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

L. Chiappini (1) , S. Verlhac (2) , R. Aujay , W. Maenhaut (3) , J. Putaud , J. Sciare (4, 5) , J. Jaffrezo , C. Liousse (6) , Corinne Galy-Lacaux (6) , L. Alleman (7) , P. Panteliadis , E. Leoz (1) , O. Favez (8)

1 INERIS - Institut National de l'Environnement Industriel et des Risques
2 Service de Radiologie [Créteil]
3 Department of Analytical Chemistry
4 LSCE - Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette]
5 CAE - Chimie Atmosphérique Expérimentale
6 LAERO - Laboratoire d'aérologie
7 IMT Lille Douai - Ecole nationale supérieure Mines-Télécom Lille Douai
8 IRCELYON - Institut de recherches sur la catalyse et l'environnement de Lyon

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.

Domaines: Environnement et Société

L. Chiappini, S. Verlhac, R. Aujay, W. Maenhaut, J. Putaud, et al.. Clues for a standardised thermal-optical protocol for the assessment of organic and elemental carbon within ambient air particulate matter. Atmospheric Measurement Techniques, 2014, 7 (6), pp.1649-1661. ⟨10.5194/amt-7-1649-2014⟩. ⟨hal-02552801⟩