The fate of airborne nanoparticles released from a leak in a nanoparticle production process into a simulated workplace environment.

Abstract

A leak in nanoparticle production equipment can cause large quantities of nanoparticles to be emitted into a workplace environment. Toxicity studies have shown hazards of inhaling nanoparticles; however these studies may not be using the proper particles. Physical and chemical changes may occur as these nanoparticles travel from the production site through ambient air, causing worker exposure. With the correct size and concentration known at distances from the leak, realistic worker exposure can be determined and appropriate worker protection and occupational monitoring schemes can be developed. Different nanoparticle materials were produced with a diffusion burner and injected through an experimentally simulated leak into a wind tunnel (simulated workplace environment). The wind tunnel background face velocity was 0.25 m/s. Soot distributions (dg = 59 and dg = 113 nm) and TiO2 (dg = 21 nm) were used as the test aerosols. A smaller distribution of particles (dg < 8 nm) was also noticed at the injection site for soot and TiO2. Lung deposited surface area concentration was measured using a NSAM and the number size distribution was measured with a SMPS at distances of 0.9 m, 1.8 m, and 3.4 m (times of 3.6 s, 7.2 s, and 13.6 s, respectively) from the injection point. TEM images were gathered at the injection point and 3.4 m downstream. The soot (dg = 113 nm) and TiO2 (dg = 21 nm) distributions produced loose, chain-type agglomerates at the injection point with primary particle sizes of dpp = 30 nm and dpp = 4.5 nm, respectively. These distributions experienced an increase in geometric mean particle size between the injection point and 0.9 m downstream. Surface area per particle (NSAM/SMPS ratio) also increased between the injection point and 0.9 m downstream. There was no additional particle change after 0.9 m. Primary particle size also increased after the injection point within the wind tunnel. Therefore the agglomerate size change may have been caused by the primary particle size change, as coagulation is an unlikely cause of particle growth in this situation. The soot (dg = 59 nm) aerosol was not relevant for this analysis. The soot (dg = 59 nm) distribution was created using a Rich fuel/air mixture (&#966; = 2.05), which produced unburned fuel in the exhaust. When the simulated leak size was changed from 27 mm to 10 mm, the Richardson number of the leak changed from 197 to 0.42, and a bi-modal distribution formed at 0.9 m downstream (1st mode: dg = 16 nm, 2nd mode: dg = 70 nm). The first mode particle formation was likely caused by turbulent mixing of the leaked exhaust gases with background air, causing local supersaturation and new particle formation.