An Investigation On Pollutant Emissions From A Laser Printer Using

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An Investigation on Pollutant Emissions from a Laser Printer using an Environmental Chamber Hai Guo*, Lok-Cheung Wong Air Quality Studies, Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hong Kong, People's Republic of China * Corresponding email: [email protected] (H. Guo) SUMMARY There has been a growing concern from the society about the health impact of printer emissions. In this study, different printing jobs with the consideration of percentage of toner coverage, cartridge rotation, and number of pages were tested in an environmental chamber with an air exchange rate of 0.8 h-1. The concentrations of particle number, volatile organic compounds (VOCs), and the fuser temperature were monitored by P-Trak, MiniRAE detector and thermocouple, respectively. Eight combinations of printing job showed particle emissions whenever toner was consumed. Cartridge in rotation mode and the printer in idling mode for over 12 hours also caused particle emissions. In contrast, total VOC emissions during the printing periods were ignorable. We also found that fuser temperature had insignificant effect on particle emissions from the printer. This study confirmed that toner was the major source of particle emissions. Ventilation for a long period and/or printing blank pages reduced particle emissions. KEYWORDS: Printer; Environmental chamber; Particle emissions; Total VOCs. 1 INTRODUCTION Laser printer is a well-known source of indoor air pollutants (Kagi et al, 2007; He et al, 2007; Lee et al, 2007; Wensing et al, 2008). Different contaminants such as volatile organic compounds (VOCs) and fine particles were emitted from printers (Lee et al, 2001; Wensing et al, 2008). The wide use of laser printers and copy machines in homes and offices may affect human health and therefore the understanding of printer emissions is of public concern. Mechanisms of particle emissions by laser printers are still unclear. Previous studies found that ultrafine particles emitted from printers were generated from secondary formation via chemical reactions of VOCs (Kagi et al, 2007; Wensing et al, 2008; Morawska et al, 2009). A recent study indicated that fuser temperature was the principal factor governing the rate of particle formation in laser printer operation (He et al, 2010). In this study, we report the measurement results from several printing job combinations to better understand the mechanism of particle emissions from laser printers including the possible factors alternating the particle emissions from laser printers, and recommend potential control strategies on the emissions from laser printers. 2 MATERIALS/METHODS Study Design Eight combinations of printing job were designed in this study. Descriptions of the combinations are given in Tables 1 and 2. The printer idled for more than 12 hours before every combination experiment was conducted. The chamber ventilation was off for 12 hours before every combination experiment except the “ventilation effect” experiment, in which the ventilation of the chamber was on for over 12 hours before the printing experiments. The interior surface of the chamber was cleaned after each combination experiment. Based on the printing combinations, in each experiment, four cycles of printing were conducted and the interval between each printing job was 120 minutes to allow the pollutant levels to return to the background value. Unless specified, 20 pages were printed for each printing job. In this study, we used a colour laserjet printer which composed four cartridges in different colours (i.e. black, blue, red and yellow). Unless manual instruction was given to the computer, the cartridges rotated in a cycle even if the printing job only needed black and white toners. Table 1: The eight combinations of printing job No. Combination Remarks 0, 0, 0, 0 1 5, 5, 5, 5 2 0, 0, 0R, 0R 3 0, 0, 5R, 5R 4 R= Cartridge rotation V= Ventilation over 12 hours No. 5 6 7 8 Combination 0, 0, 0, 0 5, 5, 5, 5 0, 0(80), 5, 5 0, 0, 5, 5 Remarks V V No. in bracket = pages printed Table 2: Details of the printing job Combination 4 7 Start Time (min) Black toner coverage (%) Cartridge rotation Pages printed Black toner coverage (%) Cartridge rotation Pages printed 0 0 No 20 0 No 20 120 0 No 20 0 No 80 240 5 Yes 20 5 No 20 360 5 Yes 20 5 No 20 An environmental chamber with controlled temperature and relative humidity was used in this study. The chamber size was 1100(H) × 1000(W) × 730(L) cm. The printer was located inside the centre of the chamber. The chamber was made of PVC. There was a small hole on the chamber surface for ventilation. The air exchange rate for the chamber was around 0.8 h-1. The environmental chamber condition was 23oC and 55%. Materials A HP LaserJet M175a printer was used in this study. It was specifically selected according to the market survey. Original toner cartridge produced by the manufacturer was used. The printer was designed to print papers with 0% and 5% black toner coverage. For the 5% black toner coverage paper, a standard printing file was used according to the European Computer Manufacturers Association (ECMA International). The paper used in this study was Fuji Xerox Explorer with a density of 75g/m2. Sampling methods The total particle number concentration in the size range of 20 - 1000nm emitted from the printing jobs was measured using an ultra-fine particle counter (Model 8525, TSI). The counter was calibrated with a Scanning Mobility Particle Sizer (SMPS). A J-type thermocouple was placed on the surface of the fuser roller to measure the fuser roller temperature. The data were