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Characterization of emissions of condensable particulate matter (CPM) in clinker kilns using a dilution sampling system. Mercedes Cano, Fernando Vega, Benito Navarrete, Antonio Plumed, and Jose Antonio Camino Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b00692 • Publication Date (Web): 17 Jul 2017 Downloaded from http://pubs.acs.org on July 17, 2017
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Energy & Fuels
Characterization of emissions of condensable particulate matter (CPM) in clinker kilns using a dilution sampling system. M. Cano*, F.Vega, B. Navarrete, A. Plumed, J.A. Camino Department of Chemical and Environmental Engineering, School of Engineering – University of Seville, C/Camino de los Descubrimientos s/n, 41092 Sevilla, Spain
ABSTRACT Although significant steps have been taken over the last few decades in terms of creating policies aimed at controlling emissions, with the consequent toughening of the emissions thresholds, the damage to air quality caused by PM2.5 particles currently represents a major worry on a global scale, mainly due to its involvement in significant harm to human health and the environment alike. Within this subgroup, the condensable particulate matter (CPM) produced in large combustion plants is susceptible to being a major contributor to the total mass of fine particles present in the air that we breathe. This work compiles the results obtained from CPM concentration measurements taken at the source of combustion gas emissions in an industrial clinker kiln, using an innovative sampling train developed at the University of Seville. In addition to this, and applying adequate analytical techniques, we have characterized the nature of the CPM emitted at this facility and its morphology, obtaining varying results, depending on the nature of the fuel in question, the raw material involved in the process and the different operating modes of the system. The conclusion to this paper confirms that Clinker production plants emit CPM in concentrations that are below the current legal limits for particle emissions in this kind of facility, although they are, for the most part, higher than the usual emissions of filterable particles. Keywords: Condensable particulate matter, Clinker, Emissions, Dilution, Sampling train. 1.
INTRODUCTION
In recent years we have seen significant progress made in terms of policies for controlling particle emissions and in the resulting lowering of maximum emissions limits, especially in the United States and Europe.1-9 However, alterations in air quality caused by PM2.5 particles have proven to be of major importance due to their effect on both the affected population and on the environment, even though there is still no legislation in place to control emissions levels of the same.10-16 Condensable particulate matter (CPM) is included within the concept of PM2.5 particles. The biggest potential emitters of this kind of particles are, in principle, electrical energy production processes (including Coal-fired power plants as one of the most important contributors of CPM emissions in this sort of processes) and industrial combustion processes, among which are cement Clinker kilns.17-25 In this sense, several studies have been made to determinate the CPM contribution to the total emissions1.
Abbreviations: CPM, Condensable particulate matter; FP, Filterable particles; DIQA, Department of Chemical and Environmental Engineering; GF, glass microfiber filter; QF, quartz microfiber filter; AMS, Automatic measuring systems.
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In this sense, there is growing interest on the part of government institutions and legislators in the subject of air quality and its repercussions on people’s quality of life and health. This interest was intensified in Europe due to the conclusions of the CAFE (Clean Air For Europe) Group in its study published in 2001.26 The study’s conclusions proposed some recommendations for European energy policy that went on to be included in the Horizon 2030 energy plan.27 The next step was to focus on the problem of second generation tropospheric pollutants (paying special attention to ozone and particulate matter with a diameter of less than 2.5 µm, also known as inhalable or ultrafine particles). One type of inhalable particles that has still not been properly studied in terms of their ideal measuring methods and their characterization are what is referred to as condensable particulate matter (hereinafter, CPM). CPM is understood to refer to fine particles (smaller than 2.5 µm), which are primary and filterable under the conditions at which they are emitted. This type of particles is found following the cooling and dilution of gas emitted into the air, forming solid or liquid particles immediately discharged from the source of the emissions. The problem posed by emissions of this type of particles was established and recognised as early as 1983 by the Environmental Protection Agency (EPA).17 Originally, the EPA established sampling procedures for CPM that are an extension of the sampling for particles PM10 and PM2.5 at the sources of emissions, such as EPA Method 201A or exclusively for CPM by means of EPA Method 202. 