Search

Wikimedia Commons U.S. Customs and Border ProtectionDuring the 2016 Presidential campaign, Donald Trump campaigned hard on the promise that he would authorize the building of a full border wall bet...

Climate change has created unexpected tipping points in the contemporary history of the Arctic. Diminishing summer sea ice has encouraged energy companies to plan for an expansion of Arctic offshor...

The word unaami from the Alaskan Native Yup'ik language translates broadly to “tomorrow”, and is commonly used with a connotation of change. There is no question that Arctic environments are changi...

Associated natural gas is a byproduct of oil extraction and a significant economic resource. It is often discarded by being burned on reaching the surface with a process called flaring or by being released into the atmosphere without burning through venting. Other than the economic loss of an energy source, flaring and venting of associated gas creates local, environmental and public health impacts, as well as contributing to the potential for climate change. This study reviews the literature and internet materials on flaring and venting of associated natural gas in producing oil fields to examine the extent and the current state of the problem, the impacts on the environment, communities and public health, with an emphasis on solutions and remedies to mitigate the problem. Our review confirms the need to recommit to an aggressive global mitigation program and makes a case for accelerated programs, especially in countries with the technical capacity to effectively participate jointly with industry, govern...

Rank—size distribution has been an important tool in characterising and analysing city size distributions across spatial and temporal scales. Zipf’s law in city rank—size distribution has been observed in many analyses and is considered an important empirical regularity describing the organisation of cities. Based on analyses of the evolution of cities in Texas from 1850 to 2000, this paper documents spatial and temporal autocorrelation in city population growth rates. A modelling strategy has been developed that accounts for the spatial and temporal autocorrelated growth in Texas cities and is effective in reconstructing the empirical rank—size distribution. This study shows that it is necessary to take into account the interdependence among cities in simulating the city size distribution.

The U.S. airline network is one of the most advanced transportation infrastructures in the world. It is a complex geospatial structure that sustains a variety of dynamics including commercial, public, and military operations and services. We study the U.S. domestic intercity passenger air transportation network using a weighted complex network methodology, in which vertices represent cities and edges represent intercity airline connections weighted by average daily passenger traffic, non-stop distance, and average one-way fares. We find that U.S. intercity passenger air transportation network is a small-world network accompanied by dissortative mixing patterns and rich-club phenomenon, implying that large degree cities (or hub cities) tend to form high traffic volume interconnections among each other and large degree cities tend to link to a large number of small degree cities. The interhub air connections tend to form interconnected triplets with high traffic volumes, long non-stop distances, and low average one-way fares. The structure of the U.S. airline network reflects the dynamic integration of pre-existing urban and national transportation infrastructure with the competitive business strategies of commercial airlines. In this paper we apply an emerging methodology to representing, analyzing, and modeling the complex interactions associated with the physical and human elements of the important U.S. national air transport and services infrastructure.

The El Niño-Southern Oscillation (ENSO) phenomenon is a well-known source of inter-annual climate variability for both precipitation and temperature in the northern Great Plains of the United States. In order to determine if ENSO has similar impacts on wind speed and wind power, we applied statistical methods, including the sign test and resampling, to hourly airport wind speed measurements for the past half century at two airports in North Dakota and at another two in South Dakota. There is strong statistical evidence that ENSO has a small effect on wind speeds in some months, which affects the amount of wind power a typical utility scale wind turbine can produce. During the El Niño phase, we found monthly mean wind power production to decrease generally, consistent with the mean wind speed decreasing and the probability of a low-speed wind event increasing, at two locations in South Dakota. The ENSO connection was weaker and harder to detect in North Dakota, but we found evidence that the sign of the change appeared generally to be consistent with that in South Dakota. These effects were smaller than the general variability of wind speeds, but nevertheless were detectable as ‘signals within the noise’.

This study examines the influence of US–China trade on national and global emissions of carbon dioxide (CO2). The three basic questions are as follows: (1) What amount of CO2 emissions is avoided in the US by importing Chinese goods? (2) How much are CO2 emissions in China increased as a result of the production of goods for export to the US? and (3) What are the impacts of US–China trade on global CO2 emissions? Our initial findings reveal that during 1997–2003: (1) US CO2 emissions would have increased from 3% to 6% if the goods imported from China had been produced in the US, (2) About 7%–14% of China's current CO2 emissions were a result of producing exports for US consumers, and (3) US–China trade has increased global CO2 emissions by an estimated 720 million metric tons. We suggest that the export of US technologies and expertise related to clean production and energy efficiency to China could be a “win–win” strategy for both countries for reducing their trade imbalance and mitigating global CO2 emissions. Improved international accounting methodologies for assigning responsibility for CO2 emissions must be designed to account for the dynamic nature of international trade.

Extreme heat is a natural hazard that could rapidly increase in magnitude in the 21st century. The combination of increasing urbanization, growing numbers of vulnerable people, and the evidence of global warming indicate an urgent need for improved heat-wave mitigation and response systems. A review of the literature on heat-wave impacts in urban environments and on human health reveals opportunities for improved synthesis, integration, and sharing of information resources that relate to the spatial and temporal nature of threats posed by extreme heat. This paper illustrates how geospatial technologies can aid in the mitigation of urban heat waves.

▪ Abstract Agriculture and industrial development have led to inadvertent changes in the natural carbon cycle. As a consequence, concentrations of carbon dioxide and other greenhouse gases have increased in the atmosphere and may lead to changes in climate. The current challenge facing society is to develop options for future management of the carbon cycle. A variety of approaches has been suggested: direct reduction of emissions, deliberate manipulation of the natural carbon cycle to enhance sequestration, and capture and isolation of carbon from fossil fuel use. Policy development to date has laid out some of the general principles to which carbon management should adhere. These are summarized as: how much carbon is stored, by what means, and for how long. To successfully manage carbon for climate purposes requires increased understanding of carbon cycle dynamics and improvement in the scientific capabilities available for measurement as well as for policy needs. The specific needs for scientific information to underpin carbon cycle management decisions are not yet broadly known. A stronger dialogue between decision makers and scientists must be developed to foster improved application of scientific knowledge to decisions. This review focuses on the current knowledge of the carbon cycle, carbon measurement capabilities (with an emphasis on the continental scale) and the relevance of carbon cycle science to carbon sequestration goals.

Satellite multi- and hyper-spectral sensors have evolved over the past three decades into powerful monitoring tools for ecosystem processes. Research in temperate environments, however, has tended to keep pace with new remote sensing technologies more so than in tropical environments. Here, we identify what we consider to be three priority areas for remote sensing research in Neotropical dry forests. The first priority is the use of improved sensor capabilities, which should allow for better characterization of tropical secondary forests than has been achieved. Secondary forests are of key interest due to their potential for sequestering carbon in relatively short periods of time. The second priority is the need to characterize leaf area index (LAI) and other biophysical variables by means of bidirectional reflectance function models. These biophysical parameters have importance linkages with net primary productivity and may be estimated through remote sensing. The third priority is to identify t...

Using 1990 conditions, we modeled carbon (C) and nitrogen (N) biogeochemical cycles in croplands of China (and, for comparison, the United States) to estimate the annual soil organic-carbon (SOC) balance for all cropland. Overall, we estimate that China's croplands lost 1.6% of their SOC (to a depth of 0.3 m) in 1990, and that U.S. cropland lost 0.1%. A key element in this difference was that ∼25% of aboveground crop residue in China was returned to the soil, compared to ∼90% in the United States. In China, SOC losses were greatest in the northeast (∼103 kg C·ha–1·yr–1), and were generally smaller (

This paper evaluates the relationships between sediment production, economic losses and land cover change in Costa Rica. Results suggest that the relationship between sediment production and the deterioration of land resources in Costa Rica is less understood than expected, and that new sediment monitoring systems must be implemented in order to be able to detect the overall impact of tropical deforestation and habitat fragmentation on sediment production. The results also indicate that the correlation between economic losses due to flooding and landscape fragmentation can be counteracted by promoting 'payment for environmental services' initiatives; a new concept that takes into consideration the role that tropical ecosystems play in protecting the environment.

Methane emissions were measured at nine U.S. landfill sites using chamber and/or tracer flux techniques. These flux measurement methodologies were compared at two sites, and excellent agreement (

We have recently completed a methane emissions inventory for the New England region. Methane emissions were calculated to be 0.91 Tg yr-1, with wetlands and landfills dominating all other sources. Wetlands are estimated to produce 0.33 Tg CH4 yr-1, of which 74% come from Maine. Active landfills emit an estimated 0.28 Tg CH4 yr-1, 60% of which are generated from twelve landfills. Although uncertainty in the estimate is greater, emissions from closed landfills are on the same order of magnitude as active landfills and wetlands; 0.25 Tg CH4 yr-1. Sources of moderate magnitude include ruminant animals (0.05 Tg CH4 yr-1) and residential wood combustion (0.03 Tg CH4 yr-1). Motor vehicles, natural gas, and wastewater treatment make only minor contributions. New England is heavily forested and the soil uptake of atmospheric methane in upland forests, 0.06 Tg CH4 yr-1, decreases emissions from soils by about 18%. Although uncertainties remain, our estimates indicate that even in a highly urbanized region such as New England, natural sources of methane make the single greatest contribution to total emissions, with state totals varying between 8% (Massachusetts) and 92% (Maine). Because emissions from only a few large landfills dominate anthropogenic sources, mitigation strategies focused on these discrete point sources should result in significant improvements in regional air quality. Current federal regulations mandate landfill gas collection at only the largest sites. Expanding recovery efforts to moderately sized landfills through either voluntary compliance or further regulations offers the best opportunity to substantially reduce atmospheric methane in New England. In the short term, however, the large contribution from closed, poorly regulated landfills may make the attribution of air quality improvements difficult. Mitigation efforts toward these landfills should also be a priority.

The National Aeronautics and Space Administration's (NASA's) Mission to Planet Earth (MTPE) may not have given Andrew Lawler the entire story on the funding of grants to analyze data from the “flotilla of Earth-observation satellites” that will be launched in the next few years (News & Comment, [29 Aug., p. 1198][1]). MTPE is certainly not “boosting” funding for science at the rate that they are increasing observations and data. Support for the MTPE grants program has, in fact, been cut significantly in recent years, from approximately $178 million in 1994 to $125 million in 1997. Program managers have been forced to sacrifice highly regarded and productive research programs. The modest restoration of funds to the research and analysis budget being proposed by MTPE leadership is, at best, a Bandaid when intensive care is needed. Every external and internal review panel over the past 3 years has been concerned that MTPE does not have a proper program balance. With an expected spending profile of more than $1 billion a year for the foreseeable future, MTPE is one of the largest civilian science programs in the world today. Yet the grants program engages less than 2000 investigators each year, a small fraction of the U.S. community with skills and interest in Earth system science and practical applications of remote sensing. More than 80% of the MTPE budget is dedicated to building and launching satellites, developing algorithms to generate data, and data management. The restoration of grants funding to $165 million by the year 2000 is totally inadequate to make productive use of MTPE data. A “bottoms up” analysis by science program managers at NASA indicated that at least $220 million would be required by 1998 to take advantage of highly rated research proposals using both existing and new data. NASA Administrator Daniel Goldin has determined that NASA programs will be science-driven. MTPE is responding very slowly to Goldin's challenge, with program investments continuing to be focused on a massive monitoring and data collection effort. The problems of understanding and adapting to climate change and moving toward sustainable development are so critical to this nation's future that it is unacceptable to let bureaucratic momentum continue to dominate budget strategy. The science community has spoken and MTPE is not listening. The productivity of the nation's premier global change research program is at risk. [1]: /lookup/doi/10.1126/science.277.5330.1198a

Atmospheric tracer release techniques have been used to quantify low-level fugitive methane emissions from components and facilities in all sectors of the natural gas system in the United States. The emission data are collected as part of a program to extrapolate the emissions from the entire U.S. natural gas industry and thus reduce uncertainties in the environmental impact of increased natural gas use. In these experiments, the total methane emission from a site is measured by releasing a tracer gas (SF6) at the natural gas facility to simulate the source. Both methane and tracer levels are measured with real-time instruments deployed in a mobile laboratory downwind of the site. A large range of emission levels for the different sectors of the entire system was determined. Within any one group of a particular facility type there is also much variability in the emission rates. The exact nature and number of gas system components in a facility are important factors in determining its emission level.

Methane (CH 4 ) mixing ratios in the South Atlantic basin were sampled from a DC-8 aircraft during the TRACE A expedition over the months of September and October 1992. This high-precision (± 0.1%), high-resolution data set (independent measurements every 5 s) includes a total of 67,335 observations and ranges from 1586.6 to 2152.8 parts per billion by volume (ppbv). The observed values were influenced by emissions from biomass burning and local urban/industrial areas, stratosphere-troposphere exchange, active convective mixing, and possible long-range transport of pollution. Average mixing ratios increased from the atmospheric mixed layer (0-2 km) to the free troposphere (2-6 km) and were greatest at altitudes above 6 km. A longitudinal trend observed between 5°N and 40°S latitude suggests that CH 4 inputs were greater on the South American side of the basin. A latitudinal trend in values between the near-surface and 11 km exhibits the expected gradient from north to south, but differs from the latitudinal gradient observed in surface level clean air at this time. Higher concentrations at altitude, at least at this time of year, indicate that ground-based atmospheric monitoring sites may underestimate pollution inputs to the region.

The current atmospheric mixing ratio of nitrous oxide (N2O), a chemically significant trace gas, is increasing at a rate of 0.25−0.31% yr-1, apparently well correlated with human activity. Better quantification of all N2O sources is required in efforts to stabilize this rate of increase. N2O emissions from the composting of wastewater sludge and livestock wastes were measured during 1993 and 1994 using enclosure methods. Static chambers were placed on the surface of the compost piles, and N2O mixing ratios within the chamber headspace were measured over time from which fluxes were calculated. The flux measurements resulted in mass-based emission factors of 0.7 g of N2O (dry kg)-1 and 0.5 g of N2O (dry kg)-1 for the sludge compost and the livestock waste compost, respectively. The derived emission factors were used in conjunction with recent waste generation and disposal statistics to estimate potential global N2O emissions from the treatment of organic wastes. Livestock waste treatment appears to hold the...

Field, laboratory, and computer modeling methods were utilized to quantitatively assess the capability of aerobic microorganisms to oxidize landfill-derived methane (CH4) in cover soils. The investigated municipal landfill, located in Nashua, New Hampshire, was operating without gas controls of any type at the time of sample collection. Soil samples from locations of CH4 flux to the atmosphere were returned to the laboratory and subjected to incubation experiments to quantify the response of oxidation in these soils to temperature, soil moisture, in situ CH4 mixing ratio, soil depth, and oxygen. The mathematical representations of the observed oxidation reponses were combined with measured and predicted soil characteristics in a computer model to predict the rate of CH4 oxidation in the soils at the locations of the measured fluxes described by Czepiel et al. [this issue]. The estimated whole landfill oxidation rate at the time of the flux measurements in October 1994 was 20%. Local air temperature and precipitation data were then used in conjunction with an existing soil climate model to estimate an annual whole landfill oxidation rate in 1994 of 10%.

Methane (CH4) emissions were measured from the Nashua, New Hampshire municipal landfill using static enclosure and atmospheric tracer methods. The spatial variability of emissions was also examined using geostatistical methods. One hundred and thirty nine enclosure measurements were performed on a regular grid pattern over the emitting surface of the landfill resulting in an estimate of whole landfill emissions of 15,800 L CH4 min−1. Omnidirectional variograms displayed spatial correlation among CH4 fluxes below a separation distance of 7 m. Eleven tracer tests, using sulfur hexafluoride (SF6) as a tracer gas, resulted in a mean emissions estimate of 17,750 L CH4 min−1. The favorable agreement between the emission estimates was further refined using the observed relationship between atmospheric pressure and CH4 flux. This resulted in a pressure-corrected tracer flux estimate of whole landfill emissions of 16,740 L CH4 min−1.

We have investigated methane emissions from urban sources in the former East Germany using innovative measurement techniques including a mobile real-time methane instrument and tracer release experiments. Anthropogenic and biogenic sources were studied with the emphasis on methane emissions from gas system sources, including urban distribution facilities and a production plant. Methane fluxes from pressure regulating stations ranged from 0.006 to 24. l/min. Emissions from diffuse sources in urban areas were also measured with concentration maps and whole city flux experiments. The area fluxes of the two towns studied were 0.37 and 1.9 μg/m2/s. The emissions from individual gas system stations and total town emissions of this study are comparable to results of similar sites examined in the United States.

Field measurements of methane emissions from landfills are essential if one is to accurately constrain uncertainties in current estimates of global methane emissions from landfills and document emissions reductions realized by currently available control technology. Two experimental techniques for the measurement of methane flux from landfills, flux chamber measurements and tracer flux techniques, have been evaluated at a 24 hectare landfill site in New England. Agreement between the two techniques was quite good, with the flux chamber technique giving a landfill wide methane flux of 16.4 m 3 CH 4 min -1 while a series of seven tracer flux tests resulted in a mean flux of 17.8 m 3 CH 4 min -1 . Model estimates suggest that the installation of gas recovery measures at the five largest landfill sites in the state of New Hampshire and the ten largest sites in Massachusetts would reduce landfill emissions in each state by approximately 75%, resulting in a total emissions reduction of 65 x 10 9 g CH 4 /yr.

