PEM-Tropics-A (Aug 15 - Oct 5, 1996)

Brief description

A NASA/GTE aircraft campaign over the central and eastern Pacific Ocean, using the NASA DC-8 and P-3B aircraft.

The major objectives of PEM-Tropics (Phases A and B) were to provide baseline data over the southern Pacific Ocean for gases important in controlling the oxidizing power of the atmosphere, including O3, H2O, NO, CO and hydrocarbons, to improve scientific understanding of the factors controlling the concentrations of these gases, and to assess the resulting sensitivity of the oxidizing power of the atmosphere to anthropogenic and natural perturbations. In addition, PEM-Tropics A had three secondary objectives: (1) to survey the concentrations of aerosol precursors and ultra- fine aerosol particles over the Southern Pacific basin; (2) to improve our understanding of sulfur gas-to-particle formation over the region; and (3) to provide detailed latitude-altitude transects of long-lived gases for the evaluation of global tropospheric models.

Special remarks concerning ETHmeg database content

PEM-Tropics data were obtained on a CD-ROM produced by NASA Langley. Among other data, the CD-ROM contains measurements from the DC-8 and P-3B aircraft and from ozonesondes.
Here are some comments for the DC8-flights and the P-3B flights.

PEM-Tropics data are in a special data format described by the documentation on the CD-ROM. Harvard University has already produced merged files at several different averaging intervals. We used the 5-min averaged merge-files and performed no further averaging (many thanks to Martin Schultz, MPI Hamburg, for providing the IDL routine gte_read.pro).

The following parameters in the merge files were included in the database:

• O3 (DC8, P3B): measured by Gregory (DC8) and Carroll (P3B) by chemiluminescence
• CO (DC8, P3B): measured by Sachse with Diode Laser Differential Absorption IR
• H2O2 (DC8, P3B): measured by Heikes with Enzyme Derivitization Fluorescence (DC8) and HPLC (P3B)
• calcQw (DC8), SH1011 (P3B). Specific humidity (calculated)
• OH (P3B)
• NO (DC8, P3B): For P3B also NO_ETU (total error) and NO_LIM (detection limit) were stored. Measured by Bradshaw with Laser induced Fluorescence (DC8) and by Carroll with Chemiluminescence (P3B)
• NO2 (DC8): measured by Bradshaw with Laser induced Fluorescence
• HNO3 (DC8, P3B): measured by Talbot with Mist Chamber/Ion Chromatography (DC8) and by Hubert with Filter Sampling
• PAN (DC8): measured by Singh with GC
• ETHANE_B (DC8, P3B): Ethane, measured by Blake with Grab Samples/GC
• Temperature (DC8, P3B)
• JNO2 (DC8, P3B). For the P3B the downwelling (JNO2_Z(enith)) and upwelling (JNO2_N(adir)) were stored separately.

• Invalid data were sometimes set to -8.88e30 instead of -9.99e30. All data with values below -5e30 were invalidated.
• Several negative NO, NO2, HNO3, and H2O2 values of several 100 pptv were eliminated.
• A few strongly negative JNO2 (less than -0.5 s-1) were removed.

Problems with ozone sounding files:

• Some negative and zero values in Easter Island sounding on 25 Oct 1996 (file cjo3se46.pmt)
• Sounding on 23 Dec 1997 (file bgo3s201.pmt) in New Zealand has only zero values for O3 mixing ratios.

DC-8: Overview of measurement techniques and uncertainties

P3B: Overview of measurement techniques and uncertainties

References