[Show abstract][Hide abstract] ABSTRACT: Carbon (C), hydrogen (H), nitrogen (N), sulfur (S) and oxygen (O) constitute the majority of the mass of ambient aerosols. Thus the CHNS analysis of aerosols is of great importance for aerosol mass closure and source apportionment, as well as for advancing the knowledge of aerosol transport and transformation in the environment. A thermal elemental analyzer was previously developed by our group to measure the CHNS composition of aerosols collected on quartz fiber filters. The analyzer was modified from a DRI model 2001 thermal/optical carbon analyzer and the measurement was based on a revised Pregl-Dumas method. However, several limitations were found with the previous analyzer, such as poor reproducibility, low R2 of the calibration curves, and limited choice for temperature programs.
This work describes our recent modifications of the analyzer. First, the previous two-oxidizer/reactor design (MnO2 followed by CuO) was replaced by a single oxidizer/reactor (MnO2). This revised design reduced the loss of CO2, H2O, NOx and SO2 along transfer lines, thus improving the reproducibility of analysis. Second, a non-dispersive infrared (NDIR) CO2 analyzer was installed in parallel to the mass selective detector (for CHNS detection). This allowed the CHNS analysis to follow “the IMPROVE_A” or any other protocols for regular carbon analysis. Solid standards, replacing filter standards, were used to build calibration curves. An R2 > 0.99 was obtained for C, H and S; while the N calibration curve exhibited a slightly lower R2 (~0.95) due to the co-existence of multiple oxidation products. With the derived calibration curves, over 30 source and ambient samples were tested. The results were in good agreement with those determined by a regular carbon analyzer (for C), an ion chromatograph (for SO4=, NO2- and NO3-) and a colorimeter (for NH4+).
[Show abstract][Hide abstract] ABSTRACT: Quantifying elemental carbon (EC) content in geological samples is challenging due to interferences of crustal, salt, and organic material. Thermal/optical analysis, combined with acid pretreatment, represents a feasible approach. However, the consistency of various thermal/optical analysis protocols for this type of samples has never been examined. In this study, urban street dust and soil samples from Baoji, China were pretreated with acids and analyzed with four thermal/optical protocols to investigate how analytical conditions and optical correction affect EC measurement. The EC values measured with reflectance correction (ECR) were found always higher and less sensitive to temperature program than the EC values measured with transmittance correction (ECT). A high-temperature method with extended heating times (STN120) showed the highest ECT/ECR ratio (0.86) while a low-temperature protocol (IMPROVE-550), with heating time adjusted for sample loading, showed the lowest (0.53). STN ECT was higher than IMPROVE ECT, in contrast to results from aerosol samples. A higher peak inert-mode temperature and extended heating times can elevate ECT/ECR ratios for pretreated geological samples by promoting pyrolyzed organic carbon (PyOC) removal over EC under trace levels of oxygen. Considering that PyOC within filter increases ECR while decreases ECT from the actual EC levels, simultaneous ECR and ECT measurements would constrain the range of EC loading and provide information on method performance. Further testing with standard reference materials of common environmental matrices supports the findings. Char and soot fractions of EC can be further separated using the IMPROVE protocol. The char/soot ratio was lower in street dusts (2.2 on average) than in soils (5.2 on average), most likely reflecting motor vehicle emissions. The soot concentrations agreed with EC from CTO-375, a pure thermal method.
PLoS ONE 01/2013; 8(12):e83462. · 3.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Measurement of carbon dioxide (CO 2) gas evolved from acidification is a method to quantify carbonate carbon (CC) in aerosols collected on quartz fiber-filters. This paper describes the installation of an add-on device in a DRI Model 2001 Thermal Optical reflectance (TOR)/Thermal Optical Transmittance (TOT) Carbon Analyzer (M-TOCA) to facilitate a direct CC measurement. In each run, a maximum of 20 filter punches (each of 0.5 cm 2) were acidified with 1 mL of 20% v/v phosphoric (V) acid in a vial under a 100% helium gas environment. The CO 2 evolved was reduced to methane (CH 4) and detected by a flame ionization detector (FID). The optimum reaction kinetics were obtained under an operational temperature of 40 C and ultrasonic agitation. Method precisions were AE3.5% on average for carbonate standards ranging from 3.0 to 60.0 mg and AE3.8% on average for ambient samples in masses ranging from 0.30 to 56.0 mg respectively. Method accuracy was on average 91.9%, ranging from 81.4 to 102.1%. Minimum detection limit (MDL) of the M-TOCA method was 0.048 mg cm À2 , corresponding to an ambient concentration of 0.098 mg m À3 for a sampled volume of air of 7.2 m 3 . The MDL is >22 times lower than the value obtained using the novel method with a regular TOCA. Comparison studies on standards and ambient samples have demonstrated that the two methods do not yield systematic differences in concentrations of the carbonate. The lower MDL value provided by the M-TOCA allows a simple, precise and accurate measurement for ambient samples having a low CC concentration.
