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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. [ABSTRACT FROM AUTHOR]