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A chemistry model of the global troposphere is presented which focuses on the hydroxyl radical, OH. Global distributions of OH are calculated based on known chemical reaction pathways, experimentally measured values of precursor species O3, H2O, NOx (defined as NO+NO2), CO, CH4, and actinic flux (which includes the effects of cloud cover and O3 column absorption). Model grid resolution is 1 km in altitude by 10 degrees latitude, and zonally divided into land or ocean. Species are calculated as seasonal averages. Global annual mean OH in the troposphere (up to 14 km altitude) is calculated to be 9.2 x 10(5) molcm(-3) with averages of 9.8 x 10(5) in the northern hemisphere, and 8.5 x 10(5) in the southern hemisphere. Global CO and CH(4) oxidation rates by OH are calculated to be 1840 Tgyear(-1) and 580 Tgyear(-1), respectively. OH is found to be most sensitive to O3 and H2O concentrations, as well as to the photolysis rate of O3 to O1D. Sensitivity of CO and CH4 oxidation rates to cloud presence shows an inverse relationship to cloud amount and optical depth. Model results are shown to be consistent with results from two other published models.

Ambient concentrations of trace gases near their sources carry precise information about the emission rates. In this paper we use ambient measurements of methane near rice fields to estimate the emissions and compare them to actual flux measurements. The data are from a seven-year study of rice fields in China when both emissions and ambient concentrations were measured. The calculations are based on an empirical model of the dilution factor that relates emissions from the rice fields to the ambient concentrations caused by these emissions. The relationship is derived from the first year of the experiment (base year — 1988) and then applied to subsequent years (1989–1994) using only ambient measurements near the rice fields, to estimate methane emissions. The ambient data are about an order of magnitude fewer than the data for the direct flux measurements. Yet, the results of the ambient proxy calculations of flux are in agreement with the seasonal patterns and whole season emissions measured from the direct flux measurements. The seasonally averaged fluxes for each year agree to within ± 25%. There is a close agreement between the actual flux measurements and the proxy estimates of the seasonal pattern of emissions in the composite of all years of data (± 10 %). The seasonally averaged emissions over all seven years are nearly the same between the proxy] and actual measurements at about 30 mg/m=/hr (within 2%).These results are an independent validation of the direct flux measurements taken at this site.

The two-dimensional statistical dynamical climate model, recently developed at the Global Change Research Center (GCRC 2D climate model) is presented and discussed. The model solves the 2-D primitive equations in finite difference form (mass continuity, Newton's second law, and the first law of thermodynamics) for the prognostic variables zonal mean density, zonal mean zonal velocity, zonal mean meridional velocity, and zonal mean temperature on a grid that has 18 nodes in latitude and 9 vertical nodes (plus the surface). The equation of state, p = ρRT and an assumed hydrostatic atmosphere, δp = − ρgδz , are used to diagnostically calculate the zonal mean pressure and vertical velocity for each grid node, and the moisture balance equation is used to estimate the precipitation rate. The performance of the model at simulating the two-dimensional temperature, zonal winds, and mass stream function is discussed here. The strengths and weaknesses of the model are highlighted and plans for future model experiments and improvements are given. The parameterization of the transient eddy fluxes of heat and momentum developed by Stone and Yao (1987 and 1990) are used with small modifications. These modifications are shown to improve the performance of the model at simulating the observed climate system as well as increase the model's computational stability.

Direct atmospheric measurements of methane have been taken only during the last 20 years or so. For earlier times the concentrations of methane are determined from the analysis of air trapped in polar ice. Here we have combined all available data to construct globally averaged concentrations on a unified absolute calibration scale that extends back to about 1500 A.D. We use these data to calculate the global annual emissions of methane during the time between now and 500 years ago. According to our calculations the combined natural and anthropogenic methane emissions were around 180 Tg/yr during the 15th century, 200 Tg/yr in the early part of the 18th century and are now about 450 Tg/yr. This is an increase of a factor of 2.5 over the last 400 years, 80% of which has occurred since the turn of the century, and 50% has occurred over the last 40 years. The changes of atmopsheric methane during the last century are dominated by changes in emissions with perhaps small effects from changes in OH. We find also that the rate of increase of atmospheric concentrations slowed between 1930 and 1945, which is also reflected in independent agricultural records of cattle populations and area under rice agriculture; both are large sources of methane that can be attributed to human activities. In recent times the trend of methane is falling rapidly, probably due mostly to a slowdown in anthropogenic emissions but also to possible increases of OH.

