The concentration of atmospheric carbon dioxide at and near Mauna Loa Observatory, Hawaii, is reported for the first six years (1958-1963) of a long-term program to document the effects of the combustion of coal and petroleum on the distribution of COs gas in the atmosphere and in the world's oceans. The majority of the measurements reported here were obtained at Mauna Loa Observatory with a continuously recording infrared gas analyzer. Also reported are measurements of 261 discrete samples of air collected in glass flasks on Mauna Loa, on the windward coast of Hawaii, and from aircraft near the Hawaiian Islands. The following results have been obtained: (1) The CO2 concentration at Mauna Loa Observatory varies with season with an average amplitude of 6 ppm and is increasing at the average rate of 0.7 ppm per year. (2) These variations reflect regional changes in the air which lies above the trade wind layer near Hawaii. (3) The concentration of COs in the trade wind layer is essentially the same as aloft except during the summer months when it is slightly lower. (4) Volcanic emanations of CO• near the summit of Mauna Loa and uptake of CO• on the forested lower slopes of the mountain influence the concentration of CO• at Mauna Loa Observatory but do not seriously interfere with the determination of regional changes. fluences. The International Geophysical Year provided an opportunity to try both these approaches, and in 1956 an extensive project to monitor atmospherie carbon dioxide was organized [Fritz et al., 1959]. In 1958 accurate continuous surface measurements began in Antarctica and at Mauna Loa Observatory, then a newly established U.S. Weather Bureau meteorological research station on the island of Hawaii. Also, samples of air were collected in glass flasks 3000 to 6000 m above the North Pacific Ocean during weather reconnaissance flights of the United States Air Force. In 1960 collections in glass flasks began in Hawaii and from ships in the Pacific and Indian oceans. In 1961 continuous surface measurements began at Point Barrow, Alaska [Kelley and Church, 1962]. Most phases of the program continued until 1962 or 1963. This article reports in detail the results obtained from Mauna Loa Observatory. Acom-6053 605z• PALES AND panion article [Brown and Keeling, 1965] reports results from Antarctica. Similar reports of the •ircrMt, ship, and Point Barrow projects are in preparation. A general summary of all of the data up to April 1962 has been presented by Bolin and Keeling [1963]. OBSERW• Mauna Loa Observatory is located on the north slope of the volcano Ma.una Loa (Figure 1). The observatory is 3400 m above sea level add 800 m below the summit of the mountain. situated at 19.5øN, 155.6øW, well within the geographic tropics, south and west of the semipermanent eastern Pacific atmospheric highpressure cell. The prevailing surface wind in the vicinity of the island is the northeasterly trade wind, which prevails 80% of the year. Over the ocean this steady moist wind extends KEELING ATMOSPHERIC CARBON DIOXIDE...

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Concurrent ice nucleus counts made twice daily at M a m a Loa Observatory (3.4 h i .) and near sea level at Hilo, Hawaii, from December 1, 1061, to February 5 , 1062, and :it intervals of a few minutes during 24 hours on July 10-11, 1963, indicated thc wide fluctuations observed elsewhere, with counts varying not oiily from day to day, but by as mnch as an order of magnitude within minutes. Background levels at M a m a Loa Observatory ran mcll below those a t Hilo and averaged tinder 10 ice crystals in 10 liters a t-24OC., values comparable with the lowest rcportecl from other isolated localities. At both sites diurnal variations, evidently reflecting thc diurnal mountain circulation and its effects, saw afternoon counts a t Mauna Loa Obscrvatory tending to increase with the influx of more turbid air from lower elevations and those at Hilo to decrease from dispersion of the accumulatcd contaminants by convection and onshore winds. Although the investigation was not designed to look into fundamental questions, the rclativcly small distance betwccn thc two stations, their large difference in elevation, and the Observatory's isolation for much of the day from the underlying atmosphere permitted inferences concerning such matters as the source and vertical distribution of the ice nuclei and the possibility of estraterrcstrial (meteoritic) influcnces. It would appear that the ice nuclei observed at Hilo did not ordinarily or in major part come from aloft, but rather from the lower atmosphere, and that-in gcncral, and in thc prescncc of the trade inversion-the number of icc nuclei decreased with height in thc Hawaiian area. Major oscillations in the four ice nucleus count-sequences (Mauna Loa Observatory and Hilo, morning and afternoon) appeared to be closcly synchronous and to accompany the air mas; changes or other synoptic events implied by the deepening and thinning of the moist layer on the Hilo sounding.

A description is given of the physical setting, facilit,ies, and current program of Mauna Loa Observatory in Hawaii, with emphasis on its suitability as a site for field studies on a wide variety of phenomena.