Associations of particulate matter size fractions and chemical composition with conjunctivitis and eczema: epidemiological evidence from the Pearl River Delta, China.

Current evidence remains limited regarding the differential impact of particulate matter (PM) characteristics, such as size fraction and chemical composition, on allergic diseases. To address this, we recruited 131,346 school-aged children and adolescents from six cities of the Pearl River Delta (PRD) region of China from 2016 through 2018. PM of different size fractions (PM1, PM2.5 and PM10) and PM2.5 chemical composition (carbonaceous fractions, ions, metals and per- and polyfluoroalkyl substances; PFAS) were measured in ambient air. Conjunctivitis and eczema, two of the most common allergic conditions, were determined by self-reported doctor diagnosed affirmations from the parents or legal guardians. Logistic regression models were employed to explore associations between PM characteristics and allergic diseases. PM chemical composition was positively associated with both allergic diseases, while PM size fraction showed a positive association only with eczema. For example, per interquartile range (IQR) increase in PM1 (IQR = 3.75 μg/m3) concentrations showed an odds ratio (OR) of 1.19 (95 % CI: 1.15, 1.22) for eczema, and 0.97 (95 % CI: 0.91, 1.04) for conjunctivitis. In quantile g-computation (qg-comp) models, PM2.5 chemical composition was associated with higher risks of eczema (RR = 1.40, 95 % CI: 1.38, 1.42) and conjunctivitis (RR = 1.46, 95 % CI: 1.40, 1.53). Furthermore, these associations were robust in younger children, and in regions with low GDP or high population density. Our findings provide a nuanced understanding of how the size fraction and composition of PM exposure to the two most occurring allergic conditions.