scholarly journals Toward a standardised thermal-optical protocol for measuring atmospheric organic and elemental carbon: the EUSAAR protocol

2009 ◽  
Vol 2 (5) ◽  
pp. 2321-2345 ◽  
Author(s):  
F. Cavalli ◽  
M. Viana ◽  
K. E. Yttri ◽  
J. Genberg ◽  
J.-P. Putaud
Keyword(s):  
Elemental Carbon ◽  
Thermal Evolution ◽  
Standard Procedure ◽  
Pyrolytic Carbon ◽  
Total Carbon ◽  
Carbonaceous Aerosol ◽  
Optical Analysis ◽  
Split Point ◽  
Aerosol Fraction ◽  
Eu Project

Abstract. Thermal-optical analysis is a conventional method for determining the carbonaceous aerosol fraction and for classifying it into organic carbon, OC, and elemental carbon, EC. Unfortunately, the different thermal evolution protocols in use can result in a wide elemental carbon-to-total carbon variation by up to a factor of five. In Europe, there is currently no standard procedure for determining the carbonaceous aerosol fraction which implies that data from different laboratories at various sites are of unknown accuracy and cannot be considered comparable. In the framework of the EU-project EUSAAR (European Supersites for Atmospheric Aerosol Research), a comprehensive study has been carried out to identify the causes of differences in the EC measured using different thermal evolution protocols; thereby the major positive and negative biases affecting thermal-optical analysis have been isolated and minimised to define an optimised protocol suitable for European aerosols. Our approach to improve the accuracy of the discrimination between OC and EC was essentially based on four goals. Firstly, charring corrections rely on faulty assumptions – e.g. pyrolytic carbon is considered to evolve completely before native EC throughout the analysis –, thus we have reduced pyrolysis to a minimum by favoring volatilisation of OC. Secondly, we have minimised the potential negative bias in EC determination due to early evolution of light absorbing carbon species at higher temperatures in the He-mode, including both native EC and combinations of native EC and pyrolytic carbon potentially with different specific cross section values. Thirdly, we have minimised the potential positive bias in EC determination resulting from the incomplete evolution of OC during the He-mode which then evolves during the He/O2-mode, potentially after the split point. Finally, we have minimised the uncertainty due to the position of the OC/EC split point on the FID response profile by introducing multiple desorption steps in the He/O2-mode. Based on different types of carbonaceous PM encountered across Europe, we have defined an optimised thermal evolution protocol, the EUSAAR_2 protocol, as follows: step 1 in He, 200°C for 120 s; step 2 in He 300°C for 150 s; step 3 in He 450°C for 180 s; step 4 in He 650°C for 180 s. For steps 1–4 in He/O2, the conditions are 500°C for 120 s, 550°C for 120 s, 700°C for 70 s, and 850°C for 80 s, respectively.

scholarly journals Toward a standardised thermal-optical protocol for measuring atmospheric organic and elemental carbon: the EUSAAR protocol

2010 ◽  
Vol 3 (1) ◽  
pp. 79-89 ◽  
Author(s):  
F. Cavalli ◽  
M. Viana ◽  
K. E. Yttri ◽  
J. Genberg ◽  
J.-P. Putaud
Keyword(s):  
Elemental Carbon ◽  
Thermal Evolution ◽  
Standard Procedure ◽  
Pyrolytic Carbon ◽  
Total Carbon ◽  
Carbonaceous Aerosol ◽  
Optical Analysis ◽  
Split Point ◽  
Aerosol Fraction ◽  
Eu Project

