- Email: [email protected]
On the applicability of XPS for quantitative total organic and elemental carbon analysis of airborne particulate matter
ARTICLE IN PRESS
Atmospheric Environment 42 (2008) 3888–3891 www.elsevier.com/locate/atmosenv
Short communication
On the applicability of XPS for quantitative total organic and elemental carbon analysis of airborne particulate matter Richard J.J. Gilham, Steve J. Spencer, David Butterfield, Martin P. Seah, Paul G. Quincey National Physical Laboratory, Hampton Road, Teddington, Middlesex TW11 0LW, UK Received 11 October 2007; received in revised form 2 January 2008; accepted 7 January 2008
Abstract X-ray photoelectron spectroscopy (XPS) is a widely used surface analysis technique that in recent years has been used by a number of groups to analyse particulate matter collected onto filters. In this communication, XPS is compared to the standard method for determining the ratio of the elemental carbon to total carbon in all forms in the particulates using a PM10 quartz filter sample. The results obtained from the two methods are significantly different, suggesting that XPS gives a better indication of the chemistry of the surface of the particle, whereas the standard method is more relevant to the composition of the particles as a whole. Therefore, each technique has valid applications—XPS may be better for use in those toxicology studies where surface chemistry is important, whereas the standard method may be best for tracing the origin of particles through knowledge of the average particle composition. Crown Copyright r 2008 Published by Elsevier Ltd. All rights reserved. Keywords: X-ray photoelectron spectroscopy; Carbon analysis; Elemental carbon; Organic carbon; Particulate matter
There are many different methods and instruments available for determining aspects of the chemical composition of airborne particulate matter. One measurement that is of particular interest is the composition of carbonaceous particles. The carbon that makes up particulate matter is broadly grouped into three categories—organic carbon (OC) such as polycyclic aromatic hydrocarbons (PAHs), elemental carbon (EC) such as graphite, and carbonate carbon usually in the form of calcium carbonate, although this is less abundant in ambient air than the others. Variation in the contributions Corresponding author. Tel.: +44 20 8943 6405; fax: +44 20 8943 6458. E-mail address: [email protected] (R.J.J. Gilham).
from each of these components to the total amount of carbon varies depending on the sources present and the atmospheric conditions. As such, carbon speciation data can provide a useful contribution to source apportionment exercises, which in turn feed into regional and national air quality strategies. EC and OC are in practice defined operationally by the methods used to analyse filter samples, and certain methods have a de facto standard status. In this paper, we compare one such method to X-ray photoelectron spectroscopy (XPS) to determine whether the latter is a suitable method for this type of analysis. XPS is a powerful technique for determining the elemental content and hybridisation of a surface and has been widely used in surface analysis for
1352-2310/$ - see front matter Crown Copyright r 2008 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2008.01.007
ARTICLE IN PRESS R.J.J. Gilham et al. / Atmospheric Environment 42 (2008) 3888–3891
many years (Briggs, 1994). Recently, there have been reports of the use of the method in the general analysis of particulate matter. Desimoni et al. (1992) were the first to do this, and there are a significant number of publications of XPS analysis of particles in an environmental measurement context (Albers et al., 2000; Atzei and Rossi, 2004; Batonneau et al., 2004; Hutton and Williams, 2000; Kendall et al., 2001; Lazzeri et al., 2003; Paoletti et al., 2003, 2006; Pastuszka et al., 2003; Qi et al., 2006; Wawros et al., 2003; Zhu et al., 2001). XPS analyses the outer surface of particulates and enables significant information to be extracted concerning the source and behaviour of such particulates. As Hutton and Williams (2000) note, particles collected can be directly analysed by XPS without further sample preparation, as XPS is capable of analysing insulating samples. The surface composition of particles can be determined for species present down to 0.1 atomic percent. Major functional groups for carbon and oxygen can be identified as well as oxidation states for other species. These characteristics are important sources of information. Here, we test the effectiveness of XPS in a particularly narrow, but important, sense of measuring the EC and OC fractions of particulates on filters. Many of these XPS studies use PTFE as the filter media although some groups used stainless steel or silver. PTFE is a widely used filter type, however the use of a carbon-based filter might cause difficulties for any analysis method that measures the carbon present in the sample due to peak overlap with the substrate. PTFE filters are likely to be less prone to this as it should be possible to resolve, and hence remove