Smog and cancer: what IARC’s Group 1 for air pollution means for Poland

October 2013: air pollution in Group 1

On 17 October 2013 IARC announced that it had classified outdoor air pollution as carcinogenic to humans (Group 1). Particulate matter, a major component of outdoor air pollution, was evaluated separately and also classified in Group 1. A summary appeared in The Lancet Oncology on 24 October 2013, and the full assessment was published as Volume 109 of the Monographs.

The Working Group reviewed more than 1000 scientific papers from studies on five continents. It found sufficient evidence that exposure to outdoor air pollution causes lung cancer, and noted a positive association with an increased risk of bladder cancer. The evaluation showed an increasing risk of lung cancer with increasing levels of exposure.

This was the first time IARC had classified outdoor air pollution as a whole. Before that, the Monographs had evaluated many individual chemicals and mixtures found in polluted air, among them diesel engine exhaust, solvents, metals and dusts.

What Group 1 does and does not tell you

Group 1 is used when the evidence that something causes cancer in people is convincing. It says nothing about how large the risk is in a particular place or for a particular person; as IARC itself notes, the composition of air pollution and levels of exposure can vary dramatically between locations. The same logic is explained on Can it, or will it? and Groups 1, 2A, 2B and 3.

Air pollution is, however, a case where the scale is large. Using the most recent data available in 2013, IARC cited an estimate of 223 000 deaths from lung cancer worldwide in 2010 resulting from air pollution. For comparison, IARC’s evaluation of processed meat quoted about 34 000 cancer deaths a year attributable to diets high in it – the case is described on Aspartame, meat and the news.

IARC listed the main sources of outdoor air pollution as transportation, stationary power generation, industrial and agricultural emissions, and residential heating and cooking.

Benzo[a]pyrene: one compound, also in Group 1

Polluted air is a mixture, and some of its ingredients have been evaluated on their own. One of them is benzo[a]pyrene, a member of the family of polycyclic aromatic hydrocarbons (PAHs) that form when organic material burns incompletely. In Volume 100F of the Monographs, published in 2012, IARC classified benzo[a]pyrene as carcinogenic to humans (Group 1).

The same volume names the major sources of PAHs in ambient air, among them residential and commercial heating with wood, coal or other biomass; heating with oil or gas produces much lower quantities. Other sources of exposure include motor-vehicle exhaust, industrial emissions, tobacco smoke, and grilled, barbecued or smoke-cured foods.

Where Europe stands

The European Environment Agency (EEA) reports each year on benzo[a]pyrene concentrations measured in Europe, in nanograms per cubic metre of air (ng/m³). The EU target value is 1 ng/m³, and the same figure has been set as an annual limit value from 2030. The EEA also shows a much lower WHO estimated reference level of 0.12 ng/m³.

In its 2026 report, covering 2024 data and published on 30 April 2026, the EEA found concentrations above 1.0 ng/m³ at 20.2% of the stations that reported, most of them urban. Levels above that value were recorded in 12 Member States: Austria, Bulgaria, Croatia, Czechia, Finland, France, Hungary, Italy, Latvia, Poland, Slovakia and Slovenia. The highest concentrations were in eastern Europe, where coal and other solid fuels are still widely used for residential heating, and in Italy, mainly because of wood burning at home.

Benzo[a]pyrene in Poland

The Chief Inspectorate of Environmental Protection (GIOŚ) publishes an annual assessment of air quality in Poland’s 46 assessment zones. In its assessment for 2024, published on 30 April 2025, it states that the biggest air-pollution problem in Poland remains the high content of benzo[a]pyrene in PM10 particulate matter.

The national annual mean concentration, calculated as an average of all stations in the country, was 1.52 ng/m³ in 2024, almost unchanged from 1.53 ng/m³ in 2023. The number of zones in which the target level for benzo[a]pyrene was exceeded also stayed the same: 21 of 46. The EEA report gives the same number of Polish zones with exceedances.

Fine particulate matter (PM2.5), the other pollutant at the centre of IARC’s evaluation, exceeded its annual limit in four zones in 2024: the Upper Silesian agglomeration, the Łódź agglomeration, the city of Częstochowa and the Łódź zone (data for 2024; status as of 3 November 2026).

How to read a smog headline

A headline that says smog “causes cancer” is accurate about the hazard: IARC has found sufficient evidence that outdoor air pollution, particulate matter and benzo[a]pyrene can cause cancer in people. What the classification cannot tell you is the risk in a given town in a given winter. That depends on concentrations and on how long people breathe them, which is why measured data such as those from GIOŚ and the EEA matter, and why limit values are set by legislators rather than by IARC.

IARC’s Advisory Group, meeting in March 2024, listed outdoor air pollution among high-priority agents for 2025–2029 because of evidence for cancer sites beyond the lung. Two other cases in which a label is often misread are explained in Is hot tea or coffee carcinogenic? and Do mobile phones cause cancer?.

This article explains how evaluations work; it is not medical advice.