Thermal-optical analysis for the measurement of elemental carbon (EC) and organic carbon (OC) in ambient air a literature review

Thermal-optical analysis is currently under consideration by the European standardization body (CEN) as the reference method to quantitatively determine organic carbon (OC) and elemental carbon (EC) in ambient air. This paper presents an overview of the critical parameters related to the thermal-optical analysis including thermal protocols, critical factors and interferences of the methods examined, method inter-comparisons, inter-laboratory exercises, biases and artifacts, and reference materials. The most commonly used thermal protocols include NIOSH-like, IMPROVE_A and EUSAAR_2 protocols either with light transmittance or reflectance correction for charring. All thermal evolution protocols are comparable for total carbon (TC) concentrations but the results vary significantly concerning OC and especially EC concentrations. Thermal protocols with a rather low peak temperature in the inert mode like IMPROVE_A and EUSAAR_2 tend to classify more carbon as EC compared to NIOSH-like protocols, while charring correction based on transmittance usually leads to smaller EC values compared to reflectance. The difference between reflectance and transmittance correction tends to be larger than the difference between different thermal protocols. Nevertheless, thermal protocols seem to correlate better when reflectance is used as charring correction method. The difference between EC values as determined by the different protocols is not only dependent on the optical pyrolysis correction method, but also on the chemical properties of the samples due to different contributions from various sources. The overall conclusion from this literature review is that it is not possible to identify the "best" thermal-optical protocol based on literature data only, although differences attributed to the methods have been quantified when possible.This work was undertaken under Mandate M/503 “Standardisation mandate to CEN, CENELEC and ETSI in support of the implementation of the Ambient Air Quality Legislation”, ENX “Ambient air – Measurement of airborne lemental carbon (EC) and organic carbon (OC) in PM 2.5 deposited on filters”.EUR 1,920 APC fee funded by the EC FP7 Post-Grant Open Access PilotPeer reviewe

Clues for a standardised thermal-optical protocol for the assessment of organic and elemental carbon within ambient air particulate matter

Along with some research networking programmes, the European Directive 2008/50/CE requires chemical speciation of fine aerosol (PM_2.5), including elemental (EC) and organic carbon (OC), at a few rural sites in European countries. Meanwhile, the thermal-optical technique is considered by the European and US networking agencies and normalisation bodies as a reference method to quantify EC–OC collected on filters. Although commonly used for many years, this technique still suffers from a lack of information on the comparability of the different analytical protocols (temperature protocols, type of optical correction) currently applied in the laboratories. To better evaluate the EC–OC data set quality and related uncertainties, the French National Reference Laboratory for Ambient Air Quality Monitoring (LCSQA) organised an EC–OC comparison exercise for French laboratories using different thermal-optical methods (five laboratories only). While there is good agreement on total carbon (TC) measurements among all participants, some differences can be observed on the EC / TC ratio, even among laboratories using the same thermal protocol. These results led to further tests on the influence of the optical correction: results obtained from different European laboratories confirmed that there were higher differences between OC_TOT and OC_TOR measured with NIOSH 5040 in comparison to EUSAAR-2. Also, striking differences between EC_TOT / EC_TOR ratios can be observed when comparing results obtained for rural and urban samples, with EC_TOT being 50% lower than EC_TOR at rural sites whereas it is only 20% lower at urban sites. The PM chemical composition could explain these differences but the way it influences the EC–OC measurement is not clear and needs further investigation. Meanwhile, some additional tests seem to indicate an influence of oven soiling on the EC–OC measurement data quality. This highlights the necessity to follow the laser signal decrease with time and its impact on measurements. Nevertheless, this should be confirmed by further experiments, involving more samples and various instruments, to enable statistical processing. All these results provide insights to determine the quality of EC–OC analytical methods and may contribute to the work toward establishing method standardisation

ECOC comparison exercise with identical thermal protocols after temperature offset correction - Instrument diagnostics by in-depth evaluation of operational parameters