the substrate signal. Quartz fibre filters are not subject to such problems and were used in the data presented in this communication. The main reason for using this filter type is that the standard OC/EC analysis method requires the use of this filter type due to the reasons discussed above. Moreover, this is the first demonstration of XPS analysis of quartz filter media of which we are aware. The reference value used here for the OC/EC composition of a particulate sample was the value given by the Sunset Laboratory Carbon Aerosol Analysis Lab Instrument. In this instrument, a 1.5 cm2 portion of the filter medium is put through a standard two-step procedure to drive off all the carbon present, which provides a quantitative measure of the carbon present in the OC and EC
3889
forms. In the first part of the analysis, the sample is heated in an inert helium atmosphere to over 800 1C causing any OC to be driven off or to be converted pyrolitically to EC. After rapid partial cooling, the second part of the analysis begins. A similar temperature ramp is employed, but the atmosphere now contains 2% oxygen. During this second period, all the remaining carbon, which consists of EC and any pyrolised carbon from the first stage, is driven from the filter. In both cases, the liberated carbon is passed through a methaniser and then detected using a Flame Ionisation Detector (FID). The FID is calibrated after each run with a known volume of a methane/helium gas mixture, and the system as a whole is regularly calibrated with a sample consisting of a known amount of sucrose on a clean quartz filter. Throughout the whole analysis procedure, a laser is used to monitor the blackness of the sample so as to allow a correction to be made to compensate for the pyrolysis of the OC. In this correction, the intensity of the laser light transmitted through the sample is monitored. As any OC is pyrolised in the first part of the analysis, the transmitted signal decreases. When the second stage of the analysis begins, this and the EC are removed from the filter resulting in the transmission increasing. Assuming that pyrolised OC and EC are indistinguishable using this transmission technique, all the pyrolised OC is deemed to have been removed when the transmission signal returns to the value recorded at the start of the whole analysis. This point is known as the split point, and any signal recorded by the FID before this point is deemed to be OC, and any signal afterwards deemed to be EC. The final results obtained can be expressed as the mass of carbon per unit filter area and the ratio of EC to total carbon (EC/TC). The error in the value of this ratio is determined by the repeatability of the optical correction, which will be primarily affected by sample-to-sample repeatability issues. When a second sample is taken from a single filter, our experience shows that the EC/TC ratio changes by o10% when comparing the two results. To compare the above technique to XPS, portions were taken from the same filter and analysed. The sample selected was collected at a central London kerbside location (Marylebone Road) for 24 h from midnight on 6 October 2006 using a Partisol 2025 sampler fitted with a PM10 head, with a total sample volume of 24 m3. For the whole-sample OC/EC technique, the reference
ARTICLE IN PRESS R.J.J. Gilham et al. / Atmospheric Environment 42 (2008) 3888–3891
measurement procedure was carried out. The XPS measurement was carried out using an analysis area of approximately 2 5 mm2 to minimise any effects caused by uneven filter coverage. In addition to the exposed filter, a clean filter was also measured, which showed negligible carbon coverage. The results from the standard OC/EC technique yielded an EC to TC ratio (EC/TC) of 0.69. The XPS measurement of the exposed filter (Fig. 1) shows a large carbon peak, but also a small signal from silicon, implying either that the surface of the filter was not completely covered or that the filter fibres had become slightly displaced during handling.
To obtain a similar value to the whole sample method for the EC/TC ratio using XPS, the peak due to carbon 1s at around 285 eV was compared to the peaks obtained from a graphite sample, and a silicon wafer covered in candle soot (Fig. 2), which consists mostly of EC. Peak fitting of the filter sample showed that three peaks at 284.52, 285.99 and 289.08 eV were needed to yield a good fit with the first the binding energy of EC. The latter two peaks arise from OC. The presence of carbonate carbon can be discounted as none was observed in the standard OC/EC technique. The small discrepancies in peak positions observed can be put down to sample charging caused by the insulating nature
25000
10000 Clean filter
Counts (clean filter)
20000
Exposed filter
O 1s 8000
C 1s
15000
6000
10000
4000 Si 2p
5000
Si 2s
2000
0 0
100
200
Counts (exposed filter)
3890
300 400 500 Binding energy (eV)
600
700
0 800
Fig. 1. XPS spectra of a clean (crosses) and exposed (circles) quartz filter showing the O, C and Si peaks. The slight displacement in the energy scale for each spectrum can be attributed to sample charging.
