AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Development and Characterization of Thermal Dissociation Cavity Attenuated Phase Shift Spectroscopy (TD-CAPS)
GAMZE ERIS, Masayuki Takeuchi, Ezra Wood, David Tanner, Greg Huey, Nga Lee Ng, Georgia Institute of Technology
Abstract Number: 310 Working Group: Instrumentation and Methods
Abstract Alkyl nitrates (AN) and peroxy nitrates (PN) are temporary NOx reservoirs in the troposphere. Formation of AN and PN terminates the chain reactions of ROx and NOx radicals; therefore the quantification of these nitrates is critical to understanding the global and regional distributions of NOx as well as it cycling and impact on ozone and SOA production. To measure these compounds, a thermal dissociation (TD) inlet can be coupled with various NOy detection techniques such as TD-CIMS, TD-LIF, TD-CRDS and TD-CAPS. Ambient measurements by TD-CAPS have been recently conducted in a remote region. However, there is no characterization study to quantify the limits and strengths of this technique. In this work, we developed a TD-CAPS instrument which consists of two quartz tube reactors at 563 K and 473 K (enabling decomposition of AN and PN, respectively, to NO2) and a reference channel that measures the ambient NO2. The NO2 concentration in each channel is measured by a CAPS monitor. Isopropyl nitrate (IPN) and peroxy acetyl nitrate (PAN) are used as AN and PN model compounds. NO2 biases from side reactions are determined by adding IPN and PAN to the reactors in the presence of atmospheric constituents such as O3, NO and NO2. In the presence of NO, the measured IPN and PAN concentrations are biased high. The presence of NO2 causes a slight overestimation of NO2 concentration for PAN. Correction factors are derived for binary reactions of model compounds with atmospheric constituents over a wide range of concentrations that is representative of both rural and urban areas. Ambient measurements from Atlanta to demonstrate the measurement capability of the instrument will be presented.