© Author(s) 2015. A comparison exercise on thermal-optical elemental carbon/organic carbon (ECOC) analysers was carried out among 17 European laboratories. Contrary to previous comparison exercises, the 17 participants made use of an identical instrument set-up, after correcting for temperature offsets with the application of a recently developed temperature calibration kit (Sunset Laboratory Inc, OR, US). Temperature offsets reported by participants ranged from -93 to +100 °C per temperature step. Five filter samples and two sucrose solutions were analysed with both the EUSAAR2 and NIOSH870 thermal protocols. z scores were calculated for total carbon (TC); nine outliers and three stragglers were identified. Three outliers and eight stragglers were found for EC. Overall, the participants provided results between the warning levels with the exception of two laboratories that showed poor performance, the causes of which were identified and corrected through the course of the comparison exercise. The TC repeatability and reproducibility (expressed as relative standard deviations) were 11 and 15% for EUSAAR2 and 9.2 and 12% for NIOSH870; the standard deviations for EC were 15 and 20% for EUSAAR2 and 20 and 26% for NIOSH870. TC was in good agreement between the two protocols, TCNIOSH870 =0.98 × TCEUSAAR2 (R2 = 1.00, robust means). Transmittance (TOT) calculated EC for NIOSH870 was found to be 20% lower than for EUSAAR2, ECNIOSH870 = 0.80 × ECEUSAAR2 (R2 = 0.96, robust means). The thermograms and laser signal values were compared and similar peak patterns were observed per sample and protocol for most participants. Notable deviations from the typical patterns indicated either the absence or inaccurate application of the temperature calibration procedure and/or pre-oxidation during the inert phase of the analysis. Low or zero pyrolytic organic carbon (POC), as reported by a few participants, is suggested as an indicator of an instrument-specific pre-oxidation. A sample-specific pre-oxidation effect was observed for filter G, for all participants and both thermal protocols, indicating the presence of oxygen donors on the suspended particulate matter. POC (TOT) levels were lower for NIOSH870 than for EUSAAR2, which is related to the heating profile differences of the two thermal protocols

Multiple sclerosis genomic map implicates peripheral immune cells and microglia in susceptibility

We analyzed genetic data of 47,429 multiple sclerosis (MS) and 68,374 control subjects and established a reference map of the genetic architecture of MS that includes 200 autosomal susceptibility variants outside the major histocompatibility complex (MHC), one chromosome X variant, and 32 variants within the extended MHC. We used an ensemble of methods to prioritize 551 putative susceptibility genes that implicate multiple innate and adaptive pathways distributed across the cellular components of the immune system. Using expression profiles from purified human microglia, we observed enrichment for MS genes in these brain-resident immune cells, suggesting that these may have a role in targeting an autoimmune process to the central nervous system, although MS is most likely initially triggered by perturbation of peripheral immune responses

Een vergelijking van de weging van fijnstoffilters door laboratoria in 2022

Measurements of particulate matter (PM10 and PM2,5) in ambient air are performed by several air monitoring networks in Europe. These PM measurements are carried out by using filters in a monitoring device that ambient air passes through. Every filter is exposed to ambient air for 24 hours. The laboratories of the air monitoring networks calculate the concentration of PM by using the weight of the filters before and after exposure. In order to investigate whether this weighing procedure – when applied by different laboratories – leads to similar results, a comparison between the laboratories is carried out every two to four years. The weighing results for 2022 were roughly similar. The results show relatively small differences between the participating laboratories, and these are well within the limit values for PM measurements. This means there is a strong basis for comparing and exchanging PM measurements between the participating laboratories. The filters have to be weighed exactly as described in a European Standard (EN 12341). For example, temperature and relative humidity in the weighing rooms have to fall within specified value ranges. All but one of the participating laboratories matched these requirements. In 2022, eight laboratories in Europe participated in this research. A total of 84 filters were compared. RIVM performs the measurements together with several air monitoring networks throughout the European Union.Verschillende luchtmeetnetten in Nederland en Europa meten de hoeveelheid fijnstof ( PM10 (fijnstof)en PM2,5 (fijnstof)) in de buitenlucht. Dit wordt gedaan met filters in een apparaat dat continu buitenlucht aanzuigt. Elk filter wordt na 24 uur vervangen. De laboratoria van de meetnetten wegen het filter voor en na de plaatsing. Hiermee wordt de concentratie fijnstof bepaald. Elke twee tot vier jaar vergelijkt het RIVM het weegproces bij een aantal van deze laboratoria. Zo wordt gecontroleerd of de fijnstofconcentraties in de verschillende laboratoria overeenkomen. De resultaten van de wegingen waren in 2022 ongeveer gelijkwaardig. Er waren kleine verschillen te zien die ruim binnen de grenzen vallen die voor fijnstofmetingen zijn bepaald. Dit betekent dat alle fijnstofmetingen onderling goed met elkaar overeenkomen en tussen de deelnemende meetnetten kunnen worden uitgewisseld. De laboratoria moeten de metingen volgens een Europees vastgestelde procedure doen (EN 12341). De weegkamers horen bijvoorbeeld een bepaalde temperatuur en luchtvochtigheid te hebben. Op één na voldeden alle deelnemende laboratoria aan deze procedure. In 2022 deden acht laboratoria uit Europa mee aan de vergelijking. In totaal zijn 84 filters gemeten. Het RIVM doet de metingen samen met Nederlandse meetnetten en enkele lidstaten van de Europese Unie. Het RIVM is het nationaal referentielaboratorium voor luchtkwaliteitsmetingen in de buitenlucht en heeft daarom deze taak