[Show abstract][Hide abstract] ABSTRACT: Accurate, precise, and valid organic and elemental carbon (OC and EC, respectively) measurements require more effort than the routine analysis of ambient aerosol and source samples. This paper documents the quality assurance (QA) and quality control (QC) procedures that should be implemented to ensure consistency of OC and EC measurements. Prior to field sampling, the appropriate filter substrate must be selected and tested for sampling effectiveness. Unexposed filters are pre-fired to remove contaminants and acceptance tested. After sampling, filters must be stored in the laboratory in clean, labeled containers under refrigeration (<4 °C) to minimize loss of semi-volatile OC. QA activities include participation in laboratory accreditation programs, external system audits, and interlaboratory comparisons. For thermal/optical carbon analyses, periodic QC tests include calibration of the flame ionization detector with different types of carbon standards, thermogram inspection, replicate analyses, quantification of trace oxygen concentrations (<100 ppmv) in the helium atmosphere, and calibration of the sample temperature sensor. These established QA/QC procedures are applicable to aerosol sampling and analysis for carbon and other chemical components.
Analytical and Bioanalytical Chemistry 05/2011; 401(10):3141-52. · 3.66 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Daily concentrations of carbonate carbon (CC) in PM2.5 collected in semi-arid area in Northeast China
(Tongyu) were quantified by acidification that measures carbon dioxide (CO2) gas evolved using DRI
Model 2001 Thermal Optical reflectance (TOR) Carbon Analyzer. The concentrations of CC during Asian
dust storm (DS) and non-dust storm (NDS) periods during 14 April to 21 June, 2006 were determined and
the transport pathways and possible sources for the CO3 2 � aerosols were identified. Concentrations of CC
in PM2.5 collected from 14 April to 23 June, 2006 in Tongyu are ranged from 0.1 to 7.5 mgCm�3 with an
average of 1.3 mgCm�3. The average CC concentration during DS events was 2.6 � 1.7 mgm�3, which was
almost 4 times the daily average concentration of 0.6 � 0.5 mgm�3 during non-dust storm (NDS) period.
Carbonate carbon accounted for 10% and 4% of total carbon in Tongyu during DS and NDS period,
respectively. Carbonate concentrations were also derived by calculating the difference between cations
and anions (ionic balance method). And good correlation is observed for the carbonate measured to the
values for carbonate calculated from the ionic balance difference (R2 ¼ 0.90). Higher correlations were
observed between Ca with selected water-soluble ions (sulfate, nitrate or chloride) and elemental carbon
in DS than in NDS periods. This is consistent with previous studies that more calcium salts (sulfate,
nitrate or chloride) were formed during atmospheric transport during DS period. During the DS in spring
2006, three groups (A to C) of air mass trajectories were identified that passed over Tongyu. In general,
when the air mass came from northwest, and south or southwest to Tongyu, high concentrations of
carbonate were observed.
[Show abstract][Hide abstract] ABSTRACT: Vehicle emissions of volatile organic compounds
(VOCs) were determined at the Shing Mun Tunnel, Hong
Kong in summer and winter of 2003. One hundred and ten
VOCs were quantified in this study. The average concentration
of the total measured VOCs at the inlet and outlet of
the tunnel were 81 250 pptv and 117 850 pptv, respectively.
Among the 110 compounds, ethene, ethyne and toluene were
the most abundant species in the tunnel. The total measured
VOC emission factors ranged from 67 mg veh−1 km−1 to
148 mg veh−1 km−1, with an average of 115 mg veh−1 km−1.