The Denitrification-Decomposition (DNDC) model was used to elucidate the role of climate, soil properties, and farming practices in determining spatial and temporal variations in the production and emission of nitrous oxide (N2O) from agriculture in the United States. Sensitivity studies documented possible causes of annual variability in N2O flux for a simulated Iowa corn-growing soil. The 37 scenarios tested indicated that soil tillage and nitrate pollution in rainfall may be especially significant anthropogenic factors which have increased N2O emissions from soils in the United States. Feedbacks to climate change and biogeochemical manipulation of agricultural soil reflect complex interactions between the nitrogen and carbon cycles. A 20% increase in annual average temperature in °C produced a 33% increase in N2O emissions. Manure applications to Iowa corn crops enhanced carbon storage in soils, but also increased N2O emissions. A DNDC simulation of annual N2O emissions from all crop and pasture lands in the United States indicated that the value lies in the range 0.9–1.2 TgN. Soil tillage and fertilizer use were the most important farming practices contributing to enhanced N2O emissions at the national scale. Soil organic matter and climate variables were the primary determinants of spatial variability in N2O emissions. Our results suggest that the United States Government, and possibly the Intergovernmental Panel on Climatic Change (IPCC), have underestimated the importance of agriculture as a national and global source of atmospheric N2O. The coupled nature of the nitrogen and carbon cycles in soils results in complex feedbacks which complicate the formulation of strategies to reduce the global warming potential of greenhouse gas emissions from agriculture.

The Langley tunable diode laser instrument package incorporated an additional channel to measure nitrous oxide (N2O) during the Pacific Exploratory Mission (PEM) West A. These measurements represent the first airborne, fast response (5-s) N2O data set obtained within the troposphere. Most data were recorded over the western Pacific between 0°N and 45°N latitude, 110°E and 180°E longitude, and 0.3 to 12 km altitude. Important observations include a decreasing N2O latitude gradient of approximately 0.4 parts per billion volume (ppbv) from northern midlatitudes to the equator, a decreasing N2O longitude gradient of 0.4 ppbv from the western Pacific to the central Pacific at northern midlatitudes, and an enhancement of 0.2 ppbv in the boundary layer (altitudes below 0.5 km) relative to the rest of the tropospheric vertical profile. Other observations include increased N2O mixing ratios within both urban and biogenic affected air masses and reduced N2O mixing ratios in stratospheric intrusions. These relationships with air mass source characteristics are exhibited in the large-scale correlations between N2O and CO, CH4, and CO2 in the free troposphere. Atmospheric inputs of N2O are examined and the relative strengths of continental biogenic and anthropogenic/industrial sources are estimated. The data set is also examined for evidence of an oceanic source of N2O.

Nitrous oxide (N 2 0) emissions from primary and secondary wastewater treatment processes were measured during spring and summer 1993 in Durham, NH. The most significant emissions occurred during secondary aeration. Dissolved N 2 0 generated as a result of denitrification during primary settling was stripped from the liquid during mechanical aeration. Emission factors derived from our field measurements included per capita emissions of 3.2 g of N 2 0 person -1 yr -1 and flow based emissions of 1.6 x 10 -6 of N 2 0 (L of wastewater) -1 .

An existing model of C and N dynamics in soils was supplemented with a plant growth submodel and cropping practice routines (fertilization, irrigation, tillage, crop rotation, and manure amendments) to study the biogeochemistry of soil carbon in arable lands. The new model was validated against field results for short-term (1–9 years) decomposition experiments, the seasonal pattern of soil CO2 respiration, and long-term (100 years) soil carbon storage dynamics. A series of sensitivity runs investigated the impact of varying agricultural practices on soil organic carbon (SOC) sequestration. The tests were simulated for corn (maize) plots over a range of soil and climate conditions typical of the United States. The largest carbon sequestration occurred with manure additions; the results were very sensitive to soil texture (more clay led to greater sequestration). Increased N fertilization generally enhanced carbon sequestration, but the results were sensitive to soil texture, initial soil carbon content, and annual precipitation. Reduced tillage also generally (but not always) increased SOC content, though the results were very sensitive to soil texture, initial SOC content, and annual precipitation. A series of long-term simulations investigated the SOC equilibrium for various agricultural practices, soil and climate conditions, and crop rotations. Equilibrium SOC content increased with decreasing temperatures, increasing clay content, enhanced N fertilization, manure amendments, and crops with higher residue yield. Time to equilibrium appears to be one hundred to several hundred years. In all cases, equilibration time was longer for increasing SOC content than for decreasing SOC content. Efforts to enhance carbon sequestration in agricultural soils would do well to focus on those specific areas and agricultural practices with the greatest potential for increasing soil carbon content.

