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Aerosol emissions from fuse-deposition modeling 3D printers in a chamber and in real indoor environments. Marina Eller Vance, Valerie Pegues, Schuyler Van Montfrans, Weinan Leng, and Linsey C. Marr Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b01546 • Publication Date (Web): 08 Aug 2017 Downloaded from http://pubs.acs.org on August 10, 2017

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Environmental Science & Technology

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Aerosol emissions from fuse-deposition modeling

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3D printers in a chamber and in real indoor

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environments.

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Marina E. Vance*1, Valerie Pegues2, Schuyler Van Montfrans3, Weinan Leng4, Linsey C. Marr4

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*1

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Engineering Drive, Boulder, CO 80309, United States. Email: [email protected],

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phone: (303) 735-8054, fax: (303) 492-3498.

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Department of Mechanical Engineering, University of Colorado Boulder, 427 UCB, 1111

Department of Environmental Health and Safety Virginia Tech, Blacksburg, VA 24061, United

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States 3

William Fleming High School, 3649 Ferncliff Ave. NW, Roanoke, VA 24017, United States 4

Department of Civil and Environmental Engineering, Virginia Tech, 418 Durham Hall, Blacksburg, VA 24061, United States

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RUNNING TITLE: Aerosol emissions from 3D printers

ACS Paragon Plus Environment

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KEYWORDS: Ultrafine aerosols, incidental nanoparticles, indoor air quality, 3D printing,

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additive manufacturing.

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ABSTRACT

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Three-dimensional (3D) printers are known to emit aerosols, but questions remain about their

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composition and the fundamental processes driving emissions. The objective of this work was to

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characterize aerosol emissions from the operation of a fuse-deposition modeling 3D printer. We

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modeled the time- and size-resolved emissions of submicron aerosols from the printer in a

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chamber study, gained insight into the chemical composition of emitted aerosols using Raman

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spectroscopy, and measured potential for exposure to aerosols generated by 3D printers under

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real-use conditions in a variety of indoor environments. Average aerosol emission rates ranged

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from ~108 to ~1011 particles min-1, and rates varied over the course of a print job. Acrylonytrile-

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butadiene-styrene (ABS) filaments generated the largest number of aerosols and wood-infused

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polylactic acid (PLA) filaments generated the smallest amount. Emission factors ranged from

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6×108 to 6×1011 per gram of printed part, depending on the type of filament used. For ABS, the

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Raman spectra of the filament and printed part were indistinguishable while the aerosol spectra

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lacked important peaks corresponding to styrene and acrylonitrile, which are both present in

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ABS. This observation suggests that aerosols are not a result of volatilization and subsequent

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nucleation of ABS or direct release of ABS aerosols.

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INTRODUCTION

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The field of indoor air quality continually grows to accommodate novel consumer products

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that may release pollutants into the indoor environment. Office equipment such as laser printers

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and photocopiers are known to emit volatile organic compounds (VOCs), ozone, and particulate

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matter.1,2 With the recent development and popularization of three-dimensional (3D) printers,

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studies are needed to understand their potential emissions to indoor environments.

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3D printing (also referred to as additive manufacturing or rapid prototyping) is a bottom-up

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process of creating a three-dimensional object layer by layer. There are several distinct 3D

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printing processes, which can utilize solid, powder, or liquid feedstock materials.3 The 3D

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printing industry has been growing steadily since 2009, when a core fuse-deposition modeling

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(FDM) patent expired.4,5 As the cost of 3D printers has decreased, they have become more

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popular in homes, offices, and schools.

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In FDM, a polymeric filament is extruded through a heated nozzle that moves to create a pre-

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designed object with layers that are typically ~0.25 mm in thickness. Common filament materials

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include acrylonytrile butadiene styrene (ABS), polylactic acid (PLA), polycarbonate, and

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blended polymers.3

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To date, eight research articles have been published on air pollutant emissions of 3D printers.