The five most abundant VOCs observed in the tunnel were,
in decreasing order, ethene, toluene, n-butane, propane and
i-pentane. These five most abundant species contributed over
38% of the total measured VOCs emitted. The high propane
and n-butane emissions were found to be associated with liquefied
petroleum gas (LPG)-fueled taxis. Fair correlations
were observed between marker species (ethene, i-pentane,
n-nonane, and benzene, toluene, ethylbenzene and xylenes –
BTEX) with fractions of gasoline-fueled or diesel-fueled vehicles.
Moreover, ethene, ethyne, and propene are the key
species that were abundant in the tunnel but not in gasoline
vapors or LPG. The ozone formation potential from the
VOCs in Hong Kong was evaluated by the maximum increment
reactivity (MIR). It was found to be 568 mg of ozone per vehicle per kilometer traveled. Among them, ethene,
propene and toluene contribute most to the ozone-formation
Atmospheric Chemistry and Physics 10/2009; 9:7491–7504. · 4.88 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The positive artifacts in particulate organic carbon measurements in a roadside environment were characterized using two filters in tandem. The experiments were performed for PM(1.0), PM(2.5), and PM(10) at 24-h interval using a URG sampler, followed by organic carbon (OC)/elemental carbon (EC) analysis by the Interagency Monitoring of Protected Visual Environments thermal/optical reflectance carbon analysis protocol. The OC concentrations, derived from the quartz filter behind a front quartz filter, were quite similar for PM(1.0), PM(2.5), and PM(10), ranging from 0.6 to 2.7 microg C m(-3) for PM(1.0), from 0.7 to 2.7 microg C m(-3) for PM(2.5), and from 1.1 to 2.7 microg C m(-3) for PM(10). They were respectively approximately 2.8%, approximately 2.4%, and approximately 1.6% of the particulate mass. The most abundant species on the backup quartz filters were OC2 (250 degrees C) and OC3 (450 degrees C), accounting for approximately 80% of measured organic carbon on the backup quartz filters. It indicates the filter artifacts are mainly composed of adsorbed semi-volatile organics (below the analysis temperature of 450 degrees C) including gaseous and particulate phase; the loading of artifacts depends on the nature of vapor and its interaction with filter substrate, rather than particle sizes. The uncorrected OC/EC ratios on the front quartz filters were approximately 10% higher than the corrected OC/EC ratios by positive organic artifacts in winter, and it is approximately 20% higher in summer. Another finding is that the separation distance of the front and backup filters influence the level of artifacts assessed by the backup filter.
Environmental Monitoring and Assessment 09/2009; 168(1-4):645-56. · 1.68 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Vehicle emissions of VOCs were determined in summer and winter of 2003 at the Shing Mun Tunnel, Hong Kong. One hundred and ten VOCs were quantified in this study. The average concentration of the total measured VOCs at the inlet and outlet of the tunnel were 81 250 pptv and 117 850 pptv, respectively. Among the 110 compounds analyzed, ethene, ethyne and toluene were the most abundant species in the tunnel. The total measured VOC emission factors ranged from 67 mg veh−1 km−1 to 148 mg veh−1 km−1, with an average of 115 mg veh−1 km−1. The five most abundant VOCs observed in the tunnel were, in decreasing order, ethene, toluene, n-butane, propane and i-pentane. These five most abundant species contributed over 38% of the total measured VOCs emitted. The high propane and n-butane emissions were found to be associated with LPG-fueled taxi. And fair correlations were observed between marker species (ethene, i-pentane, n-nonane, BTEX) with fractions of gasoline-fueled or diesel-fueled vehicles. Moreover, ethene, ethyne, and propene are the key species that were abundant in the tunnel but not in gasoline vapors or LPG. In order to evaluate the ozone formation potential emissions in Hong Kong, the maximum increment reactivity is calculated. It was found that about 568 mg of O3 is induced by per vehicle per kilometer traveled. Among them, ethene, propene and toluene contribute most to the ozone-formation reactivity.
ATMOSPHERIC CHEMISTRY AND PHYSICS 01/2009; · 5.51 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We studied the influence of acid pretreatment on the effective distinction between elemental carbon (EC) and organic carbon (OC), and between char-EC and soot-EC. Though widely employed in the pretreatment of soils and sediments for EC quantification, the use of HCl, HF, and HNO(3) could decrease soot thermal stability as acid remains, leading to an underestimation of soot-EC by thermal methods. We compared thermal optical reflectance (TOR) measurements of EC concentrations in char reference materials and in lacustrine and marine sediments following pretreatment with various acids. The results showed that pretreatment with 2M HCl, concentrated HNO(3), 7 M HNO(3), and 1 M HNO(3) did not result in EC oxidation. However, hot concentrated HNO(3) oxidized EC significantly, leading to lower concentrations of EC, char-EC and soot-EC. By comparing the removal of potentially interfering materials, which contain little fire-derived carbon, with different acid pretreatments, we recommend the HCl-HF-HCl and concentrated (not hot) HNO(3)-HF-HCl pretreatments for the determination of EC, char-EC, and soot-EC in soils and sediments using the TOR method.
