Ambient Particulate Matter and Lung Function Growth in Chinese Children

Children are particularly vulnerable to the effects of air pollution because they have a larger lung-to-body-volume ratio, their airway epithelium is more permeable to air pollutants and the lung defense mechanisms against particulate matter (PM) pollution and gaseous pollution are not fully evolved.1 Breathing the same pollutant concentrations, children may have a two- to four-fold higher dose reaching the lung parenchyma compared with adults.2 Numerous epidemiologic studies have reported effects of air pollution on children’s respiratory health.3 Of particular relevance to the present study are recent studies that examined the relationship between long-term exposure to air pollution and decreased lung function growth among children. A Southern California study found that the growth of forced expiratory volume in 1 second (FEV1) was slower in more polluted (higher PM2.5) communities and that movement away from polluted areas resulted in lower deficits in lung function growth.4,5 Similar associations have been found in Poland and Austria.6, 7 However, these studies were carried out in populations exposed to relatively low levels of air pollution (California, ~ 5 to 27 μg/m3 PM2.5; Krakow, Poland, ~33 to 52 μg/m3 suspended particulate matter; Austria: ~ 10 to 30 μg/m3 PM10). People living in many urban areas of developing countries have been exposed to much higher levels of pollution. For example, annual PM2.5 in New Delhi, India, was 102 μg/m3 in 20078; average PM10 levels in urban areas in non-European low income countries range from about 20 to 99 μg/m3, and mega cities in Asia have recorded annual levels to be above 100 μg/m3. 9,10 Whether the lung responses of children living in these highly-polluted cities are similar to those living in Western countries, is unknown. In fact, to the best of our knowledge, no prospective, longitudinal studies have been conducted to examine the effect of ambient PM on lung function growth at higher exposure levels, or have compared the sensitivity of lung function growth in relation to PM2.5 and PM10 exposure. This knowledge gap adds uncertainty to extrapolation of dose-response information from Western countries to developing countries, where PM10 is often the only metric of PM exposure collected. This provided the motivation behind the current study, where we examined the relationship between ambient PM concentrations and lung function growth among children living in four large Chinese cities.