In situ measurement of N 2O 5 in the urban atmosphere by thermal decomposition/laser-induced fluorescence technique

Abstract

The laser-induced fluorescence (LIF) detector with a thermal converter has been developed for measuring atmospheric N 2O 5. The detection limit for N 2O 5 was 11 pptv for 10-min averaging ( S / N = 2 , [NO 2]=0). The field measurements of N 2O 5 were conducted in the urban atmosphere in winter. N 2O 5 was successfully monitored during four nights. Typically, observed N 2O 5 level was in the range of 0–200 pptv. Note that N 2O 5 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 , N 2O 5 chemistry was discussed for a representative case of the urban night. Observed trend of N 2O 5 was compared with the theoretically predicted one. The heterogeneous loss rate of N 2O 5 on the aerosol surfaces was estimated as 5.2×10 −4 s −1. Consequently, it was confirmed that N 2O 5 loss was critical for NO x budget in the urban atmosphere in winter, in comparison with NO x loss via NO 3. The LIF instrument proved to be useful for studying nocturnal chemistry of N 2O 5 in the source region.