The DNDC (Denitrification-Decomposition) model is shown to simulate emissions of nitrous oxide (N 2 O), changes in soil nitrate, and nitrogen mineralization rates consistent with field measurements at three agricultural sites in Florida. As a case study of the potential policy relevance of a process-oriented biogeochemical model, we estimated N 2 O emissions to the atmosphere from all agricultural lands in Florida, a state with significant agriculture on both organic and mineral soils. Nine landscape classes (3 soil classes × 3 annual rainfall classes) were coupled with county-based data on crops (5 major crops + pasture + fallow), fertilization, irrigation, and representative areas, to generate 86 model scenarios. Annual simulations were run for each case, and county and state emissions were tabulated. Total N 2 O emissions from Florida's agricultural lands were estimated to be 0.024 Tg N 2 ON y −1 . Emissions were unevenly distributed with approximately 50 percent of the N 2 O being emitted from soils in six (of 68) Florida counties. Organic soils, while occupying only 9% of the total agricultural land area and receiving no nitrogen fertilizer additions, accounted for 38% of the state's total N 2 O flux. Sensitivity studies suggest that the most effective means for mitigating N 2 O emissions would involve a combination of measures including reductions in drainage of organic soils, injection of fertilizers to soil depths of 10 cm or greater, and increased attention to precision irrigation. Biogeochemical modeling will be critical to developing an integrated framework for assessing policies for reducing N 2 O emissions from agricultural systems.

This paper presents a methodology for improved understanding of options for managing urban water demands under the uncertainties associated with climate change. It combines a sensitivity analysis of water supply with forecasts of water demand and examines how conservation efforts may offset deficits which result from climate change. It presents a case study of Nassau County, New York State, USA, that concludes that deficits projected for warmer climate scenarios can probably be alleviated by increased conservation. For scenarios of decreased precipitation, more extreme measures (eg rationing) may be necessary, illustrating the prudence of considering climate change in planning studies for communities which already experience water supply problems.

An integration of digital elevation modelling and satellite remote sensing of land cover and land use in the Upper Reventazon Basin in Costa Rica has been used to identify possible sources of enhanced sediment erosion. The techniques described quantify the occurrence and spatial distribution of specific land use categories as a function of slope for the entire basin. The results provide a framework for the designing of focused field measurement and policy programmes related to soil conservation. In the Reventazon Basin these techniques could help resolve conflicts between agriculture, hydropower production and water quality protection.

Methyl bromide (CH(3)Br) is considered to be a major source of stratospheric Br, which contributes to the destruction of ozone. It is therefore necessary to understand the natural sinks of this compound and to accurately measure ambient mixing ratios. Methodology is described for the measurement of atmospheric CH(3)Br by cryotrapping-gas chromatography and its application to soil kinetics. A 2-propanol/dry ice cryotrap was used to preconcentrate CH(3)Br in standard and air samples, with subsequent detection using a gas chromatograph equipped with an O(2)-doped electron capture detector (GC-ECD). The GC-ECD cryotrapping method had a detection limit of 0.23 pmol of CH(3)Br. This is equivalent to the amount of CH(3)Br in a 500 mL sample of ambient air at the estimated northern hemisphere atmospheric mixing ratio of 11 parts per trillion by volume (pptv). A dynamic dilution system was developed to produce mixing ratios of CH(3)Br ranging between 4 and 1000 pptv. Calibrated mixing ratios of CH(3)Br produced with the dilution system were used to determine soil uptake kinetics employing a dynamic soil incubation method.

Measurements in the Arctic troposphere over several years show that MSA concentrations in the atmospheric boundary layer, 0.08-6.1 parts per trillion (ppt, molar mixing ration), are lower that those over mid-latitude oceans. The seasonal cycle of MSA at Alert, Canada (82.5°N, 62.3°W), has two peaks of 6 ppt in March–April and July–August and minima of 0.3 ppt for the rest of the year. At Dye 3 (65°N, 44°W) on the Greenland Ice Sheet, a similar seasonal MSA cycle is observed although the concentrations are much lower with a maximum of 1 ppt. Around Barrow, Alaska (71.3°N, 156.8°W), MSA is between 1.0 and 25 ppt in July, higher than 1.5 ± 1.0 ppt in March–April. The mid-tropospheric MSA level of 0.6-1 ppt in the summer Arctic is much lower than about 6 ppt in the boundary layer. At Alert, the ratio of MSA to non-sea-salt (nss) SO42− ranges from 0.02 to 1.13 and is about 10 times higher in summer than in spring. The summer ratios are higher than found over mid-latitude regions and, when combined with reported sulfur isotope compositions from the Arctic, suggest that on average a significant fraction (about 16–23%) of Arctic summer boundary layer sulfur is marine biogenic. The measurements show that the summer Arctic boundary layer has a significantly higher MSA/nss-SO42− ratio than aloft.

The number of emission measurements of methane (CH4) to the atmosphere has increased greatly in recent years, as recognition of its atmospheric chemical and radiative importance becomes widespread. In this report, we review progress on estimating and understanding both the magnitude of, and controls on, emissions of CH4 from natural wetlands. We also calculate global wetland CH4 emissions using this extensive flux data base and the wetland areas compiled and published by Matthews and Fung (1987). Tropical regions (20° N-30° S) were calculated to release 66 TgCH4/yr, 60% of the total wetland emission of 109 Tg/yr. Flux data from tropical wetlands, reported only within the last four years, are currently restricted in geographic coverage. Additional data from other regions will be required to confirm these calculated large emissions. Although emissions from subtropical and temperate wetlands (45° N-20° N and 30° S-50° S) were relatively low at 5 Tg/yr, the process-oriented focus of most of the research in this region suggests that work at these latitudes may serve as models to examine controls and possible uncertainties in estimating fluxes. These types of efforts are frequently not possible in more remote, globally significant wetlands. Northern wetlands (north of 45° N) were calculated to release a total of 38 TgCH4/yr (34% of total flux); 34 Tg/yr from wet soils and 4 Tg/yr from relatively dry tundra. These latitudes have been the focus of recent intensive research. Significant differences between the relatively large flux data bases accumulated in the two primary measurement areas, northern Minnesota and the Hudson Bay Lowlands of Canada, indicate that extrapolation from one wetland region to another may be subject to considerable error. Global emissions were also compared to fluxes calculated using the wetland areas published by Aselmann and Crutzen (1989) in an effort to assess uncertainties due to wetland area estimates. Further refinement of wetland CH4 emissions awaits flux measurements from large areas currently lacking data, particularly in the tropics and the Siberian Lowlands, more realistic assessments of seasonal active periods, and accurate, up-to-date habitat classification and measurement.