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Seven of these works evaluated FDM 3D printers6–12 and one evaluated a binder jetting 3D

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printer.13 Studies of FDM printers investigated a variety of polymeric filaments including ABS,6–

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10,12

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nylon,9,11 copolyester,11 and more. Three studies investigated VOCs in addition to aerosols.7,9,10

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Studies have been performed inside stainless steel9,12 and acrylic chambers7,10, in a 60 m3 clean

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room,8 and in indoor environments ranging from 30 to 180 m3 in size.6,10–13 Of these eight

PLA,6,7,9–12 PLA infused with other materials (e.g., copper, wood fiber, bamboo, etc),11


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studies, only Azimi et al. (2016) modeled total ultrafine aerosol emission rates with

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consideration of chamber wall losses and the time-varying nature of emissions, while also

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focusing on situations with low background aerosol concentrations.9 No studies to date have

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reported simultaneous time- and size-resolved aerosol emissions, information that is needed to

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model the fate of the aerosols in detail. Many research questions remain as to the fundamental

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processes driving aerosol and VOC releases from the FDM process and the resulting aerosol

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chemistry and toxicity.

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The objective of this work was to characterize aerosol emissions from FDM 3D printers.

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Specific objectives were (1) to measure the time- and size-resolved emissions of submicron

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aerosols from the operation of a FDM 3D printer using five types of filament material in a

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chamber study, (2) to gain insight into the chemical composition of these aerosols through

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electron microscopy coupled with energy dispersive X-ray spectroscopy and Raman

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spectroscopy, and (3) to determine aerosol concentrations under real-use conditions in a variety

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of indoor environments.

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MATERIALS AND METHODS

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Chamber. To assess the aerosol size distributions and emission rates of different filaments, we

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placed an Afinia desktop 3D printer (H480, Afinia 3D) inside a 520-l polyethylene chamber

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(Atmosbag, Sigma-Aldrich). The following filaments (feedstock materials) were tested: yellow

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acrylonytrile butadiene styrene (ABS) “premium” quality, orange ABS “value” quality, light-

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blue polylactic acid (PLA), wood-infused PLA, copper-infused PLA.

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All filaments were purchased from Afinia 3D. Chemical structures of ABS, PLA, and their

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monomers are shown in Figure S1 in the Supporting Information (SI). We printed a test artifact


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developed by NIST for assessing 3D printers (Fig. 1b),14 scaled to 50% in order to be completed

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within 60 min. Printer settings are described in Tables S1 and S2.

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The chamber was flushed with air that was conditioned through a high efficiency particulate

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air (HEPA, Pall Corp.) capsule filter to a background aerosol concentration of 0 cm-3 measured

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by a Scanning Mobility Particle Sizer (3936NL SMPS, TSI Inc.). The flow rate of air that was

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flushed through the chamber varied by material and is described in the SI file, along with a

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detailed description of the aerosol characterization instruments and their operational settings.

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Aerosol characterization. The concentrations and size distributions of aerosols 14.6–680 nm

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were monitored continuously at 3-min resolution with an SMPS during the entire print job.

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While the focus of this work was the aerosol component of emissions, total VOCs were

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minimally investigated using a GrayWolf (IQ-610, GreyWolf LLC) monitor, which was placed

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inside the chamber during printing with ABS “value” quality and PLA.

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For off-line analyses, aerosol samples were collected on the lowest stage of a three-stage

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impactor (Microanalysis Particle Sampler MPS-3, California Measurements). The cutpoint of

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this stage was 50 nm and the stage upstream had a cutpoint of 300 nm. For scanning electron

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microscopy (SEM), samples were collected on an ethanol-cleaned aluminum stub covered with

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carbon tape and analyzed using an environmental SEM (ESEM, FEI Quanta 600 FEG) equipped

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with electron dispersive X-ray spectroscopy (EDS) capabilities. For Raman spectroscopy,

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samples were collected on a silicon wafer which was attached to an SEM stub. The silicon wafer

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was cleaned with ethanol and sonicated in ultrapure water before use. Raman spectra were

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recorded using a confocal Raman microscope (WITec alpha 500) equipped with a 100× Olympus

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objective. Laser excitation (~10 mW at the sample) was provided by a 785-nm diode laser. Each


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spectrum was obtained as an average of 6 accumulations of 10 s each. The background signal

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from the silicon substrate was removed by subtracting a silicon spectrum.

