Review of Sunset OC/EC Instrument Measurements During the EPA’s Sunset Carbon Evaluation Project

To evaluate the feasibility of the Sunset semicontinuous organic and elemental carbon (OC/EC) monitor, the U.S. Environmental Protection Agency (EPA) sponsored the deployment of this monitor at Chemical Speciation Network (CSN) sites with OC and EC measurements via quartz fiber filter collection in Chicago, Illinois; Houston, Texas; Las Vegas, Nevada; St. Louis, Missouri; Rubidoux, California; and Washington, D.C. Houston, St. Louis, and Washington also had collocated Aethalometer black carbon (BC) measurements. Sunset OC generally compared well with the CSN OC (r2 = 0.73 across five sites); the Sunset/CSN OC ratio was, on average, 1.06, with a range among sites of 0.96 to 1.12. Sunset thermal EC and CSN EC did not compare as well, with an overall r2 of 0.22, in part because 26% of the hourly Sunset EC measurements were below the detection limit. Sunset optical EC had a much better correlation to CSN EC (r2 = 0.67 across all sites), with an average Sunset/CSN ratio of 0.90 (range of 0.7 to 1.08). There was also a high correlation of Sunset optical EC with Aethalometer BC (r2 = 0.77 across all sites), though with a larger bias (average Sunset/Aethalometer ratio of 0.56). When the Sunset instrument was working well, OC and OptEC data were comparable to CSN OC and EC.

Study on determination method of phthalates from indoor air by gas chromatograph tandem mass spectrometry technique (GC/MS)

In this report, the determination method of phthalates in indoor air has been studied. For air samples, the particulate phase was kept on a quartz fiber filter and the gas phase was collected on two polyurethane foams (PUFs) by a low speed pump during a period of 12 to 24 h. The target compounds were extracted from filter and PUFs by mixture of dichlomethane and n-hexane and performed on a GS/MS system. The method quantification limit of siloxane in the air samples ranged from 1 to 3 ng/m3, the linear range of standard solution was from 1 to 1000 ng/mL. The recoveries of method ranged from 67,9% to 117% with a RSD < 9% for both of analysis and surrogate compounds. The optimized method was applied for determination of siloxane in indoor air collected from Hanoi, Vietnam.

Refractory black carbon mass concentrations in snow and ice: method evaluation and inter-comparison with elemental carbon measurement

Accurate measurement of black carbon (BC) mass concentrations in snow and ice is crucial for the assessment of climatic impacts. However, it is difficult to compare methods used to assess BC levels in the literature as they are not the same. The single particle soot photometer (SP2) method appears to be one of the most suitable to measure low concentrations of BC in snow and ice. In this paper, we evaluated a method for the quantification of refractory BC (rBC) in snow and ice samples coupling the SP2 with the APEX-Q nebulizer. The paper reviews all the steps of rBC determination, including SP2 calibration, correction for rBC particle aerosolization efficiency (75 ± 7% using the APEX-Q nebulizer), and treatment of the samples. In addition, we compare the SP2 method and the thermal–optical method – Sunset organic carbon (OC) / elemental carbon (EC) aerosol analyzer with EUSAAR2 protocol – using snow and firn samples with different characteristics from the Greenland Summit, the French Alps, the Caucasus, and the Himalayas. Careful investigation was undertaken of analytical artifacts that potentially affect both methods. The SP2-based rBC quantification may be underestimated when the SP2 detection range does not cover correctly the existing size distribution of the sample. Thermal–optical EC measurements can be underestimated by low filtration efficiency of quartz fiber filter before analysis or dust properties (concentration and type), and overestimated by pyrolyzed OC artifacts during EC analysis. These results underline the need for careful assessment of the analytical technique and procedure for correct data interpretation.

Refractory black carbon mass concentrations in snow and ice: method evaluation and inter-comparison with elemental carbon measurement

