EVALUATION OF HEALTH EFFECTS AFTER WORKER EXPOSURE TO AIRBORNE NANOPARTICLES DURING GAS PHASE PROCESSES
Mikael Ihalainen Pro Gradu University of eastern Finland Department of environmental
and biological sciences 2020
UNIVERSITY OF EASTERN FINLAND, Faculty of science and forestry, environmental science
Author: Mikael Ihalainen, name of M.Sc. thesis: Evaluation of health effects after worker exposure to airborne nanoparticles during gas phase processes (pages 73, sources 39, appendixes 3)
Instructor: Anna Lähde, Ph.D., Doc, University of Eastern Finland, Department of Environmental science, Fine Particle and Aerosol Technology Laboratory
Key words: exposure, airborne, (engineered) nanoparticles/nanomaterials (E(NPs/NMs), safety, prevention, lung deposition model, aerosol, measurement techniques, flame spray pyrolysis (FSP), spray pyrolysis (SP)
ABSTRACT
Nanoparticle (NP) or nanopowder synthesis processes may cause accidental release of NPs in laboratory air. NP release can increase in laboratory air during synthesis, due to reactor breakage, or while synthesized powders are collected and reactors are cleaned. Objectives of this study are to measure these particle concentrations from two aerosol processes, flame spray pyrolysis (FSP) and spray pyrolysis (SP) reactors, assess the safety issues and evaluate potential risks related to these processes. FSP and SP are used for NP production in order to determine concentration levels that exist in the laboratory before, during and after the synthesis of engineered nanoparticles (ENP). After measurements, the deposition of NPs in lungs will be modeled to depict possible exposure. Existing reduction and preventation methods will be discussed for their application, but the emphasis of this study is to evaluate exposure to airborne NPs during aerosol processes and propose alternatives for preventing and reducing exposure of workers to different kinds of nanomaterials, engineered or natural (for example, in many mining occupations, exposures to natural mining residues which often are in nano- or micrometer scale, are more common than exposure to ENPs).
TABLE OF CONTENTS
1. INTRODUCTION 2. LITERATURE REVIEW
2.1 Nanomaterials in general 2.2 Health effects of nanomaterials
2.3 Exposure generally and in different occupations 2.4 Reduction and prevention alternatives
3. MATERIALS AND METHODS 3.1 Aerosol processes
3.1.1 Flame spray pyrolysis 3.1.2 Spray pyrolysis 3.2 Measurement equipment
3.2.1 Electric low pressure impactor
3.2.2 Differential mobility analyzer and condensation particle counter 3.2.3 Fast mobility particle sizer
3.2.4 Tapered element oscillating microbalance 3.2.5 Nanoparticle surface area monitor
3.2.6 Scanning electron microscopy and electron diffraction analysis 3.3 Measurement arrangements
3.3.1 Filter collection
3.3.2 Preparation of measurement equipment 3.3.3 Formation of lung deposition model 3.3.4 Data analysis
4. RESULTS
4.1 Flame spray pyrolysis
4.1.1 Before particle production 4.1.2 During particle production 4.1.3 After particle production 4.2 Spray pyrolysis
4.2.1 Before particle production 4.2.2 During particle production 4.2.3 After particle production
4.3 Modeling and evaluation of the lung deposition 5. DISCUSSION
6. SOURCES
1. INTRODUCTION
Production and applications of nanomaterials (NMs) have increased in recent years. Altered physical and chemical properties of nanoscale materials make NMs promising for many applications. NMs tend to have increased surface area concentration, when compared to their bulk counterparts, and so NMs are more reactive. Nanoparticles (NPs) are applied e.g. in medicine and electronics, and in the future NPs are likely to be applied more in environmental processes, like in water purification. Production and diversity of NPs have increased due to advances in technology and demand in market. However, this has led to industrial production of manufactured, or engineered nanoparticles (ENPs), and so work place exposures to NPs have also increased, especially in industries where NMs are handled (Ding 2016). In 2015, there were 300 000-400 000 employees in Europe working in industries where NMs are produced, transported or modified in some way (FIOH 2015). By 2020, it is estimated that 6 million workers worldwide are working in nanoindustry or with NMs. One third, 2 million, of this work force will work in the United States. (Roco 2010) In Finland, nanotechnology employs over 20 000 workers in about 800 work places (FIOH 2017).
Exposures to NPs occur generally via inhalation in work places (Oberdörster 2005, Ramachandran 2011). Workers may get exposed to increased concentrations of NPs daily, since no regulations about NP release and exposure yet exist (Lee 2010). For example, the Regulation, Evaluation, Authorization and Restriction of Chemical substances (REACH) regulations does not consider NMs. Objective of REACH regulations is to assure efficient protection of the environment and human health from chemicals. REACH implements requlations via legislative means emphasizing sustainable development, yet NPs are not regulated. (REACH EC 1907/2006) Other limits for preventing work place exposures to NPs have been developed via risk assessments, like occupational exposure limits (OELs), which exist for only few kinds of NPs yet (Schulte 2018, Ramachandran 2011). Incidental release of airborne ENPs may occur during production and collection of powders, or during cleaning of reactors, for example. Emission of particles at submicron level can also increase during NP synthesis. (Demou 2009) High-energy techniques like spray techniques can produce small particles which can reach even nanosize, while low-energy techniques like cleaning of the reactor have shown to increase, or rather release agglomerates or large particles to air from the reactor (Ding 2016). It is possible for NPs to be attached to these agglomerates, so cleaning may increase NP concentration in the air (Schneider 2011).
In this study, aerosol technology based synthesis methods, flame spray pyrolysis (FSP) and spray pyrolysis (SP) were used for NP synthesis. Measurements were done in pilot environment (FunktioMat-pilot, UEF, http://www.uef.fi/en/web/fine/funktiomat-pilotti) where functional materials are produced using different methods and tested for industrial uses.
Particle number concentrations and size distributions due to release of NPs during production were measured, as were particle areas and masses. Measurements were conducted in laboratory before, during and after NP synthesis, of which latter measurement was done during the cleaning of reactors, while manufactured powder was collected from reactor bag filters. Multiple measurement points (Fig. 4) and equipment (Ch. 3.2) were used.
Aim of this thesis is to evaluate exposure to airborne NPs in two gas phase processes, and model particle lung deposition, but also to discuss and present preventive and reductive methods for NP exposure in laboratory air and generally in industries and workplaces where NP exposures may occur.
2. LITERATURE REVIEW
2.1 Nanomaterials in general
Materials at nanometer scale are characterized as 1-100 nm long in at least one dimension.