Normalised counts
1
Exposed filter
Soot
Graphite
0.75
0.5
0.25
0 280
285 290 Binding Energy (eV)
295
Fig. 2. Detail of the carbon 1 s XPS peak for the exposed filter (crosses), candle soot deposited on a silicon wafer (circles), and a graphite wafer (triangles). Peak intensities have been normalised to the peak maximum for the exposed filter sample.
ARTICLE IN PRESS R.J.J. Gilham et al. / Atmospheric Environment 42 (2008) 3888–3891
of quartz fibre substrate. Given these assumptions, the EC/TC ratio as determined by XPS was 0.37. Additional samples were measured on a different XPS instrument that used a different charging compensation method. It was found that the effective removal of charging effects was hampered due to the relative roughness of the sample surface causing difficulties in interpretation of the results. This is an important conclusion in itself because it shows that any future measurements of samples on quartz filters should take into consideration instrument-dependent effects. Despite these difficulties, satisfactory results were gained for one sample. Peak fitting using a similar method to the previous spectrum yielded peaks at 284.2, 285.3 and 288.3 eV, with an estimated EC/TC ratio of 0.43. This compared to a result of 0.60 by the whole sample technique. There are several interesting observations arising from these data. Firstly, the XPS spectrum displays signal arising from both the filter media and the deposited particles. This highlights the need to critically evaluate any XPS data from such samples for substrate interference, especially where the filter itself contains carbon. Secondly, the values for the EC/TC ratio from the two methods differ significantly. There are a number of possible reasons for this. One postulate is that the surface and bulk speciation of the particles are different, with a coreshell segregation of the carbon types present. It is reasonable that the OC will form the shell, meaning that there would be a natural bias towards surfacespecific techniques underestimating the amount of EC present, given that many of the particles present will have a radius much larger than the penetration depth of XPS. This is in agreement with the preliminary results presented here. Furthermore, OC adsorbed on the filter would further reduce an XPS measure for EC/TC. The observed difference between these two measurements also points towards a potential difficulty with data interpretation in a toxicological context. The applicability of data obtained by each technique will depend on the relative importance of the surface and bulk composition to the biological system under study. There are two useful conclusions that come from this experiment. The first is that filter media interference can be an issue in XPS measurements due to sample charging or the presence of carbon in the filter material. The second is that comparisons between EC/TC data obtained from XPS and from other methods for particulate matter samples
3891
should be treated with care since they measure different properties.
References Albers, P.W., Klein, H., Lox, E.S., Seibold, K., Prescher, G., Parker, S.F., 2000. INS-, SIMS- and XPS-investigations of diesel engine exhaust particles. Physical Chemistry Chemical Physics 2, 1051–1058. Atzei, D., Rossi, A., 2004. Quantitative surface analysis of urban airborne particles by X-ray photoelectron spectroscopy. Annali di Chimica 94, 123–133. Batonneau, Y., Bremard, C., Gengembre, L., Laureyns, J., Le Maguer, A., Le Niaguer, D., Perdrix, E., Sobanska, S., 2004. Speciation of PM10 sources of airborne nonferrous metals within the 3-km zone of lead/zinc smelters. Environmental Science and Technology 38, 5281–5289. Briggs, D., 1994. Practical Surface Analysis: Auger and Xray Photoelectron Spectroscopy: Auger and X-ray Photoelectron Spectroscopy vol. 1, 2nd ed. John Wiley & Sons. /http://www.amazon.co.uk/Practical-Surface-AnalysisPhotoelectron-Spectroscopy/dp/0471953407/ref=sr_1_2?ie= UTF8&s=gateway&qid=1201608895&sr=8-2S. Desimoni, E., Libertini, E., Dicroce, E., Petruzzelli, L., 1992. Characterization of environmental-samples by X-ray photo