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

Abstract

Thermal-optical analysis is currently under consideration by the European standardiza-tion 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, 5 critical factors and interferences of the methods examined, method inter-comparisons, inter-laboratory exercises, biases and artifacts, and reference materials. The most com-monly used thermal protocols include NIOSH-like, IMPROVE_A and EUSAAR_2 pro-tocols either with light transmittance or reflectance correction for charring. All thermal evolution protocols are comparable for total carbon (TC) concentrations but the results 10 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 re-flectance. The difference between reflectance and transmittance correction tends to 15 be larger than the difference between different thermal protocols. Nevertheless, ther-mal 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 chemi-cal properties of the samples due to different contributions from various sources. The 20 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.