These materials could be sphere-like particles, solid films or tube-like structures, having regular and irregular morphologies depending on synthesis conditions and phase (gas, liquid, solid) where the formation of NPs takes place. (Messing 1993) Below few examples on nanomaterial morphology are shown (Fig. 1). Nanomaterials may form naturally, e.g. in different natural combustion processes. For example, evaporation from seas and eruption of volcanoes generates airborne nanosized particles and agglomerates. (Oberdörster 2005)
Other NM formation route is via anthropogenic synthesis methods. Synthetic, engineered nanomaterials are produced often via aerosol processes which are used for NP synthesis in gas phase. For example, spray techniques (spray and flame spray synthesis) and chemical vapor synthesis are both used for ENP synthesis in gas phase. Different NMs have unique properties and high applicability in different fields, but nanotechnology or nanoscience itself is still quite young field of study and has potential to be applied in more diverse manner in the future (Roco 2010). However, incidental release of ENPs as airborne particles may occur during NP synthesis processes, due to which additional exposure to these materials can happen. In the future, increased use of nanotechnology and ENP production processes are likely to increase the risk of exposure to ENPs, especially in work places and industries specializing in nanotechnology. (Ding 2016)
Fig. 1: Different nanomaterial morphologies: A) nanodots, B) nanorods and C) primary NPs and D) aggregate consisting of NPs (Pictures modified from sources: Pacholski 2002 (A&B), Grassian 2007 (C&D)).
Physicochemical properties of NPs like size and shape, alongside exposure route, influence where particles will be deposited after exposure. However, much is still unknown. Nanoscale materials exhibit different properties than their bulk counterparts, which is why nanotechnology has gained interest in many fields. Chemical activity alongside physical structure of NPs might differ from that of the bulk material, and so might observed health effects in the exposed bodies. Some effects might be harmless and others adverse, in acute or chronic sense. NPs are often generated in high quantities, so their number concentration is high, as is their effective area to interact. When the same amount of NPs is compared to the same amount of bulk matter, NPs have more surface area to interact. The high surface area of NPs is considered as important property, since this large surface area can be utilized in different applications, e.g. binding of target substance, like pollutants in water, to NPs.
Binding is much more efficient to NPs than to bulk matter of the same material since NPs have much more surface area to bind target substance. In medicine, nanomaterials are used as
drug carriers to target organ. Applicability here is clear, since bulk sized matter could never be administrated subcutaneously as drug carrier due to its size. However, it strongly seems that high particle surface area and number concentration are toxicologically very crucial characteristics, if NPs do not otherwise have clear toxic chemical properties. Also, particle shape may determine its deposition after inhalation which is important to take into account when profiling exposure potential to NPs (Oberdörster 2005, Demou 2008).
2.2 Health effects of nanomaterials
Silver (Ag) is toxic to humans at high doses, so subsequently Ag doped nanomaterials may pose a threat to human health after sufficient inhalation exposure, although some materials, like chitosan, may be used to reduce toxicity of Ag doped NPs. Due to antimicrobial properties of Ag doped NPs, they have their use in medicine, e.g. in bandaging a wound (Khan 2017, Xu 2016). Toxicological analyses have shown that cobalt oxide (CoO) NPs have toxic properties, and so have potential to induce adverse health effects in humans after exposure. One important toxicity factor of CoO NPs is their ability to induce prominent oxidative stress in normal cells after exposure has occurred to them. This results in increased amount of reactive oxygen species (ROS) in cells, which are produced intracellularly (Chattobadhyay 2015)
It is noteworthy to mention here that certain material might not have any properties in bulk size that can cause adverse effects after exposure, but this material could cause harmful effects while in nanosize. After exposure has occurred, nanomaterials may dissolve in tissues inducing even more toxicity. Potential for toxicity can be identified via in vitro or in vivo studies. (Baan 2006, Chattobadhyay 2015) For example, titanium oxide (TiO2) has long been considered as not dangerous to humans (in larger form, bulk form), but since the use of nanosized TiO2 has increased (e.g. pigments and cosmetics), so have exposures to it. In some studies, in which researchers consider the effects of nanosized TiO2 in exposed individuals, health effects have emerged later, so pathway from exposure to effects is not always clear. In case of cancer, epidemiological studies have provided inconclusive results to provide efficient tools for precise risk assessment. It is not clear if nanosized TiO2 particles are carcinogenic for humans, but they have adverse properties for sure. Today, International Agency for Research on Cancer (IARC) has classified nanosized TiO2 as a possible carcinogen, as they have classified many nanosized materials. (IARC 2010, Baan 2006) To sum, not all studies
considering health effects of nanosized TiO2 have shown them to cause adverse health effects after exposure, but there is enough controversial evidence to raise concerns.
For example, in the study of Grassian et al., mice were exposed to titanium dioxide (TiO2) NPs which induced inflammation in the lungs of mice after inhalation exposure (Grassian 2006). Mice were exposed to TiO2 NPs with average diameter of 5 nm and surface area of 210 ± 10 m2/g. Acutely to low (0,77 mg/m3) and high (7,22 mg/m3) doses of TiO2 NPs were used, and also subacutely for 4 hours/day, for 10 days, to amount of 8.88 ± 1.98 mg/m3 of TiO2 NPs. Acute exposures induced minimal toxicity, while subacute exposures induced significant but moderate toxicity in the mice. Mice recovered from subacute exposure by week three, when the number of alveolar macrophages and phagocytized NPs in them was seen to be decreased. (Grassian 2006)
Most NPs and ENPs are most likely non-toxic and innocuous to humans, but some are, and since adverse health effects of NPs are still mostly unknown, the exact toxic properties of NPs are not known. Since nanoscale materials have unique properties compared to their bulk counterparts, like high surface area and mobility, they can be utilized in many ways, but these properties might also cause adverse health effects in exposed individuals. NPs are increasingly used in industries and consumer products today, consisting of different core materials, shapes and coatings, so defining which factors, NP properties, contribute mostly in causing adverse health effects will not be easy. Increase of ENPs used in consumer products is likely to increase the potential for exposure to these nanomaterials (Ramachandran 2011, Kuhlbusch 2011) Small size of NPs is considered as an important toxicological factor, if NPs are not otherwise chemically toxic. Below are listed some of the suspected health effects (Ibald-Mulli 2002, Ganguly 2018) caused by different but potentially toxic nanomaterials after exposure:
Lung inflammation (generally lung diseases, e.g. interstitial lung disease)
Other respiratory symptoms
Oxidative stress
Cardiovascular diseases
Possible carcinogens
Asthma
After exposure to toxic NPs, adverse health effects will manifest in an acute or chronic manner. It has been observed via epidemiological studies that often respiratory symptoms develop fast in response to xenobiotic agent(s) (in this case NPs), but e.g. cardiovascular symptoms are delayed. Researchers are not sure about the mechanisms behind these cases, and so more research is needed. (Ibald-Mulli 2002, Ganguly 2018)
2.3 Exposures generally and in different occupations
Employees working in industries where manufacturing, transporting or handling of nanomaterials is carried out have an increased risk of exposure to these materials. NPs are small and light, which enables them to be released as airborne particles quite easily. This increases exposures to NPs via inhalation, but exposures via gastrointestinal and dermal routes or by injection are also possible. (Oberdörster 2005, Kuhlbusch 2011) Welding is a good example of occupation where exposure to unintentionally produced ultrafine particles (since particles are not the goal of welding), or NPs, occurs if suitable protective gear is not used (Oberdörster 2005, Ramachandran 2011). Finnish Institute of Occupational Health (FIOH) has suggested some threshold concentration levels during work and safe working times for certain kinds of released ENPs in the work place air. Table below (Table 1) has been edited from FIOH source. FIOH recommendation is that employees should not work longer than 8 hours under these circumstances. For comparison, suggested concentration level for general respirable dust is 0,5 mg/m3 (FIOH 2013).
