High time resolution measurement and source apportionment of TC, BC and OC, EC

Measurements of carbonaceous aerosols are of vital importance for local, regional and global air quality monitoring, regional and global climate change investigations. The carbonaceous fractions are frequently separated into organic carbon (OC) and elemental carbon (EC) based on their volatility using thermal-optical methods. While the results for OC and especially EC concentrations vary significantly for different thermal evolution protocols, the total carbon (TC) concentration is very consistent between methods (Karanasiou et al., 2015). Therefore, we show an equivalent method and a new and innovative instrument, capable of highly time resolved measurement of total carbon (TC), which, combined with black carbon (BC) measurements (Drinovec et al., 2014; Hansen et al., 1982), provides an equivalent of OC and EC. We call this approach TC-BC. “TC-BC” online method combines an optical method for measuring BC by the Aethalometer AE33, and a thermal method for TC determination by the Total Carbon Analyzer TCA08 is used for source apportionment of carbonaceous aerosols with high time resolution at several measuring sites around the world. TC-BC method determines equivalent organic carbon fraction of carbonaceous aerosols as eOC = TC - b·BC, where b·BC is equivalent to elemental carbon (EC). The determined proportionality parameter b is region/site specific and depends to a large extent on a thermal protocol used to determine the EC fraction with the conventional OC/EC method. TCA08 measures concentration of TC by a rapid combustion of carbonaceous matter (CM) collected on a quartz filter. Pulse of CO2 which is created during combustion phase of the analysis is detected as a large transient increase above the CO2 level in the ambient air used as the carrier gas. Simplicity of the analysis allow us to have high time resolution measurement and easier field deployment of the instrument as no high purity gases are needed. TC-BC method was validated by comparing averaged high time resolved data to the conventional OC/EC analysis on 24h filters using different thermal protocols (EUSAAR2, IMPROVE, NIOSH) in the winter campaigns in Europe, Asia and N. America: Ljubljana (Slovenia), urban background site; Loski Potok (Slovenia), rural; Ispra/Milano (Italy), urban background, Paris (France), urban background; London (United Kingdom), urban background; Zurich (Switzerland), urban background; Magadino (Switzerland), rural; Beijing (China), urban; New Delhi (India), urban; Los Angeles (United States of America), urban; Additionally, at some sites parallel measurements with aerosol mass spectrometry (AMS or ACSM) allowed us to obtain hourly comparison of OM (AMS) to OC (TC-BC) and determine the OM/OC ratio.