In modern society, printers are widely used in the office environment. This study investigated particle number and PM2.5 emissions from printers using the TSI SMPS, TSI CPC 3022 and 3025A TSI P-Trak and DustTrak.
A TSI Model 8525 P-Trak Ultrafine Particle Counter (TSI Incorporated, St. Paul, MN, USA) which measures total particle number concentration in the size range from to 0.02-1μm, was used to investigate particle emissions from the printers.
The background office particle number concentration was measured when the printer was not printing and the measurement of the concentration was then repeated immediately after the printer had printed one page. The average peak values were then used to calculate the ratio between background concentrations and those measured after printing.
Based on the ratio of particle concentrations measured immediately after the printer printed one page to the background office concentrations, the investigated printers were catalogued into four different classes in terms of particle emission levels including: non-emitters (ratio ≤ 1); low emitters (ratio > 1 and ≤ 5), medium emitters (ratio > 5 and ≤ 10); and high emitters (ratio > 10).
Various types of printers are widely used in offices and homes around the world and they have become standard indoor electronic equipment. However, they are a potential source of indoor pollutants, producing volatile organic compounds (VOCs) and ozone, as well as a variety of particles. In order to achieve good indoor air quality and to minimise human exposure to these pollutants, the International Laboratory for Air Quality and Health (ILAQH) at Queensland University of Technology (QUT) has conducted a comprehensive experimental program, with the aim of developing a better understanding of the emissions printers produce. Below is a list of the PAPERS that have resulted from this work, as well as answers to FREQUENTLY ASKED QUESTIONS about this work.
Our first paper on printer emissions published in August 2007 in Environmental Science and Technology (He, C. et al., 41: 6039-6045, 2007) sparked world-wide interest, and resulted in several thousand e-mails with various inquiries.
The paper presented results from our study, which revealed that approximately one third of popular laser printer brands emit large numbers of very small, ultrafine particles (<0.1 µm). The numbers of particles emitted are high enough to elevate particle concentration in a large office area to the levels encountered, for example, near a busy road. The study did not, however, investigate the nature of the particles, their composition, formation mechanism, or the particle concentration in an office area over the course of a typical 8-hour working day. We were also unable to explain why emissions of some printers varied; at times they were placed in a class of low emitters, while at others, among high emitters.
Paper #2 – Characteristics and Formation Mechanisms of Particles Originating from the Operation of Laser Printers
To answer some of the above questions we conducted a second, more in-depth study. The outcome was a second manuscript which was published in Environmental Science and Technology (Morawska, L. et al., 43: 1015-1022, 2009).
We were successful in explaining: (i) what differentiates high and low emitting printers, (ii) what the particle formation processes are, and (iii) what the particles are. Experimental evidence indicates that intense bursts of particles are associated with temperature fluctuations and suggest that the difference between high and low emitters lies in the speed and sophistication of the temperature control. We have also shown, for the first time, that the particles are volatile and are of secondary nature, being formed in the air from VOC originating from both the paper and hot toner. Some of the toner is initially deposited on the fuser roller, after which the organic compounds evaporate and then form particles, through one of two main reaction pathways: homogeneous nucleation or secondary particle formation involving ozone.
Paper #3 – Quantification of the Relationship between Fuser Roller Temperature and Laser Printer Emissions
Although our previous study suggests that the fuser roller temperature plays a role in affecting particle formation rate, it’s impact has never been quantified. To address this gap in knowledge, we conducted a third study, the results of which were published in the Journal of Aerosol Science in 2010 (He, C. et al. 41: 523-530, 2010).
The results showed that: (i) almost all printers were found to be high particle number emitters; (ii) colour printing generated more PM2.5 than monochrome printing; and (iii) all printers generated significant amounts of ozone. Particle number emissions varied significantly during printing and followed the cycle of fuser roller temperature variation, which points to temperature being the strongest factor controlling emissions. Other factors, such as fuser material and structure, are also thought to play a role, however ozone and total PM2.5 were not found to be statistically correlated with fuser temperature. Based on the data set for 23 printers with heating lamps, an equation for calculating the average particle number emission rate of a laser printer was derived by fitting a curve to the relationship between average fuser temperature and average particle emission rates.
While research reported above, has provided valuable information as to the composition of laser printer particles, their formation mechanisms, and explained why some printers are emitters whilst others are low emitters, fundamental questions relating to the potential exposure of office workers remained unanswered. To address these gaps in knowledge, a fourth paper was published in Environmental Science and Technology (McGarry et al. 45: 6444-6452, 2011). In this paper, we present experimental evidence on the emission and dispersion of particles during the operation of 107 laser printers within open plan offices of five buildings. We were able to answer and provide recommendations regarding the following questions: (i) what is the likely particle exposure from printers at one and two metres from printers, (ii) what is the impact of the office ventilation on the spread of particles from the printer to the general office area, (iii) what practical things can be done within an office to minimise exposure to particles from printer operation, and (iv) what methods and instruments can be used to assess exposure of people in an office to such particles. We found that although the average of printer particles over a typical 8-hr working day was very low, there could be very high, short, and intense burst of particles in a radius of at least 2 metres from a printer.