Properties of the NM might transform after their release, due to environmental factors like heat or moisture. For example, heat might cause morphology alterations in NM via melting if the temperature is higher than melting point of the NM, or high temperature could cause NMs to agglomerate. When NMs are released into environment, they often come into contact with microorganisms which also may transform NM properties via biodegradation, often increasing their toxicity (Canguly 2018). Since there exist no regulations yet for ENP exposure or environmental release, unknown amounts of different, tailored nanomaterials get released into the work place air on multiple occupations, in industries and into environment via different routes. ENP transformation due to impact of environmental/ambient factors means that their properties transform as well. This transformation may lead to ENPs which might cause even more adverse health effects in exposed individuals due to transformed physical, chemical or biological properties of these particles. For example, nanomaterials are
used in construction to enhance certain properties of construction material, like material resistance to corrosion. Physical or chemical stress, like corrosion can lead to the release of nanomaterials to the environment, and so transformation may occur (Lee 2010).
Since transformation of NPs depend on the ambient environmental factors, it is nearly impossible to prevent after NP release. Release and transformation depend also on the state (solid, powder or solution), or phase, of the material. (Ding 2016) It is possible for transformed properties of NPs to cause more adverse environmental effects and health effects after exposure, than before transformation.
Table 1: Different nanomaterials and corresponding target concentration levels which FIOH suggests for air in work places/industries. (FIOH 2013)
Nanomaterial Target level or below Examples
Fibrous, slowly decaying rigid
nanomaterials (length > 5 µm) 0,01 fibres/cm3 (8h) Carbon nanotubes Particles, slowly decaying
nanomaterials with density >
6000 kg/m3
20 000/cm3 (8h) Nanosized Ag, Au, CoO, Fe
Particles, slowly decaying nanomaterials with density <
6000 kg/m3, and fibres which possess no asbestos-like
properties
40 000/cm3 (8h) Nanosized SiO2, TiO2, ZnO, nanoclays
Mostly in agglomerate-form, particle-shaped and slowly decaying nanomaterials, with agglomerate diameter > 100 nm
0,3 mg/m3 (respirable, 8h)
Above mentioned particle-shaped
nanomaterial agglomerates like CoO
and TiO2
2.4 Reduction and prevention alternatives
Often complete prevention of exposure is not possible, at least not before all relevant factors contributing to NP release and exposure are understood. Different actions that occur in the work place might lead to the release of airborne NPs. Synthesis generates often NPs, that get released into air incidentally, due to flaws in synthesis reactor (e.g. reactor not air tight enough). Because of this synthesis and monitoring spaces should be in separate rooms minimizing potential exposure and time the workers have to spent in the synthesis room.
Separation ensures that particle concentration remains mostly normal in the monitoring space, though while there is movement in the area, between monitoring and synthesis spaces, some airborne particles may drift from synthesis space to monitoring space. Particles might also deposit on the surfaces (e.g. on floor, walls or equipment) or clothes of workers, and resuspend back into air due to movement in the area. (Benabed 2016) Exposure to particles due to resuspension is expected to be lesser if the area is kept clean and the movement is reduced.
If employees in a certain occupation or area in the work place are under higher risk to ENP exposure via inhalation, personal respiration filters or breathing masks should be used to prevent exposure. Laboratory coat or overalls and gloves are used as protection against dermal exposure, while protective goggles are used to prevent eye exposure to NPs. In extreme conditions powered hoods/helmets may be used for protection. Although, protection efficiency might decrease due to different factors, e.g. seal between skin of face and respiratory protective equipment (RPE) may not be tight enough, due to amount of facial hair in the face. While handling ENPs, nanopowders for example, work should be done in laboratory fume hood so workers in the area do not experience exposure to ENPs. During synthesis of ENPs, exhaust ventilation should be localized in the production area of ENPs so exposure is minimized in the case of incidental release of airborne ENPs. Also, ventilation in the whole work place should be optimized to work as intended so NPs do not drift elsewhere in the building. (HSG53 2013, Ding 2016) If there is speculation that NPs might get attached to clothes, e.g. shoes in the work place, use of different clothes in the work place is recommended. As mentioned above, certain protective equipment can be used to lower or eliminate NP exposure. RPE have an assigned protective factor (APF) value, which indicates the protective level of RPE. Higher the APF, stronger the protective capability of RPE is.
Different RPEs used for prevention of exposure to airborne pollutants are listed and compared below. (Table 2) If exposure is suspected, personal exposure levels to NPs can be measured
by using personal airborne exposure agent meter, which measures exposure at or near breathing zone.
Table 2: Comparison of respiratory protective equipment (RPE). Number after assigned protective factor (APF) type indicates the protective level of RPE. With powered masks or hoods/helmets, appropriate filter may be fitted to protect against particles or vapours (simultaneous protection not possible). In the table,
+
= yes/compatible and-
= no/incompatible. (Information and pictures of RPE types from HSG53 2013).Adequacy/
suitability Respirators
RPE type Disposable half mask
(particle filter)
Reusable half mask (particle
filter)
Reusable half mask
(gas/
vapour filter)
Full face mask (particle
filter)
Full face mask (gas/
vapour filter)
Powered mask
Powered hoods/
helmets
Effective for
particles
+ + - + - + +
Effective for
gas/vapour
- - + - + + +
Continuos
wear time < 1 hour < 1 hour < 1 hour < 1 hour < 1 hour
>
1 hour>
1 hourAPF4 types
+ + - + - - -
APF10 types
+ + + + - + +
APF20 types
+ + - - + + +
APF40 types
- - - + - + +
APF200
types
- - - - - - -
APF2000
types
- - - - - - -
In table 2, traditional disposable and reusable half masks and full masks are used with either particle filter or vapour filter. This means that with these types of RPEs protection against both particles and vapours is not possible, and RPE needs to be changed if different filter type is needed. However, APF value is higher with full masks, as is expected. Powered masks, hoods or helmets offer better protection and they can be used for more than one hour, which is the limit for non-powered, traditional RPE alternatives, like half and full masks. With powered RPEs, filter can be changed from particle filter to vapour filter, but protection against both particles and vapours is not possible. (HSG53 2013) In this thesis, during FSP and SP studies, disposable half masks (also known as filtering facepieces or orinasal respirators) with particle filter were used by all personnel in the area.