28, 29 These methods are based on the generation and capture of CPM in the absorbers located in the sampling train. In both cases, the methodology does not consider particulate matter produced by reactions between the pollutants emitted and the atmosphere, once the plume has cooled and been diluted, given that the actual condensation of the particles occurs within the absorbers. In 2004 the EPA published Conditional Test Method 039 (CTM-039), which established a mechanism for taking samples of gases emitted at any given source through dilution using ambient air. 30Once it has been diluted and cooled for a certain period of time, the gas is filtered in order to capture any particulate pollutants produced in a second generation. After that, in 2013, the International Organization for Standardization (ISO) published international standard ISO 25597:2013, for sampling and analysis of stationary sources, which is important in the CPM sampling methodology proposed by CTM-039, using a dilution-based sampling train. 31 Although impingers method has been established as standard method for CPM determination by EPA, CPM generation mechanisms issue has to be taken into account as a priority matter in order to determinate the real CPM nature. Therefore, a CPM determination method based on dilution system was chosen in this study to provide a high accuracy and representative CPM emission measurements. The dilution methods reproduce the phenomenon of condensation inside the sampling system, which takes place as the flue gas emitted comes into contact with the atmosphere. This article presents the results of the CPM determination exclusively, firstly segregating the filterable particles (hereinafter, FP) that are present in the emissions from a Clinker kiln using an innovative system that takes samples through dilution. It should be noted that all of the determinations evaluate the CPM generated in a condensation chamber, which reproduces the process by which they mix with atmospheric air on leaving a stack, following the elimination of the PM2.5 carried by the gas.
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2.
MATERIAL AND METHODS 2.1 Description of the sampling train.
Figure 1 shows the layout of the dilution-based sampling train developed by the Department of Chemical and Environmental Engineering (DIQA, according to its Spanish acronym) at the Higher School of Engineering of the University of Seville (hereinafter, the DIQA sampler), which was used specifically for the purposes of this work. The DIQA sampler is based on the sampling layout proposed by standard CTM-039, to which we have implemented significant changes that, among other innovations, have allowed us to exclusively determine CPM levels. T5
T2 P2
P1
T3
T4
V1
T1
Nozzles Heated set isokinetic probe
FP filter holder
INDICATOR LEGEND
Gas venturi
Forced blower
OPTION B
Mixing cone
T7 RH2
P5
Induced blower
Residence chamber V2
HEPA filter
CPM filter holder
RH1 T6
T- Temperature P- Pressure V- Valve RH- Relative Humidity
Dehumifier
Mixing cone holder
P4
Dilution venturi
P3
Cooling unit
Forced blower
OPTION A
Figure 1. DIQA Sampler. Following modifications, the DIQA sampler allows us to segregate the particles carried by the gas using a heated filter, thereby determining CPM levels independently. The sampler is made up of two lines. The principal sample gas line, which goes from the suction nozzle to the induced blower, and its main elements are: heated isokinetic probe, hereinafter referred as HIP , gas venturi tube, residence chamber and a CPM filter holder. The residence chamber consists of a stainless steel cylindrical pipe. Its main dimensions are 17” length and 4” inner diameter. The mixing cone is made of stainless steel. Its main dimensions are 4” and 3/8” inner diameters and it has series of 5 mm orifices on its surface to ensure the adequate mix between the air supplied and the sampled flue gas. The secondary line, or dilution airline, is where the air is conditioned in terms of humidity and temperature before being filtered to eliminate particles coming from ambient air. Its principal components are: forced blower, system for eliminating humidity (dehumifier or cooling unit, used respectively depending on ambient conditions), air venturi tube and HEPA filter.