Based on this study, a report titled with “Nanoparticles from printer emissions in workplace environment” was prepared by ILAQH, QUT, which was sponsored by Safe Work Australia.
To date, a number of studies have hypothesised that ozone may be involved in the particle formation process, since both ozone and volatile organic compounds (VOCs) are emitted during printing, however no studies have investigated this further. Therefore, our next study aimed to experimentally test this hypothesis, as well as to identify the potential particle precursors from a number of chamber and furnace experiments. The results have been published in Environmental Science and Technology (Wang et al. 46: 704-712, 2012). This study clearly demonstrated that ozone did react with printer-generated volatile organic compounds to form secondary organic aerosols (SOA). Squalene and styrene were the most likely SOA precursors with respect to ozone. The results of this study improved scientific understanding of the mechanism of particle formation in printer emissions.
Paper #6 – Printer-Generated Ultrafine Particles: Volatility, Hygroscopicity and Formation Processes (In Preparation)
This study investigated the nature of printer emitted ultrafine particles, including their volatility, hygroscopicity and mixing state. Based on this knowledge, we propose detailed particle formation processes for typical printing scenarios. This study not only improved scientific understanding of the nature of printer-generated particles, but it also provided significant insight into the formation and ageing mechanisms of secondary organic aerosols in the indoor environment.
Paper #7 – How to identify the optimal printer location in offices?
This study aimed to provide a framework for determining the optimal location of printers in office environments, in order to minimise the exposure of occupants to these emissions. The model used a combination of aspects, including office type, ventilation scenario, printer and occupant location, to estimate particle number concentration (PNC) in the breathing zone of each occupant, as well as particle removal efficiency. The results were published and presented at two conferences: the 12th International Conference on Indoor Air Quality and Climate, in Austin, Texas from the 5-10 June 2011; and at the 9th International Healthy Buildings Conference, in Syracuse, New York, USA from the 13-17 September 2009.
While the emission rate of ultrafine particles has been measured and quantified, there is very little information on the emission rates of ions and charged particles from laser printers. This paper describes a methodology that can be adopted for measuring the surface charge density on printed paper and the ion and charged particle emissions during operation of a high-emitting laser printer and shows how emission rates of ultrafine particles, ions and charged particles may be quantified using a controlled experiment within a closed chamber. The results have been published in the Journal of Electrostatics (Jayaratne et al., 70: 333-338, 2012).
Paper #9 – Evaluation of Ultrafine Particle Emissions From Laser Printers Using Emission Test Chambers
It has now been recognized that some hardcopy devices emit ultrafine particles (dp < 100 nm) during their operation. As a consequence, the time-dependent characterization of particle release from laser printers is of high interest, in order to evaluate the exposure of office workers to such emissions. The emission profiles of different printers can be compared in test chambers using a standardized test protocol and measuring devices with high time resolution. The extraction of meaningful and comparable data from the obtained data set is a complex procedure, due to the different emission behavior patterns of the printers. The calculation of the unit specific emission rate (SERu) is of limited use because the emission profiles during the printing process ranged between a short-term bursts and constant particle release. Therefore, other parameters such as the particle loss- rate coefficient, β, which provides information about the testing conditions, and the area below the time vs. concentration curve, F, which characterizes the particle release, allow for a comparison of the different printer tests. Variations in the emission behavior could not be associated with specific manufacturers or product lines. In addition, when performing several print jobs on the same device, with only short pauses between jobs, the emission rate was reduced in some cases. This further complicates the ability to determine the influence of printer construction and consumables, such as toner and paper, on the concentration of particles emitted. The results have been published in Environmental Science and Technology (Scripp et al., 42(12): 4338–4343, 2008).
Our work so far has demonstrated that approximately 30% of the laser printers tested were high emitters of ultrafine particles (< 0.1 µm). In order to assess how emission levels of the current generation of printers compare to the earlier models, we investigated 297 printers comprising of 138 models from 12 different manufacturers, with the measurements conducted in Brisbane, Australia and Cassino, Italy. In addition to particle number (PN – the majority of which are ultrafine particles), some of the printers were also tested for the emissions of volatile organic compounds (VOC). Based on the ratios of, respectively, PN and VOC concentrations above the printer before and after test printing, the printers were divided into four classes of emitters: non, low, medium and high emitters. Our study showed that although different printer models were investigated in Brisbane and in Cassino, the distributions according to emitter classes were similar for PN emissions, with a high percentage of non- and low PN emitters. In Brisbane, there were also mainly non- and low VOC emitters, with however, a higher percentage of VOC than PN emitters. In general we found that the emission levels were not intrinsic characteristics of specific brands or models of the printers. Finally, compared to the situation before 2007, large commercial printers have improved in term of particle emissions; however, there has not been an obvious improvement over desktop printers.
FREQUENTLY ASKED QUESTIONS
Whilst we now better understand the phenomena of particle emissions from laser printers than from the completion of the first study, there are still many questions we cannot answer, and issues which we have not investigated. Since it is not possible to individually answer the very many e-mails we receive, below are the answers to the most commonly asked questions – those which are not covered by our papers:
Is there any information on emission levels of other printers, not included in Table 1 of our 2007 paper?