This paper argues that in Kenya, environmental and economic factors will favour the continued use of biomass as a primary fuel for household an institutional cooking for the next decade or longer. The paper describes several successful projects which have improved the efficiency of urban charcoal use and of rural woodfuel use. The Kenya Ceramic Jiko, a more efficient version of the traditional charcoal stove, is a model programme sustained by free market competition, artisans participation, and widespread public acceptance. The Maendeleo stove is the best example of a successful rural woodstove project. The performance attributes of the stove, and its promotion through Kenya's largest women's organization, have resulted int he distribution of an estimated 26,000 Maendeleo stoves. Rural stove efficiency will become important as the cash-based economy expands in those areas. Agroforestry will also be critical to an enhanced use of biomass energy in Kenya. Experience to date shows that successful agroforestry programmes will have to be appropriate to local conditions and crops. (author). 25 refs, 2 figs, 3 tabs.

This paper provides a place-based approach to the organization and analysis of historic hurricane information in the context of informing decision-making in urban planning, disaster management, and mitigation, and natural resource stewardship on the Texas coast. We discuss the climatology of Texas hurricanes by analyzing the spatial and temporal patterns and some aspects of factors that contribute to their observed variability. Finally, we construct scenarios of historic hurricanes that formed and made landfall rapidly on the Texas coastline and suggest that these storms are especially challenging for emergency planners, citizens, and public officials.

METHYL bromide (CH3Br), a widely used agricultural fumigant, may be an important source of atmospheric bromine radicals, which destroy stratospheric ozone1–10. In current models of this compound's atmospheric behaviour, the main sinks are taken to be oxidation by hydroxyl radicals, photolysis and uptake by the oceans1–5,7,9,10. But there is also evidence that CH3Br is consumed in soils8,11–13. Here we report laboratory and field experiments which show that, when exposed to a variety of soil types at low mixing ratios, CH3Br is rapidly and irreversibly removed to below the levels found in the global atmosphere. We show that the uptake process is bacterially mediated. We estimate the global annual soil sink to be 42 ± 32 Gg; coupled with other removal mechanisms, this suggests an atmospheric lifetime for CH3Br of about 0.8 yr, just half the previous best estimate9, and an ozone depletion potential that is about 30% smaller than the previous estimate1.

Landfills are the largest source of anthropogenic methane (CH4) emissions to the atmosphere in the United States. However, few measurements of whole landfill CH4 emissions have been reported. Here, we present the results of a multi-season study of whole landfill CH4 emissions using atmospheric tracer methods at the Nashua, New Hampshire Municipal landfill in the northeastern United States. The measurement data include 12 individual emission tests, each test consisting of 5-8 plume measurements. Measured emissions were negatively correlated with surface atmospheric pressure and ranged from 7.3 to 26.5 m3 CH4 min(-1). A simple regression model of our results was used to calculate an annual emission rate of 8.4 x 10(6) m3 CH4 year(-1). These data, along with CH4 oxidation estimates based on emitted landfill gas isotopic characteristics and gas collection data, were used to estimate annual CH4 generation at this landfill. A reported gas collection rate of 7.1 x 10(6) m3 CH4 year(-1) and an estimated annual rate of CH4 oxidation by cover soils of 1.2 x 10(6) m3 CH4 year(-1) resulted in a calculated annual CH4 generation rate of 16.7 x 10(6) m3 CH4 year(-1). These results underscore the necessity of understanding a landfill's dynamic environment before assessing long-term emissions potential.

The preceding chapters have presented a topical synthesis of results obtained by the international scientific community after a decade of intensive research efforts focussing on the chemistry of the global atmosphere. Areas highlighted in this book are the relations between atmospheric composition and biospheric processes, the budget of atmospheric photooxidants including tropospheric ozone, and the importance of aerosols for the chemical composition of the atmosphere and for the climate system. The perturbing role of human activities has been stressed.

[1] A conceptual framework is developed using atmospheric measurements from aircraft to determine fluxes of CO2 from a continental land area. The concepts are applied to measurements of CO2 ,O 3, and CO concentrations from the Amazon Boundary Layer Experiment (ABLE-2B, April–May 1987) to estimate fluxes of CO2 for central and eastern Amazonia late in the wet season of 1987. We observed that column amounts of CO2 from 0 to 3 km decreased during the day over Amazonia at the average rate of � 6.3 ± 1 mmol m � 2 s � 1 , corresponding to an uptake flux modestly smaller than the daytime uptake (� 10.2 mmol m � 2 s � 1 ) at a flux tower in the study area. The estimated net flux of CO2, integrated over 24 hours, was � 0.03 ± 0.2 mmol m � 2 s � 1 , indicating that the carbon budget of a substantial area of central Amazonia was close to balance in April 1987. We argue that net CO2 fluxes on the continental scale of Amazonia, with its heterogeneous landscape and large areas of inundation, are strongly modified by the influence of seasonal hydrological factors that enhance respiration and decomposition in forests and wetlands, offsetting growth of forest trees in the wet season. INDEX TERMS: 0315 Atmospheric Composition and Structure: Biosphere/atmosphere interactions; 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 1610 Global Change: Atmosphere (0315, 0325)

In this Viewpoint the author examines rising greenhouse gas emissions in the context of changes in the land uses which produce them. The clearing of forested land and associated burning of biomass account for as much as 30% of global CO 2 emissions. Rice agriculture and domestic animals are major producers of methane, and significant N 2 O emissions derive from the use of nitrogen fertilizer. These activities are closely associated with efforts to increase food production, especially in the developing countries. Urgent international attention must be given to these problems if conflict is to be avoided.