Samples were taken of the combustion gases released by household cookstoves in Manila, Philippines. In a total of 24 samples, 14 cookstoves were tested. These were fueled by liquefied petroleum gas (LPG), kerosene (three kinds of stoves), charcoal, and wood. Ambient samples were also taken. All samples were analyzed for CO2, CO, CH4, N2O, and total non-methane organic compounds (TNMOC). Results generally confirm increasing emissions for most products of incomplete combustion moving down the “energy ladder” from gaseous to liquid to processed solid to unprocessed solid fuels. Although the sample size and number of background samples were too small to give great confidence in the results, extrapolation of the emission ratios (each gas relative to CO2) to global estimates indicates that published global inventories of several gases important in atmospheric chemistry may be somewhat too small for the fuelwood combustion category. When weighted by global warming potentials, the greenhouse impact of the emissions of non-CO2 greenhouse gases from wood combustion may rival or exceed those from CO2 alone. If verified, this could have substantial implications for energy and environmental policies in developing countries. These tentative findings indicate that more measurements of this type in developing countries would be justified.

Permafrost samples were taken from various sites in northern Alaska near Prudhoe Bay and inland along the Haul Road. CH4, CO2, H2, CO, and N2O were measured in these cores. Other than CH4, with a median concentration of 2.3 mg per kg of soil, and to a lesser extent CO2, with a median concentration of 28.1 mg per kg of soil, the gases were found to be negligible compared to their atmospheric concentrations. The measuring sites and methods used, data, and modeled CH4 release are presented here.

Low temperature combustion of coal, such as for heating and cooking in many countries, is a global source of methane. Emission rates may be 7 tg/yr from China and perhaps 16 tg/yr from the world.

China is one of the world's largest producers of rice and constitutes a sizable fraction of the Earth's population. As such emissions from China are of interest in understanding the global methane budget. Using geographical, agricultural and industrial data along with direct flux measurements, we have estimated the emissions of methane from China during the last century, concentrating mostly over the last 50 years. We find that: 1) the anthropogenic methane emissions from China are now more than 60 Tg/yr. 2) In recent decades there has been a decline in the emissions from agricultural sources due mostly to a dramatic decrease in the per capita emissions of methane from rice agriculture. 3) Sources related to energy (coal and natural gas consumption) are on the rise so that the reductions from agriculture are offset by increases from these energy sources. If the present trends continue, the dominating role of rice agriculture on methane emissions from China will be replaced by emissions from energy sources. This and many other aspects of the China historical methane budget parallel the global emissions of methane.

Data from surface permafrost cores are extrapolated to determine a global estimate of the trapped gases, methane in particular. This global extrapolation is used with a heat and gas transfer model, which is developed here. A Theoretical model is presented and validated with exact solutions. The model results show that, for all gases other than methane, the amounts present in permafrost are negligible. It is found that every meter depth of permafrost contains approximately 60 Tg or 12% of the yearly source of methane. The heat transfer and gas diffusion model shows that in the future permafrost is likely to contribute less than 10 Tg yr −1 or 2% of the currently yearly source of methane under current climate change scenarios.

Carbon monoxide and methane are the two largest direct sinks of atmospheric OH. Globally the reaction between OH and CO provides the largest direct sink of OH, which is about twice as large as the reaction between OH and CH 4 . However, neither CO nor CH 4 affects OH only by direct reactions. In fact, the direct reaction of OH with either CO or CH 4 initiates a series of reactions and products, which also affect the atmospheric OH and can thus be considered as feedbacks. We developed a method to calculate the total contribution of either CO or CH 4 to OH by tracing a series of reactions and products, which are initiated by the direct reaction of OH with either CO or CH 4 . With this tracing technique, we show that atmospheric methane, along with its feedbacks, may remove as much as more atmospheric OH than carbon monoxide, although CO is widely accepted as the largest sink of the atmospheric OH.

The distribution of the concentrations of the highly reactive OH radicals has been obtained with a detailed time dependent photochemical model. The model contains information on the physical nature of the atmosphere such as temperature, pressure, and solar intensity as well as on the distributions of some key species including the cycles of HOx, NOx, and other reactive compounds. Our model results show that OH has a strong diurnal variation as well as clear vertical, seasonal, and latitudinal variations due to its high reactivity and short lifetime. The globally and seasonally averaged daytime OH concentration is 1.6 × 106 molecules/cm3, which is about two orders of magnitude larger than the globally and seasonally averaged nighttime OH concentration, 1.3 × 104 molecules/cm3. During the daytime, OH production is initiated and maintained by sunlight. The reaction of O(1D) with H2O and the reactions of HO2 with NO and with O3 produce most of the tropospheric OH. At night OH is produced only by the reaction between O3 and nighttime HO2, which is largely generated by the thermal dissociation of HO2NO2. The mechanism for removing OH from the atmosphere is about the same between daytime and nighttime and results mainly from reactions with CO and CH4. Possible secular changes of OH levels, from ice ages to the present, are also evaluated in this paper. We concluded that OH levels, on the whole, decrease only slightly during the different climatic and atmospheric conditions ranging from ice ages to the present polluted global atmosphere; however, the calculated nighttime OH concentration in ice ages is about three times as large as at present.

A time dependent one dimensional radiative convective model (1D RCM) is developed to study the changes in the Earth's temperature that may be caused by increasing levels of CO 2 and other trace gases. Special emphasis is given to the theory and development of the model so that it may be easily used by others. The sensitivity of the Earth's surface temperature to variations in the solar constant, surface albedo, and cloud cover fraction and height is included. The model is found to predict an approximate change in surface temperature of 1.9 K for a doubling of atmospheric CO 2 (from 320 to 640 ppm). This compares favorably with other previously published results for similar models. The influence on mean global temperature of variations in the atmospheric concentrations of CO 2 , CH 4 , N 2 O, CCl 3 F, CCl 2 F 2 , and volcanic aerosols over the past century is simulated with the model. We find that this simulated temperature record compares well with the record of mean global temperature reconstructed from observations.

We describe results from a research program to determine the emission rates of methane and of other environmentally significant gases from Chinese rice fields and biogas generators and to determine whether these sources contribute significantly to the global cycles of these trace gases or affect local and regional air quality. Experiments to determine the global flux of methane are still in progress. We conducted about 30 experiments and obtained some 900 individual measurements of trace gases emitted from rice fields and biogas generators around Chengdu in the Sichuan Province of China. These experiments were not sufficient to determine the global or annual emissions of methane from rice fields but fulfilled the other objectives of our program. The main findings are: (1) The biogas generators are not a significant source of methane on a global scale (⪡1 tg/yr). (2) Rice fields release CO, CHCl 3 , and CO 2 at observable rates. The emission rates of CO and CHCl 3 are too small to contribute significantly to the global cycles of these gases. The CO 2 emissions are very large, but because rice fields cycle carbon, there is probably to net flux of CO 2 into the atmosphere when integrated over a few years. (3) Neither rice fields nor biogas generators contribute significantly to the local and regional CO and hydrocarbon pollution. (4) There is evidence, although not beyond reasonable doubt, that the rice fields take up some man-made chlorocarbons, particularly CCl 3 F, CCl 2 F 2 , CCl 4 , and CH 3 CCl 3 . These gases are implicated in the depletion of the ozone layer.

The concentrations of CF(3)-containing compounds in archived air samples collected at Cape Meares, Oregon, from 1978 to 1997, at Point Barrow, Alaska, from 1995 to 1998, and at Palmer Station, Antarctica, from 1991 to 1997, were determined by high resolution gas chromatography and high resolution mass spectrometry. The CF(3)-containing compounds measured by this method and discussed here are: the perfluorinated compound, C(3)F(8) (FC 218); four perhalogenated compounds, CF(3)Cl (CFC 13), CF(3)CF(2)Cl (CFC 115), CF(3)CFCl(2) (CFC 114a), and CF(3)Br (Halon 1301); and three hydrofluorocompounds, CF(3)H (HFC 23), CF(3)CH(3) (HFC 143a), and CF(3)CH(2)F (HFC 134a). For four of these compounds, very few measurements have been previously reported. The atmospheric concentrations of all of the CF(3)-containing compounds continuously increased in time over the sample collection periods. From these data, the annual rates of emission into the atmosphere have been estimated. The emission rates fall into one of three distinct categories. The annual emission rates of C(3)F(8), CF(3)H, CF(3)CH(3), and CF(3)CH(2)F have continuously increased over the last two decades. That of CF(3)CFCl(2) has decreased continuously. Emission rates for CF(3)Cl, CF(3)CF(2)Cl, and CF(3)Br reached maximum levels in the late 1980s, and have been decreasing in the 1990s. The emission rates of C(3)F(8), CF(3)CH(3) and CF(3)CH(2)F were nearly zero 20 years ago but have increased rapidly during the last decade.

Data from weekly global measurements of nitrous oxide from 1981 to the end of 1996 are presented. The results show that there is more N2O in the northern hemisphere by about 0.7 +/- 0.04 ppbv, and the Arctic to Antarctic difference is about 1.2 +/- 0.1 ppbv. Concentrations at locations influenced by continental air are higher than at marine sites, showing the existence of large land-based emissions. For the period studied, N2O increased at an average rate of about 0.6 ppbv/year (approximately 0.2%/year) although there were periods when the rates were substantially different. Using ice core data, a record of N2O can be put together that goes back about 1000 years. It shows pre-industrial levels of about 287 +/- 1 ppbv and that concentrations have now risen by about 27 ppbv or 9.4% over the last century. The ice core data show that N2O started increasing only during the 20th century. The data presented here represent a comprehensive view of the present global distribution of N20 and its historical and recent trends.

The presence of water vapor in a sample of air reduces the concentration of a trace gas measured from the sample. We present a methodology to correct for this effect for those cases when the concentration of the trace gas has already been measured from a wet sample. The conversion or correction factor that takes the wet mole fraction to a dry mole fraction is determined by the mixing ratio of water vapor inside the sampling canister. For those samples where the water vapor is saturated inside the canister, the water vapor mixing ratio is largely determined by laboratory conditions; for the unsaturated samples, the mixing ratio is determined by station conditions. If the meteorology at the sampling station is known, the equations presented here can be used directly to calculate the appropriate correction factor. For convenience, we use climatological data to derive average monthly correction factors for seven common global sampling sites: Barrow, AK, US (71 degrees N, 157degrees W); Cape Meares, OR, US (45 degrees N, 124 degrees W); Mauna Loa, HI, US (19 degrees N, 155 degrees W); Ragged Point, Barbados (13 degrees N, 59 degrees W); American Samoa (14 degrees S, 171 degrees W); Cape Grim, Tasmania, Australia (41 degrees S, 145 degrees E); South Pole (90 degrees S). These factors adjust wet mole fractions upwards within a range of 0.002% for the South Pole to over 0.8% for saturated sites. We apply the correction factors to wet nitrous oxide (N2O) mole fractions. The corrected data are more consistent with our understanding of N2O sources.

Concentrations of CCl3F (F-11), CCl2F2 (F-12), CHClF2 (F-22), C2Cl3F3 (F-113), CH3CCl3, CCl4, C2HCl3 (TCE), CH3I, CHCl3, CO, CH3Cl, CH4, and N2O were measured in and above the boundary layer (0–4 km) of the arctic troposphere near Pt. Barrow (70°N) during May 1982. The vertical structure of the concentrations is reported graphically and is analyzed statistically to reveal consistent patterns. The results are compared with analogous observations made during spring in the southern hemisphere.

Experiments have shown that the oceans release a significant fraction of the yearly global emissions of carbonyl sulfide to the atmosphere. The experimental methods used to obtain, store and analyze air and water samples for OCS measurements are discussed and measurements of the Henry's constant in seawater at temperatures between 0 and 30°C are reported. The results are applied to oceanic flux models, and the global yearly emissions of OCS from oceans to the atmosphere are calculated to be ∼8 × 1011 gm/yr (0.8 Tg yr−1).

Usually automobiles are the main source of CO in urban environments. However, this is not always the case. During winters, in areas where wood is burned to heat homes, it can contribute almost as much CO as automobiles. We show that in the Pacific Northwest wood burning may contribute 20%–30% of the CO during winters. The contribution of automobiles is a little less than 50% during the same time. Some 10% – 15% is from distant sources that make up the background, and the rest is unaccounted for.

A global time series of atmospheric methylchloride (CH 3 Cl) concentrations is reported showing the variability with latitude and season. Springtime concentrations of CH 3 Cl at 45°N latitude are 7.5%±3.5% higher than during other seasons. Lowest concentrations were generally observed during fall. CH 3 Cl was found to be more abundant by about 6% (±5% NH, ±3% SH) in the tropical regions of both hemispheres. No significant difference in the burdens of CH 3 Cl was observed between the two hemispheres. Based on these data the ratio of the average hydroxyl radical (HO) concentration over the southern hemisphere to that over the northern hemisphere was estimated to be 1.3 or less.

