Is PM₁ similar to PM_2.5? A new insight into the association of PM₁ and PM_2.5 with children's lung function

Experimental data suggests that PM₁ is more toxic than PM_2.5 although the epidemiologic evidence suggests that the health associations are similar. However, few objective exposure data are available to compare the associations of PM₁ and PM_2.5 with children lung function. Our objectives are a) to evaluate associations between long-term exposure to PM₁, PM_2.5 and children's lung function, and b) to compare the associations between PM₁ and PM_2.5. From 2012 to 2013, we enrolled 6,740 children (7-14 years), randomly recruited from primary and middle schools located in seven cities in northeast China. We measured lung function including forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1), peak expiratory flow (PEF), and maximal mid-expiratory flow (MMEF) utilizing two portable electronic spirometers. We dichotomized continuous lung function measures according the expected values for gender and age. The spatial resolution at which PM₁ and PM_2.5 estimated were estimated using a machine learning method and the temporal average concentrations were averaged from 2009 to 2012. A multilevel regression model was used to estimate the associations of PM₁, PM_2.5 exposure and lung function measures, adjusted for confounding factors. Associations with lower lung function were consistently larger for PM₁ than for PM_2.5. Adjusted odds ratios (OR) per interquartile range greater PM₁ ranged from 1.53 for MMEF (95% confidence interval [CI]: 1.20-1.96) to 2.14 for FEV1 (95% CI: 1.66-2.76) and ORs for PM_2.5 ranged from 1.36 for MMEF (95%CI: 1.12-1.66) to 1.82 for FEV1 (95%CI: 1.49-2.22), respectively. PM₁ and PM_2.5 had significant associations with FVC and FEV1 in primary school children, and on PEF and MMEF in middle school children. Long-term PM₁ and PM_2.5 exposure can lead to decreased lung function in children, and the associations of PM₁ are stronger than PM_2.5. Therefore, PM₁ may be more hazardous to children's respiratory health than PM_2.5 exposure.