Abstract. Thermal-optical analysis is a conventional method for determining the carbonaceous aerosol fraction and for classifying it into organic carbon, OC, and elemental carbon, EC. Unfortunately, the different thermal evolution protocols in use can result in a wide elemental carbon-to-total carbon variation by up to a factor of five. In Europe, there is currently no standard procedure for determining the carbonaceous aerosol fraction which implies that data from different laboratories at various sites are of unknown accuracy and cannot be considered comparable. In the framework of the EU-project EUSAAR (European Supersites for Atmospheric Aerosol Research), a comprehensive study has been carried out to identify the causes of differences in the EC measured using different thermal evolution protocols; thereby the major positive and negative biases affecting thermal-optical analysis have been isolated and minimised to define an optimised protocol suitable for European aerosols. Our approach to improve the accuracy of the discrimination between OC and EC was essentially based on four goals. Firstly, charring corrections rely on faulty assumptions – e.g. pyrolytic carbon is considered to evolve completely before native EC throughout the analysis –, thus we have reduced pyrolysis to a minimum by favoring volatilisation of OC. Secondly, we have minimised the potential negative bias in EC determination due to early evolution of light absorbing carbon species at higher temperatures in the He-mode, including both native EC and combinations of native EC and pyrolytic carbon potentially with different specific attenuation cross section values. Thirdly, we have minimised the potential positive bias in EC determination resulting from the incomplete evolution of OC during the He-mode which then evolves during the He/O2-mode, potentially after the split point. Finally, we have minimised the uncertainty due to the position of the OC/EC split point on the FID response profile by introducing multiple desorption steps in the He/O2-mode. Based on different types of carbonaceous PM encountered across Europe, we have defined an optimised thermal evolution protocol, the EUSAAR_2 protocol, as follows: step 1 in He, 200 °C for 120 s; step 2 in He 300 °C for 150 s; step 3 in He 450 °C for 180 s; step 4 in He 650 °C for 180 s. For steps 1–4 in He/O2, the conditions are 500 °C for 120 s, 550 °C for 120 s, 700 ° C for 70 s, and 850 °C for 80 s, respectively.

scholarly journals The influence of temperature calibration on the OC-EC results from a dual optics thermal carbon analyzer

2014 ◽  
Vol 7 (4) ◽  
pp. 3321-3348 ◽  
Author(s):  
J. Pavlovic ◽  
J. S. Kinsey ◽  
M. D. Hays
Keyword(s):  
Elemental Carbon ◽  
Calibration Procedure ◽  
Carbonaceous Aerosol ◽  
Temperature Calibration ◽  
Wide Spread ◽  
Optical Analysis ◽  
Point Selection ◽  
Sample Composition ◽  
Improve Accuracy ◽  
Split Point

Abstract. Thermal-optical analysis (TOA) is a widely used technique that fractionates carbonaceous aerosol particles into organic and elemental carbon (OC and EC), or carbonate. Thermal sub-fractions of evolved OC and EC are also used for source identification and apportionment; thus, oven temperature accuracy during TOA analysis is essential. Evidence now indicates that the "actual" sample (filter) temperature and the temperature measured by the built-in oven thermocouple (or set-point temperature) can differ by as much as 50 °C. This difference can affect the OC-EC split point selection and consequently the OC and EC fraction and sub-fraction concentrations being reported, depending on the sample composition and in-use TOA method and instrument. The present study systematically investigates the influence of an oven temperature calibration procedure for TOA. A dual-optical carbon analyzer that simultaneously measures transmission and reflectance (TOT and TOR) is used, functioning under the conditions of both the NIOSH 5040 and IMPROVE protocols. Application of the oven calibration procedure to our dual optics instrument significantly changed NIOSH 5040 carbon fractions (OC and EC) and the IMPROVE OC fraction. In addition, the well-known OC-EC split difference between NIOSH and IMPROVE methods is even further perturbed following the instrument calibration. Further study is needed to determine if the wide-spread application of this oven temperature calibration procedure will indeed improve accuracy and our ability to compare among carbonaceous aerosol studies that use TOA.

scholarly journals Better constraints on sources of carbonaceous aerosols using a combined <sup>14</sup>C – macro tracer analysis in a European rural background site

