Ian E. Galbally

The Production of Methanol by Flowering Plants and the Global Cycle of Methanol

Methanol has been recognised as an important constituent of the background atmosphere, but little is known about its overall cycle in the biosphere/atmosphere system. A model is proposed for the production and emission to the atmosphere of methanol by flowering plants based on plant structure and metabolic properties, particularly the demethylation of pectin in the primary cell walls. This model provides a framework to extend seven sets of measurements of methanol emission rates to the global terrestrial biosphere. A global rate of release of methanol from plants to the atmosphere of 100 Tg y−1 is calculated. A separate model of the global cycle of methanol is constructed involving emissions from plant growth and decay, atmospheric and oceanic chemical production, biomass burning and industrial production. Removal processes occur through hydroxyl radical attack in the atmosphere, in clouds and oceans, and wet and dry deposition. The model successfully reproduces the methanol concentrations in the continental boundary-layer and the free atmosphere, including the inter-hemispheric gradient in the free atmosphere. The model demonstrates a new concept in global biogeochemistry, the coupling of plant cell growth with the global atmospheric concentration of methanol. The model indicates that the ocean provides a storage reservoir capable of holding at least 66 times more methanol than the atmosphere. The ocean surface layer reservoir essentially buffers the atmospheric concentration of methanol, providing a physically based smoothing mechanism with a time constant of the order of one year.

Emissions of volatile organic compounds (primarily oxygenated species) from pasture

The volatile organic compound (VOC) emissions from pasture at a site in southeastern Victoria, Australia, were monitored over a 2 year period using a static chamber technique. Fluxes up to 23,000 μg(C) m−2 h−1 were detected, with the higher fluxes originating from clover rather than from grass species. Gas Chromatographic analyses indicated that emissions from both grass and clover were high in oxygenated hydrocarbons including methanol, ethanol, propanone, butanone, and ethanal, and extremely low in isoprene and monoterpenes. In the case of clover, butanone made up 45–50% of the total emissions. When grass and clover were freshly mown, there were significantly enhanced emissions of VOCs. These enhanced emissions included both those oxygenates emitted from uncut pasture and also C6-oxygenates, including (Z)−3-hexenal, (E)−2-hexenal, (Z)−2-hexen−1-ol, (Z)−3-hexen−l-ol, and (Z)−3-hexenyl acetate. Emissions from the undisturbed pasture increased markedly with temperature and the intensity of solar radiation, peaking at midday and ceasing at night. The fluxes, when normalized to a temperature of 30°C and a light intensity of 1000 μE m−2 s−1 were, for grass and clover respectively, about one eighth and two fifths of the equivalent fluxes reported to occur from U.S. woodlands. The annual integrated emission from the pasture was approximately 1.9 g(C) m−2 or 1.3 mg(C) g−1 (dry matter). The large transient fluxes that occurred following physical damaging of the pasture, when integrated over time, could be of the same order as those emissions that were observed from undisturbed pasture. In the case of methanol, and perhaps ethanol, the emissions from grasslands may be significant global sources of these gases.

Trends of ozone in the troposphere

Using a set of selected surface ozone (nine stations) and ozone vertical profile measurements (from six stations), we have documented changes in tropospheric ozone at a number of locations. From two stations at high northern hemisphere (NH) latitudes there has been a significant decline in ozone amounts throughout the troposphere since the early 1980s. At midlatitudes of the NH where data are the most abundant, on the other hand, important regional differences prevail. The two stations in the eastern United States show that changes in ozone concentrations since the early 1970s have been relatively small. At the two sites in Europe, however, ozone amounts increased rapidly into the mid-1980s, but have increased less rapidly (or in some places not at all) since then. Increases at the Japanese ozonesonde station have been largest in the lower troposphere, but have slowed in the recent decade. The tropics are sparsely sampled but do not show significant changes. Small increases are suggested at southern hemisphere (SH) midlatitudes by the two surface data records. In Antarctica large declines in the ozone concentration are noted in the South Pole data, and like those at high latitudes of the NH, seem to parallel the large decreases in the stratosphere.