electron-spectroscopy. Annali di Chimica 82, 1–12. Hutton, B.M., Williams, D.E., 2000. Assessment of X-ray photoelectron spectroscopy for analysis of particulate pollutants in urban air. Analyst 125, 1703–1706. Kendall, M., Hutton, B.M., Tetley, T.D., Nieuwenhuijsen, M.J., Wigzell, E., Jones, F.H., 2001. Investigation of fine atmospheric particle surfaces and lung lining fluid interactions using XPS. Applied Surface Science 178, 27–36. Lazzeri, R., Clauser, G., Iacob, E., Lui, A., Tonidandel, G., Anderle, M., 2003. ToF-SIMS and XPS characterisation of urban aerosols for pollution studies. Applied Surface Science 203, 767–771. Paoletti, L., De Berardis, B., Arrizza, L., Passacantando, M., Inglessis, M., Mosca, M., 2003. Seasonal effects on the physico-chemical characteristics of PM2.1 in Rome: a study by SEM and XPS. Atmospheric Environment 37, 4869–4879. Paoletti, L., De Berardis, B., Arrizza, L., Granato, V., 2006. Influence of tobacco smoke on indoor PM10 particulate matter characteristics. Atmospheric Environment 40, 3269–3280. Pastuszka, J.S., Wawros, A., Talik, E., Paw, K.T.U., 2003. Optical and chemical characteristics of the atmospheric aerosol in four towns in southern Poland. Science of the Total Environment 309, 237–251. Qi, J.H., Feng, L.J., Li, X.G., Zhang, M.P., 2006. An X-ray photoelectron spectroscopy study of elements on the surface of aerosol particles. Journal of Aerosol Science 37, 218–227. Wawros, A., Talik, E., Pastuszka, J.S., 2003. Investigation of winter atmospheric aerosol particles in downtown Katowice using XPS and SEM. Microscopy and Microanalysis 9, 349–358. Zhu, Y.J., Olson, N., Beebe, T.P., 2001. Surface chemical characterization of 2.5-mu m particulates (PM2.5) from air pollution in salt lake city using TOF-SIMS, XPS, and FTIR. Environmental Science and Technology 35, 3113–3121.
Atmospheric Environment 42 (2008) 3888–3891 www.elsevier.com/locate/atmosenv
Short communication
On the applicability of XPS for quantitative total organic and elemental carbon analysis of airborne particulate matter Richard J.J. Gilham, Steve J. Spencer, David Butterfield, Martin P. Seah, Paul G. Quincey National Physical Laboratory, Hampton Road, Teddington, Middlesex TW11 0LW, UK Received 11 October 2007; received in revised form 2 January 2008; accepted 7 January 2008
Abstract X-ray photoelectron spectroscopy (XPS) is a widely used surface analysis technique that in recent years has been used by a number of groups to analyse particulate matter collected onto filters. In this communication, XPS is compared to the standard method for determining the ratio of the elemental carbon to total carbon in all forms in the particulates using a PM10 quartz filter sample. The results obtained from the two methods are significantly different, suggesting that XPS gives a better indication of the chemistry of the surface of the particle, whereas the standard method is more relevant to the composition of the particles as a whole. Therefore, each technique has valid applications—XPS may be better for use in those toxicology studies where surface chemistry is important, whereas the standard method may be best for tracing the origin of particles through knowledge of the average particle composition. Crown Copyright r 2008 Published by Elsevier Ltd. All rights reserved. Keywords: X-ray photoelectron spectroscopy; Carbon analysis; Elemental carbon; Organic carbon; Particulate matter
There are many different methods and instruments available for determining aspects of the chemical composition of airborne particulate matter. One measurement that is of particular interest is the composition of carbonaceous particles. The carbon that makes up particulate matter is broadly grouped into three categories—organic carbon (OC) such as polycyclic aromatic hydrocarbons (PAHs), elemental carbon (EC) such as graphite, and carbonate carbon usually in the form of calcium carbonate, although this is less abundant in ambient air than the others. Variation in the contributions Corresponding author. Tel.: +44 20 8943 6405; fax: +44 20 8943 6458. E-mail address: [email protected] (R.J.J. Gilham).