2011 ◽  
Vol 11 (12) ◽  
pp. 5685-5700 ◽  
Author(s):  
S. Gilardoni ◽  
E. Vignati ◽  
F. Cavalli ◽  
J. P. Putaud ◽  
B. R. Larsen ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Biomass Burning ◽  
Elemental Carbon ◽  
Total Carbon ◽  
Carbonaceous Aerosol ◽  
Back Trajectory ◽  
Po Valley ◽  
Background Site ◽  
Potential Source ◽  
Source Contributions

Abstract. The source contributions to carbonaceous PM2.5 aerosol were investigated at a European background site at the edge of the Po Valley, in Northern Italy, during the period January–December 2007. Carbonaceous aerosol was described as the sum of 8 source components: primary (1) and secondary (2) biomass burning organic carbon, biomass burning elemental carbon (3), primary (4) and secondary (5) fossil organic carbon, fossil fuel burning elemental carbon (6), primary (7) and secondary (8) biogenic organic carbon. The mass concentration of each component was quantified using a set of macro tracers (organic carbon OC, elemental carbon EC, and levoglucosan), micro tracers (arabitol and mannitol), and 14C measurements. This was the first time that 14C measurements covered a full annual cycle with daily resolution. This set of 6 tracers, together with assumed uncertainty ranges of the ratios of OC-to-EC, and the reference fraction of modern carbon in the 8 source categories, provides strong constraints to the source contributions to carbonaceous aerosol. The uncertainty of contributions was assessed with a Quasi-Monte Carlo (QMC) method accounting for the variability of OC and EC emission factors, the uncertainty of reference fractions of modern carbon, and the measurement uncertainty. During winter, biomass burning composed 64 % (±15 %) of the total carbon (TC) concentration, while in summer secondary biogenic OC accounted for 50 % (±16 %) of TC. The contribution of primary biogenic aerosol particles was negligible during the entire year. Moreover, aerosol associated with fossil sources represented 27 % (±16 %) and 41 % (±26 %) of TC in winter and summer, respectively. The contribution of secondary organic aerosol (SOA) to the organic mass (OM) was significant during the entire year. SOA accounted for 30 % (±16 %) and 85 % (±12 %) of OM during winter and summer, respectively. While the summer SOA was dominated by biogenic sources, winter SOA was mainly due to biomass burning and fossil sources. This indicates that the oxidation of semi-volatile and intermediate volatility organic compounds co-emitted with primary organics is a significant source of SOA, as suggested by recent model results and Aerosol Mass Spectrometer measurements. Comparison with previous global model simulations, indicates a strong underestimate of wintertime primary aerosol emissions in this region. The comparison of source apportionment results in different urban and rural areas showed that the sampling site was mainly affected by local aerosol sources during winter and regional air masses from the nearby Po Valley in summer. This observation was further confirmed by back-trajectory analysis applying the Potential Source Contribution Function method to identify potential source regions.

scholarly journals Characterization and source apportionment of atmospheric organic and elemental carbon during fall and winter of 2003 in Xi'an, China

2005 ◽  
Vol 5 (11) ◽  
pp. 3127-3137 ◽  
Author(s):  
J. J. Cao ◽  
F. Wu ◽  
J. C. Chow ◽  
S. C. Lee ◽  
Y. Li ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Coal Combustion ◽  
Elemental Carbon ◽  
Gasoline Engine ◽  
Motor Vehicle ◽  
Total Carbon ◽  
Carbonaceous Aerosol ◽  
Shaanxi Province ◽  
Engine Exhaust ◽  
Residential Coal

