Evaluation and Inter-Comparison of Oxygen-Based OC-EC Separation Methods for Radiocarbon Analysis of Ambient Aerosol Particle Samples

Radiocarbon analysis is a widely-used tool for source apportionment of aerosol particles. One of the big challenges of this method, addressed in this work, is to isolate elemental carbon (EC) for 14C analysis. In the first part of the study, we validate a two-step method (2stepCIO) to separate total carbon (TC) into organic carbon (OC) and EC against the EUSAAR_2 thermal-optical method regarding the recovered carbon concentrations. The 2stepCIO method is based on the combustion of OC in pure oxygen at two different temperature steps to isolate EC. It is normally used with a custom-built aerosol combustion system (ACS), but in this project, it was also implemented as a thermal protocol on a Sunset OC-EC analyzer. Results for the recovered EC mass concentration showed poor agreement between the 2stepCIO method on the ACS system and on the Sunset analyzer. This indicates that the EC recovery is sensitive not only to the temperature steps, but also to instrument-specific parameters, such as heating rates. We also found that the EUSAAR_2 protocol itself can underestimate the EC concentration on untreated samples compared to water-extracted samples. This is especially so for highly loaded filters, which are typical for 14C analysis. For untreated samples, the EC concentration on long-term filter samples (two to five days sampling time) was 20–45% lower than the sum of EC found on the corresponding 24-h filter samples. For water-extracted filter samples, there was no significant difference between long-term and the sum of daily filter samples. In the second part of this study, the 14C was measured on EC isolated by the 2stepCIO method and compared to methods from two other laboratories. The different methods agree well within their uncertainty estimates

Standardisation of a European measurement method for organic carbon and elemental carbon in ambient air: results of the field trial campaign and the determination of a measurement uncertainty and working range

The European Committee for Standardisation (CEN) Technical Committee 264 'Air Quality' has recently produced a standard method for the measurements of organic carbon and elemental carbon in PM2.5 within its working group 35 in response to the requirements of European Directive 2008/50/EC. It is expected that this method will be used in future by all Member States making measurements of the carbonaceous content of PM2.5. This paper details the results of a laboratory and field measurement campaign and the statistical analysis performed to validate the standard method, assess its uncertainty and define its working range to provide clarity and confidence in the underpinning science for future users of the method. The statistical analysis showed that the expanded combined uncertainty for transmittance protocol measurements of OC, EC and TC is expected to be below 25%, at the 95% level of confidence, above filter loadings of 2 μg cm-2. An estimation of the detection limit of the method for total carbon was 2 μg cm-2. As a result of the laboratory and field measurement campaign the EUSAAR2 transmittance measurement protocol was chosen as the basis of the standard method EN 16909:2017.In particular, WG35 thank the local site operators at each of the field locations for operating the monitoring stations to such a high standard. The funding of CEN/TC264/WG35's laboratory and field trials by the European Commission's Environment Directorate-General and the contribution and discussions of the members of CEN/TC 264/WG35, are gratefully acknowledged. Funding of the UK National Measurement System by the UK Department for Business, Innovation and Skills is also gratefully acknowledged.Peer reviewe

Long-term exposure to elemental constituents of particulate matter and cardiovascular mortality in 19 European cohorts: Results from the ESCAPE and TRANSPHORM projects

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Spatial variations and development of land use regression models of PAH, EC/OC, levoglucosan and oxidative potential of PM2.5 in European study areas

