UV absorption cross sections of nitrous acid

The UV absorption cross sections of nitrous acid (HONO) and its deuterated analogue (DONO) have been measured in a slow flow system. Nitrous acid was produced by a high purity source reaching concentrations up to 22 ppm with a purity of >95% and a long-term variation of 2%. The concentrations were measured by ion chromatography. Differential absorption cross sections for a spectral resolution of 0.5 nm of (2.98±0.26)×10−19 cm2 and (3.04±0.26)×10−19 cm2 have been obtained for the HONO absorption maxima at 354.2 and 368.1 nm, respectively. In addition, differential absorption cross sections of DONO were measured for the first time. The values of (2.67±0.24)×10−19 cm2 at 353.3 nm and (3.20±0.26)×10−19 cm2 at 367.6 nm are comparable to those of HONO. Absolute absorption cross sections were also derived for these species. The values of both the differential and absolute absorption cross sections determined in this work are lower than those reported previously. Therefore, the concentrations in the atmosphere may be 30–50% higher than that reported in several publications in which DOAS spectrometers were used for the determination of the HONO concentration.