Revised Line-Strengths and Peak-Positions for cis-HONO at 1660 cm^-1 Using a New CW-QC TILDAS

Nitrous acid, HONO, is a significant source of atmospheric HOx and the production of HONO may be responsible for the recycling of deposited NOy back into the atmosphere in active form. Many current techniques rely on wet-chemical extractive methods, but are potentially prone to interferences and have not always shown good agreement with optical techniques1. Spectroscopy offers an alternative method with greater specificity, however, the rotational-vibrational transitions of HONO in the mid-infrared region are not well studied. We present results from an experiment using a new tunable continuouswave quantum cascade laser absorption spectrometer. We measured the cis-HONO spectra between 1659 and 1660 cm-1 and the trans-HONO spectra near 1275 cm−1 (both at a resolution of about 0.001 cm−1). Absolute mixing ratios of total HONO were determined by catalytic conversion to NO followed by calibrated absorption spectroscopy. The effective line-strengths for cis-HONO near 1660 cm−1 were about a factor of 2.5 smaller than those listed in the ATMOS database, but line-strengths for trans-HONO around 1275 cm−1 agreed well with reported values.