Concentration, chemical composition and toxicological responses of the ultrafine fraction of urban air particles in PM1

Epidemiological and toxicological evidence show that PM1 is a key driver of PM2.5. However, the particle sizes that play the major damaging role in PM1 is unclear. Our aims were to (1) explore the concentration and chemical composition of ultrafine particles in PM1; (2) evaluate and compare the differences in toxicity of PM1-0.2 and PM0.2 to different airway cell models. We collected PM1-0.2 and PM0.2 in Guangzhou in December 2017, monitored and detected their concentrations, size, and components. A549, THP-1 mono-cultures and A549/THP-1 co-cultured cells were exposed to PM1-0.2 and PM0.2, and evaluated for toxicological responses. PM0.2 contributed to15% PM1 mass and 87.67% to particle number (PN). Most of PM0.2 was PM0.1 (exceed 75%). Structure of particles in PM0.2 were mostly spherical, whereas in PM1-0.2 they were more diverse. Within the same mass unit, PM0.2 contained more chemical components than PM1-0.2; within the same volume, a higher mass of components was found in PM1-0.2. IL-6 and IL-8 were secreted by co-cultured cells in higher manner compared to mono cell cultures. PM0.2-induced higher toxicological responses compared to PM1-0.2. Our findings suggest that high PN concentration and toxicity of ultrafine or PM1 cannot be ignored. Mono-cell culture may underestimate the true PM toxicity