For a complete list of all printers tested by us to date, please the results from different printer models.
Can it be assumed that emissions from some other models, not investigated in the study, are similar to some of the models covered by the study?
It cannot. The emissions are model-specific and therefore, based on this information we cannot deduce what the emission levels are from other printers not included in our studies.
What is the exposure of people sitting in the proximity to the printers?
Some of you asked very specific questions in relation to specific distances. To simplify, exposure is defined as the concentration in the microenvironment(s) where the exposure occurs, multiplied by the exposure duration. Concentration on the other hand, depends of the source strength over time but also on the dispersion properties, which in turn depend on ventilation and flow characteristics. Therefore, without knowing all these factors (and a few more), it is not possible to calculate exposure. In addition, since such calculations are complex and time consuming, we would not be able to conduct them for all those who expressed interest in knowing the figures. This was the subject of our fourth paper (see above) and we are currently conducting further work in relation to this.
What are the particles?
The particles are completely volatile when heated to over 130 degrees Celsius, are generally water insoluble, and secondary in nature (formed in the air from vapour of gaseous emissions). This was the focus of our sixth paper (see above), which will be submitted for publication very soon.
What were the sources of the cartridges installed in the printers?
We believe that when the 2007 study was conducted, the cartridges on the Australian market were mostly the originals, whist now it is becoming common to use refilled cartridges. We did not include information about the cartridges for the printers investigated in the office, because we did not have this information available. However, for the printers investigated in the laboratory (chamber part of the study) original cartridges were used. We expect that different cartridges (original, refilled by the original manufacturer, refilled by the others, as well as the number of refillings) may have different particle emission properties. This would certainly be a topic for an extension of this study.
What happens to the particles with time?
Their behaviour would be similar to the behaviour of other particles of a similar size range. Some of them will be removed from the indoor air by ventilation and some will be deposited onto indoor surfaces (not only the floor). Re-suspension from the surfaces is not a likely process for particles in such a small size range.
In what sense is the exposure (and health effects) from inhalation of these printer emitted particles similar to those from inhalation of other ultrafine particles, from different sources?
This question was asked in relation to cigarette smoke particles, as well as those emitted by motor vehicles or household appliances such as toasters. The similarity is in the particles size range and concentrations. Particles emitted by printers, likewise with those from cigarette smoke, vehicles or toasters, are in the ultrafine size range (< 0.1 micrometer) and therefore can penetrate into the deep regions of the respiratory tract. Increasing numbers of toxicological studies point to the health risks resulting in the inhalation of ultrafine particles (WHO (2005). Guidelines for Air Quality. Geneva, World Health Organization). The indoor concentration of the particles from printer operations can reach similar levels as indoor concentration of second hand cigarette smoke or outdoor concentrations near busy roads.
This is, however, where the comparison ends. Cigarette smoke, and likewise vehicle emitted particles contain in the first instance, primary particles comprised of solid carbonaceous material, which are not volatile. Also the chemistry of particles originated from these different sources is different to the printer particles.
How do we protect ourselves from exposure to the particles emitted by printers?
Ensure your exposure to laser printer particles is “as low as reasonably achievable”. This can be achieved by doing the following. In general, increasing ventilation where the printers are, and/or moving printers to well ventilated areas away from people, would help reduce exposure. In mechanically ventilated office areas, ensure the ventilation is operating at all times when printers are likely to be used, and ensure ventilation is in operation before people arrive to the office every day. In non-mechanically ventilated offices, ensure fresh air is supplied via open doors and windows. Also, avoid having printers operating frequently in the areas where people sit. Try to buy low emitting printers – while at this point there is still very little information available on this, it is hoped that this situation will change very soon.
Did we compare our results with the Blue Angel Environmental Label in Germany?
No, we did not.
What is the risk from our home printers?
It all depends how you use them and what the ventilation is like in your home. If you print a page or so from time to time, in a reasonably ventilated house (some windows opened), it is unlikely that particle concentration would reach levels of concern. If multiple documents are being printed over a long period of time in an enclosed room, then particle concentrations could reach levels of concern.
How do we test printers? Is there any hand held equipment which could be used to test printers?
We would not like to recommend any specific method or equipment. There is no standard for testing printer emissions, and this kind of investigation requires some level of expertise, even when using hand held equipment (without expert interpretation, the results would not be justifiable).
Would regular cleaning and maintenance of the printers prevent/lower the emissions of ultrafine particles?
We have not conducted investigations into the relationship between the maintenance of ultrafine particle emissions, but based on our understanding of the mechanisms of emissions, maintenance is not a factor affecting it.
Is there any benefit in conducting further measurements of printer emissions in actual office areas?
Yes. A properly designed study could identify the influence of office mechanical ventilation on particle transport and dispersion. This information would be very useful in developing guidelines on minimum ventilation requirements for offices operating laser printers, including location and positioning of laser printers with respect to work stations. Some preliminary work has already been conducted on this.
International Laboratory for Air Quality and Health,
Queensland University of Technology