Characterization of a Cavity-Enhanced Absorption Spectrometer For Studying Nitrous Acid Formation Pathways in the Laboratory

Field and laboratory studies suggest that nitrous acid (HONO) may be formed photochemically on boundary layer surfaces through mechanisms that have previously been impossible to study due to analytical limitations. Recent advances in highly sensitive and economical instrumentation for the detection of HONO at trace levels enable studies of surface photochemistry under atmospherically relevant conditions of pressure, relative humidity, and HONO levels. We report here studies of HONO derived from surface photochemistry using a newly built incoherent broad band, cavity-enhanced absorption spectrometer (IBBCEAS). Simultaneous measurements of HONO and NO2 concentrations are enabled using differential optical absorption spectroscopy (DOAS) retrievals. In addition, we compare IBBCEAS measurements of HONO to those made concurrently using a chemical ionization mass spectrometer (CIMS) and discuss the application of these techniques to studying surface photochemistry under atmospherically relevant conditions.