recorded by a digital multi-logger at 1s interval. Total VOCs were continuously monitored using a MiniRAE Plus photoionization detector (PGM 76K). The distance between the printer and the two sampling instruments (i.e. MiniRAE and the multilogger) was about 0.5 m inside the chamber. Since the alcohol in the ultrafine particle counter significantly influenced the TVOC concentrations, it was located outside the chamber and linked to the chamber by antistatic tube with the length of around 0.5 m. 3 RESULTS Totally eight experiments were carried out as listed in Table 1. Figure 1 presents the time series of particle number concentrations emitted from the printer for the eight experiments. Fig 1. Times series of particle number concentrations for the combined printing jobs No.1-8 For combination #1, four printing jobs with 0% toner coverage and without cartridge rotation were conducted. A small peak with a value of 118 particle cm-3 was found for the 1st printing job. No peaks were observed from the 2nd printing job and afterwards. For combination # , four printing jobs with 5% toner coverage and without cartridge rotation were conducted. Peaks were found in all the printing jobs. The peak values reached 283, 470, 369 and 358 particle cm-3 from the 1st to 4th printing jobs, respectively. For combination #3, four printing jobs were conducted as well. The 1st and 2nd printing jobs were done with 0% toner coverage and without cartridge rotation, while the 3rd and 4th printing jobs were carried out with 0% toner coverage and with cartridge rotation. It is noteworthy that 20 pages with 0% toner coverage and with cartridge rotation were printed 12 hours before the 1st printing job to avoid any interference from the cartridge. Peaks were found in the 3rd and 4th printing jobs with concentrations of 194 and 179 particle cm-3, respectively. No peaks were observed in the 1st and 2nd printing jobs. For combination #4, four printing jobs were undertaken. The 1st and 2nd printing jobs were done with 0% toner coverage and without cartridge rotation. The 3rd and 4th printing jobs were undertaken with 5% toner coverage and with cartridge rotation. Three peaks with values of 179, 2484 and 2528 particle cm-3 were found in the 1st, 3rd and 4th printing jobs, respectively. No peak was monitored in the 2nd printing job. For combination #5, four printing jobs with 0% toner coverage and without cartridge rotation were conducted. The chamber was ventilated at an air exchange rate of 0.8 h-1 for over 12 hours before the 1st printing job started. No observable peaks were found in all the printing jobs. For combination # , four printing jobs with 5% toner coverage and without cartridge rotation were conducted. The chamber was ventilated for over 12 hours before the 1st printing job started. Four peaks were found in this combined experiment, with values of 261, 363, 382 and 654 particle cm-3, respectively. For combination #7, four printing jobs were conducted. The 1st and 2nd printing jobs were carried out with 0% toner coverage and without cartridge rotation. However, different from other printing jobs which used 20 pages, the 2nd printing job used 80 pages. The 3rd and 4th printing jobs were undertaken with 5% toner coverage and without cartridge rotation. Peaks were found for the 1st, 3rd and 4th printing jobs with concentrations of 359, 184 and 539 particle cm-3, respectively. The 2nd printing job did not generate any peak. For combination #8, four printing jobs were conducted. The 1st and 2nd printing jobs were done with 0% toner coverage and without cartridge rotation. Both printing jobs used 20 pages. The 3rd and 4th printing jobs were completed with 5% toner coverage and without cartridge rotation. Three peaks with values of 157, 160 and 222 particle cm-3 were found in the 1st, 3rd and 4th printing jobs, respectively. No peak was observed in the 2nd printing job. 4 DISCUSSION It is obvious that peaks were usually found after the printing jobs started in the eight combinations. Therefore, the increase in particle number concentration in the chamber was mainly due to the printer emissions. The summary of particle emission rates in this study, calculated using the equation in He et al. (2007), is tabulated in Table 3. Table 3 Summary of particle emission rate (particle per minute) Combination Printing order 1st 2nd 3rd 4th 1 0, 0, 0, 0 -- -- 2 5, 5, 5, 5 128.17 *425.88 3 0, 0, 0R, 0R -- -- 50.65 46.08 4 0, 0, 5R, 5R 29.63 -- 1004.53 986.01 5 0, 0, 0, 0 (v) -- -- -- -- 6 5, 5, 5, 5 (v) 68.41 179.01 70.96 156.90 7 0, 0(80), 5, 5 246.63 -- 87.43 288.75 8 0, 0(20), 5, 5 26.91 -- 38.90 64.21 Note: R = cartridge rotation * = paper jammed 59.47 -- st (v) = ventilation for 12 h before the 1 printing job -- = Not Observable Initial start effect: Among the eight combinations, six of them showed a peak of particle number concentration in the 1st printing job. The 1st printing job in combinations #1, #4, #7 and #8 was completed with 0% toner coverage and without cartridge rotation. All showed a peak. Interestingly, though exactly the same type of paper (0% toner coverage) and cartridge rotation (no rotation) were used in the 2nd printing job in combinations #1, #4, #7 and #8, no particle emissions were identified. The opposite results suggested that the printer emission had an “initial start effect” which was irrelevant to the toner coverage. The possible reason for the “initial start” effect may be due to the particle coagulation and accumulation. During the period when the ventilation system of the chamber was off (usually >12 h), particles could coagulate/accumulate and adhere to the printer. Once the 1st job was initiated, the particles in the printer were then