The first measurements of methacrolein (MACR) and methyl vinyl ketone (MVK) in the atmosphere are reported. The compounds both show a strong seasonal variation, with a maximum in the summer. The concentrations of MACR and MVK are highly correlated with each other and with the concentration of isoprene, in accord with the expectation that they are the major initial products of isoprene oxidation. However, the observed MACR/MVK ratio does not agree with the model predictions over the range of conditions normally observed in the nonurban continental boudary layer. We suggest that this indicates a major gap in our understanding of the photochemistry of hydrocarbons in the nonurban troposphere.

Recent measurements of the exhaust gases in the stacks of power plants burning coal and natural gas have shown high levels of nitrous oxide. Calculations based upon the known combustion parameters of the power plants and extrapolated to the current world production of coal and natural gas indicate that combustion may be a significant source of nitrous oxide in the atmosphere. In view of the predicted increases in the combustion of fossil fuels, particularly coal, it is likely that the importance of combustion as a source of atmospheric nitrous oxide will increase. As a result of the current uncertainty regarding the size of the various sources and sinks of nitrous oxide in the atmosphere, it would appear that the question of the importance of combustion to the atmospheric nitrous oxide budget deserves further scrutiny.

Direct measurements of ambient levels of N 2 O are possible using a hot electron capture detector. The method is very precise with a standard error of less than 1% obtained for automated analysis of ambient air samples. The system is applicable to unattended automated field studies as well as discrete laboratory analyses and/or intensive calibration studies. The system described has been used extensively in the field from mobile laboratories and on board Oceanographic research vessels.

In March 1976 the first N,O measurements were made in the sea water and marine air of the eastern tropical Pacific Ocean during a cruise from San Diego, California, to San Martin, Peru. Continuous measurements of N,O in the marine atmosphere were made throughout the duration of the cruise. The tropospheric mixing ratio was 332 f 9 p.p.b. v/v N,O. The concentration of N,O in the marine air appeared to show a direct relationship to the N,O concentration in the surface sea water, with the highest N,O mixing ratios over regions which were highly supersaturated, off the coasts of Baja California and Peru, and in the equatorial upwelling region. The surface sea water samples were generally supersaturated with N,O, with an average saturation of 145% relative to the marine atmosphere. The average flux of N,O from the surface sea water into the atmosphere was 0.5 x s-I. Only one surface sea water sample showed significant undersaturation; the other 28 surface water samples were approximately saturated or supersaturated. Water samples were also collected down to depths of 300 m during seven hydrocast stations. The stations showed two distinct distribution patterns for N,O concentration versus depth for the region between the surface and 300 m. At five of the seven stations the N,O concentration increased rapidly from the surface to a depth of 100 m, and then remained relatively constant down to the maximum depth of 300 m. At the other two stations the N,O concentration showed the same rapid increase between the surface and 75-100 m, but then the N,O concentration decreased in the next 5&75 m until the concentration of N,O at 150 m was lower than that found at the surface. At these two stations the water from 150 m to 300 m was just saturated or undersaturated with N,O with respect to the atmosphere. These two stations were located in the oxygen-deficient region off the coast of Mexico, which suggests that the low N,O concentrations below the thermocline may be due to denitrification. However, stations in the oxygen-deficient region off the coast of Peru showed considerable N,O supersaturation at all depths. Recent results indicate that the role of N,O in the nitrogen cycle of the ocean may be more complex than has previously been suggested. g N,O 004(12826/80/010056-17$02.50/0 @ 1980 Munksgaard, Copenhagen Tellus 32 (1980), 1

Measurements of nitrous oxide in the earth's atmosphere over the past 40 years indicate a concentration of between 250 and 400 ppb vol/vol N:O. There is some disagreement among researchers about the degree to which nitrous oxide varies at the surface, both on land and over the ocean. Measured variations in the surface concentration of N:O range from 10% to less than 0.5%, implying atmospheric lifetimes from 1.4 years to greater than 28 years, respectively. Recent extensive measurements by the authors and co-workers indicate extremely little variation of nitrous oxide in the troposphere, with a concentration of approximately 330 ppb vol/vol. Continuous measurements made over a 3-month period showed a variation of less than 1%. Samples collected from 80øN to 90øS latitude showed no significant variation. Measurements in the troposphere and lower stratosphere showed a constant level of N:O from the ground to the tropopause and then a gradual decrease in the lower stratosphere. The only large-scale variation found for nitrous oxide in the troposphere appears to be associated with the northeast trade winds system and may originate in North Africa. There also appears to be a bias inherent in the different methods of measuring N:O, and a program of intercalibration among the laboratories making measurements is necessary to resolve the question of the absolute concentration of nitrous oxide in the atmosphere. ß = $ ß ß ß ß ß ß ß ß