Nitrous acid (HONO) plays an important role in the formation of hydroxyl radical and the nitrogen cycle in atmospheric chemistry. Cavity ring-down spectroscopy (CROS) has been utilized for detection of gaseous HONO in the near-UV spectral region. At the maximum absorption wavelength (354.2 nm), HONO can be detected with a low limit of 5 parts per billion (ppb) in 15 s sampling time, while at a low absorption wavelength, with a high value of 10 parts per million (ppm). The CRDS technique has a large dynamic range of detection, with a good linearity of absorbance versus concentration. The detection sensitivity demonstrated in this study is in the range of the ambient HONO concentration (0.1-10 ppb), and it can be readily improved to a sub-ppb level with upgraded optics and longer cavity. Moreover, this high detection sensitivity is realized with a relatively compact setup (in ～ meters) and with a short sampling time (in 15 s). CRDS renders a promising technique for real-time and absolute measurements of HONO in laboratory and ambient studies. Absorption spectrum and cross sections of HONO near 354 nm have also been examined.
展开▼