from each of these components to the total amount of carbon varies depending on the sources present and the atmospheric conditions. As such, carbon speciation data can provide a useful contribution to source apportionment exercises, which in turn feed into regional and national air quality strategies. EC and OC are in practice defined operationally by the methods used to analyse filter samples, and certain methods have a de facto standard status. In this paper, we compare one such method to X-ray photoelectron spectroscopy (XPS) to determine whether the latter is a suitable method for this type of analysis. XPS is a powerful technique for determining the elemental content and hybridisation of a surface and has been widely used in surface analysis for
1352-2310/$ - see front matter Crown Copyright r 2008 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2008.01.007
ARTICLE IN PRESS R.J.J. Gilham et al. / Atmospheric Environment 42 (2008) 3888–3891
many years (Briggs, 1994). Recently, there have been reports of the use of the method in the general analysis of particulate matter. Desimoni et al. (1992) were the first to do this, and there are a significant number of publications of XPS analysis of particles in an environmental measurement context (Albers et al., 2000; Atzei and Rossi, 2004; Batonneau et al., 2004; Hutton and Williams, 2000; Kendall et al., 2001; Lazzeri et al., 2003; Paoletti et al., 2003, 2006; Pastuszka et al., 2003; Qi et al., 2006; Wawros et al., 2003; Zhu et al., 2001). XPS analyses the outer surface of particulates and enables significant information to be extracted concerning the source and behaviour of such particulates. As Hutton and Williams (2000) note, particles collected can be directly analysed by XPS without further sample preparation, as XPS is capable of analysing insulating samples. The surface composition of particles can be determined for species present down to 0.1 atomic percent. Major functional groups for carbon and oxygen can be identified as well as oxidation states for other species. These characteristics are important sources of information. Here, we test the effectiveness of XPS in a particularly narrow, but important, sense of measuring the EC and OC fractions of particulates on filters. Many of these XPS studies use PTFE as the filter media although some groups used stainless steel or silver. PTFE is a widely used filter type, however the use of a carbon-based filter might cause difficulties for any analysis method that measures the carbon present in the sample due to peak overlap with the substrate. PTFE filters are likely to be less prone to this as it should be possible to resolve, and hence remove the substrate signal. Quartz fibre filters are not subject to such problems and were used in the data presented in this communication. The main reason for using this filter type is that the standard OC/EC analysis method requires the use of this filter type due to the reasons discussed above. Moreover, this is the first demonstration of XPS analysis of quartz filter media of which we are aware. The reference value used here for the OC/EC composition of a particulate sample was the value given by the Sunset Laboratory Carbon Aerosol Analysis Lab Instrument. In this instrument, a 1.5 cm2 portion of the filter medium is put through a standard two-step procedure to drive off all the carbon present, which provides a quantitative measure of the carbon present in the OC and EC
3889
forms. In the first part of the analysis, the sample is heated in an inert helium atmosphere to over 800 1C causing any OC to be driven off or to be converted pyrolitically to EC. After rapid partial cooling, the second part of the analysis begins. A similar temperature ramp is employed, but the atmosphere now contains 2% oxygen. During this second period, all the remaining carbon, which consists of EC and any pyrolised carbon from the first stage, is driven from the filter. In both cases, the liberated carbon is passed through a methaniser and then detected using a Flame Ionisation Detector (FID). The FID is calibrated after each run with a known volume of a methane/helium gas mixture, and the system as a whole is regularly calibrated with a sample consisting of a known amount of sucrose on a clean quartz filter. Throughout the whole analysis procedure, a laser is used to monitor the blackness of the sample so as to allow a correction to be made to compensate for the pyrolysis of the OC. In this correction, the intensity of the laser light transmitted through the sample is monitored. As any OC is pyrolised in the first part of the analysis, the transmitted signal decreases. When the second stage of the analysis begins, this and the EC are removed from the filter resulting in the transmission increasing. Assuming that pyrolised OC and EC are indistinguishable using this transmission technique, all the pyrolised OC is deemed to have been removed when the transmission signal returns to the value recorded at the start of the whole analysis. This point is known as the split point, and any signal recorded by the FID before this point is deemed to be OC, and any signal afterwards deemed to be EC. The final results obtained can be expressed as the mass of carbon per unit filter area and the ratio of EC to total carbon (EC/TC). The error in the value of this ratio is determined by the repeatability of the optical correction, which will be primarily affected by sample-to-sample repeatability issues. When a second sample is taken from a single filter, our experience shows that the EC/TC ratio changes by o10% when comparing the two results. To compare the above technique to XPS, portions were taken from the same filter and analysed. The sample selected was collected at a central London kerbside location (Marylebone Road) for 24 h from midnight on 6 October 2006 using a Partisol 2025 sampler fitted with a PM10 head, with a total sample volume of 24 m3. For the whole-sample OC/EC technique, the reference