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The sampling system is controlled using a control unit, which includes the main settings that must be monitored such as differential pressure, temperature and relative humidity. This equipment was manufactured based on an own design criteria. Particles present in emissions from stationary sources can be captured isokinetically using the HIP, which also has a sensor to determine the temperature of the gases emitted. During sampling, the gas is filtered using a filter for FP housed in a FP filter holder at the head of the probe and inside the duct that the gas circulates around (in stack filter) or at the rear of the HIP inside a heated box. Once the aliquot withdrawn from the same has been filtered, the gas flow is regulated by the valve V1 and is carried along the heated probe line. The aspiration flow is established by reading the differential pressure in the venturi located at the outlet of the probe. After that, the gas goes through the mixing cone, where atmospheric air is injected, with a flow rate measured by the air venturi tube and regulated by a valve V2. This air current firstly passes through a humidity elimination system and is filtered by a HEPA filter. The corresponding temperature and humidity sensors allow us to establish the correct air conditioning along the line. The flow of gas aspirated by the induced blower is adjusted to carry out the sampling within the permitted dilution ratio, expressed as air/sampled gas flow rate ratio, ranging from 10:1 to 40:1. The operation within the indicated dilution ratio interval allows to sample close-to-ambient conditions. Besides, if it should prove necessary to carry out the sampling in isokinetic conditions to determinate the FP concentration, this adjustment in the flow rate will also be imposed by the use of a suction nozzle designed to keep the percentage of isokinetic content close to 100% in each sampling. After that, the mix of sample gas and dilution air originating in the mixing cone goes through a residence chamber, where the CPM is generated under the conditions of humidity, temperature and residence time established by the reference standard. On leaving the residence chamber, the condensable particles generated during the passage of the mix through the same are held in a CPM filter housed in the CPM filter holder. The main parameters, such as the temperature of the various parts of the sampling train, the sampling gas or the dilution air, as well as the relative humidity at each point of interest along the sampling train and the differential pressures needed to calculate the gas flow rate and speed, are checked using the different measurement and control elements installed in the sampling train. These measurement elements, such as differential pressure meters, controllers and temperature and humidity meters, allow us to instantly monitor temperature and gas speed and flow rate in the channel at all times. 2.2 Experimental plan. 2.2.1
Description of the facility that is the subject of the study.
The experimental measures were carried out at a clinker production plant. The clinker production procedure is performed using the “dry process”, with a system than includes a rotary kiln and a four-stage heat exchanger. The raw materials used to carry out clinker production are limestone, marl and sand, while the main materials used to manufacture cement, besides the clinker, are gypsum, blast furnace slag, fly ash, pozzolana, limestone, dust recovered from the hybrid filter, Cr VI reducing agents and grinding additives. The fuels used in the clinkering process are petroleum coke, as the main fuel, or alternative fuels and fuel-oil, the latter being used for start-up operations.
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The flue gases leaving the kiln are brought into a direct four-stage heat exchange with the fresh material coming out of the kiln. At this point the flue gases are at a temperature of 190 to 200ºC. From this point on there are two alternatives for the path taken by the gases until they reach the atmosphere, depending on the plant’s mode of operation: 1.
Sending them to raw material mills (raw mills) for drying (Compound Mode), reducing their temperature to 140ºC approximately. They are then sent to an SNCR process and a hybrid filter for dusting, before being emitted through the stack.
2.
Sending them to a quenching system for thermal conditioning until the gases reach a safe temperature (Direct Mode), prior to being sent to an SNCR process and the dusting system using a hybrid filter, before leaving through the stack.
The flue gases are emitted into the atmosphere through a round stack with a diameter of 2.9 m and a height of 80 m, after being treated in a selective non-catalytic reduction (SNCR) reactor and a hybrid filter (ESP+BF), as shown in Figure 2. The CPM emissions are measured in the stack through 3 sampling outlets on a platform 52 metres up. RAW MATERIAL STORAGE (AS RECEIVED)
RAW MILL
HOMOGENIZATION AND STORAGE OF RAW MATERIALS
KILN STACK PREHEATER TOWER
DUST COLLECTING SYSTEM
ROTARY KILN GRATE COOLER
CLINKER STORAGE
Figure 2. Diagram of the Clinker production plant.
Figure 3. Image of the train during sampling.
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FUEL STORAGE
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2.2.2
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Plan of measures.
Two different test campaigns were carried out to determine CPM levels for the facility. In the first test campaign we carried out a total of three CPM samplings, with a further seven samplings being performed in the second campaign. In all of these cases we chose to eliminate filterable particles from the sampled gas current using a particle filter at the end of the heated isokinetic probe, in a hot box (EPA Method 5). 2.2.2.1 First campaign. Relevant aspects. In this first campaign we used a flat glass microfiber filter measuring 140 mm Φ, (GF140). The plant’s operating conditions during the sampling periods are shown in Table 1. Table 1. Tests performed in first test campaign. Test no. 1 2 3
Type of filter
Sampling time (min)
Main fuel
GF140 GF140 GF140
120
Coke Coke Coke
240 120
Type of Operationa,b D C C
a D: Direct Mode, preheated gases into the stack. b C: Compound Mode, raw mill for gases prior to expulsion.
