Establishing the exposure-outcome relation between airborne particulate matter and children's health.

With increasing urbanisation, industrialisation and economic growth worldwide, air pollution has emerged as one of the greatest global public health epidemics in the 21st century. The impacts of air pollution on human health are enormous. Globally, nine in ten people breathe air containing high levels of pollutants, and one in nine of the deaths are caused by exposure to air pollution, reaching an annual premature mortality of over seven million.1 Air pollutants comprise a complex mixture of gases and particulate matter (PM), which are directly emitted from natural and anthropogenic sources or are formed in air via a multitude of chemical processes.2 In particular, fine PM (diameter smaller than 2.5 µm or PM2.5) has been unequivocally linked to various adverse human health effects, ranging from aggravated allergies to the development of chronic diseases, to premature death.3 Exposure of vulnerable individuals to air pollution is especially worrisome, such as pregnant women and children.4 5 The morbidity and mortality associated with air pollution for children are relevant to both prenatal and postnatal exposures. For example, epidemiological and animal model studies have revealed that maternal exposure to fine PM results in adverse birth outcomes and postnatal health conditions.5 Specifically, animal model experiments employing ultrafine particles (diameter smaller than 0.1 µm or UFP) have shown that prenatal exposure predisposes offspring to long-term metabolic syndrome and pulmonary immunosuppression, with profound implications for respiratory infection risks.6 7 In this issue, Fang …