Abstract. Continuous measurements of atmospheric organic and elemental carbon (OC and EC) were taken during the high-pollution fall and winter seasons at Xi'an, Shaanxi Province, China from September 2003 through February 2004. Battery-powered mini-volume samplers collected PM2.5 samples daily and PM10 samples every third day. Samples were also obtained from the plumes of residential coal combustion, motor-vehicle exhaust, and biomass burning sources. These samples were analyzed for OC/EC by thermal/optical reflectance (TOR) following the Interagency Monitoring of Protected Visual Environments (IMPROVE) protocol. OC and EC levels at Xi'an are higher than most urban cities in Asia. Average PM2.5 OC concentrations in fall and winter were 34.1±18.0 μg m−3 and 61.9±;33.2 μg m−3, respectively; while EC concentrations were 11.3±6.9 μg m−3 and 12.3±5.3 μg m−3, respectively. Most of the OC and EC were in the PM2.5 fraction. OC was strongly correlated (R>0.95) with EC in the autumn and moderately correlated (R=0.81) with EC during winter. Carbonaceous aerosol (OC×1.6+EC) accounted for 48.8%±10.1% of the PM2.5 mass during fall and 45.9±7.5% during winter. The average OC/EC ratio was 3.3 in fall and 5.1 in winter, with individual OC/EC ratios nearly always exceeding 2.0. The higher wintertime OC/EC corresponded to increased residential coal combustion for heating. Total carbon (TC) was associated with source contributions using absolute principal component analysis (APCA) with eight thermally-derived carbon fractions. During fall, 73% of TC was attributed to gasoline engine exhaust, 23% to diesel exhaust, and 4% to biomass burning. During winter, 44% of TC was attributed to gasoline engine exhaust, 44% to coal burning, 9% to biomass burning, and 3% to diesel engine exhaust.

scholarly journals Improved measurement of carbonaceous aerosol: evaluation of the sampling artifacts and inter-comparison of the thermal-optical analysis methods

2010 ◽  
Vol 10 (17) ◽  
pp. 8533-8548 ◽  
Author(s):  
Y. Cheng ◽  
K. B. He ◽  
F. K. Duan ◽  
M. Zheng ◽  
Y. L. Ma ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Elemental Carbon ◽  
Correction Method ◽  
Optical Methods ◽  
Carbonaceous Aerosol ◽  
Series Method ◽  
Optical Analysis ◽  
Quartz Filter ◽  
Sampling Artifacts ◽  
In Series

Abstract. The sampling artifacts (both positive and negative) and the influence of thermal-optical methods (both charring correction method and the peak inert mode temperature) on the split of organic carbon (OC) and elemental carbon (EC) were evaluated in Beijing. The positive sampling artifact constituted 10% and 23% of OC concentration determined by the bare quartz filter during winter and summer, respectively. For summer samples, the adsorbed gaseous organics were found to continuously evolve off the filter during the whole inert mode when analyzed by the IMPROVE-A temperature protocol. This may be due to the oxidation of the adsorbed organics during sampling (reaction artifact) which would increase their thermal stability. The backup quartz approach was evaluated by a denuder-based method for assessing the positive artifact. The quartz-quartz (QBQ) in series method was demonstrated to be reliable, since all of the OC collected by QBQ was from originally gaseous organics. Negative artifact that could be adsorbed by quartz filter was negligible. When the activated carbon impregnated glass fiber (CIG) filter was used as the denuded backup filter, the denuder efficiency for removing gaseous organics that could be adsorbed by the CIG filter was only about 30%. EC values were found to differ by a factor of about two depending on the charring correction method. Influence of the peak inert mode temperature was evaluated based on the summer samples. The EC value was found to continuously decrease with the peak inert mode temperature. Premature evolution of light absorbing carbon began when the peak inert mode temperature was increased from 580 to 650 °C; when further increased to 800 °C, the OC and EC split frequently occurred in the He mode, and the last OC peak was characterized by the overlapping of two separate peaks. The discrepancy between EC values defined by different temperature protocols was larger for Beijing carbonaceous aerosol compared with North America and Europe, perhaps due to the higher concentration of brown carbon in Beijing aerosol.

scholarly journals Source apportionment of carbonaceous aerosol in southern Sweden

