Ambient particulate matter of <2.5 μm (PM_2.5) pollution is recognized as a major health concern worldwide. PM_2.5 was associated with an increased risk of disease mortality and morbidities (1–4), and a 10-μg/m³ increment in PM_2.5 was associated with a 4.3% increment in total mortality (5). However, ambient particulate matter pollution continues to be one of the largest increases in risk exposures from 1990 to 2019 worldwide (6).

In 2019, according to the Global Burden of Disease (GBD) 2019 study, among the 87 risk factors identified, long-term exposure to PM_2.5 caused 118.2 million disability-adjusted life-years (DALYs), representing 4.7% of global DALYs in 204 countries and territories (7). Approximately 4,140,971 all-causes deaths and 307,680 lung cancer deaths in 2019 were attributed to ambient PM_2.5 globally. However, the ambient PM_2.5 risk-oriented health problems have mainly occurred in low- and middle-income countries (LMICs) according to previous studies (1, 8). In 2017, ambient particulate matter pollution ranked as the eighth leading risk for death, with a total of 2.94 million deaths globally and 1.05 million deaths in Southeast Asia, East Asia, and Oceania (2). Based on a newly published global comparative risk assessment in 2019, nearly all locations in south Asia, many parts of Southeast Asia, and most provinces in China had 10–15% of DALYs attributable to air pollution (6).

Lung cancer has been the leading cause of cancer deaths for many years worldwide, with the incidence and mortality markedly varying between countries (9, 10). Asia has extremely diverse lung cancer incidences, and it is the leading cause of cancer death in China (10, 11). The major risk factor for the burden of lung cancer was tobacco smoking, followed by air pollution-related age-standardized rates (12). This study aims to focus on lung cancer death caused by particulate matter pollution. Previous studies have evaluated the association of ambient air pollution with lung cancer (13–15). Few studies have been conducted regarding ambient air pollutant-related lung cancer death (16), while no national study has comprehensively evaluated the long-term trend in lung cancer death due to long-term exposure to ambient particulate matter in East Asia countries. Although a recent study reported that the age-standardized death rate attributable to air pollution decreased by 60.6% for China overall between 1990 and 2017 (17), the temporal trend in lung cancer death attributable to air pollution was not clearly analyzed. Therefore, this study aimed to estimate the trend and risk for long-term exposure to PM_2.5 caused by lung cancer death from 1990 to 2019 among East Asia countries, including China, Mongolia, the Democratic People's Republic of Korea, the Republic of Korea, and Japan.

This study comprehensively estimates on temporal trends in lung cancer death caused by long-term exposure to ambient PM_2.5 in East Asia. We found that the lung cancer attributable death caused by PM_2.5 generally increased in younger and older people in both the Democratic People's Republic of Korea and Mongolia by Joinpoint analysis. APC analysis demonstrated that the risk of lung cancer death attributed to PM_2.5 generally increased from young to old age, and the risk increased continuously in China, the Democratic People's Republic of Korea, and Japan from 1994–1998 to 2019–2023 period. The Republic of Korea and Mongolia showed a different period risk trend. The cohort effect declined to the most recent birth cohorts, which demonstrated a decreasing risk from the old generation to the new generation.

