JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 91, NO. Dll, PAGES 11,911-11,914, OCTOBER 20, 1986 Day and Night Profiles of Tropospheric Nitrous Oxide WESLEY R. COFER III, VICKIE S. CONNORS, AND JOELS. LEVINE Atmospheric Sciences Division, NASA Lan•7ley Research Center,Hampton,Vir•iinia ROBERT A. EDAHL, JR. Materials Division,NASA Lanqley ResearchCenter, Hampton, Virqinia Daytime and nighttime vertical profiles of the tropospheric tracegasN20 weredetermined from grab sample collections off theAtlantic andGulf coasts of Florida. The grabsamples were collected during the week of October 7-13, 1984,from a Lear Jet during descent spirals over an altitude rangeof 12.5-0.3 km in approximately 1.2-km intervals. During this period there weretwo distinct airflowregimes sampled: the surface boundary layer (< 2 km), in which the wind direction was typicallyeasterly; and the regime above the boundary layer, which waspredominantly characterized by westerly flow. N20 mixing ratios, normalized to dry air, weredetermined from 148daytimeand nighttime samplings. N20 wasfoundto be uniformly mixed at all altitudes at 301.9 4- 2.4 parts per billion by volume. INTRODUCTION In the stratosphere the decomposition of nitrous oxide (N20) leadsto the destruction of ozone [Crutzen, 1970; John- ston, 1971; McElroy and McConnell, 1971], and globally, it may account for as much as 70% of the chemicaldestruction of stratospheric ozone [Turco, 1985]. Sincethe troposphere is the primary source of stratospheric N20, recentmeasurements indicating that tropospheric concentrations of N20 may be increasing at a rate of as much as 0.2% per year [Weiss, 1981; Khalil and Rasmussen, 1983] are of seriousconcern. In addi- tion to its role in the destruction of stratospheric ozone, ni- trous oxide is a "greenhouse" absorber of long-wave infrared radiation [Wan•l et al., 1976; Donner and Ramanathan, 1980]. Calculations have indicated that a doubling in N20 con- centration could lead to a global temperature increase in the range of 0.35-0.86 K [Wan•l and Molnar, 1985]. Nitrous oxide is produced at the surface primarily by mi- crobial activity in soils [Anderson and Levine, 1986], with smaller contributions from biomassburning and anthropoge- nic combustion processes. N20 is believed to be chemically inert in the troposphere, reaching the stratosphereby atmo- spheric transport and diffusion. About 90% of the strato- spheric N20 is thought to be destroyed by ultraviolet pho- tolysis producing nitrogen (N2) and excited atomic oxygen O(•D). The remaining N20 is destroyed by reactionwith (O(•D)), producing eithernitric oxide (NO), whichis respon- siblefor the catalyticdestruction of stratospheric ozone [Crut- zen, 1970; Johnston, 1971; McElroy and McConnell, 1971], or molecular nitrogen (N2) and molecular oxygen (02). The at- mospheric lifetime of N20 has been estimated at about 100 years by Turco [1985]. This relatively long atmosphericlife- time suggests that there are no tropospheric sinks for N20 and that global tropospheric N20 levels should not exhibit short-term temporal variations. However, several studieshave questioned theseideas about the variability and lifetime of N20 in the troposphere.N20 has been shown to undergo both thermal and photochemical decompositon (at wave- lengths greater than 280 nm) when it is adsorbed on various dry sands, which may explain the measured drop in N2 ¸ concentrations associated with the dust regions in eastern This paper is not subject to U.S. copyright. Published in 1986 by the American Geophysical Union. Paper number6D0416. North Africa [Rebbert and Ausloos,1978]. Diurnal variations in N20 concentrations have been reported near the surface by Brice et al. [1977], by Cicerone et al. [1978], and by Matthias et al. [1979]. The Brice et al. [1977] measurements indicated a diurnal variation amplitude of about 10% that could be ex- plained as the result of a possible tropospheric N20 sink. Matthias et al. [1979] also observed significant diurnal vari- ations in N20 but attributed their variations to sourceemis- sions. Smaller diurnal variations in N20 were reported by Cicerone et al. [1978]. While a substantial number of N20 surfacemeasurements [Sin•lh et al., 1979; Weiss, 1981; Khalil and Rasmussen, 1983] and stratospheric profiles [Goldan et al., 1980; Fabian et al., 1981; Galla•lher et al., 1983; Jones and Pyle, 1984] have ap- peared in the literature, relatively few profiles have been ob- tained that characterize N20 concentrations betweenthe sur- face and the tropopause.Most of the reported profiles,though no.tnecessarily spanningthe vertical extent of the troposphere, are found in the work of Ehhalt et al. [1975], Goldan et al. [1978, 1981], Fabian et al. [1979, 1981-1, and Robinsonet al. [1983]. Even less information exists on nighttime profiles of N20. To remedy thesedeficiencies, we have obtained a series of daytime and nighttime profilesof N20 in the troposphere. EXPERIMENT During the week of October 7-13, 1984, an airborne sam- pling program was conducted from Homestead Air Force Base (HAFB), Homestead, Florida. Grab samples were col- lected during descending spiral manuevers (12.5-0.3 km) per- formed by a NASA Lewis Research Center Lear Jet off the Atlantic and Gulf coasts of Florida. These measurements were obtained as part of a correlativemeasurement effort support- ing the MAPS (Measurement of Air Pollution from Satellites) experiment's carbon monoxide and nitrous oxide sensors. The MAPS instrument was launched October 5, 1985, as part of the spaceshuttle Office of Spaceand Terrestrial Applications OSTA 3 experimentalpallet. Grab samples were collected in 0.3-L heat-treatedstainless steel bottles. During flights, air was continuouslycirculated (fed by aircraft ram pressure) through a samplingmanifold. Two metal diaphragm pumps connected in series were at- tached to the manifold and were used to charge the sample bottles to about 3.5 atm. The evacuated bottles were charged as samplingwas initiated, immediately discharged, the process 11,911