2011 ◽  
Vol 11 (22) ◽  
pp. 11387-11400 ◽  
Author(s):  
J. Genberg ◽  
M. Hyder ◽  
K. Stenström ◽  
R. Bergström ◽  
D. Simpson ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Source Apportionment ◽  
Fossil Fuels ◽  
Elemental Carbon ◽  
Transport Model ◽  
Total Carbon ◽  
Carbonaceous Aerosol ◽  
Anthropogenic Sources ◽  
Biomass Combustion ◽  
Southern Sweden

Abstract. A one-year study was performed at the Vavihill background station in southern Sweden to estimate the anthropogenic contribution to the carbonaceous aerosol. Weekly samples of the particulate matter PM10 were collected on quartz filters, and the amounts of organic carbon, elemental carbon, radiocarbon (14C) and levoglucosan were measured. This approach enabled source apportionment of the total carbon in the PM10 fraction using the concentration ratios of the sources. The sources considered in this study were emissions from the combustion of fossil fuels and biomass, as well as biogenic sources. During the summer, the carbonaceous aerosol mass was dominated by compounds of biogenic origin (80%), which are associated with biogenic primary and secondary organic aerosols. During the winter months, biomass combustion (32%) and fossil fuel combustion (28%) were the main contributors to the carbonaceous aerosol. Elemental carbon concentrations in winter were about twice as large as during summer, and can be attributed to biomass combustion, probably from domestic wood burning. The contribution of fossil fuels to elemental carbon was stable throughout the year, although the fossil contribution to organic carbon increased during the winter. Thus, the organic aerosol originated mainly from natural sources during the summer and from anthropogenic sources during the winter. The result of this source apportionment was compared with results from the EMEP MSC-W chemical transport model. The model and measurements were generally consistent for total atmospheric organic carbon, however, the contribution of the sources varied substantially. E.g. the biomass burning contributions of OC were underestimated by the model by a factor of 2.2 compared to the measurements.

scholarly journals Characterization and source apportionment of atmospheric organic and elemental carbon during fall and winter of 2003 in Xi'an, China

2005 ◽  
Vol 5 (3) ◽  
pp. 3561-3593 ◽  
Author(s):  
J. J. Cao ◽  
J. C. Chow ◽  
S. C. Lee ◽  
Y. Li ◽  
S. W. Chen ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Diesel Exhaust ◽  
Coal Combustion ◽  
Elemental Carbon ◽  
Motor Vehicle ◽  
Principal Component ◽  
Total Carbon ◽  
Carbonaceous Aerosol ◽  
Vehicle Exhaust ◽  
Carbon Fraction

Abstract. Continuous observation of atmospheric organic and elemental carbon (OC, EC) were conducted at Xi'an during high pollution seasons from September 2003 to February 2004. PM2.5 samples were collected on pre-fired quartz-fiber filters with battery-powered mini-volume samplers every day and PM10 samples were collected every third days. Three types of source samples (i.e., coal-combustion, motor vehicle exhaust, and biomass burning) were also collected during ambient sampling period. Ambient and source samples were analyzed for OC and EC by thermal/optical reflectance (TOR) following the Interagency Monitoring of Protected Visual Environments (IMPROVE) protocol. The average PM2.5 OC concentrations in fall and winter were 34.1±18.0 µg m-3 and 61.9±33.2 µg m-3, respectively, while EC were 11.3±6.9 µg m-3 and 12.3±5.3 µg m-3, respectively. Most of OC and EC were associated with fine particle (PM2.5) mode. The OC and EC levels at Xi'an are higher than most urban cities in Asia. The OC and EC in fall were found to be strongly correlated (R2>0.9), with moderate correlation in winter (R2=0.66). The carbonaceous aerosol accounted for 48.8±10.1% of the PM2.5 during fall and 45.9±7.5% during winter. Average OC/EC ratio was 3.3 in fall and 5.1 in winter with individual OC/EC ratios constantly exceeding 2.0. Elevated OC/EC ratios were found during heating seasons with increased coal combustion. The contribution of secondary organic carbon was not significant during winter. The time series of OC and EC showed periodic variability. Traffic contributes 5 and 7 day peaks in the spectrum, precipitation appears as a 10 day periodicity and biomass burning can be identified as a 24 day periodicity. Total carbon (TC) was apportioned by absolute principal component analysis (APCA) using the 8 carbon fraction data (OC1, OC2, OC3, OC4, EC1, EC2, EC3, and OP [a pyrolyzed carbon fraction]). TC attributes 73% to gasoline exhaust, 23% to diesel exhaust, and 4% to biomass burning during fall. However, TC attributes 44% each to gasoline exhaust and coal burning, 9% to biomass burning, and 3% to diesel exhaust during winter.

