AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
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Choice of OC/EC Ratio in the EC Tracer Method to Estimate Secondary Organic Carbon over a National Park in Bhopal, India: A Sensitivity Analysis
SHILPI SAMIKSHA, Ramya Sunder Raman, Samresh Kumar, Indian Institute of Science Education and Research, Bhopal
Abstract Number: 671 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract In this study, ambient PM2.5 samples were collected over Van Vihar National Park in Bhopal, central India over a period of two years (01 January, 2012 to 31 December, 2013). Samples were collected on to Teflon, Nylon, and Tissue quartz filter substrates. Punches of the quartz fibre filters were analyzed for organic and elemental carbon (OC/EC) using a thermal-optical-transmittance/reflectance (TOT-TOR) analyzer operating with a 632 nm laser diode. In this observation-based approach, EC is used as a tracer for primary OC (POC), which allows for the estimation of secondary OC (SOC).
The elemental carbon (EC) tracer method has been the most popular choice to estimate the primary and secondary organic carbon fractions using field measurements of organic carbon (OC) and EC. The estimation of primary OC/EC ratio is crucial in estimating the SOC. Typically periods of minimal or no SOC formation are used to estimate this ratio. In the mid-latitudes measurements made during cold winter months with few hours of sunlight have often been used to determine the primary OC/EC ratio. However, in a hot tropical country with abundant sunshine all-year round, the identification of periods when SOC formation is expected to minimum is rather tricky.
Thus, this study was conducted to explore and examine the various methods appropriate for estimation of primary OC/EC ratio at the study location. The influence of random measurement errors in both primary OC and EC measurements on the estimation of this ratio will also be examined. Finally, the sensitivity of SOC estimates to the choice of primary OC/EC ratio will be discussed and guidelines for choosing an appropriate ratio will be provided.