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A sample of copper-infused filament was also analyzed for metal content by inductively-

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coupled plasma mass spectrometry (ICP-MS, Thermo Electron X-Series, detection limit of 0.5

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ppb). Pieces of filament 40 – 65 mg in mass were dissolved in ~100 mL of dichloromethane

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(DCM, 99.9%, Fisher Scientific). The DCM was allowed to evaporate overnight in a fume hood,

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after which 80 ml of ultrapure water (18 MΩ cm, Barnstead) and 20 ml of trace-metal grade

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nitric acid (HNO3 67 - 70%, PlasmaPure, SCP Science) were added. This solution was heated at

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70 ºC overnight and then 1 ml of this solution was added to 9 ml of ultrapure water and analyzed

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by ICP-MS.

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Aerosol emissions modeling. Aerosol concentrations in the chamber were used to obtain an

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empirical, size-resolved and time-resolved emission rate for each tested material. The chamber

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was modeled as a continuously-stirred tank reactor (CSTR), and size-resolved aerosol wall losses

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were determined experimentally (Table S3). The initial mass balance equation (Eq. 1) was

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solved discretely for the emissions term, which varies over time (Eq. 2). These equations were

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solved separately for each size range of particles measured by the SMPS. The SI file presents a

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detailed description of this model.

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()

= + − −

Eq 1.

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In Eq. 1, V is the volume of the chamber (cm3), C is the concentration of aerosols (cm-3), Qin is

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the flow rate of air that is introduced into the chamber (cm3 s-1), Cin (cm-3) is the concentration of

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aerosols in the inflow air, zero in these experiments, E is the emission rate (s-1), β is the wall-loss

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coefficient (s-1), Qout is the flow rate of air exiting the chamber (cm3 s-1), and C is the


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concentration of aerosols exiting the chamber (cm-3), which is assumed to be equal to the

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concentration of aerosols inside the chamber.

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( ) =

( )( )

+ ( ) + ( )

Eq. 2

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In Eq. 2, tn is the current period of aerosol measurements, and tn-1 is the previous period of

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measurement. For this study, these periods are 3 min apart. Eq. 2 was used to determine the size-

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resolved and time-resolved emission rates in units of number of particles per second.

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Emission rates were summed over each size bin to determine the total aerosol emission rate

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over time. While the emissions model accounts for size-specific wall-losses, it does not account

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for aerosol agglomeration, which is likely to occur at high aerosol concentrations.15 To adjust for

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this effect, negative emission values were eliminated before total aerosol emissions were

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calculated, as done in a previous study.9 Finally, the aerosol emission factor was determined by

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summing the total number of aerosols emitted during the printing activity and dividing it by the

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mass of printed part.

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Field measurements. Field measurements took place in five sampling locations at Virginia

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Tech. Each location had an unenclosed FDM 3D printer equipped with ABS filament, and users

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volunteered to print a typical part as they would during normal operations. The locations

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included two laboratories, two offices, and one classroom. Tables S5 and S6 describe all printers,

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filament materials, parts printed, and indoor environments. Figure S2 presents photos of typical

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parts printed for this study.

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Field measurements occurred in two phases: (1) using a handheld condensation particle

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counter (CPC model 3800, Kanomax USA, Inc.), and (2) using both the CPC and a portable

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SMPS (Nanoscan model 3910, TSI, Inc.). The classroom was only tested during phase 1 because


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the printer was not available during the second phase, and one of the offices was only tested

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during phase 2 for the same reason. Instruments were placed at seated breathing height (1 – 1.2

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m) and ~1 m away from the 3D printer nozzle, to mimic a realistic exposure scenario of a user

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working near the printer. The maximal contribution of the 3D printer to indoor aerosols was

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estimated by subtracting the background size distribution, measured before printing began, from

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the size distribution obtained at the time of maximum aerosol concentrations.

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RESULTS AND DISCUSSION

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Aerosol size distributions in chamber experiments. As shown in Figure 1, the aerosol size

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distributions at the time of maximum total concentration differed substantially by type of

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filament.

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Figure 1. Aerosol size distributions at the time of peak concentration inside the chamber for each

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filament material. For improved legibility, the results for copper-infused and wood-infused PLA


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are plotted on a separate panel (b), whose y-axis range is two orders of magnitude smaller than in

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the top panel (a). Dark lines represent average among replicates, and shaded areas represent

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standard errors.

