[AAS04-P22] Measurement on the 17O-excess of tropospheric nitrogen oxides
Keywords:nitrogen oxides, troposphere, triple oxygen isotope
Nitrogen oxides are important trace gases that influence the concentrations of atmospheric oxidants that drive tropospheric and stratospheric chemistry. Triple oxygen isotopes (Δ17O values; deviation of 17O from the mass dependent fractionation line) have been used to understand complex chemical systems such as the cycling and oxidation of NOx. For example, Δ17O valuesof atmospheric nitrate (HNO3, NO3-, and p-NO3-), indicates the proportion of NOx that reacts with ozone (O3) during its oxidation (Michalski et al., 2003; Tsunogai et al., 2010; Nelson et al., 2018). Δ17O values of atmospheric nitrous acid (HONO; recognized as a potentially important source of OH radicals) have also been used recently to decipher their production pathways. In these studies, however, predicted Δ17O values were used for NO2. Here, we tried to establish a method to determine Δ17O values of atmospheric NO2.
Δ17O value of NO2 was determined, together with Δ17O value of HONO, by combining sensitive determination method on isotope compositions of NO2-(Komatsu et al., 2008; Tsunogai et al., 2010) with a slightly modified filter-pack method (Noguchi et al., 2007), in which both NO2 and HONO were collected simultaneously as NO2-on triethanolamine (TEA)-coated filter and alkaline (K2CO3) impregnated filter, respectively. Periodical sampling of atmospheric NO2 and HONO was carried out at Hokkaido Institute of Environmental Sciences, Sapporo and at Nagoya University, which is located in a suburban area of Nagoya City. The sample collection period was fixed to one week with a flow rate of 10 L/min. In order to determine diurnal variation in Δ17O value of NO2 and HONO, an automated system for time-interval air sampling equipped with 6 four-stage-filter-packs were made and used it to collect atmospheric samples every 4 hours.The Δ17O values of NO2 and HONO showed similar diurnal variations; higher value on the day time than the night time. The result suggests that the atmospheric HONO is formed mainly by chemical reaction of NOx in the urban atmosphere.
Δ17O value of NO2 was determined, together with Δ17O value of HONO, by combining sensitive determination method on isotope compositions of NO2-(Komatsu et al., 2008; Tsunogai et al., 2010) with a slightly modified filter-pack method (Noguchi et al., 2007), in which both NO2 and HONO were collected simultaneously as NO2-on triethanolamine (TEA)-coated filter and alkaline (K2CO3) impregnated filter, respectively. Periodical sampling of atmospheric NO2 and HONO was carried out at Hokkaido Institute of Environmental Sciences, Sapporo and at Nagoya University, which is located in a suburban area of Nagoya City. The sample collection period was fixed to one week with a flow rate of 10 L/min. In order to determine diurnal variation in Δ17O value of NO2 and HONO, an automated system for time-interval air sampling equipped with 6 four-stage-filter-packs were made and used it to collect atmospheric samples every 4 hours.The Δ17O values of NO2 and HONO showed similar diurnal variations; higher value on the day time than the night time. The result suggests that the atmospheric HONO is formed mainly by chemical reaction of NOx in the urban atmosphere.