HR: 1340h
AN: A53C-0901    [Abstracts]
TI: Observation of nocturnal NO3 and N2O5 in the urban atmosphere by laser-induced fluorescence technique
AU: * Kajii, Y J
EM: kajii@atmchem.apchem.metro-u.ac.jp
AU: Imai, H
EM: k-dub@atmchem.apchem.metro-u.ac.jp
AU: Kosugi, N
EM: knaohiro@atmchem.apchem.metro-u.ac.jp
AU: Matsumoto, J
EM: mjun@atmchem.apchem.metro-u.ac.jp
AU: Kato, S
EM: shungo@atmchem.apchem.metro-u.ac.jp
AB: Nitrate radical (NO$_{3}$) and dinitrogen pentoxide (N$_{2}$O$_{5}$) play critical roles in the nocturnal atmosphere. NO$_{3}$ and N$_{2}$O$_{5}$ are important as intermediates in the NOx loss process. NO$_{3}$ can react with various hydrocarbons and contribute the lifetimes of them. N$_{2}$O$_{5}$ can be removed from the atmosphere on the aerosol surface. To discuss lifetime of NOx in the atmosphere, it is essential to know the nighttime chemistry of NO$_{3}$ and N$_{2}$O$_{5}$ accurately. However, there are few studies on the observation of NO$_{3}$ and N$_{2}$O$_{5}$ previously. In this study, a sensitive analyzer for measuring NO$_{3}$ and N$_{2}$O$_{5}$ has been developed utilizing the thermal conversion and laser-induced fluorescence (LIF) technique. The calibration of the analyzer has been carried out by the series of N$_{2}$O$_{5}$ decomposition and gas phase titration of NO$_{3}$ by NO. As a result of characterization and optimization of the instrument, the sensitivity of the NO$_{3}$ detector was 0.21 cps ppbv$^{-1}$ mW$^{-1}$ and the limit of detection reached 4 and 6 pptv for NO$_{3}$ and N$_{2}$O$_{5}$, respectively, for {\it S/N} = 1 and 10-min averaging. The analyzer has sufficient potential to detect nighttime NO$_{3}$ and N$_{2}$O$_{5}$ in the atmosphere. Then, to discuss NOx loss, a field observation of NO$_{3}$ and N$_{2}$O$_{5}$ were conducted during winter and spring at an urban site. In the urban atmosphere, NO$_{3}$ level was quite low due to significant abundance of NO. However, 100 - 800 pptv of N$_{2}$O$_{5}$ was observed. The steady-state analysis for NO$_{3}$ and N$_{2}$O$_{5}$ was conducted to know the loss rate of NOx via NO$_{3}$ and N$_{2}$O$_{5}$. Consequently, the loss rates of NO$_{3}$ and N$_{2}$O$_{5}$ were estimated as 1.0 x 10$^{-2}$ and 5.2 x 10$^{-4}$ s$^{-1}$, respectively. Nocturnal loss of NOx was determined as 5.6 ppbv night$^{-1}$, as significant as the daytime loss of NOx via NO$_{2}$ + OH. N$_{2}$O$_{5}$ is important as NOx sink when the ambient temperature is low enough for N$_{2}$O$_{5}$ to survive for a long time. To discuss NOx budget, it is important to know how much NOx can survive and be supplied out of the source area.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0317 Chemical kinetic and photochemical properties
DE: 0345 Pollution--urban and regional (0305)
DE: 0394 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting