicated solid fuel burning was the majority reason for worse air quality days in the year. They also provided two peer-reviewed studies and some information relating to measured ambient PM2.5 concentrations on the most polluted day of 2025 in support.
Where local monitoring was concerned, they said 50 air monitoring sensors had been installed in Sussex in 2024, of which 40 were placed in Brighton & Hove. They looked at air pollution levels from eight places across Brighton & Hove, which included main roads and the primary schools mentioned in the ad. They compared pollution levels in two parts of the year – period one covered winter months when wood burners and open fires were used more often (December 2024 to April 2025), and period two covered warmer months (April 2025 to October 2025). Across all eight monitoring sites PM2.5 pollution was 91% higher in period one than period two. The same results showed a 79% increase across the four primary schools between the two periods. They provided a memorandum of scientific support from an academic who specialised in air pollution.
Assessment
Upheld
The ad claimed harmful particle pollution around four primary schools in Brighton & Hove had increased between summer and winter of the previous year. Small text at the bottom of the ad gave the names of the specific schools where ambient particulate matter (PM) 2.5 concentrations had been measured, and set out that “winter” referred to the period December 2024 to April 2025, and “summer” referred to May 2025 to November 2025. Further text, alongside a stylised image of a woodburning stove, referred to wood burners and open fires as “the cosy killer”. The ASA understood the terms “winter” and “summer” in the ad had been used as shorthand for “cooler months” and “warmer months”.
We considered people would understand from the ad that particle pollution, had been measured at four primary schools in the Brighton & Hove area across two monitoring periods – the cooler months and warmer months – and that a 78% increase in particle pollution had been observed. They would interpret the ad’s reference to “harmful” particle pollution” and the claim “cosy killer” as meaning exposure to the emissions was harmful to human health, and potentially fatal. They would further understand from the ad’s text and the imagery used that the increase in ambient particle pollution at those locations was due to the use of wood burners and open fires, and that there was a direct link between the two.
We first assessed the data and calculations provided by Brighton & Hove City Council, which related to the monitoring periods and primary schools set out in the ad’s small text. The evidence showed a 79% difference in ambient PM2.5 concentrations measured at those monitoring sites between the two periods. We acknowledged Brighton & Hove’s comments that the surrounding circumstances at the time of the winter data collection – such as PM peaks after commuting rush hours, lack of proximity to motorways and heavy industry, and local renewable energy generation – suggested the increase in measured ambient PM2.5 concentrations was unlikely to be attributable to those sources. We also acknowledged the memorandum of scientific support from an academic who specialised in air pollution, which stated agreement with the messaging in the ad campaign, and that the results were consistent with the burning of wood and solid fuel. However, the ad implied there was a direct causal link between the use of wood burners and open fires and the claimed increase in particulate pollution, and that those heat sources were the sole cause of the increase. While we understood domestic wood burning was a significant contributor to urban PM2.5 emissions, we had not seen evidence in support of the direct link claimed in the ad.
We next assessed the further evidence provided. The first peer-reviewed study, published in 2017, sought to quantify PM emissions from wood smoke in cities in the UK using aethalometer data from Defra’s black carbon network from 2009 to 2016. An aethalometer was a device used to monitor, among other things, black carbon, also known as “soot”. A key finding in the study was that air pollution from wood burning was greater in winter than in summer. The second peer-reviewed study, published in 2025, used Energy Performance Certificates from 26 million properties in England and Wales to map the concentration of wood burners in small areas. Wood burners were found in the highest concentration in affluent urban areas. The information provided about ambient PM2.5 concentrations on the most polluted day of 2025 (10 February) pertained to traffic emissions on a specific main road in Brighton. It showed ambient PM2.5 concentrations peaked after traffic and vehicle movements had fallen. The studies and information did not make findings on the claimed increase in particulate pollution at the primary schools referenced in the ad.
The ad implied that wood burners and open fires were the cause of the claimed increase in particulate pollution around four city primary schools. However, we had not seen evidence to substantiate the claim. We therefore concluded the ad was likely to mislead.
The ad breached CAP Code (Edition 12) rules 3.1 (Misleading advertising) and 3.7 (Substantiation).
Action
The ad must not appear again in the form complained of. We told Brighton & Hove City Council to ensure that robust evidence was held to substantiate any claims where a direct causal link between the use of wood burners and open fires and an increase in particle pollution was stated or implied.