ARTICLE IN PRESS R.J.J. Gilham et al. / Atmospheric Environment 42 (2008) 3888–3891
measurement procedure was carried out. The XPS measurement was carried out using an analysis area of approximately 2 5 mm2 to minimise any effects caused by uneven filter coverage. In addition to the exposed filter, a clean filter was also measured, which showed negligible carbon coverage. The results from the standard OC/EC technique yielded an EC to TC ratio (EC/TC) of 0.69. The XPS measurement of the exposed filter (Fig. 1) shows a large carbon peak, but also a small signal from silicon, implying either that the surface of the filter was not completely covered or that the filter fibres had become slightly displaced during handling.
To obtain a similar value to the whole sample method for the EC/TC ratio using XPS, the peak due to carbon 1s at around 285 eV was compared to the peaks obtained from a graphite sample, and a silicon wafer covered in candle soot (Fig. 2), which consists mostly of EC. Peak fitting of the filter sample showed that three peaks at 284.52, 285.99 and 289.08 eV were needed to yield a good fit with the first the binding energy of EC. The latter two peaks arise from OC. The presence of carbonate carbon can be discounted as none was observed in the standard OC/EC technique. The small discrepancies in peak positions observed can be put down to sample charging caused by the insulating nature
25000
10000 Clean filter
Counts (clean filter)
20000
Exposed filter
O 1s 8000
C 1s
15000
6000
10000
4000 Si 2p
5000
Si 2s
2000
0 0
100
200
Counts (exposed filter)
3890
300 400 500 Binding energy (eV)
600
700
0 800
Fig. 1. XPS spectra of a clean (crosses) and exposed (circles) quartz filter showing the O, C and Si peaks. The slight displacement in the energy scale for each spectrum can be attributed to sample charging.
Normalised counts
1
Exposed filter
Soot
Graphite
0.75
0.5
0.25
0 280
285 290 Binding Energy (eV)
295
Fig. 2. Detail of the carbon 1 s XPS peak for the exposed filter (crosses), candle soot deposited on a silicon wafer (circles), and a graphite wafer (triangles). Peak intensities have been normalised to the peak maximum for the exposed filter sample.
ARTICLE IN PRESS R.J.J. Gilham et al. / Atmospheric Environment 42 (2008) 3888–3891
of quartz fibre substrate. Given these assumptions, the EC/TC ratio as determined by XPS was 0.37. Additional samples were measured on a different XPS instrument that used a different charging compensation method. It was found that the effective removal of charging effects was hampered due to the relative roughness of the sample surface causing difficulties in interpretation of the results. This is an important conclusion in itself because it shows that any future measurements of samples on quartz filters should take into consideration instrument-dependent effects. Despite these difficulties, satisfactory results were gained for one sample. Peak fitting using a similar method to the previous spectrum yielded peaks at 284.2, 285.3 and 288.3 eV, with an estimated EC/TC ratio of 0.43. This compared to a result of 0.60 by the whole sample technique. There are several interesting observations arising from these data. Firstly, the XPS spectrum displays signal arising from both the filter media and the deposited particles. This highlights the need to critically evaluate any XPS data from such samples for substrate interference, especially where the filter itself contains carbon. Secondly, the values for the EC/TC ratio from the two methods differ significantly. There are a number of possible reasons for this. One postulate is that the surface and bulk speciation of the particles are different, with a coreshell segregation of the carbon types present. It is reasonable that the OC will form the shell, meaning that there would be a natural bias towards surfacespecific techniques underestimating the amount of EC present, given that many of the particles present will have a radius much larger than the penetration depth of XPS. This is in agreement with the preliminary results presented here. Furthermore, OC adsorbed on the filter would further reduce an XPS measure for EC/TC. The observed difference between these two measurements also points towards a potential difficulty with data interpretation in a toxicological context. The applicability of data obtained by each technique will depend on the relative importance of the surface and bulk composition to the biological system under study. There are two useful conclusions that come from this experiment. The first is that filter media interference can be an issue in XPS measurements due to sample charging or the presence of carbon in the filter material. The second is that comparisons between EC/TC data obtained from XPS and from other methods for particulate matter samples
3891
should be treated with care since they measure different properties.