scholarly journals Source apportionment of carbonaceous aerosol in southern Sweden

2011 ◽  
Vol 11 (5) ◽  
pp. 13575-13616 ◽  
Author(s):  
J. Genberg ◽  
M. Hyder ◽  
K. Stenström ◽  
R. Bergström ◽  
D. Simpson ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Source Apportionment ◽  
Fossil Fuels ◽  
Elemental Carbon ◽  
Total Carbon ◽  
Carbonaceous Aerosol ◽  
Anthropogenic Sources ◽  
Biomass Combustion ◽  
Southern Sweden ◽  
One Year

Abstract. A one-year study was performed at the Vavihill background station in southern Sweden to estimate the anthropogenic contribution to the carbonaceous aerosol. Weekly samples of the particulate matter PM10 were collected on quartz filters, and the amounts of organic carbon, elemental carbon, radiocarbon (14C) and levoglucosan were measured. This approach enabled source apportionment of the total carbon in the PM10 fraction using the concentration ratios of the sources. The sources considered in this study were emissions from the combustion of fossil fuels and biomass, as well as biogenic sources. During the summer, the carbonaceous aerosol mass was dominated by compounds of biogenic origin (82 %), which are associated with biogenic primary and secondary organic aerosols. During the winter months, biomass combustion (38 %) and fossil fuel combustion (33 %) were the main contributors to the carbonaceous aerosol. Elemental carbon concentrations in winter were about twice as large as during summer, and can be attributed to biomass combustion, probably from domestic wood burning. The contribution of fossil fuels to elemental carbon was stable throughout the year, although the fossil contribution to organic carbon increased during the winter. Thus, the organic aerosol originated mainly from natural sources during the summer and from anthropogenic sources during the winter. The result of this source apportionment was compared with results from the EMEP model. The model and measurements were generally consistent for total atmospheric organic carbon, however, the contribution of the sources varied substantially. E.g. the biomass burning contributions of OC were underestimated by the model by a factor of 8.2 compared to the measurements.

13C signatures of aerosol organic and elemental carbon from major combustion sources in China and worldwide

2021 ◽  
Author(s):  
Peng Yao ◽  
Haiyan Ni ◽  
Norbertas Kairys ◽  
Lu Yang ◽  
Ru-Jin Huang ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Source Apportionment ◽  
Elemental Carbon ◽  
Raw Materials ◽  
Total Carbon ◽  
Carbonaceous Aerosols ◽  
Thermal Methods ◽  
Dual Isotope ◽  
Atmospheric Processing ◽  
Split Point