A model of the daily carbon balance of a black spruce/feathermoss boreal forest ecosystem was developed and results compared to preliminary data from the 1994 BOREAS field campaign in northern Manitoba, Canada. The model, driven by daily weather conditions, simulated daily soil climate status (temperature and moisture profiles), spruce photosynthesis and respiration, moss photosynthesis and respiration, and litter decomposition. Model agreement with preliminary field data was good for net ecosystem exchange (NEE), capturing both the asymmetrical seasonality and short-term variability. During the growing season simulated daily NEE ranged from -4 g C m(exp -2) d(exp -1) (carbon uptake by ecosystem) to + 2 g C m(exp -2) d(exp -1) (carbon flux to atmosphere), with fluctuations from day to day. In the early winter simulated NEE values were + 0.5 g C m(exp -2) d(exp -1), dropping to + 0.2 g C m(exp -2) d(exp -1) in mid-winter. Simulated soil respiration during the growing season (+ 1 to + 5 g C m(exp -2) d(exp -1)) was dominated by metabolic respiration of the live moss, with litter decomposition usually contributing less than 30% and live spruce root respiration less than 10% of the total. Both spruce and moss net primary productivity (NPP) rates were higher in early summer than late summer. Simulated annual NEE for 1994 was -51 g C m(exp -2) y(exp -1), with 83% going into tree growth and 17% into the soil carbon accumulation. Moss NPP (58 g C m(exp -2) d(exp -1)) was considered to be litter (i.e. soil carbon input; no net increase in live moss biomass). Ecosystem respiration during the snow-covered season (84 g Cm(exp -2)) was 58% of the growing season net carbon uptake. A simulation of the same site for 1968-1989 showed about 10-20% year-to-year variability in heterotrophic respiration (mean of + 113 g C m-2 y@1). Moss NPP ranged from 19 to 114 g C m(exp -2) y(exp -1); spruce NPP from 81 to 150 g C nt-2 y,@l; spruce growth (NPP minus litterfall) from 34 to 103 g C m(exp -2) y(exp -1); NEE ranged from +37 to -142 g C m(exp -2) y(exp -1). Values for these carbon balance terms in 1994 were slightly smaller than the 1969 - 89 means. Higher ecosystem productivity years (more negative NEE) generally had early springs and relatively wet summers; lower productivity years had late springs and relatively dry summers.

Environ. Sci. Techno/. 1995, 29, 1468-1 479 Introduction Tracer -Methods To Measure Downloaded by UNIV OF CALIFORNIA IRVINE on August 26, 2015 | http://pubs.acs.org Publication Date: June 1, 1995 | doi: 10.1021/es00006a007 Gas Faciliies and U h n Areas BRIAN K. LAMB,*,’ J. BARRY MCMANUS,* JOANNE H. SHORTER,* CHARLES E . KOLB,* BYARD MOSHER,$ R O B E R T C . HARRISS,§ EUGENE ALLWINE,’ DENISE BLAHA,$ T O U C H E H O W A R D , ” A L E X GUENTHER,l ROBERT A. LOTT,A ROBERT SIVERSON,’ HAL WESTBERG,’ AND PAT ZIMMERMAN- Laboratory for Atmospheric Research, Department of Civil & Environmental Engineering, Washington State University, Pullman, WA 99164-2910, Center for Chemical and Environmental Physics, Aerodyne Research, Inc., Billerica, Massachusetts 01821, Institute for the Study of Earth, Oceans and Space, University of New Hampshire, Durham, New Hampshire 03824, Indaco Air Quality Services, Inc., Pullman, Washington 99163, National Center for Atmospheric Research, Boulder, Colorado 80303, and Gas Research Institute, Chicago, Illinois 60631 -3562 A new, integrated methodologyto locate and measure methane emissions from natural gas systems has been developed. Atmospheric methane sources are identified by elevated ambient CH4 concentrations measured with a mobile laser-based methane analyzer. The total methane emission rate from a source is obtained by simulating the source with a sulfur hexafluoride (SFS) tracer gas release and by measuring methane and tracer concentrations along downwind sampling paths using mobile, real-time analyzers. Combustion sources of methane are dis- tinguished from noncombustion sources by concur- rent ambient carbon dioxide measurements. Three variations on the tracer ratio method are described for application to (1) small underground vaults, (2) above- ground natural gas facilities, and (3) diffuse methane emissions from an entire town. Results from controlled releases and from replicate tests demonstrate thatthe tracer ratio approach can yield total emission rates to within approximately &15%. The estimated accuracy of emission estimates for urban areas with a variety of diffuse emissions is &50%. Methane (CH4) has been a contributor to the increasing burden of greenhouse gases in the earth’s atmosphere for more than a century (1). Faced with significant risks identified in scenarios of increasing greenhouse gas con- centrations, many countries are developing plans to reduce emissions. However, uncertainties in specific source emission rates for CH4 and other non-COz greenhouse gases currently limit the quantitative risk-benefit analysis needed to answer key policy questions related to the socioeconomic impacts of large-scale mitigation actions (2, 3 ) . Initial attempts to estimate CH4 losses to the atmosphere from natural gas production and use assumed that emis- sions could be approximated by industry reports of “unac- counted for” gas (e.g., ref 4). Unaccounted for gas, defined as the difference between the amount of natural gas metered into a system and the amount of gas metered out of a system, does not account for gas losses from wells to the processing plant, gas used as fuel in facilities, theft of gas, meter inaccuracies, and differences in accounting procedures between companies (4,5). Thus, the unaccounted for gas estimates cannot unambiguously be considered an upper or lower bound on emissions (5). Extrapolation of engi- neering estimates or data obtained from component by component sniffing methods also leads to large uncertain- ties in estimated emissions. In the United Kingdom, the British Gas Company estimates CH4 emissions from gas distribution system components to be less than 1% of throughput, while others estimate losses as high as 11% of gas throughput (6). A recent estimate of CH4 leakage from the natural gas system in the former Soviet Union, which was characterized as “tentative and highly conditional” suggested a range of total losses from 3.3% to 7% of gas production ( 7 ) . The U.S. Environmental Protection Agency (EPA) and the Gas Research Institute (GRI) have recently sponsored an integrated field measurement and analysis program to better define methane emissions from the U.S. natural gas system. Drawing on initial measurements using some of the techniques reported here as weil as engineering estimates, GRI has developed a preliminary estimate of methane emissions from the gas industry that equals approximately 1.5 i 0.5% of annual throughput (8). In the case of CH4 emissions due to the use of natural gas, there is an added motivation for correctly prescribing the methane source strength. Since natural gas typically produces 32-45% less COz per unit of thermal output compared to coal and 30% less compared to fuel oil, switching from coal and fuel oil to natural gas has the potential to reduce carbon dioxide emissions and reduce global warming (5). However, CH4 is a more potent greenhouse gas than CO2 on a molecule for molecule basis (9- 1 I). As a result, increasing the usage of natural gas may * To whom correspondence should be addressed: e-mail address: blamb@wsu.edu. + Washington State University. Aerodyne Research, Inc. 5 University of New Hampshire. I’ Indaco Air Quality Services, Inc. National Center for Atmospheric Research. A Gas Research Institute. 1468 ENVIRONMENTAL SCIENCE &TECHNOLOGY / VOL. 29, NO. 6, 1995 0013-936)(/95/0929-1468$09.00/0 @ 1995 American Chemical Society