A study of peroxy radicals and ozone photochemistry at coastal sites in the northern and southern hemispheres

Peroxy radicals and other important species relevant to ozone photochemistry, including ozone, its photolysis rate coefficient jO(1D), NOx (NO + NO2), and peroxides, were measured at the coastal sites of Cape Grim, Tasmania, in January/February 1995 during the Southern Ocean Atmospheric Photochemistry Experiment (SOAPEX 1) and Mace Head, Western Ireland, in May 1995 during the Atlantic Atmospheric Photochemistry Experiment (ATAPEX 1). At both sites it was observed that the relationship between peroxy radical (HO2 + RO2) concentrations and jO(1D) switched from a square root dependence in clean oceanic or “baseline” air to a first-order dependence in more polluted air. Simple algorithms derived from a photochemical reaction scheme indicate that this switch-over occurs when atmospheric NO levels are sufficient for peroxy radical reaction with NO to compete with radical recombination reactions. At this crucial point, net tropospheric ozone production is expected to occur and was observed in the ozone diurnal cycles when the peroxy radical/jO(1D) dependencies became first order. The peroxy radical/jO(1D) relationships imply that ozone production exceeds destruction at NO levels of 55±30 parts per trillion by volume (pptv) at Mace Head during late spring and 23±20 pptv at Cape Grim during summer, suggesting that the tropospheric ozone production potential of the southern hemisphere is more responsive to the availability of NO than that of the northern hemisphere.

ATMOSPHERIC EFFECTS FROM POST-NUCLEAR FIRES

During a large nuclear war, the atmosphere would be loaded with huge quantities of pollutants, which are produced by fires in urban and industrial centers, cultivated lands, forests and grasslands. Especially detrimental are the effects of light absorbing airborne particles. An analysis of the amounts of the various types of fuels which could burn in a nuclear war indicates that more than 1014 g of black smoke could be produced by fires started by the nuclear explosions. Due to this, the penetration of sunlight to the earths surface would be reduced greatly over extended areas of the northern hemisphere, maybe even globally. This could temporarily cause extreme darkness in large areas in midlatitudes and reduce crop growth and biospheric productivity.This situation would last for several weeks and cause very anomalous meteorological conditions. Much solar radiation would be absorbed in the atmosphere instead of at the earths surface. The land areas and lower atmosphere would, therefore, cool and the overlying atmosphere warm, creating strong vertical thermal stability in a highly polluted atmosphere. For extended periods and in large parts of the world, weather conditions would be abnormal. The resulting cold, probably freezing, temperatures at the ground would interfere severely with crop production during the growing season and cause extreme conditions for large sections of the biosphere. The combination of lack of sunlight, frost and other adverse meteorological conditions would add enormously to the already huge problems of the survivors.

The Annual Cycle of Peroxides and Ozone in Marine Air at Cape Grim, Tasmania

The concentration of gas-phase peroxides has been measured almost continuously at the Cape Grim baseline station (41° S) over a period of 393 days (7702 h of on-line measurements) between February 1991 and March 1992. In unpolluted marine air a distinct seasonal cycle in concentration was evident, from a monthly mean value of>1.4 ppbv in summer (December) to <0.2 ppbv in winter (July). In the summer months a distinct diurnal cycle in peroxides was also observed in clean marine air, with a daytime build-up in concentration and decay overnight. Both the seasonal and diurnal cycles of peroxides concentration were anticorrelated with ozone concentration, and were largely explicable using a simple photochemical box model of the marine boundary layer in which the central processes were daytime photolytic destruction of ozone, transfer of reactive oxygen into the peroxides under the low-NOx ambient conditions that favour self-reaction between peroxy radicals, and continuous heterogeneous removal of peroxides at the ocean surface. Additional factors affecting peroxides concentrations at intermediate timescales (days to a week) were a dependence on air mass origin, with air masses arriving at Cape Grim from higher latitudes having lower peroxides concentrations, a dependence on local wind speed, with higher peroxides concentrations at lower wind speeds, and a systematic decrease in peroxides concentration during periods of rainfall. Possible physical mechanisms for these synoptic scale dependencies are discussed.