[Show abstract][Hide abstract] ABSTRACT: Sixty five urban road dust samples were collected from different land use areas of ∼240 km2 in Xi’an, China. The concentrations of Ag, As, Cr, Cu, Hg, Pb, Sb and Zn were determined to investigate potentially harmful element (PHE) contamination, distribution and possible sources. In addition, the concentrations in different size fractions were measured to assess their potential impact on human health. The highest concentrations were found in the fraction with particle diameters between 80 μm and 101 μm, the finest particles (<63 μm) were not the most important carriers for Ag, As, Cd, Cr, Cu, Hg, Pb and Zn. The percentages of these elements in particles with diameters less than 63 μm (PM63) and less than 101 μm (PM101) were in the range of 7–15%, and 30–55%, respectively. Three main factors influencing element distributions have been identified: (a) industrial activities; (b) prior agricultural land use; and (c) other activities commonly found in urban areas, such as traffic, coal combustion, waste dumping, and building construction/renovation. The highest concentrations were found in industrial areas for As (20 mg kg−1), Cr (853 mg kg−1), Cu (1071 mg kg−1), Pb (3060 mg kg−1) and Zn (2112 mg kg−1), and in previous agricultural areas for Ag and Hg, indicating significant contributions from industrial activities and prior agricultural activities.
[Show abstract][Hide abstract] ABSTRACT: The IMPROVE thermal/optical reflectance (TOR) method, commonly used for EC quantification in atmospheric aerosols, is applied to soils and sediments and compared with a thermochemical method commonly applied to these non-atmospheric samples. TOR determines elemental carbon (EC) by an optical method, but it also yields thermally defined EC fractions in a 2% O2/98% He oxidizing atmosphere at 550 degrees C (EC1), 700 degrees C (EC2), and 800 degrees C (EC3). Replicate TOR TC, OC, and EC values exhibited precisions of approximately +/-10% as determined from multiple analyses of the same samples. EC abundances relative to total mass concentrations were within the ranges reported by other methods for diesel exhaust soot, n-hexane soot, wood and rice chars, and coals, as well as for environmental matrices. A direct comparison with the chemothermal (CTO) method of Gustafson et al. for ten soil and sediment samples demonstrated that almost all of the OC and EC1 are eliminated, as is part of the EC2. The CTO soot carbon is bounded by the EC3 and EC2+EC3 fractions of the IMPROVE TOR analysis. It might be possible to adjust these fractions to obtain better agreement between atmospheric aerosol and soil/sediment analysis methods. Given its linking the EC measurement in the atmosphere to sediments, the TOR method will not only provide useful information on the explanation and comparison between different environmental matrices, but also can be used to derive information on global cycling of EC.
[Show abstract][Hide abstract] ABSTRACT: Many optical, thermal and chemical methods exist for the measurement of elemental carbon (EC) but are unable or neglect to differentiate between the different forms of EC such as char- or soot-EC. The thermal/optical reflectance (TOR) method applies different temperatures for measuring EC and organic carbon (OC) contents through programmed, progressive heating in a controlled atmosphere, making available eight separate carbon fractions - four OC, one pyrolyzed organic carbon, and three EC. These fractions were defined by temperature protocol, oxidation atmosphere, and laser-light reflectance/transmittance. Stepwise thermal evolutional oxidation of the TOR method makes it possible to distinguish char- from soot-EC. In this study, different EC reference materials, including char and soot, were used for testing it. The thermograms of EC reference materials showed that activation energy is lower for char- than soot-EC. Low-temperature EC1 (550 degrees C in a 98% He/2% O2 atmosphere) is more abundant for char samples. Diesel and n-hexane soot samples exhibit similar EC2 (700 degrees C in a 98% He/2% O2 atmosphere) peaks, while carbon black samples peaks at both EC2 and EC3 (800 degrees C in a 98% He/2% O2 atmosphere). These results supported the use of the TOR method to discriminate between char- and soot-EC.
