Global measurements of methyl iodide (CH3I) show that typical concentrations in background air are between 1 and 3 pptv (1 ppt = 10−12) in the boundary layer and drop to half of these values above the boundary layer. Concentrations of CH3I over cities in Oregon were found to be similar to background levels. These low concentrations suggest that CH3I may not affect atmospheric concentrations of free radicals, O3, or the NO2/NO ratio, as recent model calculations had shown. We also found that near‐oceanic regions characterized by high biomass productivity, there is 10 pptv −20 pptv of CH3I. By using these results in conjunction with measurements of CH3I in seawater we calculated a global flux of about 1.3 Tg/year from the oceans, most of it (1 Tg/year) from the small fraction of the ocean with high biomass productivity. All these results are based on more than 450 measurements of CH3I at locations ranging from the arctic circle to the south pole. Uncertainties relating to the global distribution, sources, and sinks are identified and discussed.

Atmospheric methyl bromide is of considerable environmental importance as the largest reservoir of gaseous bromine in the atmosphere. Bromine gases can catalytically destroy stratospheric ozone. Since agricultural activities, automobiles, biomass burning, and other human activities produce CH3Br , it is of interest to know its global mass balance and particularly the specific sources and sinks. In this paper we provide a decadal time series of global CH3Br concentrations in the Earth's atmosphere. The data show that average concentrations are about 10 pptv and during the last 4 years may be increasing at 0.3 +_ 0.1 pptv/yr (3%/yr +_ 1%/yr). We estimate that the atmospheric lifetime of CH3Br that is due to reaction with OH, is about 2 years, resulting in a calculated global emission rate of about 100 GgJyr. Ocean supersaturations of 140-180% are observed, and atmospheric concentrations over the open oceans are higher than at comparably located coastal sites. The ocean source is estimated to be about 35 GgJyr. The remaining emissions must come from other natural sources and anthropogenic activities. Our results are based on some 2200 samples obtained over more than a decade. Mass balance calculations explain most aspects of the present data but other implications are not easily reconciled, leaving open the possibility of undiscovered sources and sinks. 1. INTRODUCTION Methyl bromide is probably the most abundant reservoir of gaseous bromine in the Earth's atmosphere. While it is generally believed to come from the oceans, there are identified man-made sources such as automobiles, agricultural fumigants, and biomass burning that have been increas!ng in recent decades. Bromine gases, particularly methyl bromide (CH3Br) because of its relatively high concentrations, may be of considerable importance in the global environment since such gases can destroy the ozone layer and contribute to forming the Antarctic ozone hole. According to recent calculations bromine gases, in their capacity to destroy stratospheric ozone, may be up to 100 times more effective than chlorine from the well known chlorofiuorocarbons [Wofsy et al., 1975; Yung et al., 1980; McElroy et al., 1986; Solomon, 1990; World Meteorology Organization, 1989]. Methyl bromide is considered of sufficient importance for ozone depletion that plans to reduce production are being considered by the parties to the Montreal Protocol [Global Enviromnental Change Report, 1992]. In spite of its importance, there are very few published data on CH3Br , and little is known about its trends and global mass balance. We have three goals for this paper. (1) We present global concentration data that include a time series at six sites, latitudinal distributions in air and in the waters of open oceans and the variation of CH3Br with altitude in the troposphere.(2) These data are taken into account to construct a global mass balance from which we estimate the total global emissions and discuss the apportionment of these emissions between natural and man-made sources. (3) Finally, ...

While air quality and other perceived benefits of oxygenated fuel programs are currently the topic of much debate, there are very few reports of ambient concentrations of oxygenated fuels (e.g., ethanol) and fuel additives (e.g., ethanol, methyl tert-butyl ether, hereafter called MTBE) in urban air. Ambient concentrations of MTBE and ethanol have been measured by GC−FID and GC−MS analysis of samples collected in electropolished canisters at a downtown location in Porto Alegre, Brazil, where 17% of the vehicles run on ethanol, 74% run on a mixture of 85% gasoline and 15% MTBE, and 9% use diesel fuel. During the ca. 1-year period of March 20, 1996−April 16, 1997, ambient levels of MTBE ranged from 0.2 to 17.1 ppbv (average = 6.6 ± 4.3 ppbv); those of ethanol ranged from 0.4 to 68.2 ppbv (average = 12.1 ± 13.3 ppbv). Ambient levels of ethanol and MTBE are compared to those of carbon monoxide (for which vehicle exhaust accounts for ca. 99% of total emissions in the city of Porto Alegre) and of acetylene. Linear regression of the ambient concentration data (44 samples) yielded near-zero intercepts and slopes of 11.40 ± 0.45 for acetylene (ppbv) vs CO (ppmv), 1.73 ± 0.20 for MTBE (ppbv) vs CO (ppmv), 0.153 ± 0.016 for MTBE (ppbv) vs acetylene (ppbv), and 4.64 ± 0.78 for ethanol (ppbv) vs CO (ppmv). These slopes together with an estimated vehicle exhaust emission rate for CO in mid-1996 are used to estimate vehicle emission rates of 2338 ± 393 t/year for ethanol and 1668 ± 193 t/year for MTBE.

GC-MS analysis of extracts from temporal gland secretions of an African elephant has revealed the presence of several farnesol-related sesquiterpenes. Among these are (E)-2, 3-dihydrofarnesol (3), a bumblebee pheromone not seen before in mammals, and a rare component of a Greek tobacco, drimane-8alpha, 11-diol (4), never observed before in an animal.

A procedure for headspace sampling and long-term storage of organic volatiles coupled with gas chromatographic-mass spectrometric (GC-MS) analysis was used to study the volatile chemosignals in a biological secretion prior to bioassay. The approach involved collecting the volatiles in evacuated canisters from an apparatus in which 1 ml of secretion was dispersed for headspace sampling. These canisters, stainless steel, 850 ml, and 100% internally electropolished, have been demonstrated to store volatile compounds, in chemically stable form, for several weeks. The GC-MS analyses provided the quantitation and identification of compounds from C3 through C14 at concentrations as low as 0.10 parts per billion volume. The approach was used to study chemosignals of musth temporal gland secretions (TGS) from a male Asian elephant (Elephas maximus). Fresh TGS material loses its biological activity within 1 hr. TGS material stored at -20°C usually looses its activity within 30 days. The usefulness of this method for long-term storage of the volatile chemosignals was demonstrated by the retention of biologically active TGS headspace compounds, as determined through bioassays, stored in these canisters for one year.