2.2.2.2 Second campaign. Relevant aspects. We decided to use quartz microfiber filters measuring 70 mm Φ (QF070) in order to concentrate the solid samples obtained. Ultra-pure quartz microfiber was chosen due to its low reactivity with the gases measured, as opposed to glass microfiber, almost 20% of the weight of which is from alkaline materials. In this second campaign, the duration of the tests was established based on the required preliminary tests following the change of filter type. Table 2. Tests performed in second test campaign. Test no.
Type of filter
Sampling time (min)
Main fuel
1
QF070
120
Coke
C
2 3 4 5 6 7
QF070 QF070 QF070 QF070 QF070 QF070
180
Coke Coke Coke Coke Coke Coke
C D D C D/C D
220 480 480 480 160
Type of Operationa,b
a D: Direct Mode, preheated gases into the stack. b C: Compound Mode, raw mill for gases prior to expulsion.
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2.2.3
Methodology used for sampling.
The methods used to carry out the preliminary gas stream characterisation tests were: EPA Method 1 “Sample and Velocity Traverses for Stationary Sources (40 CFR Part 60, Appendix A)”, EPA Method 2 “Determination of Stack Gas Velocity and Volumetric Flow Rate (Type S Pitot Tube) (CFR Part 60, Appendix A)”, EPA Method 3 “Gas Analysis for Carbon Dioxide, Oxygen, Excess Air, and Dry Molecular Weight (40 CFR Part 60, Appendix A)”, EPA Method 4 “Determination of Moisture Content in Stack Gases (40 CFR Part 60, Appendix A)”, EPA Method 5 “Determination of Particulate Matter Emissions from Stationary Sources (40 CFR Part 60, Appendix A)”, and EPA Method 17 “Determination of Particulate Matter Emissions from Stationary Sources (In stack filter) (40 CFR Part 60, Appendix A)”. Based on the above standards, the following parameters were set:
-
Selection of sections and measurement points along the flue. Temperature reading, calculation of gas velocity for nozzle selection. Establishing the composition of the gas stream using previously calibrated automatic gas analysers. Establishing the humidity content of the gas.
It should be pointed out that even though the research was carried out in an industrial facility and, consequently, the availability and operation of the kiln were subject to the plant’s production conditions, we were able to meet the objectives of the testing and obtain satisfactory results. 2.2.4
Methodology used to analyse samples.
The analytical techniques used to characterise CPM consisted mainly of a gravimetric analysis of all samples in order to quantify the CPM emissions, and of the use of a Scanning Electron Microscope (SEM) for the morphological analysis and chemical composition analysis of the samples. The method of manual gravimetric analysis consisted of calculating particle concentration from the difference in filter weights both subsequently and prior to being employed in the assay sampling. This method has been selected for calculation of condensable particles deposited in the filter, based on standard CTM-039. The morphology of the CPM is analysed using a Scanning Electron Microscope (SEM). This technique has been used exclusively to verify the presence of CPM in filters, as well as the quantity and size of any particles. Most of the samples can be examined with little preparation and their only limitation is that the sampling surface must be electrically conductive in order to eliminate or reduce the electrical charge that quickly appears on the surface of the nonconductive sample when swept with a beam of high energy electrons. The compositional analysis of the condensable particles was performed using the EDS technique, which is integrated in the Scanning Electron Microscope (SEM). This technique allows us to obtain a qualitative and semi-quantitative analysis of the components of the particles deposited in the filter.
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3.
RESULTS AND DISCUSSION
The results obtained in the different tests for the characterization of samples from a gravimetric, morphological and chemical point of view, and a discussion thereof is provided below. As regards the characterization of the gases emitted, Table 3 shows the average obtained and the relative deviation of the results in the compositional analyses included in the two test campaigns: Table 3. Characterization of the gas stream during readings. Parameters N2 O2 (%v/v) CO2 (%v/v) SO2 (ppmv) NOx (ppmv) CO (ppmv) Humidity (%) GasT (ºC) “Direct Mode” “Compound Mode” Dry base flow rate (Nm3/h)
Average values (± standard deviation) Campaign 1 Campaign 2 72(±0.8) 74(±0.9) 11(±0.7) 12(±0.7) 17(±1.4) 14(±1.2) 0 0 369(±76.8) 362(±64.6) 147(±46.6) 128(±51.1) 10(±0.9) 10(±0.8) 211(±4) 211(±5) 154(±3) 158(±3) 199884(±14245)
240704(±16132)
Table 3 reported the average values of the O2 and CO2 compostion of the gas stream during the campaigns. These values are consistent with the conventional flue gas composition from cement plants.32 3.1 Gravimetric Analysis. Figures 4 and 5 show the results of the samplings performed during the test campaigns. These show both the total CPM, understood to be that obtained from the different parts of the sampling train plus that obtained at each filter, and the total volume of sampled process gas. Finally, the CPM and FP concentration are reported for each sampling, expressed as mg/m3 (std).