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The ABS filaments introduced the largest number of aerosols in the chamber, with the less

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expensive, “value” ABS introducing significantly more aerosols than the “premium” ABS

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material. Despite this difference in concentration, both “value” and “premium” ABS filaments

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yielded similarly-shaped size distributions, with modes at 51 ± 9 nm and 51 ± 4 nm, respectively.

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These results are in agreement with Yi et al., who reported SMPS aerosol geometric mean

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diameters (GM) ranging from 45 to 79 nm for different color ABS filaments in a chamber of

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similar volume (0.5 m3).12 The maximum total aerosol concentrations in the chamber were quite

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high, 2×106 cm-3 and 5×105 cm-3 for ABS “value” and “premium”, respectively. Agglomeration

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may have shifted the size distribution and the mode to larger diameters than originally emitted.

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Very near the printer nozzle, it is likely that particle concentrations were even higher and that

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some agglomeration occurred, even if concentrations in the bulk chamber air did not exceed 106

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cm-3. Analogous to studies of particles in vehicle exhaust, these measurements represent

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emissions after some near-source aerosol processing has occurred.

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The PLA filament yielded the smallest aerosols, with a mode of 22 ± 2 nm. For PLA, Yi et al.

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reported a GM of 28 – 32 nm. Stabile et al. performed measurements in a 40 m3 room and

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reported a mode of 13 – 15 nm for PLA.11,12 The copper-infused and wood-infused PLA

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filaments yielded peak concentrations about 2 orders of magnitude smaller than did the other

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materials. Peaking at approximately 28 ± 3 nm, the size distribution generated by wood-infused

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PLA was similar in shape to that produced by PLA. The copper-infused PLA emitted much


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larger aerosols than did other filaments, with a peak at 470 ± 13 nm. Stabile et al. reported a

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mode 12 – 24 nm for wood-infused and copper-infused PLA.11

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Size-resolved aerosol emissions over time. Using Equation 2, we calculated the aerosol

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emission rate as a function of size and time. The results obtained for ABS filaments appear in

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Figure 2 and those for PLA-based filaments are shown in Figure 3.

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Figure 2. Size- and time-resolved aerosol emission rates (min-1) obtained in chamber studies

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using (a) ABS “value” and (b) ABS “premium” filaments. This figure is better visualized in

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color as the scale on the right represents a color code for emission rate magnitude. The color

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scale is the same for Figures 2 and 3. The results represent one replicate for each material.

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Duplicates in S3 show good visual agreement.

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The ABS “premium” filament led to lower aerosol emissions than did the ABS “value”

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filament, although aerosol size distributions were similar in shape. Figure 2 shows that aerosol

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emissions continued throughout the print job for ABS “value,” whereas they seemed to stop after

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the first ~ 10 min for ABS “premium,” at which time ultrafine aerosol emissions decreased by an


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order of magnitude, even when printing the same object. Figure 2b shows a characteristic

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“banana” shape that describes aerosol formation and subsequent coagulation and growth.16

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Figure 3. Size- and time-resolved aerosol emission rates (min-1) obtained in chamber study using

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(a) PLA, (b) copper-infused PLA, and (c) wood-infused PLA filaments. This figure is better

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visualized in color as the scale on the right represents a color code for emission rate magnitude.

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This color scale is the same for Figures 2 and 3. The results represent one replicate for each

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material. Duplicates in Figure S4 show good visual agreement.

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The aerosol mode for ABS “premium,” PLA, and wood-infused PLA continually increased

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throughout the printing activity (Figure S5), indicating that the aerosols present in the chamber

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continued to grow over time due to agglomeration, even after total concentrations dropped below

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106 cm-3. The aerosol mode for ABS “value” behaved differently, decreasing twice throughout

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the printing activity, indicating new aerosol emissions.

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While the emissions model accounts for size-specific wall-losses, it does not account for

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aerosol agglomeration, which occur at concentrations > 106 cm-1. Rapid agglomeration is likely

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to occur in close proximity to the nozzle, as discussed previously. Agglomeration leads to

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negative values (Table S4) of emission factors for smaller aerosols and may lead to positive

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emission factors for larger aerosols even when actual emissions are zero. Thus, the emission


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rates shown in Figures 2 and 3 are “effective” emission rates representing a scenario in which the

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air in a small volume around the printer is relatively stagnant, where particles can accumulate

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and agglomerate, or the printer is in an enclosure. This phenomenon was also observed by Azimi

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et al.9 and in one of the indoor environments, as described below.