&lt;p&gt;Isotopic source apportionment is commonly used to gain insight into sources and atmospheric processing of carbonaceous aerosols. Since elemental carbon (EC) is chemically stable, it is possible to apportion the main sources of EC (coal/biomass burning and traffic emissions) using a dual &lt;sup&gt;14&lt;/sup&gt;C-&lt;sup&gt;13&lt;/sup&gt;C isotope approach. However, dual-isotope source apportionment crucially relies on accurate knowledge of the &lt;sup&gt;13&lt;/sup&gt;C source signatures, which are seldom measured directly for EC. In this work, we present extensive measurements of organic carbon (OC) and EC &lt;sup&gt;13&lt;/sup&gt;C signatures for relevant sources in China. The EC &lt;sup&gt;13&lt;/sup&gt;C source signatures are provided first time using the optical split point in a thermal-optical analyzer to isolate EC, which can greatly reduce the influence of pyrolyzed organic carbon (pOC). A series of sensitivity studies (pOC/EC separation) were conducted to investigate the reliability of our method and its relation to other EC isolation methods. Meanwhile, we summarized and compared the literature &lt;sup&gt;13&lt;/sup&gt;C signatures in detail of raw source materials, total carbon (TC) and EC using a variety of thermal methods. Finally, we recommend composite EC &lt;sup&gt;13&lt;/sup&gt;C source signatures with uncertainties and detailed application conditions. There are two points worth noting. First, the traffic &lt;sup&gt;13&lt;/sup&gt;C signatures of raw materials and EC are separated into three groups according to geographical distribution. Second, the EC &lt;sup&gt;13&lt;/sup&gt;C signature of C4 plant combustion can be influenced greatly if pOC and EC are not well separated, so the thermal-optical method is necessary. Using these EC &lt;sup&gt;13&lt;/sup&gt;C source signatures in an exemplary dual-isotope source apportionment study shows improvement in precision. In addition, some interesting distinct and repeatable patterns were discovered in &lt;sup&gt;13&lt;/sup&gt;C source signatures of semi-volatile, low-volatile, and non-volatile primary OC fractions.&lt;/p&gt;

scholarly journals Improved measurement of carbonaceous aerosol in Beijing, China: intercomparison of sampling and thermal-optical analysis methods

2010 ◽  
Vol 10 (6) ◽  
pp. 15671-15712
Author(s):  
Y. Cheng ◽  
K. B. He ◽  
F. K. Duan ◽  
M. Zheng ◽  
Y. L. Ma ◽  
...  
Keyword(s):  
Elemental Carbon ◽  
Correction Method ◽  
Optical Methods ◽  
Carbonaceous Aerosol ◽  
Series Method ◽  
Optical Analysis ◽  
Quartz Filter ◽  
Sampling Artifacts ◽  
In Series ◽  
Beijing China

Abstract. The sampling artifacts (both positive and negative) and the influence of thermal-optical methods (both charring correction method and the peak inert mode temperature) on the split of organic carbon (OC) and elemental carbon (EC) were evaluated in Beijing. The positive sampling artifact constituted 10% and 23% of OC concentration determined by the bare quartz filter during winter and summer, respectively. For summer samples, the adsorbed gaseous organics were found to continuously evolve off the filter during the whole inert mode when analyzed by the IMPROVE-A temperature protocol. This may be due to the oxidation of the adsorbed organics during sampling (reaction artifact) which would increase their thermal stability. The backup quartz approach was evaluated by a denuder-based method for assessing the positive artifact. The quartz-quartz (QBQ) in series method was demonstrated to be reliable, since all of the OC collected by QBQ was from originally gaseous organics. Negative artifact that could be adsorbed by quartz filter was negligible. When the activated carbon impregnated glass fiber (CIG) filter was used as the denuded backup filter, the denuder efficiency for removing gaseous organics that could be adsorbed by the CIG filter was only about 30%. EC values were found to differ by a factor of about two depending on the charring correction method. Influence of the peak inert mode temperature was evaluated based on the summer samples. The EC value was found to continuously decrease with the peak inert mode temperature. Premature evolution of light absorbing carbon began when the peak inert mode temperature was increased from 580 to 650 °C; when further increased to 800 °C, the OC and EC split frequently occurred in the He mode, and the last OC peak was characterized by the overlapping of two separate peaks. The discrepancy between EC values defined by different temperature protocols was larger for Beijing carbonaceous aerosol compared with North America and Europe, perhaps due to the higher concentration of brown carbon in Beijing aerosol.

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