It has been shown that human exposure to air pollution causes adverse health effects. The most used indicator of air quality is the concentration of particulate matter with diameters smaller than 2.5 or 10 µm (PM2.5, PM10, respectively). PM is a chemically complex mixture and it has been suggested that observed adverse health effects depend on PM chemical composition. Most studies of PM composition have investigated short term health effects. Recently, the ESCAPE project (www.escapeproject.eu) contributed knowledge of adverse health effects of long term exposure to PM elemental constituents. Little is known about health effects caused by long-term exposure to organic PM components. The thesis contributes to characterization of air quality by monitoring and modelling of organic components and oxidative potential. Its main goals were: - Determination of the spatial contrast of the ambient concentration of organic components (EC/OC, PAH and hopanes/steranes, levoglucosan) and oxidative potential measured with dithiothreitol assay (OP DTT) within and between ten European study areas. - Assessment of the relationship between those components with other components measured more routinely (NO2, NOx, PM2.5 mass and absorbance). - Development and evaluation of Land use Regression models of spatial variation of the measured air pollutants. Substantial spatial variability was found for all measured pollutants. EC, OC and OP DTT concentrations had similar patterns in Europe as the previously reported components: NO2, PM2.5 and PM absorbance. The highest concentrations for those pollutants were found in southern Europe. ΣPAH and levoglucosan exhibited a different trend. In southern and northern Europe ΣPAH concentrations were similar with the highest concentrations in Copenhagen, Rome and Athens. Levoglucosan concentrations (marker for wood burning) did not differ significantly between the four study areas. The contribution of wood-smoke calculated based on levoglucosan measurements to PM2.5 mass was 9 to 28% in the cold season. Concentrations of all pollutants were higher at street locations. The highest median Street to urban background ratio was found for EC (1.62). The median S/UB ratio for ΣPAH and OC was lower (1.44 and 1.32, respectively) suggesting the importance of other sources in addition to local traffic. The correlation between PM2.5and most components was moderate on average, suggesting they provide additional information on air quality. The highest median explained variance (R2) was found for EC – 84%. PAH and OC LUR models had moderate performance. The lowest performance was for OP DTT – 30%. Levoglucosan models had moderate performance in all four areas, but models were non-specific as we did not have predictor variables associated with wood smoke emissions. Traffic predictors were included in most models with exception to levoglucosan model. In conclusion, substantial variability was found in spatial patterns of all investigates air pollutants both within and between European study areas. The application of this highly standardized measurement and modelling approach across different locations will contribute to a consistent assessment of air pollutant levels and potentially contribute to understanding health effects associated with them

Technical note : Aerosol light absorption measurements with a carbon analyser – Calibration and precision estimates

Equivalent Black Carbon (EBC) and Elemental Carbon (EC) are different mass metrics to quantify the amount of combustion aerosol. Both metrics have their own measurement technique. In state-of-the-art carbon analysers, optical measurements are used to correct for organic carbon that is not evolving because of pyrolysis. These optical measurements are sometimes used to apply the technique of absorption photometers. Here, we use the transmission measurements of our carbon analyser for simultaneous determination of the elemental carbon concentration and the absorption coefficient. We use MAAP data from the CESAR observatory, the Netherlands, to correct for aerosol-filter interactions by linking the attenuation coefficient from the carbon analyser to the absorption coefficient measured by the MAAP. Application of the calibration to an independent data set of MAAP and OC/EC observations for the same location shows that the calibration is applicable to other observation periods. Because of simultaneous measurements of light absorption properties of the aerosol and elemental carbon, variation in the mass absorption efficiency (MAE) can be studied. We further show that the absorption coefficients and MAE in this set-up are determined within a precision of 10% and 12%, respectively. The precisions could be improved to 4% and 8% when the light transmission signal in the carbon analyser is very stable

Technical note : Aerosol light absorption measurements with a carbon analyser – Calibration and precision estimates

Equivalent Black Carbon (EBC) and Elemental Carbon (EC) are different mass metrics to quantify the amount of combustion aerosol. Both metrics have their own measurement technique. In state-of-the-art carbon analysers, optical measurements are used to correct for organic carbon that is not evolving because of pyrolysis. These optical measurements are sometimes used to apply the technique of absorption photometers. Here, we use the transmission measurements of our carbon analyser for simultaneous determination of the elemental carbon concentration and the absorption coefficient. We use MAAP data from the CESAR observatory, the Netherlands, to correct for aerosol-filter interactions by linking the attenuation coefficient from the carbon analyser to the absorption coefficient measured by the MAAP. Application of the calibration to an independent data set of MAAP and OC/EC observations for the same location shows that the calibration is applicable to other observation periods. Because of simultaneous measurements of light absorption properties of the aerosol and elemental carbon, variation in the mass absorption efficiency (MAE) can be studied. We further show that the absorption coefficients and MAE in this set-up are determined within a precision of 10% and 12%, respectively. The precisions could be improved to 4% and 8% when the light transmission signal in the carbon analyser is very stable

Measurement of the oxidative potential of PM2.5 and its constituents : The effect of extraction solvent and filter type

The capacity of Particulate Matter (PM) to oxidise target molecules, defined as its oxidative potential (OP), has been proposed as a biologically more relevant metric than PM mass. Different assays exist for measuring OP and their methodologies vary in the choice of extraction solvent and filter type. Little is known about the impact of extraction and filter type on reported OP. Four a-cellular assays; electron spin resonance (ESR), dithiothreitol (DTI'), ascorbate acid depletion (AA) and reductive acridinium triggering (CRAT) assay were chosen to evaluate whether these differences affect the OP measurement, the correlation between OP from different assays and the association with PM chemical composition. We analysed 15 urban 48-72 h PM2.5 samples collected on quartz and Teflon filters. The choice of extraction solvent had only a significant effect on OPDTT, while all OP measures for quartz filters were heavily attenuated. OP values derived from quartz were, however, highly correlated with those derived from Teflon. OPDTT correlated highly with OPCRAT, and OPESR correlated highly with OPAA. These correlations were affected by the choice of filter type. Correlations between OP and PM chemical composition were not affected by filter type and extraction solvent. These findings indicate that the measurement of relative OP reactivity is not greatly influenced by filter type and extraction solvent for the investigated assays. This robustness is also promising for exploratory use in monitoring and subsequent epidemiological studies. (C) 2013 The Authors. Published by Elsevier Ltd. All rights reserved

