A new method for the atmospheric detection of the nitrate radical (NO3)

Cavity ring-down spectroscopy (CRDS) has been used for the first time to detect the nitrate radical, NO3. The NO3 radical was detected in ambient room air that had been dosed with a precursor of the radical, dinitrogen pentoxide, N2O5. The absorption spectrum of the NO3 radical was recorded around its maximum absorbance at 662 nm, confirming that the species observed was the NO3 radical. The noise-equivalent mixing ratio (i.e. the mixing ratio where the observed signal equals the r.m.s. baseline noise) is 2 pptv in a 30 s averaging period. Experimental improvements are expected to reduce both the acquisition time and lower the detection limit.