Characterization of laser printer nanoparticle and VOC emissions, formation mechanisms, and strategies to reduce airborne exposures

Abstract

To better evaluate the health effects and indoor air quality impacts of nanoparticles generated by laser printers, measurements were made to characterize the number concentration, size distribution, morphology, and chemical composition of the emitted nanoparticles as a function of printer distance, idle time, cold start state, cartridge states, and number of pages printed. Emitted ion concentrations, nanoparticles, volatile organic compound (VOC) emissions, and toner particles were characterized using multiple analytical techniques. Finally, particle generation mechanisms and emission control strategies are discussed. Emission measurements were conducted using a commonly used black and white office printer (HP LaserJet4100) operating in a small (12 m2) office conference room environment and a stainless steel environmental chamber of similar size. Particle concentrations and size distributions were monitored using condensation particle counter (CPC) and scanning mobility particle sizer (SMPS) directly above the printer and at distances of 1-2 m away. Emitted ion concentrations and VOCs were measured by ion density meter and thermal desorption gas chromatography/mass spectrometry (GC/MS), respectively. Aerosols emitted from the printer were collected using an electrostatic precipitator (ESP) sampler and analyzed with transmission electron microscopy/energy-dispersive X-ray spectroscopy (TEM/EDS). Toner particles from the LaserJet printer cartridge were analysis using thermogravimetric analyzer (TGA), differential scanning calorimetry (DSC), inductively coupled plasma/atomic emission spectroscopy (ICP/AES), scanning electron microscopy (SEM)/EDS, and TEM/EDS. Repeated measurements revealed that the LaserJet printer emitted nanoparticles: (1) with a concentration from 104 to 106 #/cc and single-mode peak size between 20 and 150 nm, depending on the number of printed pages and aerosol age, (2) primarily during the cold power up of the printer and at the start of printing, or under conditions when the printer was allowed sufficient time to cool down the internal surfaces (about 30-90 min depending on the number of pages printed), (3) likely generated from ion-induced nucleation of vapor-phase organic compounds, which are released from the toner powder during the rapid heating of internal printer surfaces. TGA and ICP analysis revealed that about 0.064% (wt) of the toner materials (iron oxide coated with copolymer resin) are evaporated at the printer operating temperature, which allowed evaluation of the upper limit of nanoparticle formation by condensation of the vapor phase VOCs. SEM/EDS and TEM/EDS results suggest that fugitive toner particles and paper coatings were not important aerosol sources. Reducing toner solvent content, preventing the internal printer surfaces from cooling down, or increasing preheating time before printing may be helpful in reducing the VOC emissions and the generation of these polymer nanoparticles, which may represent a potential human health hazard. Copyright © American Association for Aerosol Research.