This section discusses the attributable death of lung cancer due to ambient particulate matter. Among East Asia countries, we found that China and Mongolia had high mortality and YLL rates attributable to ambient PM_2.5. The high population density in China exhibited a huge lung cancer burden attributed to ambient PM_2.5 and was a major contributor to the death and YLL burden caused by PM_2.5 in East Asia. This finding was related to the fact that more than a quarter of global deaths caused by ambient particulate matter pollution occurred in China, which is the third risk factor affecting the health of Chinese people (16). A huge proportion of attributable YLL to PM_2.5 was related to China, which is consistent with studies by the World Bank and the WHO. The Chinese Academy for Environmental Planning on the effect of air pollution on health concluded that between 350,000 and 500,000 people die prematurely each year as a result of outdoor air pollution in China (18, 24). This finding could be contributed to the fact that PM_2.5 pollution in the winter is worse in China (4), in addition to the increasing high mortality of lung cancer in China (7). Mongolia has a relatively high level of age-standardized attributable death and YLL rates. This is because, during the cold wintertime in Mongolia, a lot of coal is burnt for domestic heating. As reported, ambient particulate levels frequently exceed 100 times the WHO-recommended safety level for sustained periods and account for the majority of personal particulate matter exposure (25). Reducing home heating emissions in traditional housing areas has been the primary focus of air pollution control efforts for Mongolian cities (26). Moreover, we observed that Mongolia still has a much higher level of lung cancer mortality in 2019, which is only second to China, although it has been decreasing over the past decades. Differing from China and Mongolia, Japan's age-standardized attributable death and YLL rates were the lowest from 1990 to 2019. This may be related to the fact that Japan has a declining relatively low level of air pollution, and its mortality rate from lung cancer is relatively low compared with other Asian countries (14, 27). A relatively low level of attributable burden was observed in both the Democratic People's Republic of Korea and the Republic of Korea, while the difference was that the death and YLL rate of lung cancer due to PM_2.5 increased in the former but declined in the latter. Ambient air pollution is recognized as a major environmental health hazard in the Republic of Korea and the average PM_2.5 exposure concentration for the whole period was estimated to be 30.2 μg/m³ during 1990–2013 (28). However, the mortality rate from lung cancer was much lower than in other countries. Therefore, although the Republic of Korea's air pollution is relatively high, the lung cancer attributable burden related to PM_2.5 is not at a high level. During 1990–2019, lung cancer death and YLL rates to PM_2.5 have increased in China, the Democratic People's Republic of Korea, and Mongolia, and decreased in Japan and the Republic of Korea. In East Asia countries, these trends were consistent with mean PM_2.5 concentrations, which showed substantial increases in China, with decreases observed in Japan during 1990–2013 (29).

We observed gender and area-specific distributions of lung cancer attributable burdens due to PM_2.5. Lung cancer deaths caused by ambient particulate matter were 2.34 times higher in East Asia men than women in 2019. Furthermore, the age-standardized death and YLL rates of lung cancer attributed to PM_2.5 were much higher in men than women in all countries, which was consistent with the gender difference in trends of lung cancer mortality. A previous study also reported that long-term PM_2.5 exposure has led to a much higher number of lung cancer premature death in male patients than in female patients (28).

In East Asia, the YLL burden of lung cancer caused by PM_2.5 was also mainly driven by China, especially in men. This finding was consistent with another previous study, which indicated that the elderly and men had higher health risks than younger people and women. When the PM_2.5 concentrations meet the WHO air quality guidelines of 10 μg/m3, 84% of the premature deaths would be avoided (30). Compared to 1990, the age-standardized death rate of lung cancer attributed to PM_2.5 increased in 2019, while the increase rate was smaller in males than females in the Democratic People's Republic of Korea, Republic of Korea, and Mongolia. Outdoor air pollution occurs predominantly in developing countries, particularly in Asia (1, 31). In China, industrial and residential sources were the two leading sources of mortality due to exposure to ambient PM_2.5 (32), and annual concentrations of ambient PM_2.5 are more than 5 times higher than the WHO guideline values in many populous cities. In Mongolia, sources concentrated on increased coal consumption in the cold season (33). Whether females were exposed to a higher risk of death in these countries, need to be further explored in relation to the different sources of mortality caused by ambient PM_2.5. In Japan, we observed that lung cancer death attributable to PM_2.5 decreased in both sexes. Increasing automobile traffic has caused considerable increases in concentrations of particulate matter, and concentrations have gradually decreased since control measures based on the automobile PM law were enforced in 2001 (34).

It is well-known that the major risk factor for lung cancer is tobacco smoking (12). Reactive oxygen or nitrogen species (ROS, RNS) and oxidative stress in the respiratory system could initiate or promote mechanisms of carcinogenesis, and the lungs are likely exposed to oxidants generated exogenously (air pollutants, cigarette smoke, etc.) daily (35). As reported, inhalable quartz, metal powders, mineral asbestos fibers, ozone, soot from gasoline and diesel engines, tobacco smoke, and ambient PM are involved in various oxidative stress mechanisms (35–38). It seems to be highly possible that PM_2.5 not only adds to lung cancer risk but also smoking habits over the years might be related to some of the differences of lung cancer, especially for men and women. Because smoking significantly increases the risk of lung cancer, which has been reported to be the main cause of lung cancers in 90% of male and 79% of female patients (39, 40). China is still facing heavy tobacco use, and lung cancer is the leading cause of cancer death and morbidity. A series of policies to control tobacco consumption and prevent lung cancer have been carried out. However, the burden of lung cancer is still serious, and the smoking rate in men is still very high (41).