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Total aerosol emissions over time. Figure 4 shows the total aerosol emission rate, in units of

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min-1 in chamber experiments, averaged among replicates for the five tested filaments.

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Figure 4. Total aerosol emission rates measured in chamber experiments for each filament

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material. For improved legibility, the results for copper-infused and wood-infused PLA are

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plotted in a separate panel (b), whose y-axis range is three orders of magnitude smaller than in

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the top panel (a). The dark line represents the average among replicates, and the shaded areas

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represent standard errors.


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As reported in other studies,9,11,12 aerosol emission rates were not constant over time.

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Emissions may be affected by the different activities performed by the printer. All filaments

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generated a peak of aerosol emissions at the start of printing activities that lasted ~5 – 10 min,

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the period when the support raft was printed. At ~20 min, the printer finished printing the bottom

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shell of the object and began printing the filling. At ~38 min, the top shell began to be printed

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and at ~47 min, the pins at the top of the object started being printed.

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For copper-infused PLA, a large, broad peak also occurred at 24 – 44 min. Average aerosol

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emission rates, presented in Table 1, ranged from ~108 to ~1011 min-1, in agreement with

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measurements performed by Azimi et al.9 for ABS and PLA filaments. Emission factors in terms

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of particle number per gram of printed part, which can be used to estimate total emissions from

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printed jobs of different sizes, ranged over three orders of magnitude, from 6×108 g-1 for copper-

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infused PLA to 6×1011 g-1 for ABS “value.”

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Table 1. Average aerosol emission rates and emission factors (per mass of 3D printed part) for

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each filament material (± standard errors). Average aerosol emission rate (min-1)

Aerosol emission factor (g-1)

ABS “value”

(1.08 ± 0.01) ×1011

(6.2 ± 0.3) ×1011

ABS “premium”

(1.25 ± 0.01) ×1010

(7.8 ± 0.2) ×1010

PLA

(1.48 ± 0.01) ×1010

(7.6 ± 0.2) ×1010

Wood-infused PLA

(1.10 ± 0.01) ×108

(5.7 ± 0.5) ×108

Copper-infused PLA

(1.58 ± 0.01) ×108

(6.4 ± 0.8) ×108

Filament material

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Aerosol composition, ABS. Optical images of impacted aerosols resulting from ABS “value”

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3D printing are shown in Figure 5 alongside Raman spectra of aerosols, the raw ABS filament,

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and a printed part.

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Figure 5. Optical images of ABS “value” aerosols impacted onto a silicon wafer (a) and insets

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with larger (≥10µm) aerosols (b) and smaller (≤1µm) aerosols (c) and resulting Raman spectra

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(d). Broader peaks are associated with smaller aerosols (c). Peaks associated with the benzene

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ring present in styrene are located at 620, 1001, 1031, 1157, and 1183 cm-1. The peaks associated

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with the carbon-nitrogen triple bond in acrylonitrile (ABS) is located at 2236 cm-1.

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The Raman spectra of the filament and printed part were indistinguishable while the aerosol

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spectra lacked important peaks that correspond to the benzene ring present in styrene and the

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carbon-nitrogen triple bond present in acrylonitrile, both present in the ABS structure. The

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extrusion temperatures (210 – 270 ºC) were higher than the boiling points of both styrene (145

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ºC) and acrylonitrile (77 ºC). This disproves the hypothesis that the aerosol is a result of

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volatilization and subsequent condensation/nucleation of ABS or direct release of ABS aerosols.

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A second hypothesis is that aerosols may be formed as a product of the thermal degradation of

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the ABS polymer, which would involve the release of semi-volatile compounds—likely


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oligomers—that are volatile at extrusion temperatures but not at room temperature, thus causing

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condensation, nucleation, and subsequent growth of aerosols. Suzuki and Wilkie performed a

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thermogravimetric analysis coupled with infrared spectroscopy (TGA / FTIR) on ABS among

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other polymers and observed that its degradation begins at 340 ºC with the release of butadiene

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monomer, which is quickly followed at 350 ºC with the release of aromatics from the original

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styrene monomer. The release of acrylonitrile occurs last, at ~400 ºC.17 These thermal

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degradation processes occur at a significantly higher temperature than the extrusion temperature

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observed in a 3D printer (up to 270 ºC). In contrast, a study by Tiganis et al. demonstrated that

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after 168 h at 90 – 120 ºC the polybutadiene component of ABS may undergo thermo-oxidative

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degradation that may lead to the formation of carbonyl and hydroxyl products.18 Unwin et al.

