Abstract
Abstract. We developed thermal dissociation cavity-enhanced absorption spectroscopy (TD-CEAS) for the in situ measurement of NO2, total peroxy nitrates (PNs, RO2NO2), and total alkyl nitrates (ANs, RONO2) in the atmosphere. PNs and ANs were thermally converted to NO2 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 NO2, NO2+ PNs, and NO2+ 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, 1σ) for retrieving NO2 was 97 parts per trillion by volume (pptv) in 6 s. The measurement uncertainty of NO2 was 9 %, while the uncertainties of PN and AN detection were larger than those of NO2 due to chemical interferences that occurred in the heated channels, such as the reaction of NO (or NO2) 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 NO2. 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.
Highlights
Organic nitrates (ONs) act as temporary NOx reservoir species, which affect atmospheric circulation and impact air quality and climate (Mellouki et al, 2015)
gas chromatography (GC) is used for the separation of species, and the separated substances are quantified by electron capture detectors (ECDs), luminol chemiluminescence (CL), or mass spectrometry (MS) (Atlas, 1988; Blanchard et al, 1993; Flocke et al, 2005; Gaffney et al, 1998; Hao et al, 1994; Luxenhofer et al, 1994; Tanimoto et al, 1999)
The source was used for the laboratory experiments after the temperature of the Hg lamp stabilized at 39.0 ◦C, and the source level and stability were double-checked by a GC-ECD instrument
Summary
Organic nitrates (ONs) act as temporary NOx reservoir species, which affect atmospheric circulation and impact air quality and climate (Mellouki et al, 2015). Peroxy nitrates (PNs, RO2NO2) and alkyl nitrates (ANs, RONO2) are two important kinds of organic nitrates They are closely related to the distribution of oxidants in the atmosphere by terminating the HOx cycle. GC is used for the separation of species, and the separated substances are quantified by electron capture detectors (ECDs), luminol chemiluminescence (CL), or mass spectrometry (MS) (Atlas, 1988; Blanchard et al, 1993; Flocke et al, 2005; Gaffney et al, 1998; Hao et al, 1994; Luxenhofer et al, 1994; Tanimoto et al, 1999) These methods measure individual species accurately (Roberts et al, 2003), but the individual standards are incomprehensive. The detailed setup of the instrument, laboratory characterizations, and its first field application in China are presented
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