Variation in Ultrafine Particle Exposure in Laboratory Workplace Settings

Research Trainee: Jessica Axson, PhD, Postdoctoral Fellow, Dept. of Environmental Health Sciences at the University of Michigan

Faculty Sponsor: Andrew Ault, PhD, Assistant Professor of Environmental Health Sciences and Chemistry at the University of Michigan

Weekday aerosol number size distributions collected from two rooms in SPH II, one room in Chemistry building, and a normal outdoor environment in Fall 2015. This multi-dimensional plot has the time of sampling on the x-axis, the particle aerodynamic diameter ranging from 10 to 150 nm on the y-axis and the color scale representing the number concentration of particles. These plots show that the number concentration of aerosol particles ranging from 10 nm – 30 nm had highest number concentrations in SPH II basement and SPH II 7050 with number concentrations in the chemistry building and SPH II 7019 (not shown here) showed similar patterns to outdoor particles.

Aerosols are solid or liquid particulate matter whose diameters can range from as small as 1 nm up to about 10 mm. Outdoor aerosols are widely studied for their impact on earth’s climate with a lesser focus on human health. More recently, there is a growing focus on the exposure to indoor aerosols given the frequency and duration in which people are indoors and the various indoor environments that exist. Ultrafine particles, whose diameter is less than 100 nm, or 1/500 the width of human hair, are of particular interest due to their ability to penetrate pulmonary tissue and enter the blood circulation, leading to oxidative stress and damage to organ functions. It has been long known that indoor aerosol particles present in various working environments are associated with occupational respiratory illnesses. However, it is difficult to assess exposure to these particles when compared to other workplace hazards such as gasses, due to their small size and chemical complexity. For example, although ultrafine particles are much smaller in mass than larger particles, they contain a greater surface to volume ratio and are present in higher concentration than the larger particles. Additionally when compared to gasses, the chemical complexity of one aerosol particle is much greater. For example if you had a 10 nm particle could contain up to 104 molecules. Therefore, inhalation of ultrafine indoor aerosol particles remains a critical role in the field of today’s occupational health studies.

Prior indoor air quality research in the workplace has been performed in industrial environments to determine worker exposure to aerosol particles. However, the scientists researching these environments often neglect their own working environment (i.e. laboratories), which have fewer potential founders than real industries. This makes laboratory working environments necessary and unique to be studied to quantify the occupational ultrafine particle exposure. We had the unique opportunity to examine indoor aerosols in four locations on the University of Michigan central campus during the summer and fall seasons to determine temporal trends in aerosol size and concentration given that different air circulation (cooling and heating) was used during these seasons. The working environments examined included three laboratories within the School of Public Health building II (SPH II) and Chemistry building and one office in SPH II. The two buildings are located on the University of Michigan central campus, within a distance a half-mile from each other. The three laboratories were chosen to compare ultrafine particles in laboratory environments within the same building, SPH II, and between two different buildings. Aerosol sizing instruments which measured the size distribution and total particle concentration of particles ranging from 0.01 – 20 μm were used to measure aerosol particles for an entire work day during each of these seasons and at each location.

Results from this study show that the indoor particulate concentration and size varied between location and season with in buildings on the University of Michigan campus. Importantly, the particulate size most encountered in these labs is below 100 nm, indicating that these particles are capable of being inhaled deeper into the lungs. Our results indicate that particulate of these size and large concentrations occur in both the laboratory and office space studied in the SPH II building, where as the Chemistry building showed less particulate and at larger sizes. This indicates the need to further examine the particulate source to determine if any actions can be taken to minimize exposure of workers to these potentially harmful particulates.

Publications resulting from this project:

Ault, A. P.*; Shen, H.; Axson, J. L.; Gardner, D. J. “Seasonal Differences in Indoor Ultrafine Particles: Nucleation and Growth Events” In preparation for Aerosol Science and Technology.

Project Abstract