Figure 4. Gravimetric analysis during 1st campaign with GF140.
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Figure 5. Gravimetric analysis during 2nd campaign with QF070. Figures 4 and 5 show that the results obtained for the CPM concentrations in the different tests are all in the range of 1-12 mg/m3 (std). Glass microfiber filters measuring 140 mm Φ, (GF140) were used in first campaign and quartz microfiber filters measuring 70 mm Φ (QF070) were used in second campaign. There were no remarkable differences in terms sampling operation mode between both campaigns. Variation proposed in the type and diameter of filter used has no impact on the effectiveness of the CPM collection. The variations observed in the concentration results obtained could be attributed mainly to the variations in operating conditions during working hours (alternating “compound/direct modes”, changes in the composition of the fuel and the raw materials fed into the kiln). As seen in Figures 4 and 5, there is a direct relationship between both CPM and FP concentration. The CPM/FP concentration ratio is approximately to 1.5 for all the results obtained during the test campaigns. In addition, CPM mass distribution is shown on Table 4 for each campaing. Table 4. CPM mass distribution. Campaign no.
1st
2nd
Test no.
CPM filter (g)
CPM wall rinses (g)
1
0.0089
0.0011
2
0.0119
0.0014
3
0.0026
0.0004
1
0.0028
0.0014
2
0.0068
0.0030
3
0.0045
0.0015
4
0.0048
0.0030
5
0.0031
0.0031
6
0.0050
0.0036
7
0.0038
0.0014
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3.2 Chemical characterization. Table 5 shows the results of chemical composition analysis carried out using EDS technology for samples collected from glass and quartz microfiber filters, used during the first and second test campaigns. Table 5. Compositional analysis, 1st and 2nd text campaigns. Elements Cl Hg Al/K/Ca/I
1st Campaign concentrations mg/m3, std % w/w 0.1-0.3 0.7-2.2 -
2nd Campaign concentrations mg/m3, std % w/w 0.1-0.3 3.1-5.9 0.1-0.2 3.9-2.6 0.01/0.01/0.01/0.1 0.4/0.5/0.6/8.8
In general, the variation proposed in the type and diameter of filter used allowed to improve the accuracy of the selected analytical method (EDS). Sample collected in a quartz microfiber filters measuring 70 mm Φ (QF070) reported more information about CPM chemical composition due to the increase of sample mass per unit area. In the case of test performed with a glass microfiber filter, the analytical method detects the appearance of traces of Cl in all of the 140 mm glass microfiber filter analysed, except for in the analysis of the filter mesh. Cl is a parameter that could be identified as a possible component of CPM, given that it is one of the pollutants usually present in emissions from the raw materials fed into the kiln. In the case of test performed with a quartz microfiber filter, it is especially remarkable that the analytical method detects the appearance of Hg in some of the filters analysed, namely in the samples of emissions from “direct mode” operations. This could be due to the fact that in operations in the “compound mode” a fraction of the gases coming from the kiln go through the raw mill and get cooled (approx. GasT 145 °C). At this temperature, it is feasible for there to be Hg absorption from the raw materials used in the process, meaning that the concentration of Hg in the emissions could be drastically reduced. On the other hand, in “compound mode” operations, the temperature of the process gas is higher (approx. GasT ≈ 200 °C), meaning that Hg absorption no longer takes place (maximum absorption temperature ≈ 170 °C). This dynamic was detected by the cement plant by continuously monitoring Hg and the temperature of the gases using Automatic Measuring Systems (AMS) located in the stack. In view of the above, Hg must be considered to be a chemical component of CPM, given that, like Cl, is also a common pollutant emitted by the cement plant. The analysis has also demonstrated the appearance of trace levels of Al, K, Ca and I in some samples. 3.3 Morphological characterization. A first visual inspection allowed us to verify that there were no imperfections in the filters caused by the act of removing them from the filter holder or due to circumstances arising from carrying out the sample taking itself, such as breakages due to a sudden increase or decrease in the line vacuum or due to the presence of condensed matter in the filter, or traces of any other type of contamination that can be seen at first sight.
