Using Airborne VOC Measurements to Derive a Transit Time Spectrum: Variabilities and Uncertainties

The concept of Age of Air and the Age Spectrum have been highly successful in diagnosing and characterizing transport behavior in the stratosphere. In this work, we take inspiration from these foundational tools and investigate the use of airborne VOC measurements in deriving a transit time spectrum (TTS) to describe boundary layer to upper troposphere lower stratosphere (UTLS) transport. Forty-two chemical species measured by Whole Air Sampler and TOGA instruments with lifetimes ranging from less than a day to several decades are analyzed, using in-situ samples collected during the Convective Transport of Active Species in the Tropics (CONTRAST) experiment. The CONTRAST campaign was conducted over the highly convective tropical western Pacific during January and February of 2014. The vertical distributions of chemical species are found to be strongly influenced by convective transport. The ratio of upper troposphere to boundary layer concentration forms a compact relationship with the species lifetime, which reveals the information content of the measurements, and allows us to derive the TTS (Luo et al. 2018). In continuing research to establish the application of this method, we have investigated 1) the capability of the TTS to represent atmospheric variability, 2) the uncertainty due to assumption of constant lifetime and uncertainty in calculated lifetimes, and 3) sensitivity of derived TTS to BL conditions. Our findings highlight the method's robustness, its ability to successfully characterize transport pathways, its future applications in a wide range of airborne data analyses, and its potential for model evaluations.