In situ measurement of N₂O₅ in the urban atmosphere by thermal decomposition/laser-induced fluorescence technique

The laser-induced fluorescence (LIF) detector with a thermal converter has been developed for measuring atmospheric N₂O₅. The detection limit for N₂O₅ was 11 pptv for 10-min averaging (S/N=2, [NO₂]=0). The field measurements of N₂O ₅ were conducted in the urban atmosphere in winter. N ₂O₅ was successfully monitored during four nights. Typically, observed N₂O₅ level was in the range of 0-200 pptv. Note that N₂O₅ reached 800 pptv at one night, when NO_x level was extremely high and the temperature was low. After the data were selected by the stability of NO_x, N₂O ₅ chemistry was discussed for a representative case of the urban night. Observed trend of N₂O₅ was compared with the theoretically predicted one. The heterogeneous loss rate of N₂O ₅ on the aerosol surfaces was estimated as 5.2×10^-4 s^-1. Consequently, it was confirmed that N₂O₅ loss was critical for NO_x budget in the urban atmosphere in winter, in comparison with NO_x loss via NO₃. The LIF instrument proved to be useful for studying nocturnal chemistry of N₂O ₅ in the source region.