Filter efficiency decrease lowers the protective ability of RPEs. This decrease occurs with particle diameter interval between 0,05 µm and 0,5 µm. The maximum decrease occurs with particle diameters close to 0,2 µm, decreasing filter efficiency over 20 percent. Particles in this size range (0,05-0,5 µm) are too small for deposition mechanisms like interception or impaction to cause efficient deposition of these particles on the filter, yet these particles are also too large for diffusion to stop them completely from advancing through the filter into the respiratory system. (Hinds 1999)
3. MATERIALS AND METHODS
3.1 Aerosol processes
In this study, release of NPs was monitored in two aerosol processes. Silver (Ag) doped lithium titanate (Li4Ti15O12) particles produced via FSP and cobalt oxide (CoO) particles produced via SP were monitored. Exposure to them, i.e. the deposition of these particles in alveolar and tracheobronchial regions in lungs were modeled using models constructed by International Commission on Radiological Protection (ICRP) to evaluate possible health effects caused by exposure to them, but only in the case of airborne particles (Li4Ti15O12) released from the FSP reactor. In this chapter, used gas-phase synthesis methods for pilot- scale nanoparticle production are presented.
3.1.1 Flame spray pyrolysis
Flame spray pyrolysis (FSP) reactor is a flame aerosol technology based method, which is increasingly used today to produce differently modified ENPs in a gas phase. (Strobel 2006) Developed in 1977 in Switzerland, FSP has received much attention afterwards due to its high potential in production of different nanoscale materials. (Strobel 2006, Teoh 2010, Gröhn 2014) FSP applies for industrial production of ENPs. Universities, research facilities and industries have shown their interest in FSP, and much research has been conducted regarding FSP applications. For example, Johnson Matthew Co (Headquarters in United Kingdom) has investigated FSP method in catalyst production, achieving production rate of 100 g/h of NP powder. The company has offices in more than 30 countries, including in Finland, Helsinki.
(Johnson Matthew 2011)
Applicability of FSP for large, industrial-scale production of ENPs is excellent, although FSP and ENP production via FSP have mostly been examined in pilot and research scale. FSP applies well for NP synthesis, since FSP method is able to produce vast amounts of particles in nanoscale with desired properties. For example, different oxides of metals can be produced in nanoscopic scale by FSP method. (Teoh 2010)
FSP production parameters can be varied in order to achieve target nanomaterials, for example flame temperature may be altered, or concentration of precursor solution changed, in order to achieve e.g. particles with smaller diameters (Teoh 2010). FSP provides production of ENPs with efficient control of their functional properties, making FSP method promising for NP industries. (Gröhn 2014) Schematic of the processes taking place in the FSP reactor (along with the FSP reactor) is shown below (Fig. 2). FSP method uses metal organic precursors dissolved in organic solvents. First, precursor solution is fed through the bottom of FSP reactor. Dispersion gas (O2, air) is used for atomization of the precursor solution, which is then ignited using methane-oxygen flamelet. This results in a high temperature flame (up to 3000 K) where organic components of the used precursor solution combust completely to CO2 and water, while organometallic components decompose and evaporate. Decomposed metallic components will form target particulates, metal oxides by nucleation and condensation. Due to high temperatures used in the FSP, some aggregation of produced particles often occur. (Karhunen 2011)
Fig 2: Schematic of the processes involved inside FSP reactor for particle formation (Figure modified from Karhunen 2011).
In this thesis, Ag doped lithium titanate (Li4Ti15O12) ENPs were produced via FSP. The release of Li4Ti15O12 particles into laboratory air were monitored using plethora of measurement equipment (presented in Ch. 3.2) at pilot-scale production facility owned by the University of Eastern Finland (UEF). The FSP reactor used in the study is shown above, along with processes marked in the figure which are involved in the production of particles (Fig. 2). The reactor consisted of precursor solution feed line at the bottom, a capillary tube at the center of the atomizer via which precursor solution was fed (annual aperture around it provides dispersion gas O2), flamelets (O2, CH4) that ignited the dispersed precursor and
residence time tube. The particles formed in the reactor were collected in the baghouse filter.
In figure 2, reactor feed line and the start of capillary tube may be seen at the bottom of the reactor.
3.1.2 Spray pyrolysis
In conventional spray pyrolysis (SP), particles are also produced in a gas phase. SP is based on aerosol technology, and it is used to produce metals, component materials and other materials with functional properties from nano- to micron-size. Usually products manufactured with SP are oxides of metals due to ambient oxidative environment (air) and/or high temperatures utilized in the spray pyrolysis process, but manufacture of nonmetals, metals and alkali salts is also possible. Processes in the SP take place inside the produced droplets or on their surface (Koshukharov 2013)
Schematic showing processes involved in particle synthesis via SP reactor used in this study is shown below, the SP reactor and droplet production are shown as well (Fig. 3). Reagents, i.e. precursor solution or suspension, may be atomized into droplets in the SP reactor using e.g. pressurized atomizer, twin fluid atomizer or ultrasonic nebulizer. In this study, pressurized atomizer was used to atomize precursor solution into droplets. The chosen atomizing technique and initial concentration of precursor solution determines size and size distribution of formed droplets, which subsequently affects size distribution and concentration of final (target) particles. Particle formation is also affected by interparticle reactions. Formed droplets are carried by gas (air, N2, O2, etc.) to the heated furnace, where the reactions take place inside the droplets and final dry particles are formed after cooling. Formation may occur e.g. via precipitation, evaporation or pyrolysis, depending on how synthesis proceeds. Particle morphology may be affected e.g. via sintering (Okuyama 2003) For example, ceramic powders may also be manufactured via SP method (Messing 1993)
Fig. 3: The SP reactor, schematic of processes involved in particle production with the SP reactor, and droplet production (modified from source UEF FINE).
