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 less than or equal to 2%. Th e concentrations were measured by ion chromatography. Differential absorpti on cross sections for a spectral resolution of 0.5 nm of (2.98 +/- 0.26) x 10(-19) cm(2) and (3.04 +/- 0.26)x 10(-19) cm(2) have been obtained for the HONO absorption maxima at 354.2 and 368.1 nm, respectively. In addition, d ifferential absorption cross sections of DONG were measured for the first t ime. The values of (2.67 +/- 0.24) x 10(-19) cm(2) at 353.3 nm and (3.20 +/ - 0.26) x 10(-19) cm(2) at 367.6 nm are comparable to those of MONO. Absolu te absorption cross sections were also derived for these species. The value s of both the differential and absolute absorption cross sections determine d in this work are lower than those reported previously. Therefore, the con centrations in the atmosphere may be 30-50% higher than that reported in se veral publications in which DOAS spectrometers were used for the determinat ion of the HONO concentration. (C) 1999 Elsevier Science Ltd. All rights re served.