Physical and chemical characterisation of PM emissions from two ships operating in European Emission Control Areas

In this paper emission factors (EFs) for particulate matter (PM) and some sub-components as well as gaseous substances were investigated in two onboard measurement campaigns. Emissions from two 4-stroke main engines were measured under stable-load conditions. The impact of varying engine load on the emissions was investigated on one of the engines, and the impact of fuel quality on the other, where heavy fuel oil (HFO) with sulphur content 1% and 0.5% and marine gas oil (MGO) with sulphur content 0.1% were used. Furthermore, emissions from one auxiliary engine were studied. The measured EFs for PM mass were in the range of 0.3 to 2.7 g kg−1 fuel with the lowest values for emissions from the combustion of MGO, and the highest values for HFO with a sulphur content of 1%. The PM mass size distribution was dominated by particles in accumulation mode. Emission factors for particle numbers EF(PN) in the range of 5 × 1015–1 × 1017 # kg−1 fuel were found, the number concentration was dominated by particles in the ultrafine mode and ca. 2/3 of the particle number were non-volatile

Standardisation of a European measurement method for organic carbon and elemental carbon in ambient air: results of the field trial campaign and the determination of a measurement uncertainty and working range

The European Committee for Standardisation (CEN) Technical Committee 264 ‘Air Quality’ has recently produced a standard method for the measurements of organic carbon and elemental carbon in PM2.5 within its Working Group 35 in response to the requirements of European Directive 2008/50/EC. It is expected that this method will be used in future by all Member States making measurements of the carbonaceous content of PM2.5. This paper details the results of a laboratory and field measurement campaign and the statistical analysis performed to validate this method, assess its uncertainty and define its working range to provide clarity and confidence in the underpinning science for future users of the method. The statistical analysis showed that the expanded combined uncertainty for transmittance protocol measurements of OC, EC and TC is expected to be below 25 %, at the 95 % confidence interval, above filter loadings of 2 ug/cm2. An estimation of the detection limit of the method for total carbon was 2 ug/cm2. As a result of the laboratory and field measurement campaign the EUSAAR_2 transmittance measurement protocol was chosen as the basis of the standard method EN 16909:2017.JRC.C.5-Air and Climat

Toxicological characterization of diesel engine emissions using biodiesel and a closed soot filter

This study was designed to determine the toxicity (oxidative stress, cytotoxicity, genotoxicity) in extracts of combustion aerosols. A typical Euro Ill heavy truck engine was tested over the European Transient Cycle with three different fuels: conventional diesel EN590, biodiesel EN14214 as 8100 and blends with conventional diesel (B5, 810, and 1320) and pure plant oil DIN51605 (PPO). In addition application of a (wall flow) diesel particulate filter (DPF) with conventional diesel EN590 was tested. The use of B100 or PPO as a fuel or the DPF reduced particulate matter (PM) mass and numbers over 80%. Similarly, significant reduction in the emission of chemical constituents (EC 90%, (oxy)-PAH 70%) were achieved. No significant changes in nitro-PAH were observed. The use of B100 or PPO led to a NOx increase of about 30%, and no increase for DPF application. The effects of B100, PPO and the DPF on the biological test results vary strongly from positive to negative depending on the biological end point. The oxidative potential, measured via the DDT assay, of the B100 and PPO or DPF emissions is reduced by 95%. The cytotoxicity is increased for B100 by 200%. The measured mutagenicity, using the Ames assay test with TA98 and YG1024 strains of Salmonella typhimurium indicate a dose response for the nitroarene sensitive YG1024 strain for B100 and PPO (fold induction: 1.6). In summary B100 and PPO have good potential for the use as a second generation biofuel resulting in lower PM mass, similar to application of a DPF, but caution should be made due to potential increased toxicity. Besides regulation via mass, the biological reactivity of exhaust emissions of new (bio)fuels and application of new technologies, needs attention. The different responses of different biological tests as well as differences in results between test laboratories underline the need for harmonization of test methods and international cooperation. (C) 2011 Elsevier Ltd. All rights reserved