In terms of age difference, the attributable death to PM_2.5 of lung cancer generally increased among elderly people (age ≥75 years) in both China and the Republic of Korea. This finding was also observed in other studies, which showed that long-term exposure to PM_2.5 was associated with an increased risk of disease death among people aged 65 years and older (42, 43). However, it is noteworthy that lung cancer death attributable to PM_2.5 increased for all age groups in the Democratic People's Republic of Korea and Mongolia. We also found that the percentage change of ASR of lung cancer death caused by PM_2.5 for China was significantly higher than that in any age groups in Table 2. This result was related to the age-standardized rate, which eliminates the influence of different age components of the population, and ensures the comparability of the lung cancer death rate.

Days of heavy pollution regularly occur in Asian megacities (23). China and the Democratic People's Republic of Korea had increasing attributable deaths rates of lung cancer caused by PM_2.5, and the period risk has also increased over the past few decades. According to the most up-to-date risk factor assessment, global exposure to harmful environmental risks has been declining, with the notable exception of ambient particulate matter pollution (6). In China, a large proportional increase in PM_2.5 was observed between 1990 and 2013 (29). While the early air pollution policies were ineffective at reducing emissions since the 1980s, and air pollution problems dominated by PM_2.5 have emerged and worsened since 2005 (44). As PM_2.5 was not been included in the National Air Reporting System until 2013, we collected data on the national annual mean PM_2.5 concentrations in China and found that it declined with a range of 72–36 μg/m³ from 2013 to 2019 (Supplemental Figure 1). Another previous study also reported that the average annual population-weighted PM_2.5 exposure in China was 52.7 μg/m³ in 2017, which is 9% lower than in 1990 (17). This decline is because of effective air pollution control policies after the winter-long PM_2.5 episode in China (44). However, the annual average PM_2.5 concentration in China was 36 μg/m³ in 2019 and the planned reductions in annual average PM_2.5 concentration from the current level to 10 μg/m³ still have not been achieved. As early as 2013, 87% of the global population lived in areas exceeding the WHO air quality guideline of 10 μg/m³ PM_2.5 (annual average) (29). Thus, the changes derived from the policy evolution have implications for future studies, as well as further reforming the management of health risk and air quality control. More interventions are required to achieve the guideline levels of PM_2.5 as the Chinese population is still facing a high exposure level. The lung cancer death attributable to PM_2.5 declined in Japan but the period risk in this country still be increasing. This is possibly related to long-term exposure to particulate matter causing health problems, such as normal lung function not being restored even after the improvement of air pollution in Japan (45). It is therefore essential for countries in East Asia to prevent air pollution.

This study has limitations. Although GBD 2019 collected missing data and improved the quality of data and its comparability by modifying and adjusting data sources and collection and evaluation methods, there might be uncertainty about exposure estimates, as there was no measurement in some areas or the data was not available in the GBD 2019 study. Therefore, the results should be carefully interpreted for these countries. Second, the majority of air quality monitoring stations were located in urban areas where air pollution mean concentrations are expected to be high. Third, the APC analysis only takes the effects of age, period, and cohort into account and does not further analyze other risk factors underlying lung cancer death.

Our study showed that ambient air pollution could impose a substantial burden in terms of lung cancer death in East Asia, where China is facing the highest attributable death rate for lung cancer caused by PM_2.5. An increasing trend of lung cancer death attributed to PM_2.5 was observed in East Asia from 1990 to 2019, except for Japan and the Republic of Korea. However, the period effect nevertheless suggests a remarkably increasing risk in China, the Democratic People's Republic of Korea, and Japan in the long-term, and overall reduction of air pollution would have significant benefits for the health of the populations in these countries.

The original contributions presented in the study are included in the article/Supplementary Material, further inquiries can be directed to the corresponding author/s.

CY conceived of the study and participated in its design and coordination. XL led data collection and analysis, wrote the original draft, and oversaw editing of the final manuscript. All authors contributed to the drafting and revision of the article, read, and approved the final manuscript.

This work was funded by the Wuhan Medical Research Program of Joint Fund of Hubei Health Committee (grant number WJ2019H304), the National Key Research and Development Program of China (grant numbers 2018YFC1315302 and 2017YFC1200502), and the National Natural Science Foundation of China (grant number 81773552).

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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