The first 12 years (1974–1985) of continuous atmospheric CO2 measurements from the NOAA GMCC program at the Mauna Loa Observatory in Hawaii are analyzed. Hourly and daily variations in the concentration of CO2 due to local sources and sinks are described, with subsequent selection of data representing background concentrations. A digital filtering technique using the fast Fourier transform and low‐pass filters was used to smooth the selected data and to separate the seasonal cycle from the long‐term increase in CO2. The amplitude of the seasonal cycle was found to be increasing at a rate of 0.05±0.02 ppm yr−1. The average growth rate of CO2 was 1.42±0.02 ppm yr−1, and the fraction of CO2 remaining in the atmosphere from fossil fuel combustion was 59%. A comparison between the Mauna Loa continuous CO2 data and the CO2 flask sample data from the sea level site at Cape Kumukahi, Hawaii, showed that the amplitude of the seasonal cycle at Cape Kumukahi was 23% larger than at Mauna Loa, with the phase of the cycle at Mauna Loa lagging the cycle at Cape Kumukahi by about 1–2 weeks.

Electrochemical concentration cell (ECC) ozonesondes flown by NOAA and NASA Wallops Flight Facility (WFF) personnel during the Stratospheric Ozone Intercomparison Campaign (STOIC) conducted at the Jet Propulsion Laboratory's Table Mountain Facility, Wrightwood, California, July 21 to August 1, 1989, exhibited highly similar ozone measurement precisions and accuracies even though considerably different methods were used by the two research groups in preparing the instruments for use and in calibrating the instruments. The Table Mountain data as well as data obtained in the past showed the precisions to range from about ±3 to ±12% in the troposphere, remain relatively constant at ±3% in the stratosphere to 10 mbar, then decrease to about ±10% at 4‐mbar pressure altitude. Corresponding ozone measurement accuracies for individual ozonesonde soundings were estimated to be about ±6% near the ground, decrease to −7 to 17% in the high troposphere where ozone concentrations are low, increase to about ±5% in the low stratosphere and remain so to an altitude of about 10 mbar (∼32 km), then decrease to −14 to 6% at 4 mbar (∼38 km) where ozone concentrations are again low. Stratospheric ozone measurements were also made during STOIC with ground‐based lidars and a microwave radiometer that will be used for ozone measurements in the future at sites of the Network for the Detection of Stratospheric Change (NDSC). The ECC ozonesonde observations provided useful comparison data for evaluating the performance of the lidar and microwave instruments.

The 1992 global average total ozone, measured by the Total Ozone Mapping Spectrometer (TOMS) on the Nimbus-7 satellite, was 2 to 3 percent lower than any earlier year observed by TOMS (1979 to 1991). Ozone amounts were low in a wide range of latitudes in both the Northern and Southern hemispheres, and the largest decreases were in the regions from 10 degrees S to 20 degrees S and 100N to 60 degrees N. Global ozone in 1992 is at least 1.5 percent lower than would be predicted by a statistical model that includes a linear trend and accounts for solar cycle variation and the quasi-biennial oscillation. These results are confirmed by comparisons with data from other ozone monitoring instruments: the SBUV/2 instrument on the NOAA-11 satellite, the TOMS instrument on the Russian Meteor-3 satellite, the World Standard Dobson Instrument 83, and a collection of 22 ground-based Dobson instruments.

Details are presented concerning the derivation of new, standard, effective ozone absorption coefficients for use with Dobson ozone spectrophotometers. The work was performed under auspices of the World Meteorological Organization (WMO) Global Ozone Research and Monitoring Program, with the goal of improving and standardizing ozone measurements throughout the world. The new coefficients, based on the laboratory measurements of Bass and Paur (1985), were sanctioned for use worldwide, beginning January 1, 1992, by the WMO Executive Panel on Environmental Pollution and Atmospheric Chemistry. The new coefficients, together with use of slightly improved Rayleigh molecular scattering coefficients also adopted as standard, yield total ozone amounts 2.6% smaller than values obtained during July 1, 1957 to December 31, 1991, derived from the use of Vigroux (1953, 1967) ozone absorption coefficients. Information is provided also on correcting ozone data obtained in the past to the new ozone absorption coefficient scale. 1. INTRODUCTION Early Dobson ozone spectrophotometer observations were processed using ozone absorption coefficients based on the laboratory data of Ny and Choong [1933]. At the beginning of the International Geophysical Year (IGY) (July 1, 1957), new absorption coefficients were adopted for use [Dobson, 1957a], employing the laboratory values of Vigroux [1953]. Pre-IGY Dobson spectrophotometer ozone values were converted to the Vigroux [1953] scale by multiplying them by 1.36. Because the Vigroux [1953] coefficients (Table 1) gave inconsistent ozone values from observations on different combinations of wavelengths (e.g., CD-wavelength and ABwavelength observations yielded 10% less and 13% more ozone, respectively, than did AD-wavelength observations), the Vigroux AD-wavelength ozone absorption coefficients were adopted as standard. Based on a redetermination of the ozone absorption coefficients by Vigroux [1967] and an examination of the coefficients by G.M.B. Dobson in light of atmospheric observations made in Canada, the United Kingdom and elsewhere, a modified set of ozone absorption coefficients (Table 2) was derived [World Meteorological Organization (WMO), 1968] which gave highly consistent ozone amounts from observations made on different wavelengths (Table 3). These modified coefficients, which preserved the original Vigroux AD-wavelengths coefficient as standard, were recommended for use by the International 1Now at by the WMO throughout the world beginning January 1, 1968 [WMO, 1968]. Rayleigh molecular scattering coefficients used with the ozone absorption coefficients in processing ozone data were derived from the Rayleigh-Cabanes formula [Dobson, 1957a]. Komhyr [1980] reexamined the Vigroux [1953] ozone absorption coefficients and concluded that the ADwavelengths coefficient of 1.388 cm -1, adopted as standard, may be too small, causing Dobson instrument ozone values to be overestimated by up to 5%. Discussion of the problem with A. Bass (U.S. Bureau of Standards, Gaithersburg, Maryland) promp...

Surface ozone data are presented from up to 12 years of continuous measurements at Point Barrow, Alaska; Mauna Loa, Hawaii; American Samoa, South Pacific; and South Pole, Antarctica. Annual cycle characteristics of the data are described relative to atmospheric mixing and transport processes that give rise to the observed annual ozone distributions. Both positive and negative long‐term trends are exhibited by the data. From examination of trends in the seasonal and monthly data, it is concluded that the cause of the trends is most likely a fluctuation over the years in the stratospheric‐tropospheric exchange and tropospheric circulation processes that distribute ozone within the troposphere, coupled with tropospheric circulation disturbances such as those associated with the El Niño/Southern Oscillation events of 1976 and 1982–1983. Because the positive ozone trend at Barrow occurs during summer months, photochemical ozone production in increasingly polluted Arctic air cannot be ruled out. Ozonesonde data are used to show that the surface ozone observations at Mauna Loa observatory in the downslope wind regimes, and at South Pole, are representative of ozone measurements in the free troposphere, and that the ozone trends observed at Point Barrow and Samoa are likely representative of the lower free troposphere even though the measurements are made in air modified within the boundary layer.