Variations in atmospheric nitrous oxide observed at Hateruma monitoring station

In situ measurement of atmospheric nitrous oxide (N₂O) has been carried out at Hateruma monitoring station (lat 24°03^′N, long 123°48^′E) since March 1996 by the National Institute for Environmental Studies (NIES). A fully automated gas chromatograph equipped with an electron capture detector (ECD) measures the N₂O concentrations at a frequency of 3 air samples per hour. Details of the experimental methods and procedures are presented in this paper. The N₂O concentrations observed from March 1996 to February 1999 increased at an average rate of 0.64 ppb/yr. The observed data also suggest that there is a weak annual cycle of N₂O concentration, increasing in autumn and winter and decreasing in spring and summer, with a peak-to-peak amplitude of at most 0.3 ppb. The N₂O mixing ratios, smoothed with the 24-h running average, clearly showed short-term variability with synoptic timescales and had peak-to-peak amplitudes of about 1 ppb or less. These short-term variations correlated positively with the short-term variations of CO₂ during the period from winter to early spring when the air masses arriving at Hateruma are dominantly transported from the Asian continent. The ΔN₂O/ΔCO₂ ratios could be used to constrain the relative strengths of these fluxes on a regional scale.