Relationships between ozone photolysis rates and peroxy radical concentrations in clean marine air over the Southern Ocean

Measurements of the sum of inorganic and organic peroxy radicals (RO2) and photolysis rate coefficients J(NO2) and J(O1D) have been made at Cape Grim, Tasmania in the course of a comprehensive experiment which studied photochemistry in the unpolluted marine boundary layer. The SOAPEX (Southern Ocean Atmospheric Photochemistry Experiment) campaign included measurements of ozone, peroxides, nitrogen oxides, water vapor, and many other parameters. This first full length paper concerned with the experiment focuses on the types of relationships observed between peroxy radicals and J(NO2), J(O1D) and √[J(O1D)] in different air masses in which ozone is either produced or destroyed by photochemistry. It was found that in baseline air with ozone loss, RO2 was proportional to √[J(O1D)], whereas in more polluted air RO2 was proportional to J(O1D). Simple algorithms were derived to explain these relationships and also to calculate the concentrations of OH radicals in baseline air from the instantaneous RO2 concentrations. The signal to noise ratio of the peroxy radical measurements was up to 10 for 1-min values and much higher than in other previous deployments of the instrument in the northern hemisphere, leading to the confident determination of the relationships between RO2 and J(O1D) in different conditions. The absolute concentration Of RO2 determined in these experiments is in some doubt, but this does not affect our conclusions concerned either with the behavior of peroxy radicals with changing light levels or with the concentrations of OH calculated from RO2. The results provide confidence that the level of understanding of the photochemistry of ozone leading to the production of peroxide via recombination of peroxy radicals in clean air environments is well advanced.

Mid‐latitude marine boundary‐layer ozone destruction at visible sunrise observed at Cape Grim, Tasmania, 41°S

An analysis is made of 13 years of observations of ozone concentrations in the remote marine boundary layer at Cape Grim, Tasmania 41°S. These data reveal a decrease in ozone concentration in the first few hours following sunrise at a rate of around 0.1 ppb h−1 in mid-summer and in mid-winter. This ozone destruction phenomenon causes an asymmetry in the daily ozone loss rate with enhanced destruction following sunrise, is statistically distinguishable from the O3-HOx destruction cycle that peaks at mid-day, and occurs at similar rates in mid-summer and in mid-winter. The cause of this sunrise ozone decrease is examined using the conservation equation for ozone. We speculate that ozone destruction at sunrise arises due to halogen chemistry. The absence of sunrise ozone decrease in models of marine boundary-layer photochemistry means that the ozone destruction rate in the remote marine boundary layer is underestimated by perhaps a factor of two.

Man-Made Carbon Tetrachloride in the Atmosphere

The emissions of man-made carbon tetrachloride and the rates of its removal from the atmosphere by natural sinks are evaluated. A large fraction, perhaps all of the carbon tetrachloride observed in the atmosphere, could be man-made, and carbon tetrachloride is a global atmospheric pollutant.

Emission of nitrogen oxides (NO x ) from a flooded soil fertilized with urea: Relation to other nitrogen loss processes

Emissions of nitric oxide and other odd nitrogen oxides (NOx) from a flooded rice field were studied after urea had been broadcast into the floodwater.The NOx flux from the fertilized area was very low (0.2×10-9 g N m-2 s-1) for the first few days after application of urea and was high (0.95×10-9 g N m-2 s-1) in the subsequent period when significant nitrite and nitrate were present in the floodwater. At night, little if any NOx was exhaled but ambient NO2 was absorbed by the floodwater. An uptake velocity for NO2 of 3×10-4 m s-1 was measured during one night. Maximum NOx losses were observed near 1300 h when temperature and solar ultraviolet light were maximum.While the amounts of nitrogen oxides emitted are of little agronomic importance (∼2×10-3 per cent of the fertilizer nitrogen was lost as NOx during the 10-day study period), they may well be of significance as a source for some gas reactions in the atmosphere and for the global nitrogen cycle.Of the fertilizer nitrogen applied (as urea) approximately 30% was lost to the atmosphere by NH3 volatilization, 15% by denitrification, presumably as N2, and the remainder, less minor losses of NO and N2O, remained in the plant/soil/water system.