However, conventional SP method might not be applied for NP synthesis, since low solution concentrations often generate low amounts of low purity particles. Okuyama et. al. (2003) reports that if atomized droplet has a diameter of 5 μm, and target particle has a diameter of 100 nm, the initial volume fraction must be less than 0.0008 % for dissolved solute in involatile form (e.g. metal). This is a low solution concentration for NP synthesis, and SP method remains often incapable of producing materials at nanoscale. However, conventional SP method has been developed and enhanced for NP production and control over morphology and size of the synthesized particles is more efficient today. Produced droplet size may be reduced in which case produced particle size will also be reduced, making achieving nanoscale particles with SP possible. (Okuyama 2003)
Mass of nanoparticles produced via the SP synthesis is usually quite small, due to small amount of NPs produced, yet larger particles may be produced in larger quantities. With the FSP method, mass of produced particles may range from grams/hour to kilograms/hour.
Unlike the FSP products, conventional SP products in the range of several micrometers are often too large to form hard agglomerates. In this study, cobalt oxide (CoxOy) particles were produced from aqueous cobalt sulfate solution using the SP reactor. Possible releases of airborne ENPs into the lab air were monitored using measurement equipment listed in the next chapter.
3.2 Measurement equipment
In this study, particle masses and number concentrations, surface areas of particles equivalent to lung deposition, mass mean diameter (MMD) and geometric number mean diameter (GMD) of particles were monitored using multiple measurement equipment (ME). In addition, the filter samples were collected and the morphology and elemental composition of the collected particles were analyzed with scanning electron microscopy (SEM) and electron diffraction spectroscopy (EDS). Since multiple measurement devices were used in this study, separate chapters about the used equipment are included below here to demonstrate what was done and why it was done with each measurement device.
3.2.1 Electric low pressure impactor
Electric low pressure impactor (ELPI, Outdoor Air ELPI, Dekati Ltd.) is used for real-time measurement of particle number concentrations and size distributions. In this thesis, particle number size distribution was determined by ELPI. ELPI has an impactor consisting of impactor plates that categorizes particles according to their size. By using particle charge values obtained from each impactor plate, the total number concentration of released particles was determined. ELPI measures with 10 Hz time resolution and collects sample with sample flow rate of 10 L/min. ELPI is used for work place air measurements, and it also applies for measurements of nanoscale particles. Aerodynamic diameter of particles with diameter between 6 nm and 10 μm is measured by ELPI. Since ELPI measures aerodynamic diameter of particles, it can model these particles by assuming that their shape is spherical and density uniform, 1000 kg/m3. Number concentration data obtained with ELPI during the FSP was
compared to the ICRP models, which depicted lung deposition separately in alveolar and tracheobronchial regions (see chapter 3.3.3). (Dekati Ltd. 2018, Hinds 1999)
The mass size distribution can be derived from the number size distribution by converting the data. However, the conversion includes several assumptions. The assumption that particles are spherical may cause some errors and the data should be treated with some reservation, since in real life particles rarely are spherical in form. ELPI mass models are still used, for example in medicine. ELPI measures particle number concentration values in real time, and is used widely with other particle number concentration measurement methods, presented below.
3.2.2 Differential mobility analyzer and condensation particle counter
Differential mobility analyzer (DMA) was coupled with condensation particle counter (CPC) to form scanning mobility particle sizer (SMPS). SMPS has been used for a few decades for the measurement of particle number size distributions (Demou 2008). In this thesis, DMA (electrostatic classifier, TSI model 308100) was connected to ultrafine CPC (TSI model 3776) which can count particles as small as 1 nm, with 50 Hz time resolution and flow rate of 0,3 L/min. (TSI Inc.) In SMPS, DMA generates an electric field, in which particles move according to their electric mobility. The current voltage can be chosen as measurement parameter to define particle sizes that are measured, i.e. are able to pass through the slit at the end of the DMA column. The particles that pass through the slit can be measured with the CPC. The working principle of CPC is as follows: 1) to enlarge particles as small as 1 nm by condensation of n-butanol (water and isopropanol are also used) on the particles and then 2) to measure optically these enlarged particles (TSI Inc.) CPC can be used also for the measurement of total particle concentrations without connecting it to DMA. CPC is often used in work place air measurements, air quality measurements, and in experimental studies (TSI Inc.)
SMPS consisted of DMA and CPC can be further modified to answer different measurement challenges by choosing different models of the same equipment provided by TSI. (TSI Inc.) International Organization for Standardization (ISO) has recognized electrical mobility method as suitable for particle size measurements for particles that have diameter between 1 nm and 1 μm (ISO 15900:2009). However, these equipment are expensive, heavy and
stationary, i.e. they cannot be carried around with the worker. Hence, measurements must be conducted on site.
In this thesis, equipment for measuring background particle concentration and total number concentration included three condensation particle counters: CPC downstairs in the monitoring space (TSI model 3025 A), CPC upstairs in the synthesis space (TSI model 3022 A), and ultrafine CPC downstairs in the synthesis space (UCPC, TSI model 3776), which was connected to DMA. (Demou 2008)
3.2.3 Fast mobility particle sizer
Fast mobility particle sizer (FMPS) is used for the measurement of particles that have diameter between 5,6 nm and 560 nm. In this study, FMPS (TSI model 3091) was used to measure particle number concentrations for later comparison of results gained with SMPS, ELPI and CPC. FMPS measures with 1 Hz time resolution, so it applies for aerosols that are changing fast. Unlike SMPS which uses CPC for particle detection or counting, FMPS utilizes low-noise electrometers for detection of particles. Since FMPS measures particles in quite small scale, flow rate for measured particles must be high, 10 L/min, in order to minimize particle losses due to diffusion. (TSI Inc.)
Minimizing diffusion losses is important with nanoscale particles, which are mostly affected by diffusion forces. If flow velocity in FMPS is low, small nanoscale particles will be lost into equipment by diffusion, distorting measured data. With high flow velocity in FMPS, measured particle concentrations are realistic and gained results reliable.
3.2.4 Tapered element oscillating microbalance
Tapered element oscillating microbalance (TEOM) (Thermo Scientific, TEOM Series 1405) was used for the measurement of particle mass concentration. TEOM is a direct-reading instrument for continuous measurement of particle mass that is collected during measurements on a filter which is attached to the vibrating micro-balance element. Collected mass on the filter decreases the resonant frequency of the filter, which TEOM detects electronically. TEOM converts detected electrical response to corresponding mass concentration. TEOM applies for mass measurement of total suspended particles (TSP).