cleaned by re-suspension. It is obvious that no peak was found for the 1st printing job in combination #3 though the same paper (0% toner coverage) and cartridge rotation mode (no) were used. This was caused by the fact that a printing job of 20 pages with 0% toner coverage and with cartridge rotation was conducted 12 h prior to the 1st printing job, and the ventilation was off between these two jobs for 12 h. The detailed mechanism is unclear. However, it seems that particles were removed from the printer by the former job and hence few particles could be coagulated and accumulated in the printer. Toner emissions effect: Both combinations #1 and #5 were printed with 0% toner coverage and without cartridge rotation. Except for the 1st printing job in combination #1, no peaks were found in the rest seven printing jobs. In contrast, the combinations #2 and #6 were printed with 5% toner coverage and without cartridge rotation. Peaks were found in every printing job suggesting that toner coverage was a main factor responsible for particle emissions. The peak found in the 1st printing job in combination #1 may be attributable to the “initial start” effect, whereas no peak in the 1st printing job in combination #5 was caused by the “ventilation” effect, in which the ventilation was on for 12h before the 1st printing job. More detail was given below. Ventilation effect: Same papers and rotation modes were used for combinations #1 and #5 (0% toner coverage), and for combinations #2 and #6 (5% toner coverage). The only difference was that the ventilation system was on at an air exchange rate of 0.8 h-1 for over 12 hours prior to the 1st printing job for combinations #5 and #6. Particle emission rates for the four printing jobs in combination #2 were all higher than that in combination #6. Also, no peaks were found in combination #5 while a small peak was found in the 1st printing job in combination #1. This provided evidence that long time ventilation could reduce particle emissions during printing. It appears that the ventilation could prevent the particles from accumulation in the chamber. Hence, a lower particle number concentration was found in combinations #5 and #6. Cartridge rotation effect: For combinations #3 and #4, 20 pages were printed in the 1st and 2nd printing jobs with 0% toner coverage and without cartridge rotation. However, the 3rd and 4th printing jobs were conducted with cartridge rotation. Obviously, particle emissions were found when cartridges were rotated, suggesting that cartridge rotation was a factor responsible for particle emissions. Since the cartridges contained different colours of toners, rotating the cartridges would be like “shaking” the cartridges which caused toner floating in the printer. It can also be seen that a printing job with 5% toner coverage and with cartridge rotation had a greater impact than a printing job with 0% toner coverage and with cartridge rotation, indicating that there was a synergy effect for printing jobs with certain percentages of toner coverage and cartridge rotation. Cleaning or accumulation effect: The 1st and 2nd printing jobs in combinations #7 and #8 were all undertaken with 0% toner coverage and without cartridge rotation. The 1st peak was caused by “initial start” effect in both combinations. The 2nd printing job of combinations #7 and #8 used 80 and 20 pages, respectively, with 0% toner coverage and without cartridge rotation. Particle emissions in the 3rd printing job were lower than that in the 4th printing job in both combinations, suggesting that the 1st and 2nd printing jobs with 0% toner coverage acted as a cleaning process, which tentatively reduced particle emissions in the 3rd job. The higher emissions in the 4th printing job may also indicate the accumulation effect of particles generated from the 3rd printing job due to the fact that particles adhered to the printer after the 3rd printing job. Particle emissions in the 3rd printing job in combinations #7 and #8 revealed that number of pages with 0% toner coverage had insignificant impact on the cleaning effect of the 2nd printing job. In addition, the emissions of total volatile organic compounds (TVOCs) from the printing jobs among the eight combinations were undetectable, indicating that the printer was not the major source of VOCs. Moreover, though the fuser roller temperature increased during each printing job, it did not show any correlations with the particle emissions for each printing job. 5 CONCLUSIONS In this study, we found that toner coverage was the main source of particle emissions from the printer. Printing jobs with cartridge rotation were another factor responsible for the particle emissions. Synergy effect on particle emissions was found if toner was used together with cartridge rotation. Also, long time ventilation and printing papers with 0% toner coverage would reduce particle emissions. Particle re-suspension after st coagulation/accumulation was a potential reason for the particle emissions in the 1 printing job in every combination. The findings suggest that people who use laser printers in their offices should choose one without cartridge rotation. Additionally, ventilation system should remain on and high enough whenever possible. At last, to minimize the initial start effect, it is recommended that 20 pages of blank paper be printed after each printing job. ACKNOWLEDGEMENTS This study was supported by the Environment and Conservation Fund (ECF 20/2008) and the Hong Kong Polytechnic University Internal Grants (1-ZV7A, A-PK25 and A-PL40). REFERENCES He, C. R., Morawska, L., Wang, H., Jayaratne, R., McGarry, P., Johnson, G. 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