Variability of aerosol mass and number concentrations during taconite mining operations

Abstract

This study characterized concentration metrics of airborne nanoparticles and their time series across major operations of a taconite mine through monitoring respirable and ultrafine particle concentrations at four major processing departments of the mine: crushing, dry milling, wet milling, and pelletizing (United Taconite Mine, Iron Junction, MN, USA). We used three area stations of direct-reading instruments to estimate concentration metrics including PM₁ (particles with an aerodynamic diameter <1 µm), respirable dust (particles sampled according to the respirable convention with a 50% sampling efficiency at an aerodynamic diameter of 4 µm), PN (total number concentration of particles), and lung-deposited surface area concentrations (LDSA) of particles smaller than 300 nm, on two different days. Results for each station were compared using bivariate correlation analysis to obtain insight into the spatial distribution, and intra-class correlation coefficients (ICCs) to evaluate the between-day repeatability between the measurements. Comparability of the LDSA concentrations measured by two different devices was also investigated using linear regression. Results revealed that the pelletizing operation produced the highest average LDSA concentration on both days (with a maximum concentration of 199 ± 48 µm²/cm³ in pelletizing, 141 ± 52 µm²/cm³ in crushing, 91 ± 9 µm²/cm³ in dry milling, and 85 ± 7 µm²/cm³ in wet milling). Concentrations in all operations showed a fair to excellent between-day repeatability but they were significantly different within stations of each operation. Measured LDSA concentrations did not show a linear correlation between different instruments, except for crushing.

Keywords:

• Aerosol
• crushing
• DiSCmini
• exposure
• LDSA
• milling
• partector
• pelletizing
• UFP

Acknowledgments

This research was funded by the National Institute of Occupational Safety and Health (Grant No. OH010662). Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the Centers for Disease Control and Prevention or the Department of Health and Human Services. Authors are thankful to Mr. Karl Braun from Cleveland-Cliffs Inc. for his insightful consultation and assistance in the data collection. Authors are grateful to Dr. Tran Huynh and Dr. Harrison Quick for their insights regarding the statistical analyses.

Disclaimer

The authors deny any conflict of interest in the present study.

Additional information

Funding

This research was funded by the National Institute of Occupational Safety and Health (Grant No. OH010662).