A thermal dissociation cavity attenuated phase shift spectroscopy (TD-CAPS) instrument was developed for measuring total peroxy nitrates (PNs) and organic nitrates (ONs) concentrations in the clean atmosphere. This instrument is easy to operate and can be applied to continuous measurement of PNs and ONs. A continuously measurable system is convenient to perform observations, especially in remote areas. Three lines (NO2, PNs, and ONs lines) were used for thermal dissociation. The NO2 line contains a quartz tube that is not heated, while the PN and ON lines contain quartz tubes that are heated at 433 K and 633 K, respectively. The concentrations of NO2, NO2 + PNs, and NO2 + PNs + ONs can be obtained from the NO2, PN, and ON lines, respectively. The lower limit values of the detection limit (3σ) for PNs and ONs were estimated to be 21 parts per trillion by volume with an integration time of 2 min. PNs were selectively thermally decomposed in the PNs line and formed NO2 quantitatively. In the ONs line, both PNs and ONs were thermally decomposed to produce NO2 quantitatively, but partial decomposition of HNO3 at 633 K interfered with the ONs measurement. Therefore, a HNO3 scrubber is required before the ONs line. Continuous observations were conducted with the TD-CAPS instrument in a remote area, and the instrument performed well for obtaining PNs and ONs concentrations.
To investigate long-range transport and oxidation states of nitrogen compounds from the Asian continent, especially of total odd nitrogen species (NO y ), we carried out continuous observations of NO y , total nitrate (T.NO 3 ; the sum of gaseous nitric acid and particulate nitrate) and NO x (= NO + NO 2 ) at Fukue Island, located in westernmost Japan. NO y and T.NO 3 exhibited similar seasonal cycles, with maximum concentrations observed during winter-spring seasons, and minimum concentrations during summer. NO x had a seasonal cycle, with maximum and minimum concentrations in winter and summer, respectively; NO x concentrations also decreased markedly from winter to spring. High-concentration event analyses to assess transboundary pollution of NO y were performed. Transboundary pollution events for NO y were extracted, and classified as either "Case 1" or "Case 2". Case 1 involved transport of NO y , T.NO 3 , and NO x from the Asian continent to Fukue Island, while Case 2 involved transport of NO y and T.NO 3 , but not NO x . Case 1 and Case 2 occurred predominantly in winter and spring, respectively. Air mass trajectories indicated that in Case 1, 52% of air masses passed through Korea, while only 5% passed through Korea in Case 2. These results indicate that some NO x emitted from the Asian continent is transported to Fukue Island as NO x , without it undergoing oxidation, reflecting low photochemical activity and/or short transport times.
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