Particulate matter of size classes PM10, PM2.5 and PM1, can be measured if preselection of particle size is done. Total sample flow rate for TEOM is usually 16,67 L/min (in this study as well), but it may be modified separately by changing main and bypass flow rates. TEOM measures with 0,1 Hz time resolution (Thermo Scientific TEOM, Hinds 1999)
3.2.5 Nanoparticle surface area monitor
Nanoparticle surface area monitor (NSAM, TSI model 3550) was used to measure particle surface area deposition in alveolar and tracheobronchial regions in human respiratory system, which required separate measurements. In NSAM, a cyclone with the cut size of 1 µm is installed to the aerosol inlet. The particles are charged by diffusion charging and detected with an electrometer. (TSI Inc.) Alveolar and tracheobronchial deposition models (ICRP) are compared to particle surface areas monitored with NSAM. Particle surface area was monitored since it seems a very crucial toxicological parameter along with particle size, charge and morphology if particles do not have any clear toxic chemical properties.
3.2.6 Scanning electron microscopy and electron diffraction analysis
Scanning electron microscopy (SEM) (Zeiss Sigma HD VP) equipped with energy dispersive X-ray spectroscopy (EDS, Thermo Noran, 60 mm2) was used to depict the morphology of particles collected on the filters during the pilot-scale processes. Maximum resolution of 1 nm is achievable with Zeiss Sigma HD VP SEM equipment. (UEF SIB Labs)
3.3 Measurement arrangements
Monitoring of released airborne particles in laboratory produced via FSP synthesis were conducted during 17.9-19.9.2018. FSP reactor was used to produce silver (Ag) doped lithium titanate particles. Spray pyrolysis reactor was used after FSP reactor during 15.10.-19.10.2018 to produce cobalt oxide (CoxOy) particles. FSP and SP reactors were located in the Funktiomat-pilot laboratory at rooms separated by walls and doors. Measurement points during FSP and SP synthesis are shown below, in schematic (Fig. 4) of the measurement area (rooms, stairs and doors not in real scale). Measurement equipment was used before, during
and after syntheses of particles to measure number concentration, size distribution, mass and surface area of particles in monitoring room, downstairs and upstairs synthesis spaces separately.
3.3.1 Filter collection
Filter collection (FC) method was used for measurement of particle mass concentrations during both syntheses. Zefluor filters made of polytetrafluoroethylene (PTFE) were used as filter material. Support material for filters is also made of PTFE. Pump equipped with a rotameter and a gasometer was attached to FC for collecting sample with constant flow (20.5 L/min). Collection of sample starts at the moment when the synthesis of target materials begins with both reactors, SP and FSP (in this study, collection time for FSP was about 43 min and for SP 1 hour and 3 min). All measurements were conducted during morning and early afternoon. See appendix 1 for more information about measurement run times.
Fig. 4: Schematic of the measurement points. FSP and SP markings indicate the location of reactors that are placed in separate rooms. Two stationary CPCs were used, i.e. CPC 3025a at downstairs monitoring space and CPC 3022a at upstairs synthesis space. Other ME were stationary and placed downstairs (moved only between FSP and SP experiments). The monitoring space was downstairs on the left, below the stairs.
3.3.2 Preparation of equipment
In FSP measurements, all ME were placed in downstairs synthesis space (Fig. 5 and 6), except for the CPC in the synthesis space upstairs, as described in chapter 3.2.2. Tygon tubes were used to collect samples from all spaces including upstairs and downstairs, since relocating the tubes between synthesis and monitoring spaces was a time saving and simple method. Tubes were hold down/up by duct tape for gathering of samples and the sampling height was around the breathing zone (marked with red arrow in figure 5). Before measurements started, all ME were switched on to warm up.
Fig. 5: Downstairs FSP synthesis space: NSAM on the left and SMPS on the right. Red arrow between ME shows the placement of tygon tube.
Fig. 6: Downstairs FSP synthesis space, TEOM down on the front, FMPS higher on the left and ELPI down on the right.
In the SP experiment, equipment was placed in downstairs synthesis space shown in Fig. 7.
During the SP experiment, CPC (3022a) in synthesis space upstairs collected sample from the room above the SP reactor, as it was used to collect sample from the room above the FSP reactor during the FSP experiment (Fig. 4).
Fig. 7: Downstairs SP synthesis space TEOM and ELPI in the front, SMPS and NSAM back in the center and FMPS on the right.
3.3.3 Formation of lung deposition model
For lung deposition modeling, number concentration measured by ELPI during the FSP synthesis was transformed into area concentration (dS/dlogDp). ICRP experimental models were used for the depiction of particle deposition separately in tracheobronchial (TB) and alveolar (AL) regions. For the tracheobronchial region, the deposition fraction DFTB may be calculated using the following equation (eq. 1)
( ) * ( ) ( ( ) )+ (eq. 1)
For the alveolar region, the deposition fraction DFAL may be calculated using the following equation (eq. 2)
( ) * ( ) ( ( ) )+ (eq. 2)
In the above equations, dp marks measured particle diameter. ICRP models also offer deposition models for the deposition fraction in head airways, and for the total deposition which sums deposition fractions in head airways, tracheobronchial region and alveolar region.
(equations 11.3 (TB) and 11.4 (AL) from Hinds 1999) ICRP models were constructed to depict particle lung deposition in both, adults and children, males and females (Hinds 1999).
In this study, only deposition fractions in alveolar and tracheobronchial regions were modeled separately, since nanoscale materials like NPs most likely deposit further in respiratory system than in head airways, due to the small size and mass of NPs.
3.3.4 Data analysis
Due to multiple ME used in this thesis, a massive library of data was received from the FSP and SP measurements. This meant that selection of representative data from all data was needed. Excel (Microsoft Excel 2010) and Matlab (Matrix Laboratory, version R2016b) were used in the data analysis. Selections of representative samples were chosen from raw data for depiction of number concentration, total number concentration, mass and area of measured particles. Representative samples were those samples, which were in stable phase during each measurement period. Certain actions during measurements were clearly causing peaks in aerosol concentrations, e.g. door opening between synthesis space(s) and monitoring room (see figure 8, peaks seen approximately at time points 13:25 and 13:30).
Fig. 8: ELPI spike values during FSP synthesis in monitoring room (MR). Upper picture color maps number concentration showing higher concentration values as red, and lower as blue.
Center picture depicts number concentration as function of time, while lower picture shows geometric mean diameter (GMD) and geometric standard deviation (STD) as function of time.
4. RESULTS
Sizes of the generated particles were expected to consist of nanoscale agglomerates during the FSP experiment, and micron sized particles during the SP studies. Since the SP reactor used in this study is mostly air tight and produces larger particles than the FSP reactor, concentration of incidental particles in laboratory air during the SP synthesis were expected to be lower than during the FSP synthesis.
