Development of instrumentation for simultaneous analysis of total non-methane organic carbon and volatile organic compounds in ambient air

Here we describe the development of a new instrument to measure the total airborne non-methane organic carbon concentration (TNMOC), and the ratio of this value to the sum of speciated volatile organic compounds (VOCs) measured by standard gas chromatography. The TNMOC and sum of speciated VOC analyses are made simultaneously. Samples are collected in situ, with an inlet designed to minimize contact of samples with surfaces. Whole air samples are cryo-trapped with minimal collection of CO2, CO and CH4. Organics are desorbed and converted to CO2 using an oxidation catalyst. The resulting CO2 is analyzed with a flame ionization detector after reduction to methane. The instrument is tested and found to perform well on gas mixtures, ambient air and on smog chamber samples. The detection limit for the instrument is 35 ppbC, and the accuracy of the ratio of TNMOC to the sum of speciated VOCs is ±0.05 for most samples.