[Show abstract][Hide abstract] ABSTRACT: Thermal methods of various forms have been used to quantify carbonaceous materials. Thermal/optical carbon analysis provides measurements of organic and elemental carbon concentrations as well as fractions evolving at specific temperatures in ambient and source aerosols. Detection of thermally desorbed organic compounds with thermal desorption-gas chromatography/mass spectrometry (TD-GC/MS) identifies and quantifies over 100 individual organic compounds in particulate matter (PM) samples. The resulting mass spectra contain information that is consistent among, but different between, source emissions even in the absence of association with specific organic compounds. TD-GC/MS is a demonstrated alternative to solvent extraction for many organic compounds and can be applied to samples from existing networks. It is amenable to field-deployable instruments capable of measuring organic aerosol composition in near real-time. In this review, thermal stability of organic compounds is related to chemical structures, providing a basis for understanding thermochemical properties of carbonaceous aerosols. Recent advances in thermal methods applied to determine aerosol chemical compositions are summarized and their potential for uncovering aerosol chemistry are evaluated. Current limitations and future research needs of the thermal methods are included.
Journal of Environmental Science and Health Part A 10/2007; 42(11):1521-41. · 1.25 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: To determine the levels and variations of carbonaceous aerosol in Hong Kong, PM<sub>2.5</sub> and PM<sub>10</sub> samples were collected by high volume (Hi-vol) samplers at three monitoring stations (representing middle-scale roadside, urban-, and regional-scale environments) during winter (November 2000 to February 2001) and summer (June 2001 to August 2001) periods. The highest concentrations of organic carbon (OC), elemental carbon (EC), and water-soluble organic carbon (WSOC) were found at the middle-scale roadside site with the lowest at the regional-scale site. The percentages of WSOC in total carbon at these sites were inversely correlated with their concentrations (i.e., the highest percentages of WSOC were observed at the regional-scale site). A high WSOC fraction may be associated with aged aerosol because of the secondary formation by photochemical oxidation of organic precursors of anthropogenic pollutants during transport. The annual average of isotope abundances (δ<sup>13</sup>C) of OC and EC were –26.9±0.5‰ and –25.6±0.1‰, respectively. There were no notable differences for seasonal distributions of carbon isotopic composition, consistent with motor vehicle emissions being the main source contributors of carbonaceous aerosol in Hong Kong. OC <sup>13</sup>C abundances at the regional-scale site were higher than those at the middle-scale roadside and urban sites, consistent with secondary organic aerosols of biogenic origin.
Atmospheric Chemistry and Physics 01/2006; 6:4569-4576. · 4.88 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Simultaneous measurements of PM2.5 mass, OC and EC and eight carbon fractions were conducted in a roadside microenvironment around Hong Kong for a week in May-June 2002 toobtain the characterization of freshly emitted traffic aerosols. Traffic volume (diesel-powered, liquefied-petroleum gas and gasoline-powered vehicles), meteorological data, and sourcedominatedsamples were also measured. PM2.5 samples were collected on pre-fired quartz filters with a mini-volume sampler and a portable fine-particle sampler, then analyzed for OC and ECusing thermal optical reflectance (TOR) method, following the IMPROVE protocol. High levels of PM2.5 mass (64.4 ì g m-3), OC (16.7 ì g m-3) and EC (17.1 ì g m-3) observed in the roadsidemicroenvironment were found to be well-correlated with each other. The average OC/EC ratio was 1.0, indicating that OC and EC were both primary pollutants. Marked diurnal PM2.5 mass OCand EC concentration profiles were observed in accordance with the traffic pattern (especially for diesel vehicles). Average daytime concentrations were 1.3-1.5 times greater than nighttime values.Carbon profiles from source-dominated samples (diesel, LPG and gasoline vehicles) and diurnal variations of eight carbon fractions (OC1, OC2, OC3, OC4, EC1, EC2, EC3 and OP) demonstrated EC2 and OC2 were the major contributors to the diesel exhaust, and OC3 and OC2 were the larger contributors to the LPG and gasoline exhaust. Thus, carbon fractions derived from the IMPROVE protocol could be used to identify different carbon sources.
