[1] Emissions of CH 3 Cl, CH 3 Br and CH 3 I were measured biweekly for 12-to 24-month periods between March 2002 and March 2005 from monospecific stands of four dominant southern California coastal salt marsh plants. These measurements revealed large inherent differences between species and more detailed patterns of seasonal production than previously reported. Marsh plants displayed intrinsic abilities to produce methyl halides. Salt marsh plants produced 92% of CH 3 Cl and 90% of CH 3 Br emitted and only 41% of the emitted CH 3 I. Unvegetated areas emitted 7.9% of CH 3 Cl, 9.9% CH 3 Br, and 59% of the emitted CH 3 I. The accuracy of the estimated methyl halide emissions from a coastal marsh and probably other ecosystems can be dramatically improved with increasing the number of species being measured and including emission from barren (mudflats and soil) areas. Estimates of global salt marsh emissions based on vegetated and barren area are 130, 21, 5.5 (mg m À2 yr À1 ) for CH 3 Cl, CH 3 Br, and CH 3 I, respectively, or 1.2, 3.9, and 0.8% of total global fluxes of these gases.

[1] Two mangrove species, Avicennia germinans and Rhizophora mangle, were greenhouse grown for nearly 1.5 years from saplings. A single individual of each species was monitored for the emission of methyl halides from aerial tissue. During the first 240 days, salinity was incrementally increased with the addition of seawater, and was maintained between 18 and 28% for the duration of the study. Exponential growth occurred after 180 days. Methyl halide emissions normalized to leaf area were measured throughout the study and varied dramatically. Emission rates normalized to land area (mg m À2 y À1 ), assuming a LAI = 5, yielded 82 and 29 for CH 3 Cl, 10 and 1.6 for CH 3 Br, and 26 and 11 for CH 3 I, for A. germinans and R. mangle, respectively. From these preliminary determinations, only CH 3 I emissions emerge as being of possible global atmospheric significance. This study emphasizes the need for field studies of methyl halide emissions from mangrove forests.

Abstract. Methyl bromide is the most abundant brominated hydrocarbon gas in the atmosphere and is significant as a source of stratospheric bromine radicals that destroy ozone. However, estimated sources and sinks of methyl bromide exhibit a deficit in sources of--•70 Gg/yr (one Gg -109 g), and the proportion of natural and anthropogenic sources is not known well. Known sources include agricultural fumigation (preplant and postplant), structural fumigation, biomass burning, gasoline additives, and oceans. The oceans, however, also act as a net sink for methyl bromide; that is, globally, consumption is greater than production. Early estimates of emissions of methyl bromide from fumigated agricultural fields from models were 30-60% of the amount applied. To test this estimate, we studied emissions from six field fumigations using chambers to measure the flux of methyl bromide, soil bromide analyses to measure degradation, and soil gas down to 90 cm or more to monitor methyl bromide with time in the soil profile. We found between 24-74% of applied methyl bromide was emitted. The average emission found in these experiments was 49 _+ 19% based on chamber measurements and 52 +_ 20% based on the soil bromide measurements. Factors affecting emissions included the polyethylene film covering the soil, the injection method, the injection depth, and the chemical and physical properties of the soil. The main factors controlling the emissions in our studies are discussed. IntroductionMethyl bromide is the most abundant organic brominecontaining gas in the atmosphere [Schauf-fier et al., 1993]. Methyl bromide is destroyed by hydroxyl radicals in the troposphere, but some can be transported into the stratosphere where it is photooxidized releasing bromine atoms, which attack ozone catalytically [Wofsy et al., 1975]. Unlike chlorofluorocarbons, methyl bromide has both natural and man-made sources, and it is difficult to assess the fraction of atmospheric methyl bromide produced from man-made sources, and whether it significantly affects the global environment. Recent research is redefining our understanding of the sources and sinks of methyl bromide.Estimated budgets of atmospheric methyl bromide have been deduced by Yvon-Lewis and Butler [1997] There are many advantages in using methyl bromide for field fumigations. Because of methyl bromide's high vapor pressure and low boiling point, transport is rapid, and depth of penetration is extensive. A polyethylene film is typically used to cover the soil just after fumigation for several days to minimize emissions and maximize retention in the soil. A few days after fumigation, farmers prepare the field for planting making the waiting period between fumigation and planting very short. Because it is a broad spectrum fumigant, methyl bromide eliminates the major pests that occur in the soil, and thus a variety of chemicals is not needed. However, methyl bromide is very toxic to humans, and bromide from the decomposition of methyl bromide can be concentrated in plant tissue which is to...

In a recent study of the reaction between nitrous acid and hydrogen peroxide in dilute perchloric acid solution [l], it was postulated, on the basis of the [H+] dependence of the reaction rate, that the equilibrium constant K,, for the protonation of nitrous acid according to eq. (1) (1) has a value of 116M-' a t 25°C. The purpose of this communication is to point out that such a high value of Keq is incompatible with published kinetic and equilibrium studies of nitrous acid in acidic solutions, and to direct attention to some internal inconsistencies in the data reported in the title paper.It has been established conclusively that one of the active nitrosating species in acidic solutions of nitrite is the nitrous acidium ion, HzNOz+ (and/or its anhydride NO+) [2]. The rate law corresponding to a nitrosating pathway involving H2N02+ is given by k [HNOz] Equilibrium measurements are also incompatible with a high affinity of HN02 for H+. Thus potentiometric titrations of sodium nitrite solutions [5] in the pH range of 4.59-2.54 have been accounted for quite accurately on the basis of the single equilibrium HNO2 * H+ + NOz-with pK, = 3.14 at 20°C. If the equilibrium constant for eq. (1) were as high as 116M-', 25% of the nitrous acid would have been present as the nitrous acidium ion at the lowest pH used [5]. Under these circumstances, marked fluctuations in the measured pK, value of HNOz would have been observed, in contrast HNO2 + H+ = + HzN02+