Ambient air pollution, particularly particulate matter (PM), has grown to be one of the biggest threats for worldwide public health. Globally, 2.94 million deaths from all causes and 83 million disability-adjusted life-years (DALYs) were attributable to ambient particle mass with an aerodynamic diameter less than 2.5 μm (PM2.5) in 2017 (Lancet, 2018). Numerous epidemiological studies have demonstrated a link between PM exposure and an increased risk of mortality and morbidity, such as cardiovascular diseases and respiratory diseases (Chen et al., 2017; Hu et al., 2018; Lin et al., 2018; Lin et al., 2016a, Lin et al., 2016b; Shah et al., 2015). With 1.24 million deaths and 1513.1 per 100,000 age-standardised DALY rate estimated to be attributed to air pollution in 2017 (Yin et al., 2020), China is suffering greatly from disease and economic burdens brought on by ambient air pollution. Around 310 billion yuan in losses were caused by air pollution in China (Niu et al., 2017).

A variety of particle size fractions, including PM10 (inhalable particles, < 10 μm), PM2.5 (fine particles, < 2.5 μm) and PM1 (very fine particles, < 1 μm) were associated with respiratory mortality and respiratory diseases (Liu et al., 2019; Wang et al., 2021; Zhang et al., 2020; Zhao et al., 2017). PM can induce airway epithelial cell damage and barrier dysfunction, and inhibit the defense systems of the respiratory system (Ciencewicki and Jaspers, 2007). Additionally, there is a positive association between PM2.5/PM10 exposure and influenza-like illness (ILI) (Chen et al., 2017; Huang et al., 2016; Liu et al., 2019; Su et al., 2019; Toczylowski et al., 2021). ILI is a common respiratory syndrome that has a big impact on public health and causes a significant amount of morbidity and mortality annually (Paget et al., 2019).

According to recent studies, smaller PM particles may be more toxic to humans (Wang et al., 2021; Yang et al., 2019). In China, PM1 makes up around 80% of the PM2.5 mass (Chen et al., 2018). However, due to the absence of ground-based PM1 measurement, only a small number of research have concentrated on the relationship between PM1 and health. Besides that, there is presently no research on how PM1 may affect ILI. In this study, we aimed to investigate the short-term effects of ambient PM1, PM2.5 and PM10 on the incidence of ILI in a megacity in southern China.