In the journal Lancet Oncol, Ole Raaschou-Nielsen and colleagues published the results of a 17-cohort study conducted in Europe, suggesting that particulate-rich air increases the risk of lung cancer, particularly lung adenocarcinoma, and that this effect persists even when the concentrations of these particulate matter are below the current EU air pollution limit values (40 μg/m3 for PM10 and 25 μg/m3 for PM2.5), this effect persists. The design of these studies is complex and overcomes some of the shortcomings of previous studies. Some of the earlier studies examining the effect of air pollution on lung cancer risk focused on evaluating geographic correlations, such as intercommunity air pollution concentration data and pooled lung cancer data, but there may have been some misclassification and confounding factors in these studies (mainly the effect of smoking). Subsequently, researchers have used regional exposure assessments or more precise individual exposure level assessments in an attempt to reduce these systematic errors by converting studies to individual studies (case-control studies or cohort studies) to obtain more accurate conclusions. Raaschou-Nielsen and colleagues conducted a meta-analysis of 17 studies with standardized study protocols, which could increase the number of subjects on the one hand and reduce the likelihood of sample bias and publication bias on the other. The study had a high follow-up rate while adjusting for possible confounders (including a range of smoking-related variables). Therefore, systematic and random errors that may have existed in previous studies can be reduced. There is no accepted conclusion on whether air pollution is the cause of lung cancer. Researchers are still continuing to gather evidence. Although the risk of lung cancer is associated with air pollution, this association is significantly lower than the risk associated with smoking. The WHO estimates that smoking caused 5.1 million deaths worldwide in 2004, while air pollution caused 1.2 million deaths worldwide in the same year. There is no safe threshold for evaluating the health effects of either short-term or long-term exposure to PM2.5 pollution. In addition, Raaschou-Nielsen et al. demonstrated a link between air pollution and the risk of lung cancer. However, the results of three Danish cohort studies conducted by the same investigators suggest a greater association between lung squamous and small cell lung cancer and air pollution compared to lung adenocarcinoma. Given the shift in the type of lung cancer (e.g., from squamous cell carcinoma to adenocarcinoma) and the variation in the frequency of this shift across the world, more targeted studies are needed in the future. Today, we may need to include air pollution as a cause of lung cancer development and need to recognize that air pollution can have a significant impact on public health. Fortunately, air pollution, like smoking, is a manageable risk factor.