References Albers, P.W., Klein, H., Lox, E.S., Seibold, K., Prescher, G., Parker, S.F., 2000. INS-, SIMS- and XPS-investigations of diesel engine exhaust particles. Physical Chemistry Chemical Physics 2, 1051–1058. Atzei, D., Rossi, A., 2004. Quantitative surface analysis of urban airborne particles by X-ray photoelectron spectroscopy. Annali di Chimica 94, 123–133. Batonneau, Y., Bremard, C., Gengembre, L., Laureyns, J., Le Maguer, A., Le Niaguer, D., Perdrix, E., Sobanska, S., 2004. Speciation of PM10 sources of airborne nonferrous metals within the 3-km zone of lead/zinc smelters. Environmental Science and Technology 38, 5281–5289. Briggs, D., 1994. Practical Surface Analysis: Auger and Xray Photoelectron Spectroscopy: Auger and X-ray Photoelectron Spectroscopy vol. 1, 2nd ed. John Wiley & Sons. /http://www.amazon.co.uk/Practical-Surface-AnalysisPhotoelectron-Spectroscopy/dp/0471953407/ref=sr_1_2?ie= UTF8&s=gateway&qid=1201608895&sr=8-2S. Desimoni, E., Libertini, E., Dicroce, E., Petruzzelli, L., 1992. Characterization of environmental-samples by X-ray photo electron-spectroscopy. Annali di Chimica 82, 1–12. Hutton, B.M., Williams, D.E., 2000. Assessment of X-ray photoelectron spectroscopy for analysis of particulate pollutants in urban air. Analyst 125, 1703–1706. Kendall, M., Hutton, B.M., Tetley, T.D., Nieuwenhuijsen, M.J., Wigzell, E., Jones, F.H., 2001. Investigation of fine atmospheric particle surfaces and lung lining fluid interactions using XPS. Applied Surface Science 178, 27–36. Lazzeri, R., Clauser, G., Iacob, E., Lui, A., Tonidandel, G., Anderle, M., 2003. ToF-SIMS and XPS characterisation of urban aerosols for pollution studies. Applied Surface Science 203, 767–771. Paoletti, L., De Berardis, B., Arrizza, L., Passacantando, M., Inglessis, M., Mosca, M., 2003. Seasonal effects on the physico-chemical characteristics of PM2.1 in Rome: a study by SEM and XPS. Atmospheric Environment 37, 4869–4879. Paoletti, L., De Berardis, B., Arrizza, L., Granato, V., 2006. Influence of tobacco smoke on indoor PM10 particulate matter characteristics. Atmospheric Environment 40, 3269–3280. Pastuszka, J.S., Wawros, A., Talik, E., Paw, K.T.U., 2003. Optical and chemical characteristics of the atmospheric aerosol in four towns in southern Poland. Science of the Total Environment 309, 237–251. Qi, J.H., Feng, L.J., Li, X.G., Zhang, M.P., 2006. An X-ray photoelectron spectroscopy study of elements on the surface of aerosol particles. Journal of Aerosol Science 37, 218–227. Wawros, A., Talik, E., Pastuszka, J.S., 2003. Investigation of winter atmospheric aerosol particles in downtown Katowice using XPS and SEM. Microscopy and Microanalysis 9, 349–358. Zhu, Y.J., Olson, N., Beebe, T.P., 2001. Surface chemical characterization of 2.5-mu m particulates (PM2.5) from air pollution in salt lake city using TOF-SIMS, XPS, and FTIR. Environmental Science and Technology 35, 3113–3121.