Formaldehyde early atmosphere

THE YOUNG SUN, THE EARLY EARTH AND THE PHOTOCHEMISTRY OF OXYGEN, OZONE AND FORMALDEHYDE IN THE EARLY ATMOSPHERE... 

The Photochemistry of Oxygen, Ozone, and Formaldehyde in THE Early Atmosphere... 

Silver Catalyst Process. In early formaldehyde plants methanol was oxidized over a copper catalyst, but this has been almost completely replaced with silver (75). The silver-catalyzed reactions occur at essentially atmospheric pressure and 600 to 650°C (76) and can be represented by two simultaneous reactions ... 

AltshuUer and McPherson used spectrophotometiy to analyze aldehydes in the Los Angeles atmosphere in the fall of 1%1. Table 4-16 shows the diurnal variation in both formaldehyde and acrolein oonoentrations. Both rise early, remain relatively constant throughout the day, and decrease... 

The oceans at this time can be thought of as the solution resulting from an acid leach of basaltic rocks, and because the neutralization of the volatile acid gases was not restricted primarily to land areas as it is today, much of this alteration may have occurred by submarine processes. The atmosphere at the time was oxygen deficient anaerobic depositional environments with internal CO2 pressures of about 10-2-5 atmospheres were prevalent, and the atmosphere itself may have had a CO2 pressure near lO-25 atmospheres. If so, the pH of early ocean water was lower than that of modern seawater, the calcium concentration was higher, and early global ocean water was probably saturated with respect to amorphous silica (—120 ppm). Hydrogen peroxide may have been an important oxidant and formaldehyde, an important reductant in rain water at this time (Holland et al., 1986). Table 10.5 is one estimate of seawater composition at this time. 

This is the most explosive of the nitrate esters. Not only will it bum in an atmosphere of oxygen, nitric oxide or nitrogen dioxide, but also it can support a stationary decomposition flame which can be stabilized on a burner [122]. At low pressures the various zones of the decomposition flame are clearly separated and the early stages show strong formaldehyde bands in emission. 

Despite this practical progress, great uncertainty still exists as to the precise mechanism by which formaldehyde is held within a board and slowly released as a gas to the atmosphere. Historically, many have considered the emission potential of a board to be governed, particularly in a board s early life, by the board s so-called free formaldehyde content (9). 

Free formaldehyde could only accumulate over areas where relatively little HCN was being produced. This suggests a seasonal variation, or perhaps even an oceanic environment. Although the concentration problem for formaldehyde is less severe than for HCN, there would still be a formidable problem. Stratification of the primitive ocean would have reduced the effects of dilution by making only the upper 100—200 m readily accessible to the atmosphere (compare Weyl, 1968). A global ocean as suggested by Hargraves (1976) as a consequence of the early formation of a thin sialic crust, would... 

The steady state concentrations of HCN would have depended on the pH and temperature of the early oceans and the input rate of HCN from atmospheric synthesis. Assuming favorable production rates, Miyakawa et al (30) estimated steady state concentrations of HCN of 2 x 10 M at pH 8 and 0°C in the primitive oceans. At 100° C and pH 8 the steady state concentration was estimated as 7 x 10 M. HCN hydrolyzes to formamide which then hydrolyzes to formic acid and ammonia. It has been estimated that oligomerization and hydrolysis compete at approximately 10 M concentrations of HCN at pH 9 (31), although it has been shown that adenine is still produced from solutions as dilute as 10 M (32). If the concentration of HCN were as low as estimated, it is possible that HCN tetramer formation may have occurred on the primitive Earth in eutectic solutions of HCN-H2O, which may have existed in the polar regions of an Earth of the present average temperature. High yields of the HCN tetramer have been reported by cooling dilute cyanide solutions to temperatures between -10° C and -30° C for a few months (31). Production of adenine by HCN polymerization is accelerated by the presence of formaldehyde and other aldehydes, which could have also been available in the prebiotic environment (29). 

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