Evaluation of Thermal Optical Analysis (TOA) using an aqueous binary mixture

Area of Science:

• Environmental Science
• Analytical Chemistry
• Atmospheric Chemistry

Background:

• Thermal-Optical Analysis (TOA) is a standard technique for measuring organic carbon (OC) and elemental carbon (EC) in particulate matter.
• Accurate characterization of TOA methods is crucial for reliable atmospheric carbon measurements.
• Existing methods may require complex sample preparation or lack precision in distinguishing carbon fractions.

Purpose of the Study:

• To develop and validate a novel method for characterizing the Thermal-Optical Analysis (TOA) transmission technique.
• To assess the accuracy and reproducibility of TOA measurements using a prepared aqueous mixture of EC and OC.
• To evaluate different temperature protocols for their effectiveness in quantifying carbonaceous aerosols.

Main Methods:

• An aqueous binary mixture containing known amounts of elemental carbon (EC) and organic carbon (OC) was prepared.
• The mixture was deposited onto quartz-fiber filters using a low-volume deposition technique.
• Samples were analyzed using Thermal-Optical Analysis (TOA) with various temperature protocols, including the NIST-EPA-C protocol.

Main Results:

• The NIST-EPA-C temperature protocol achieved agreement with reference values better than 2% for EC, OC, total carbon (TC), and EC/TC.
• All tested temperature protocols indicated total carbon (TC) within 5% of the reference value.
• All protocols reproduced EC/TC ratios with an uncertainty of less than 10%.

Conclusions:

• The developed aqueous mixture method provides a reliable and accurate way to characterize TOA instruments.
• The NIST-EPA-C protocol demonstrates high accuracy for quantifying EC and OC in atmospheric samples.
• This method enhances the precision and reliability of atmospheric carbonaceous aerosol analysis.