EARTHLY POLITICS: LOCAL AND GLOBAL IN ENVIRONMENTAL GOVERNANCE edited by Sheila Jasanoff and Marybeth Long Martello; MIT Press. Cambridge. MA. 2004; 376 pp., $67.00 cloth (ISBN 0-262-10103-3). $27.00 paper (ISBN 0-262-60059-5). URBAN SPRAWI AND PUBLIC HEALTH: DESIGNING, PLANNING, AND BUILDING FOR HEALTHY COMMUNITIES by Howard Frumkin, Lawrence Frank. and Richard Jackson; Island Press. Washington, DC. 2004; 288 pp., $60.00 cloth (ISBN 1-55963-912-1). $30.00 paper (ISBN 1-55963-305-0).

Human activities are changing the chemical composition of the Earth’s atmosphere. Emissions of pollutant gases from the burning of fossil fuels, production and use of synthetic chemicals, and the conversion of natural environments to agricultural systems have increased the atmospheric concentrations of carbon dioxide, methane, nitrous oxide, and chlorofluorocarbons to the highest levels known for at least 160,000 years of Earth history. Trapped ancient gases in ice cores, and direct monitoring of more recent changes in air chemistry, have convincingly documented the links between the growth of the human population, the evolution of industrial societies, and increasing concentrations of these gases (e.g., Rowland and Isaksen, 1988; Chappellaz et al., 1990; Lorius et al., 1990). One likely consequence of the increasing concentrations of atmospheric gases like carbon dioxide and methane is a change in global climate. These gases have long lifetimes in the atmosphere, and as they accumulate they trap, in the lower atmosphere, increasing amounts of energy emitted from the earth’s surface (Ramanathan et al., 1987). The current consensus among climate experts is that the increasing burden of atmospheric gases projected for the next century will result in a global climate warming of some 2–6°C (Dickinson, 1986; Levine, Chapter 1, this volume). A warming of this magnitude would be unprecedentedly rapid and extreme in the history of industrial society.

A major portion of tropospheric photochemistry occurs in the tropics. Deforestation, colonization, and development of tropical rain forest areas could provoke significant changes in emissions of radiatively and photochemically active trace gases. A brief review of studies on trace-gas emissions in pristine and disturbed tropical habitats is followed by an effort to model regional tropospheric chemistry under undisturbed and polluted conditions. Model results suggest that changing emissions could stimulate photochemistry leading to enhanced ozone production and greater mineral acidity in rainfall in colonized agricultural regions. Model results agree with measurements made during the NASA ABLE missions. Under agricultural/pastoral development scenarios, tropical rain forest regions could export greater levels of N2O, CH4, CO, and photochemical precursors of NOy and O3 to the global atmosphere with implications for climatic warming.

Mineral dust is ubiquitous in our world. The generation, transport, and deposition of dust are normal geological processes that have helped to shape and create many features on the surface of the earth. Often this normal process is accelerated by man’s activities.

The carefully measured decrease in the growth rate of atmospheric methane (CH4) in 1992 reported by Dlugokencky et al. (1994) is an impressive accomplishment, and testimony for the importance of maintaining high-quality, long-term monitoring of atmospheric composition. The changing growth rate of atmospheric CH4 has important implications for assessing and understanding the potential magnitude and rates of a future greenhouse gas-induced climate change. Furthermore, the CH4 data from the current Climate Monitoring and Diagnostics Laboratory (CMDL) globally-distributed network of cooperative air sampling sites are clearly the best record of global CH4 trends and distribution currently available. However, we argue briefly here that the speculation by Dlugokencky et al. (1994) on possible mechanisms for the decreased growth rate in 1992 is only one scenario of many that could possibly fit with the constraints imposed by the reported data. Our comments are to (1) illustrate the difficulties of deducing small changes in complex, poorly understood, geographically diverse natural and anthropogenic sources of CH4 from measurements at the remotely-located CMDL sampling sites and (2) emphasize that detailed bottoms-up analyses are necessary to really advance the understanding of changes in source strengths; we are not promoting alternative mechanisms to explain the 1992 decrease in atmospheric CH4.