LAUSR

Abstract. We developed thermal dissociation cavity-enhanced absorption spectroscopy (TD-CEAS) for the in situ measurement of NO 2 , total peroxy nitrates (PNs, RO 2 NO 2 ), and total alkyl nitrates (ANs, RONO 2 ) in the atmosphere. PNs and ANs were thermally converted to NO 2 at the corresponding pyrolytic temperatures and detected by CEAS at 435–455 nm. The instrument sampled sequentially from three channels at ambient temperature, 453 and 653 K, with a cycle of 3 min, to measure NO 2 , NO 2+  PNs, and NO 2+  PNs  +  ANs. The absorptions between the three channels were used to derive the mixing ratios of PNs and ANs by spectral fitting. The detection limit (LOD, 1 σ ) for retrieving NO 2 was 97 parts per trillion by volume (pptv) in 6 s. The measurement uncertainty of NO 2 was 9 %, while the uncertainties of PN and AN detection were larger than those of NO 2 due to chemical interferences that occurred in the heated channels, such as the reaction of NO (or NO 2 ) with the peroxy radicals produced by the thermal dissociation of organic nitrates. Based on laboratory experiments and numerical simulations, we created a lookup table method to correct these interferences in PN and AN channels under various ambient organic nitrates, NO, and NO 2 . Finally, we present the first field deployment and compare it with other instruments during a field campaign in China. The advantages and limitations of this instrument are outlined.