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reported the release of styrene, 1,3-butadiene, acrylonitrile, and 4-vinyl-1-cyclohexene from the

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vacuum forming of ABS sheets at 160 – 180 ºC.19

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A third hypothesis is that this type of thermal degradation may be occurring, but in chemical

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additives rather than in the ABS polymer itself, or perhaps in both. Bai et al. used gas

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chromatography/mass spectrometry (GC/MS) to investigate the release of additives from virgin

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ABS polymer and waste ABS plastics from reprocessing at 230 – 270 ºC. They found that

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commonly-used antioxidants and lubricants oxidize, degrade, and, in some cases, volatilize at

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that temperature range.20

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Pigments and dyes are another class of commonly used additive in ABS filaments, whose

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original color ranges from translucent to white. To our knowledge, there have not been studies

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on the thermal degradation of pigments and dyes present in ABS plastics.

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Aerosol composition, PLA. The Raman spectra of filament, printed part, and aerosols are

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shown in SI Figures S6 – S9 online. In contrast to ABS, the spectrum of the PLA part differed


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from that of its raw filament material (Figure S7), and the printed part itself was not spatially

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homogeneous with regards to its Raman spectra (Figure S8). Aerosols presented broad Raman

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peaks at ~1300 and ~1600 cm-1. Unlike ABS, the chemical structure of PLA does not contain

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any bonds with characteristic Raman peaks (Figure S9). Aerosols emitted from copper-infused

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PLA were investigated using SEM/EDS and no discernible copper peak was identified in the

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aerosols (Figure S10), although the copper filament contained 21.1 ± 0.3 % copper as determined

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by ICP-MS. The filament also contained 500 ± 76 ppm zinc, 214 ± 53 ppm silicon, and 175 ± 29

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ppm iron. We hypothesize that the presence of copper affected aerosol emissions but the copper

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itself was not aerosolized. However, further investigation into the aerosol composition is needed

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to prove the absence of copper or other metals.

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VOC and CO emissions. The total VOC concentrations in the chamber reached 0.83 ± 0.01

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ppm and CO concentrations reached 0.69 ± 0.01 ppm above background during printing with

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ABS “value”. During printing with PLA, neither pollutant reached detectable levels inside the

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chamber.

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Field measurements. In five of the eight indoor measurements, aerosol concentrations

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increased after the start of printing activities (Figure 6), which demonstrates that the operation of

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3D printers can impact the air quality of indoor environments. The average aerosol background

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level for indoor environments ranged from 854 ± 12 cm-3 in the classroom to (1.7 ± 4)×104 cm-3

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in Laboratory 2. Maximum aerosol concentrations ranged from 3.9×103 cm-3 in Office 1 to

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6.6×104 cm-3 in Laboratory 1. In one set of measurements in Office 1, there were large peaks in

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aerosol concentration during background measurements ~15 min before printing and at ~40 – 45

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min, which could not be explained by 3D printing activities.


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Dilution appeared to impact concentrations, even though all measurements were conducted ~1

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m from the printer. The smallest increase in aerosol concentrations during printing was observed

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in Office 1, which was also the largest room, with a volume of ~780 m3 (Table S6). One of the

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largest increases in concentrations was observed in Office 2, which was the smallest environment

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investigated (36 m3). For comparison, Steinle was able to detect a 1.2 × 103 cm-3 increase in

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aerosol concentrations at a distance of ~0.3 m but not at 2.5 m from the printer in a 180-m3 room

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with a 2 h-1 air exchange rate.10

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Figure 6. Total aerosol concentrations observed in real indoor environments during typical 3D

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printing activities, using ABS filaments only. These filaments were purchased from different

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manufacturers and were not subcategorized as “premium” or “value”. At time 0 min, printing

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activities began and continued through the end of measurements. The Classroom and Office 2

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were only tested once because the printer was not available during the second phase. Sampling

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inlets were placed at seated breathing height (1 – 1.2 m) and ~1 m away from the 3D printer

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nozzle.