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This first visual inspection was complemented by an analysis carried out using the Scanning Electron Microscope (SEM) technique. By employing this technique it was possible to establish the existence of particles, their approximate geometric shape and their size, although it was not possible to perform a granulometric distribution, as such. Figures 6 and 7 show the image captured by the SEM of a flat 140 mm filter mesh made of glass microfibers, compared to the same after the sampling. Figure 6 shows a close up of the fibrillar structure of the filter mesh, with a complete absence of any particles or of any other pollutant that might interfere with the ability to discern the same, while in Figure 7 we can easily distinguish the presence of CPM attached to the fibres in the filter, with a pretty regular size and distribution.
Figure 6. SEM X800 image of the mesh of a glass microfiber filter.
Figure 7. SEM X800 image of a glass microfiber filter after sampling.
Figure 8 show some of these particles in greater detail. As we can see in the image, these are particles of a very small size (about 1-2 µm) with a porous surface, which makes them look apparently light.
Figure 8. SEM X15000 image of a 140 mm glass filter after sampling.
Figures 9 and 10 show the image captured by the SEM of a flat 70 mm mesh from a quartz microfiber filter, and then the same mesh after sampling.
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Figure 9 shows a close up of the fibrillar structure of the filter mesh, and in Figure 10 we can easily distinguish the abundant presence of CPM with a fairly homogenous size and shape and with quite a regular distribution of these particles attached to the fibers in the filter.
Figure 10. SEM X800 image of a 70 mm quartz filter after sampling.
Figure 9. SEM X800 image of the mesh of a quartz microfiber filter.
Figure 11 show a more magnified view of the CPM attached to the filter fibers. In these images we should noted the presence of irregular shapes with a more pronounced shine, which correspond to the areas where the presence of Hg was detected. Figure 12 show in greater detail how a huge number of particles almost entirely cover the quartz microfibers that the filter is composed of. The size of these particles is about 1-2 µm and their superficial appearance is spherical.
Figure 12. SEM X4500 image of a 70 mm quartz filter after sampling.
Figure 11. SEM 45000 image of a 70 mm quartz filter after sampling. 4.
CONCLUSIONS
Following testing in the field and subsequent analysis of the samples taken, we can draw the following conclusions from the results obtained, subject to the uncertainty associated with the limitations inherent in the plant’s operating conditions during sampling (starting/stopping of the raw mill). First of all, based on the results of the analytical methods used, we could arrive at the conclusion that clinker production plants emit CPM. Furthermore, it is remarkable that the measured concentrations are relatively small compared with the emissions limits for filterable particles that are applicable to these plants, currently set
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at 30 mg/Nm3. In particular, CPM/FP concentration ratio obtained from this work was near to 1.5 for all the results reported and the maximum concentration measurements for each campaign were 7.8 and 3.2 mg/Nm3, respectively. Despite the above, it is especially interesting to point out that CPM emissions can double the concentration of filterable particles emitted in some tests, especially if we bear in mind that emissions of filterable particles in facilities that use hybrid filters to reduce particle emissions are usually over 5 mg/Nm3. The morphological analysis of the filters carried out using the SEM technique allows us to conclude that the average size of the particles observed in the different tests performed is about 2 micron and that their distribution over the surface of the filter is quite homogeneous. With regard to the chemical analysis of the CPM deposited in the filters, the compositions revealed by EDS show that there is Cl present, as well as Hg that is present primarily in the “direct mode” of operation for clinker production. Also, the analysis detected the presence of trace amounts of other elements like Al, K, Ca and I. The existence of these components in the CPM is only to be expected, as they are common components of the raw materials used in these types of processes. Based on the greatest number of samples and the modifications made in the diameter and the type of filter, QF070 filter is recommended instead of GF140. QF070 filter improved the accuracy of the results in terms of CPM chemical composition. The use of a lower filter size increased the quantity of CPM per filter area and provided more accuracy in the results of CPM chemical composition during the second campaign.
AUTHOR INFORMATION Corresponding Author. *E-mail address:
[email protected] ORCID:
0000-0002-6157-9517
Phone Number: +34 954481397
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