AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
A Steady State Continuous Flow Chamber for the Study of Daytime and Nighttime Chemistry at Atmospherically Relevant NO Levels
XUAN ZHANG, John Ortega, Yuanlong Huang, Geoffrey Tyndall, John Orlando, National Center for Atmospheric Research
Abstract Number: 723 Working Group: Aerosol Chemistry
Abstract Understanding of fundamental kinetics and mechanisms in atmospheric chemistry has been derived largely from experiments performed in laboratory chambers. Two chemical regimes, classified by ‘high-NO’ versus ‘NOx-free’ conditions, have been extensively studied in previous chamber experiments. Results derived from these two chemical scenarios are widely parameterized in chemical transport models to represent key atmospheric processes in urban and pristine environments. As the anthropogenic NOx emissions in the United States have decreased remarkably in the past few decades, the classic ‘high-NO’ and ‘NOx-free’ conditions are no longer applicable to many regions in the world that constantly intercept both polluted and background air masses. We present here the development and characterization of the NCAR Atmospheric Simulation Chamber, which is operated in steady state continuous flow mode for the study of atmospheric chemistry under ‘intermediate NO’ conditions. This particular chemical regime is characterized by constant sub-ppb levels of NO in the well-mixed chamber and is created by precise control of the inflow NO concentration and the ratio of chamber mixing to residence timescales. Under such conditions, the peroxy radicals (RO2), a key intermediate from the atmospheric degradation of volatile organic compounds (VOCs), are expected to survive up to minutes and undergo a diversity of reaction pathways instead of combining with NO and HO2 as predominantly observed in classic ‘high-NO’ and ‘NOx-free’ chamber experiments. Characterization experiments under photolytic and dark conditions were performed and, in conjunction with model predictions, provide a basis for interpretation of prevailing atmospheric processes in environments with alternated biogenic and anthropogenic activities. We demonstrate the proof of concept of the steady state chamber operation method through measurements of major first-generation products, methacrolein (MACR) and methyl vinyl ketone (MVK), from OH- and NO3-initiated oxidation of isoprene.