Accurate measurement of black carbon (BC) mass concentrations in snow and ice is crucial for the assessment of climatic impacts. However, it is difficult to compare methods used to assess BC levels in the literature as they are not the same. The single particle soot photometer (SP2) method appears to be one of the most suitable to measure low concentrations of BC in snow and ice. However, deriving BC concentrations with SP2 is not straightforward and different measurement options may lead to different results. In this paper, we propose an optimized method for the quantification of refractory BC (rBC) in snow and ice samples using SP2. The paper reviews all the steps of rBC determination including SP2 calibration, correction for rBC particle aerosolization, and treatment of the samples. In addition, we compare the SP2 method and the thermal-optical method (Sunset organic carbon (OC)-elemental carbon (EC) aerosol analyzer with EUSAAR-2 protocol), using snow and firn samples with different characteristics from the Greenland Summit, the French Alps, the Caucasus, and the Himalayas. The EC : rBC ratio was 1.8 ± 1.2 for the Greenland site, 0.4 ± 0.2 for the Alpine site, 0.9 ± 0.3 for the Caucasus site, and 3.0 ± 1.2 for the Himalayan site. Careful investigation was undertaken of analytical uncertainties in both methods, concerning the analytical range of detection of BC, aerosolization correction for rBC, filtration efficiency of quartz fiber filter before EC analysis, the impact of dust, and pyrolyzed organic carbon artifacts during EC analysis. We conclude that the complexity of artifacts can lead to inaccurate rBC or EC determination. In particular, we observed significant under-estimation of EC due to incomplete filtration together with positive artifacts caused by OC. These results underline the need for careful assessment of the analytical technique and procedure for correct data interpretation.

Measurement of overall uptake coefficients for HO₂ radicals by aerosol particles sampled from ambient air at Mts. Tai and Mang (China)

HO2 uptake coefficients for ambient aerosol particles, collected on quartz fiber filter using a high-volume air sampler in China, were measured using an aerosol flow tube coupled with a chemical conversion/laser-induced fluorescence technique at 760 Torr and 298 K, with a relative humidity of 75%. Aerosol particles were regenerated with an atomizer using the water extracts from the aerosol particles. Over 10 samples, the measured HO2 uptake coefficients for the aerosol particles at the Mt. Tai site were ranged from 0.13 to 0.34, while those at the Mt. Mang site were in the range of 0.09–0.40. These values are generally larger than those previously reported for single-component particles, suggesting that reactions with the minor components such as metal ions and organics in the particle could contribute to the HO2 uptake. A box model calculation suggested that the heterogeneous loss of HO2 by ambient particles could significantly affect atmospheric HOx concentrations and chemistry.

MEASUREMENT OF AEROSOLS IN ENGINEERED NANOMATERIALS FACTORIES FOR RISK ASSESSMENT

In relation to potential health risks, there is little available information on exposure to aerosols containing nanometer-size particles in work environments in factories producing engineered nanomaterials. We measured the concentrations and size distributions of particles of nanometer-sized to coarse-sized particles in an engineered carbon nanomaterial factory and a titanium dioxide factory. In addition, particles were collected with a quartz fiber filter in the engineered carbon nanomaterial factory, and their morphology was examined by scanning electron microscopy and their carbon composition was examined with a carbon analyzer. In the carbon nanomaterial factory, the particle number increased to more than 105 cm-3 when a vacuum cleaner was used to clean the inside of the producing device, and the particle number increased for particles with a diameter of about 100 nm compared with the background. This is the only case an increase in particle numbers is observed during this measurement. The emitted particles appear to consist of agglomerates of carbon nanomaterial particles smaller than 100 nm. The major fraction was the EC3 fraction (EC: elemental carbon; combustion at 800°C in a 98:2 He / O 2 atmosphere), which is a minor fraction in diesel engine particulate matter. This suggests that the combustion temperature can be used to differentiate atmospheric particulate matter from engineered carbon material. Personal sampling conducted in addition to stationary measurements in the titanium dioxide factory indicated that stationary measurements can be used to generate representative data on the basis of the particle number but not the particle mass.

Performance of a Quartz Fiber Filter Operating in the Filtration of Gases at High Temperatures

Experimental results describing the pressure drop and collection efficiency of a quartz micro-fiber filter are presented in this study. The filter utilized had a porosity of 0.698 and mean fiber diameter of 1.1!m. For the tests performed, the filter was a disk with an effective diameter of 3 cm. The permeability tests of the filters were measured by varying the superficial gas velocity from 0.013 to 1.49m/s and the temperature from 26.5 to 666oC. The collection efficiency tests were accomplished for temperatures ranging from ambient to 700oC at a filtration velocity of 0.05 m/s. The test powder utilized was a phosphate rock concentrate with a density 2973 kg/m3 and average diameter of 4.6!m. The permeability test results showed that, for the same gas velocity, the pressure drop increased with the gas temperature. This dependence was reflected in the measured values of the permeability constant, k1, which increased with temperature. The experimental points were well fitted by a linear correlation. The filtration tests also showed a clear dependence between filter efficiency and test temperature: smaller filter efficiencies were obtained as the gas temperature was increased.