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The y-axis range in the bottom two panels (Office 1 and Classroom) is one order of magnitude smaller than in the upper three panels.

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Figure S11 shows the estimated size distribution of aerosols contributing to indoor

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environments by 3D printing activities. These were obtained by subtracting background size

331

distributions from those obtained at the time of maximum concentration. The size distributions

332

differed by location, likely reflecting the different types of printers used in each location. In

333

Office 2, the mode occurred at 15.4 nm, which was significantly smaller than the ~51 nm mode

334

observed in chamber experiments with the same printer and filament material (Afinia H480 and

335

ABS “premium”, respectively). Figure S12 shows aerosol emission rates calculated for Office 2

336

in two replicate measurements, one of which shows aerosol growth from ~15 nm to ~54 nm

337

throughout the first ~45 min of printing. This finding confirms that the aerosol growth observed

338

in some of the chamber experiments may also occur in indoor environments and might especially

339

occur in enclosed, unvented 3D printers.

340

Office 2 had a much larger volume than the chamber (36.2 m3 versus 0.52 m3) and a different

341

air exchange rate. It appears that dilution in the room was sufficient to avoid the high

342

concentrations that led to agglomeration in the chamber experiments. The air exchange rates of

343

indoor environments were not measured for this study; they are typically 0.5 h-1 but may reach as

344

high as 5 – 7 h-1.21,22 The American Society of Heating, Refrigerating and Air-Conditioning

345

Engineers (ASHRAE) recommends a minimum ventilation rate of > 0.35 h-1 for living areas.23

346

The air exchange rate in the chamber was ~2.5 h-1 for ABS measurements.

347 348

INHALATION EXPOSURE


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349

The size-resolved emission rates developed in this study can be used to estimate the inhalation

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exposure to aerosols.24 Assuming that an average adult engaged in light work25 operates a 3D

351

printer in a 30 m3 room with an air exchange rate of 0.5 h-1 and remains in the room during a 1-h

352

print time (the print duration of this study), the person would inhale 107 – 1010 particles or up to

353

5.6 µg of aerosols, assuming spherical aerosols of 1 g cm-3 density15 (Tables S7 and S8). Of

354

course, actual exposure may differ because emissions will not mix instantaneously and

355

homogeneously throughout the room. In terms of particle number, inhalation exposure associated

356

with 3D printers appears to be similar to that for laser printers, as the variability and range of

357

concentrations is comparable to that observed in a study of laser printers in offices in Australia26

358

and Germany.27 The mean particle number emission rates of 3D printers in this study, and thus

359

the resulting exposure, are lower than for combustion sources in the home and comparable to

360

those generated by appliances such as an electric space heater, laser printer, and vacuum

361

cleaner.28,29 Of course, differences in particle composition are also important for assessing effects

362

of these sources. The results presented in this work can be used by exposure science and life-

363

cycle assessment modelers as input data for further modeling and, more importantly, by toxicity

364

researchers as realistic dosing metrics for FDM 3D printers.30,31

365 366 367

ASSOCIATED CONTENT

368

SUPPORTING INFORMATION

369

Includes detailed descriptions of the 3D printers, filaments, printed parts, as well as

370

descriptions of the chamber setup, emissions model and inhalation dose calculations, 12 figures,

371

and 8 tables. This material is available free of charge via the Internet at http://pubs.acs.org/.


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372

AUTHOR INFORMATION

373

Corresponding Author

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* Phone: (303) 735-4567; Email: [email protected].

375

Author Contributions

376

The manuscript was written through contributions of all authors. All authors have given approval

377

to the final version of the manuscript.

378

Notes

379

The authors declare no competing financial interest.

380

ACKNOWLEDGMENTS

381

Funding for this work was provided by the Institute for Critical Technology and Applied

382

Science (ICTAS) at Virginia Tech, the Center for Sustainable Nanotechnology (VTSuN), the

383

Center for Innovation-Based Manufacturing (CIBM), and the National Science Foundation

384

(NSF) and the Environmental Protection Agency (EPA) under NSF Cooperative Agreement EF-

385

0830093, Center for the Environmental Implications of Nanotechnology (CEINT). This work has

386

not been formally reviewed by EPA, and no official endorsement should be inferred. This work

387

used shared facilities at the Virginia Tech National Center for Earth and Environmental

388

Nanotechnology Infrastructure (NanoEarth), a member of the National Nanotechnology

389

Coordinated Infrastructure (NNCI), supported by NSF (ECCS 1542100). We acknowledge A.