It is evident that the global concentrations of methylchloroform (CH3CCl3) are increasing although at much lower rates than in the past. The ratio of concentrations in the two hemispheres has varied and is now declining, which reflects the constancy of the industrial emissions over the past 5 years. Observations show that the mid-latitude concentrations in both hemispheres are slightly lower during the summer than at other times, probably reflecting the greater removal of CH3CCl3 by OH radicals during summer. Calculations show that the lifetime of CH3CCl3 is about 6 (±1.5) years, which is considerably shorter than many previous estimates. It implies that there are probably 8 × 105 molecules of OH/cm3 of air, although this estimate may be uncertain by ±75%. The shorter lifetime is partly due to a revision of the estimated absolute concentration of CH3CCl3 in the atmosphere, which was found to be about 20% less than estimated previously. The relatively short lifetime suggests that in the future CH3CCl3 will contribute

Glosed cell polyurethane foams now constitute the major use of F-11 which is a relatively recent occurrence. The residence time of F-11 in various types of polyurethane foams is extremely long, probably more than a hundred years. Because of the long residence time, polyurethane foams constitute a significant and growing reservoir of F-11 from which the fluorocarbon will leak out into the atmosphere at increasing rates for a very long time. The temporal behavior of the emission rate of F-11 is characterized by slow, relatively constant emission rates once the effects of cutting the foam have subsided. Bruising or breaking the polyurethane foams can release large amounts of F-11. There is considerable variability in the average emission rates between foams made by different manufacturers (∼ 400 %) but very little variability in average emission rates from samples of the same larger piece of foam (≤ 20%). Consequently the residence time of F-11 is different for foams from different manufacturers, but in all cases the residence time is very long. Emission rates increase rapidly with increasing temperature at an average rate of about 5% per degree F in the temperature range between 70°F and 80°F. In actual applications the temperature may be an important determinant of the residence time of F-11 in polyurethane foams.

Statistical analyses of global atmospheric concentrations provide evidence that C2Cl4, CHCl3 and CH3CCl3 (methylchloroform) are more abundant in the tropical boundary layer than above it (α ⩽ 0.09) by 27% (±27%), 21% (−21%, +12%) and 6.4% (±6%) respectively. The air samples on which these results are based were collected by cryogenic techniques during the June 1978 project GAMETAG flights and analyzed soon afterwards by gas chromatography (EC/GC and GC/FID), thus providing latitudinal concentrations of CO, CH4, CCl3F, CCl2F2, CH3CCl3 and light C2-hydrocarbons, both in and above the boundary layer. In August 1980, after further development of analytical techniques, the stored air samples were re-analyzed to establish the latitudinal distributions of CH3I, CHCl3, C2Cl4, C2F3Cl3 (F-113) and CHClF2 (F-22) in and above the boundary layer. Stability studies, spanning a year, show that the concentrations of these gases do not change in the flasks.

We demonstrate how air pollution from residential woodburning may vary over the day in suburban environments. The concentration of a unique gaseous tracer of low temperature combustion, methyl chloride (CH 3 Cl), is related to the mass of fine particles in the ambient air from woodburning stoves and fireplaces. Four ambient air samples per day were collected every 3 days during the winter of 1983–1984 at a residential site in southeast Portland, Oregon. An integrated sampling system was also used over the winter of 1984 in nearby Hillsboro, Oregon, to collect 4–8 hour samples over the day and determine the longer period averaged pollutant concentrations. The maximum averaged wintertime concentrations were found in the evenings as expected, with a few surprisingly high levels in the morning during the 6–10 a.m. period, usually associated with stagnant meteorological conditions.

Due partly to human activities the present yearly emissions of CH 4 exceed the atmospheric sinks, thus leading to a 1.2–1.9% per year atmospheric increase in the concentration of CH 4 . New evidence based on studies of polar ice cores suggests that several hundred years ago the concentrations of CH 4 were perhaps only half of current values. These diverse findings are tied together in a single unified logistic model of atmospheric concentrations past, present and future. Using realistic growth rates of the sources of CH 4 caused by human activities, the model explains the concentrations and current growth rates. It also predicts that a doubling of CH 4 relative to present levels is possible given the long (9-year) atmospheric lifetime. Such increases of CH 4 concentrations may have already perturbed our global environment and may continue to do so in the future. The environmental effects include increased surface temperature of the earth, additional O 3 and CO in the clean non-urban atmosphere, depletions of tropospheric OH radicals, but perhaps also protection of the stratospheric ozone layer from destruction by man-made fluorocarbons.