4.1 Flame Spray Pyrolysis
The particle number concentrations, mass and surface areas before, during and after the FSP synthesis are shown in Table 3 along with physical and aerodynamic diameters of released particles. Figures 9, 10, 11 and 12 show the corresponding number size distributions measured with ELPI. Time of monitoring and duration of the FSP synthesis are also presented in ELPI figures, and in more detail in appendixes 1 (measurement run times), 2 (result run times) and 3 (synthesis run times). There was some deviation in the concentration values obtained with different devices, but the values were still in relatively good agreement.
4.1.1 Before particle production
In the synthesis spaces, monitored particle background number concentration varied between 6,1*104 1/cm3 and 1,1*105 1/cm3 in SSD, and 7,4*104 1/cm3 and 1,4*105 1/cm3 in SSU, as monitored by different ME (Table 3). The background particle number concentrations observed varied from 1,0*103 1/cm3 to around 7,7*104 1/cm3 in the monitoring room (MR).
Before synthesis, physical particle diameter varied between 103 nm and 121 nm measured by SMPS and FMPS in synthesis spaces, while aerodynamic diameter varied between 111 nm and 121 nm measured by ELPI. In MR, physical particle diameter varied between 116 nm and 126 nm, while aerodynamic diameter was monitored as 132 nm by ELPI (Table 3).
Surface area concentration by NSAM before the synthesis was 461,6 ± 10,6 μm2/cm3 for alveolar region and 34,1 ± 20,5 μm2/cm3 for tracheobronchial region in SSD, while in MR it was 312,7 ± 63,4 μm2/cm3 for tracheobronchial region. Before the synthesis, mass concentration monitored with TEOM varied between 261,4 ± 85,5 μg/m3 (SSD) and 867,7 ± 19,8 μg/m3 (SSU), while in MR mass concentration monitored was 531,9 ± 21,9 μg/m3. (Table 3)
Monitored with ELPI, particle number concentration was increased in all spaces even before the synthesis, being at the highest in synthesis spaces, slightly higher in SSD than SSU (red curve for SSD and green curve for SSU, Fig. 9), and being at the lowest, close to the normal particle number concentration range at MR (black line, Fig. 9). In downstairs (SSD), Ntot
keeps increasing as can be seen from the blue and red curves (Fig. 9). In upstairs (SSU) however, there was a decrease in Ntot before the synthesis was started (green, yellow and black dashed curves, Fig. 9). Before the synthesis, number concentration increases in SSD and decreases in SSU. The number concentration was high in SSU before the start of the FSP experiment, most likely due to the renovation of air conditioning system and pressure differences between synthesis and monitoring spaces. The number concentration increased in SSD before the synthesis, due to the particles shifting from SSU to SSD, e.g. due to free fall of heavier particles.
4.1.2 During particle production
During the FSP synthesis, particle number concentration in the laboratory air was elevated.
Number concentrations between 6,5*105 1/cm3 and 3,1*106 1/cm3 were measured during the synthesis in SSD, and between 7,5*105 1/cm3 and 2,7*106 1/cm3 in SSU, with different ME (Table 3). In MR, number concentrations between 1,7*104 1/cm3 and 2,6*105 1/cm3 were monitored by CPC and FMPS. Different ME measured similar number concentrations with some deviation. Thus, airborne particles were released increasingly during the synthesis.
Particles released to the laboratory air were in nanosize with a diameter approximately between 40-100 nm, or slightly larger agglomerates/particles with a diameter approximately between 100-350 nm (Fig. 10 and Table 3). Larger particles and/or agglomerates (with diameter between 350-1000 nm) were also released into laboratory air during the synthesis, but in lesser amounts. The size distributions shown in results during the synthesis were not multimodal, the average particle diameter being between 100-350 nm. Larger agglomerates
(350-1000 nm) released consisted of these smaller particle sizes, as may be seen in SEM picture (Fig. 17).
During the synthesis, physical particle diameter monitored varied between 145 nm and 333 nm between synthesis spaces, and aerodynamic diameter monitored varied between 210 nm and 313 nm. In addition, size of released particles increased during the synthesis, varying between 209 nm and 313 nm measured by ELPI. Similar increase was also recorded by SMPS (dp between 282,3 nm and 333,1 nm) and FMPS, although the increase in particle size measured by FMPS was little lower (dp between 144,5 nm and 159,9 nm, see Table 3 for results and appendix 2 for result run times). In MR, similar physical and aerodynamic particle diameter sizes were monitored with some deviation. However, monitored diameters by different ME are in good agreement. Sample flow rate through the baghouse filter was reduced during the synthesis due to some unknown reason, which made it possible for nanosized particles to be released into laboratory air in high amounts. The release of particles increased consequently the mass concentration. The mass concentration measured by TEOM increased to 22418 µg/m3 during the synthesis in SSD. This clearly indicates the release of particles from the reactor during the synthesis. Fortunately, the synthesis particles did not enter monitoring room where the total mass concentration was actually decreased from background value of 532 µg/m3 to 442 µg/m3 during the synthesis (Table 3).
Using NSAM, the deposition of particles in tracheobronchial (Tr) and alveolar (Al) regions were depicted separately. The NSAM result run times and calculated surface area concentrations contributing to those run times are presented in appendix 2 (Tables 13-15).
The surface area of particles in relation to the alveolar deposition decreased during the synthesis, but in relation to the tracheobronchial deposition the surface area was increased greatly: from background level of 34,10 ± 20,53 μm2/cm3 in SSD to 4158 ± 1433 μm2/cm3 during the synthesis in SSU. In MR, deposited surface area concentration of 356,5 ± 279,6 μm2/cm3 in tracheobronchial region was monitored during the synthesis. (Table 3)
During the FSP, particle number concentration Ntot and size distribution were depicted as before the synthesis. The total particle concentration was considerably higher compared to the background concentrations, i.e. the total number of particles increased from 1,4*105 1/cm3 to 2,2*106 1/cm3 in SSU, and from 1,1*105 1/cm3 to 1,7*106 1/cm3 in SSD, measured by ELPI.
However, the concentrations in MR remained close to the background level (1,0*103 1/cm3 by CPC) which indicated that particles were not released into MR during the synthesis. (Table 3)
Ntot was clearly at the lowest in MR, as can be seen in ELPI dN/dlogDp figures (black and green curves, Fig. 10 and Fig. 11). In SSU, blue and red curves depict the measured Ntot
during the synthesis, and in SSD the yellow curve depicts the measured Ntot during the synthesis (Fig. 10). Engineered nanoscale particles and their agglomerates were clearly released into laboratory air as airborne particles, as increased Ntot indicates.