Aerosol and Air Quality Research 01/2006; 6:106-122. · 2.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Six residences were selected (two roadside, two urban, and two rural) to evaluate the indoor-outdoor characteristics of PM(2.5) (aerodynamic diameter <2.5 microm) carbonaceous species in Hong Kong during March and April 2004. Twenty-minute-averaged indoor and outdoor PM(2.5) concentrations were recorded by DustTrak samplers simultaneously at each site for 3 days to examine diurnal variability of PM(2.5) mass concentrations and their indoor-to-outdoor (I/O) ratios. Daily (24-h average) indoor/outdoor PM(2.5) samples were collected on pre-fired quartz-fiber filters with battery-powered portable mini-volume samplers and analyzed for organic and elemental carbon (OC, EC) by thermal/optical reflectance (TOR) following the Interagency Monitoring of Protected Visual Environments (IMPROVE) protocol. The average indoor and outdoor concentrations of 24 h PM(2.5) were 56.7 and 43.8 microg/m(3), respectively. The short-term PM(2.5) profiles indicated that the penetration of outdoor particles was an important contributor to indoor PM(2.5), and a household survey indicated that daily activities were also sources of episodic peaks in indoor PM(2.5). The average indoor OC and EC concentrations of 17.1 and 2.8 microg/m(3), respectively, accounted for an average of 29.5 and 5.2%, respectively, of indoor PM(2.5) mass. The average indoor OC/EC ratios were 5.8, 9.1, and 5.0 in roadside, urban, and rural areas, respectively; while average outdoor OC/EC ratios were 4.0, 4.3, and 4.0, respectively. The average I/O ratios of 24 h PM(2.5), OC, and EC were 1.4, 1.8, and 1.2, respectively. High indoor-outdoor correlations (r(2)) were found for PM(2.5) EC (0.96) and mass (0.81), and low correlations were found for OC (0.55), indicative of different organic carbon sources indoors. A simple model implied that about two-thirds of carbonaceous particles in indoor air are originated from outdoor sources. PRACTICAL IMPLICATIONS: Indoor particulate pollution has received more attentions in Asia. This study presents a case study regarding the fine particulate matter and its carbonaceous compositions at six residential homes in Hong Kong. The characteristics and relationship of atmospheric organic and elemental carbon were discussed indoors and outdoors. The distribution of eight carbon fractions was first reported in indoor samples to interpret potential sources of indoor carbonaceous particles. The data set can provide significant scientific basis for indoor air quality and epidemiology study in Hong Kong and China.
Indoor Air 06/2005; 15(3):197-204. · 3.30 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Thermal/optical methods have been widely used for quantifying total carbon (TC), organic carbon (OC), and elemental carbon (EC) in ambient and source particulate samples. Thermally defined carbon fractions have been used for source identification. Temperature precision in thermal carbon analysis is critical to the allocation of carbon fractions. The sample temperature is determined by a thermocouple, which is usually located in the oven near the sample. Sample and thermocouple temperature may differ owing to different thermal properties between the sample filter punch and the thermocouple, or inhomogeneities in the heating zone. Quick-drying temperature-indicating liquids (Tempil Inc., South Plainfield, NJ) of different liquefying points are used as temperature calibration standards. These consist of chemicals that change their appearance at specific temperatures and can be optically monitored to determine the sample temperature. Temperature measures were evaluated for three different models of carbon analyzers. Sample temperatures were found to differ from sensor temperatures by 10 to 50°C. Temperature biases of 14 to 22°C during thermal analysis were found to change carbon fraction measurements. The temperature indicators allow calibration curves to be constructed that relate the sample temperature to the temperature measured by a thermocouple.
Atmospheric Chemistry and Physics 01/2005; 5(4):2961-2972. · 4.88 Impact Factor
[Show abstract][Hide abstract] 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 PM<sub>2.5</sub> samples daily and PM<sub>10</sub> 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 PM<sub>2.5</sub> OC concentrations in fall and winter were 34.1±18.0 μg m<sup>−3</sup> and 61.9±;33.2 μg m<sup>−3</sup>, respectively; while EC concentrations were 11.3±6.9 μg m<sup>−3</sup> and 12.3±5.3 μg m<sup>−3</sup>, respectively. Most of the OC and EC were in the PM<sub>2.5</sub> 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 PM<sub>2.5</sub> 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.
Atmospheric Chemistry and Physics 01/2005; 5:3127-3137. · 4.88 Impact Factor