390

Tiwari for assisting in the chamber set up, E. Vejerano for repairing the SMPS in a time of need,

391

C. Williams for Coordinating the CIBM research experience for teacher’s program that allowed

392

for the participation of S. V. M. in this project. We also thank A.J. Prussin, J. Parks, and Y. Wu


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393

for their assistance in performing ICP-MS sample preparation and analysis. Finally, we thank the

394

many 3D printer users who allowed for sample collection in their workspaces.

395

REFERENCES

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Destaillats, H.; Maddalena, R. L.; Singer, B. C.; Hodgson, A. T.; McKone, T. E. Indoor Pollutants Emitted by Office Equipment: A Review of Reported Data and Information Needs. Atmos. Environ. 2008, 42, 1371–1388. Morawska, L.; He, C.; Johnson, G.; Jayaratne, R.; Salthammer, T.; Wang, H.; Uhde, E.; Bostrom, T.; Modini, R.; Ayoko, G.; et al. An Investigation into the Characteristics and Formation Mechanisms of Particles Originating from the Operation of Laser Printers. Environ. Sci. Technol. 2009, 43, 1015–1022. Wong, K. V.; Hernandez, A. A Review of Additive Manufacturing. ISRN Mech. Eng. 2012, 2012, 1-12. Laplume, A. O.; Petersen, B.; Pearce, J. M. Global Value Chains from a 3D Printing Perspective. J. Int. Bus. Stud. 2016, 47, 595–609. Bourell, D. L. Perspectives on Additive Manufacturing. Annu. Rev. Mater. Res. 2016, 46, 1–18. Stephens, B.; Azimi, P.; El Orch, Z.; Ramos, T. Ultrafine Particle Emissions from Desktop 3D Printers. Atmos. Environ. 2013, 79, 334–339. Kim, Y.; Yoon, C.; Ham, S.; Park, J.; Kim, S.; Kwon, O.; Tsai, P.-J. Emissions of Nanoparticles and Gaseous Material from 3D Printer Operation. Environ. Sci. Technol. 2015, 49, 12044–12053. Zhou, Y.; Kong, X.; Chen, A.; Cao, S. Investigation of Ultraﬁne Particle Emissions of Desktop 3D Printers in the Clean Room. Procedia Eng. 2015, 121, 506–512. Azimi, P.; Zhao, D.; Pouzet, C.; Crain, N. E.; Stephens, B. Emissions of Ultrafine Particles and Volatile Organic Compounds from Commercially Available Desktop ThreeDimensional Printers with Multiple Filaments. Environ. Sci. Technol. 2016, 50, 1260– 1268. Steinle, P. Characterization of Emissions from a Desktop 3D Printer and Indoor Air Measurements in Office Settings. J. Occup. Environ. Hyg. 2016, 13, 121–132. Stabile, L.; Scungio, M.; Buonanno, G.; Arpino, F.; Ficco, G. Airborne Particle Emission of a Commercial 3D Printer: The Effect of Filament Material and Printing Temperature. Indoor Air 2016, 398 - 408. Yi, J.; LeBouf, R. F.; Duling, M. G.; Nurkiewicz, T.; Chen, B. T.; Schwegler-Berry, D.; Virji, M. A.; Stefaniak, A. B. Emission of Particulate Matter from a Desktop ThreeDimensional (3D) Printer. J. Toxicol. Environ. Health A 2016, 79, 453–465. Afshar-Mohajer, N.; Wu, C.-Y.; Ladun, T.; Rajon, D. A.; Huang, Y. Characterization of Particulate Matters and Total VOC Emissions from a Binder Jetting 3D Printer. Build. Environ. 2015, 93, 293–301. Moylan, S.; Slotwinski, J.; Cooke, A.; Jurrens, K.; Donmez, M. A. Proposal for a Standardized Test Artifact for Additive Manufacturing Machines and Processes. In; 2012; pp. 902–920.


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