Quantification of Several Hydroxyl and Hydroperoxyl Measurement Interferences for GTHOS/ATHOS

Abstract:

Measuring atmospheric oxidants is central to the development of an improved understanding of tropospheric chemistry. The hydroxyl radical (OH) and the hydroperoxyl radical (HO₂) are two important atmospheric oxidants that are present in only trace amounts, and yet these radicals are responsible for a significant fraction of daytime tropospheric oxidation. Atmospheric detection of OH and HO₂ is often accomplished using Laser Induced Fluorescence (LIF) as part of the Fluorescence Assay by Gas Expansion (FAGE) technique. The OH radical is detected directly using 308 nanometer laser light, and the HO₂ radical is detected through reaction with NO to produce OH. The LIF-FAGE instruments, the Ground Tropospheric Hydrogen Oxides Sensor (GTHOS) and the Airborne Tropospheric Hydrogen Oxides Sensor (ATHOS), developed by our group at the Pennsylvania State University, have been operated in laboratory experiments and field campaigns for more than two decades. Recent discoveries of chemical interferences in LIF-FAGE instruments have highlighted the need for accurate, updated calibrations for each instrument in order to standardize measurements of OH and HO₂. In this presentation, we will investigate the extent to which certain chemical species frequently found in forest air may interfere with the measurement of OH and HO₂ for GTHOS/ATHOS. We will discuss the results from laboratory studies involving interferences found for OH and for HO₂, including the recent suggestion that NO₃ can cause interference for FAGE-type HO_x measurements. Our results may contribute to the improvement of inter-instrument agreement and reproducibility of complex diurnal forest data sets.