Airborne fiber particles: Types, size and concentration observed in Beijing

Airborne fibers are of public concern because of their potential threat to the environment, however their physical and chemical properties are poorly understood. Fibers are defined as having an aspect ratio >3:1. Fiber particles were collected in the near surface air, surface deposited dust and building materials in Beijing. They were examined using analytical scanning electron microscopy. The particles were initially classified into two categories: organic and inorganic. Organic fibers comprised microplastic and natural organic fiber particles. Inorganic fibers were mainly man-made mineral fibers (MMMFs), asbestos (represented by chrysotile), calcium sulfate and metal fiber particles. Microplastic and MMMFs fibers were most abundant, accounting for 34.6% and 40.3% in total, respectively, followed by asbestos (7.8%), calcium sulfate (7.2%), metal fibers (5.6%) and natural organic fiber particles (4.5%). The number-concentration of these particles was about 16.7 × 10^-3 fibers/ml at 1.5 m above the ground and about 14.1 × 10^-3 fibers/ml at about 18 m, suggesting the particles were mainly derived from surface and were re-suspended. Approximately 80% of the airborne fiber were smaller than 20 μm in length, which is possibly the critical size for fiber particles to re-suspend into the air. Surface dust and construction sites were speculated to be the major contributors of the fiber particles.