4.1.3 After particle production
The particle removal from the baghouse filter and the reactor cleaning were carried out after the synthesis. Monitored particle parameters in the air during the cleaning are also shown in Table 3. Number concentration remained normal in MR, as NTot of 1,2*103 1/cm3 was measured by CPC in MR during the reactor cleaning. The particle concentrations remained low compared to the concentrations observed during the synthesis phase and were close to the background levels measured earlier. Particle diameters and aerodynamic particle diameters monitored after the synthesis were also lower than during the synthesis, as were monitored surface areas in both alveolar and tracheobronchial regions by NSAM. Total particle concentrations (Ntot), geometric mean diameters (GMD) and standard deviations (STD) measured before, during and after the FSP synthesis by ELPI, SMPS, FMPS and CPC, mass concentration by TEOM and deposited particle surface areas (Stot) by NSAM are all listed below. (Table 3) After the FSP synthesis, Ntot and size distribution of released airborne particles were also measured with ELPI, but only in SSD (Fig. 12). Number concentration decreases as a function of time onwards from the shut down/end phase of the synthesis, as was expected.
tracheobronchial regions by NSAM before, during and after the FSP synthesis (*).
*Abbreviations in table 3 are: SSD = synthesis space downstairs, SSU = synthesis space downstairs, MR = monitoring room, Alv = alveolar, Tra
= tracheobronchial, n.a. = not available
Before synthesis
Dp (nm) Da (nm) GSD (nm) Ntot (1/cm3) TEOM
Mass (μg/m3)
NSAM Stot (μm2/cm3)
SMPS FMPS ELPI SMPS FMPS ELPI SMPS FMPS ELPI CPC Alv Tra
SSD 111,3 103,0 111,2 1,8 1,6 1,9 6,1*104 7,6*104 1,1*105 n.a. 261,4
± 85,5
461,6 ±
10,6 34,1 ± 20,5
SSU 120,7 108,7 120,8 1,9 1,7 2,0 9,1*104 1,1*105 1,4*105 7,4*104 867,7
± 19,8
n.a. n.a.
MR 125,7 116,5 132,9 1,9 1,7 2,1 4,9*104 5,7*104 7,7*104 1,0*103 531,9
± 21,9
312,7 ±
63,4 n.a.
During synthesis
Dp (nm) Da (nm) GSD (nm) Ntot (1/cm3) TEOM
mass (μg/m3)
NSAM Stot (μm2/cm3)
SMPS FMPS ELPI SMPS FMPS ELPI SMPS FMPS ELPI CPC Alv Tra
SSD 333,1 156,7 313,1 1,7 1,7 1,8 6,5*105 3,1*106 1,7*106 n.a. 22418 ±
2664,6 349,2 ±
28,3 n.a.
SSU 282,3 144,5 208,6 1,8 1,7 1,9 7,5*105 2,7*106 2,2*106 1,2*106 10451 ±
3164,2 n.a. 4158 ± 1433
MR 330,0 159,9 245,6 1,6 1,6 1,9 2,1*105 2,6*105 5,2*104 1,7*104 442,3 ±
339,4 n.a. 356,5 ± 279,6 After
synthesis
Dp (nm) Da (nm) GSD (nm) Ntot (1/cm3) TEOM
Mass (μg/m3)
NSAM Stot (μm2/cm3)
SMPS FMPS ELPI SMPS FMPS ELPI SMPS FMPS ELPI CPC Alv Tra
SSD 97,7 85,9 131,1 1,8 1,7 2,3 1,2*104 1,6*104 1,5*104 n.a. 46,9
± 23,8
44,0 ±
11,8 n.a.
SSU 92,1 n.a 110,5 2,0 n.a 2,6 1,5*103 n.a 1,8*103 2,2*103
511,4
±
195,8 n.a. 1,9 ± 0,2
In the FSP studies, data collected by ELPI (dN/dlogDp) was used to depict particle number concentration Ntot and size distribution before (Fig. 9), during (Fig. 10&11) and after the synthesis (Fig. 12). The mass size distributions obtained by ELPI were also examined, but not included in the study. The mass size distributions should be used with reservation as ELPI makes assumptions (spherical, unit density particles) during the data transformation. In the ELPI dN/dlogDp figures, colored lines depict where the monitoring has been executed (MR=monitoring room, SSD=synthesis space downstairs, SSU=synthesis space upstairs).
Fig. 9: ELPI particle number size distribution before the FSP synthesis (MR=monitoring room, SSD=synthesis space downstairs, SSU=synthesis space upstairs).
Fig. 10: ELPI particle number size distribution during the FSP synthesis phases. Synthesis duration: 12:54 – 13:48, see Table 22 in appendix 3 for details (MR=monitoring room, SSD=synthesis space downstairs, SSU=synthesis space upstairs).
Fig. 11: ELPI particle number size distribution during the FSP synthesis in MR (MR=monitoring room).
Fig. 12: ELPI particle number size distribution after the FSP synthesis in SSD (SSD=synthesis space downstairs).
FSP TEOM Figures
Particle mass concentration was monitored using TEOM, and released particles were collected also on a filter (FC). Figures 13 (before the FSP synthesis), 14 (during the initial FSP synthesis phase), 15 (during the final FSP synthesis phase) and 16 (after the FSP synthesis) depict the total mass of particles per cubic meter (see also Table 3) measured with TEOM, in corresponding measurement areas (SSU=synthesis space upstairs, SSD=synthesis space downstairs and MR=monitoring room). Online filter sampling i.e. FC of laboratory air and released particles in it was only conducted during the synthesis of Ag doped lithium titanate particles (the total mass of collected filter sample = 10,994 mg). Total mass concentration (measured by TEOM) as a function of time before the FSP synthesis is shown below in SSD, SSU and MR (Fig. 13). When compared to the background mass concentration, the mass concentration decreased in MR during the synthesis (fig. 15 E and table 3). Also, standard deviation (STD) during the FSP synthesis was calculated.
Fig 13: Mass concentration (μg/m3) by TEOM before the FSP synthesis in different monitoring spaces A) SSD=synthesis space downstairs, B) SSU=synthesis space upstairs and C) MR=monitoring room.
Fig. 14: Mass concentration (μg/m3) by TEOM during the initial phases of the FSP synthesis (in different monitoring spaces): A) Initiation (SSD=synthesis space downstairs), B) Initial synthesis phase (SSD) and C) Initial synthesis phase (SSU=synthesis space upstairs).
Fig. 15: Mass concentration (μg/m3) by TEOM during the final phases of the FSP synthesis (in different monitoring spaces): D) Final synthesis phase (SSU=synthesis space upstairs), E) Final synthesis phase (MR=monitoring room), F) Final synthesis phase (SSD=synthesis space downstairs) and G) Shut down phase (SSD).
