Instrument: NO, NO₂, and NO_y

Principal Investigator: Yutaka Kondo

Co-Investigators: Makoto Koike, Kazuyuki Kita, Nobuyuki Takegawa

Organization:
Research Center for Advanced Science and Technology, University of Tokyo
4-6-1 Komaba, Meguro, Tokyo
153-8904, Japan
Tel: 81-3-5452-5145, Fax: 81-3-5452-5148
kondo@atmos.rcast.u-tokyo.ac.jp

Principle of Operation: Nitric oxide (NO) is measured using an NO/O₃ chemiluminescence technique.   The absolute sensitivity of the entire system is calibrated every 50 minutes by adding known amount of NO in N₂ gas to the sample air.  Systematic errors in the mixing ratios of NO arise from uncertainties in the sensitivity and artifact (zero bias).   The overall accuracy of the NO measurements is 10%.

The precision of the NO measurements can be determined by the fluctuation in the photon counts, as was done previously.  The sensitivity of the instrument used for SOLVE was about 14 cps pptv^-1 for NO.  The estimated limit of detection (LOD) and precision for the data integrated for 1s are in the upper troposphere was 4 pptv (1-sigma) for a 1 s integration time.

Our NO measurements were compared with those of GIT during PEM-W-A and B and DLR during SONEX.  All of these measurements showed good agreement, within about 10 % for NO levels higher than 50 pptv during SONEX.  During the SONEX and SOLVE measurements, numerous spikes in NO were encountered in the North Atlantic Flight Corridor (NAFC).  Our NO data could resolve the rapid change in NO caused by aircraft exhaust.

Nitrogen dioxide (NO₂) is measured by UV photolytic conversion to NO followed by chemiluminescence detection.  UV radiation between 320 and 400 nm effectively dissociates NO₂ without dissociating other reactive nitrogen species, such as HNO₃ and HO₂NO₂.   During the SOLVE measurements the NO₂ conversion efficiency of our system was stable to be 50±2 %.  A higher conversion efficiency will be achieved by increasing the photolysis cell pressure for the measurements in the free troposphere.

By controlling the temperature of the cell to about 10 °C, thermal decomposition of reservoir species other than NO₂, such as N₂O₅ and HO₂NO₂, can be suppressed to a negligibly small amount. The 1-sigma detection limit for the NO₂ data integrated for 10 s was estimated to be 13 pptv based on our SOLVE data.  With careful temperature control and cleaning of the photolysis cell, artifact and interferences from other reactive nitrogen species can be minimized.

In addition to NO and NO₂, gas phase-NO_y measurements are made by sampling air through the rearward facing inlet which discriminates against particles of diameter larger than 1 μm.  The mixing ratios of total NO_y (gas phase-NO_y + amplified particulate-NO_y) are also measured by sampling air through the  forward facing inlet which is heated to 100 °C.  We are able to make these data and available if required by TRACE-P science team.

Accuracy of NO measurement: 10 %

Detection limit for NO measurements: 4 pptv for 1s integration time

Detection limit for NO₂ measurements: 13 pptv for 10s integration time

Sample time: 1 second

References:

Kondo, Y., M. Koike, S. Kawakami, H.B. Singh, R. Talbot, H. Nakajima, G.L. Gregory, D.R. Blake, G.W. Sachse, and J.T. Merrill, Profiles and partitioning of reactive nitrogen over the Pacific Ocean in winter and early spring, J. Geophys. Res., 102, 28405-28424, 1997.

Kondo, Y., S. Kawakami, M. Koike, D.W. Fahey, H. Nakajima, Y. Zhao , N. Toriyama, M. Kanada, G.W. Sachse, and G.L. Gregory, The performance of an aircraft instrument for the measurement of NOy, J. Geophys. Res., 102, 28663-28671, 1997.

Kondo, Y., M. Koike, H. Ikeda, B.E. Anderson, K.E. Brunke, Y. Zhao, K. Kita, T. Sugita, H.B. Singh, S.C. Liu, A. Thompson,. G. L. Gregory, R. Shetter, G. Sachse, S.A. Vay, E.V. Browell, and M. J. Mahoney, Impact of aircraft emissions on NOx in the lowermost stratosphere at northern midlatitudes, Geophys. Res. Lett., 26, 3065-3068, 1999.

Koike, M., Y. Kondo, G.L. Gregory, B.E. Anderson, G.W. Sachse, D. Blake, H.B. Singh, A. Thompson, K. Kita, Y. Zhao, T. Sugita, R. Shetter, H. Ikeda, S.C. Liu, L. Jeagle, and N. Toriyama, Impact of aircraft emissions on reactive nitrogen over the North Atalantic Flight Corridor region, J. Geophys. Res., 105, 3665-3677, 2000.