Radiative forcing from household fuel burning in Asia

Household fuel use in developing countries, particularly as biomass and coal, is a major source of carbonaceous aerosols and other air pollutants affecting health and climate. Using state-of-the-art emission inventories, a global three-dimensional photochemical tracer/transport model of the troposphere, and a global radiative transfer model based on methods presented in the latest IPCC Assessment Report (2007-AR4), we estimate the radiative forcing (RF) attributable to household fuel combustion in Asia in terms of current global annual-mean RF and future global integrated RF for a one-year pulse of emissions (2000) over two time horizons (100 and 20 years). Despite the significant emissions of black carbon (BC) aerosols, these estimates indicate that shorter-lived (non-Kyoto) air pollutants from household fuel use in the region overall seem to exert a small net negative RF because of the strong influence of reflective aerosols. There are, however, major uncertainties in emission estimates for solid fuel burning, and about the sustainability of household fuel wood harvesting in Asia (the carbon neutrality of harvesting). In addition, there is still substantial uncertainty associated with the BC radiative forcing. As a result we find that the sign of the RF from household biomass burning in the region cannot be established. While recognizing the value of integrating climate change and air pollution policies, we are concerned that for a ‘Kyoto style’ post-Kyoto treaty (with global cap-and-trade and the Global Warming Potential as the metric) expanding the basket of components with a selection of short-lived species without also including the wider range of co-emitted species may lead to unintended consequences for global-scale climate. Additional measurement, modelling, and policy research is urgently needed to reduce the uncertainties so that the net impact on climate of emissions and mitigation measures in this sector can be accurately assessed.     

Historical and projected emissions of major halocarbons in China

The halocarbons studied here are chemicals controlled in the 1987 Montreal Protocol on Substances that Deplete the Ozone Layer and its Amendments, which have both high ozone depleting potentials (ODPs) and high global warming potentials (GWPs). These halocarbons are mainly used for refrigeration, air-conditioning, foam blowing, tobacco expansion, aerosol propulsion, solvent cleaning, and fire fighting. China ratified the Montreal Protocol in 1991 and has been implementing the phase-out of halocarbons since then. In this paper, the emissions of halocarbons from China were estimated for 1995–2024 based on the historical consumption, the country program for complying with the Montreal Protocol, and the sector plans for phasing out halocarbons. The results show that China's compliance with the Montreal Protocol contributes greatly to both ozone protection and climate protection.     

Atmospheric composition change – global and regional air quality

Air quality transcends all scales with in the atmosphere from the local to the global with handovers and feedbacks at each scale interaction. Air quality has manifold effects on health, ecosystems, heritage and climate. In this review the state of scientific understanding in relation to global and regional air quality is outlined. The review discusses air quality, in terms of emissions, processing and transport of trace gases and aerosols. New insights into the characterization of both natural and anthropogenic emissions are reviewed looking at both natural (e.g. dust and lightning) as well as plant emissions. Trends in anthropogenic emissions both by region and globally are discussed as well as biomass burning emissions. In terms of chemical processing the major air quality elements of ozone, non-methane hydrocarbons, nitrogen oxides and aerosols are covered. A number of topics are presented as a way of integrating the process view into the atmospheric context; these include the atmospheric oxidation efficiency, halogen and HO_x chemistry, nighttime chemistry, tropical chemistry, heat waves, megacities, biomass burning and the regional hot spot of the Mediterranean. New findings with respect to the transport of pollutants across the scales are discussed, in particular the move to quantify the impact of long-range transport on regional air quality. Gaps and research questions that remain intractable are identified. The review concludes with a focus of research and policy questions for the coming decade. In particular, the policy challenges for concerted air quality and climate change policy (co-benefit) are discussed.     

Present and potential future contributions of sulfate,black and organic carbon aerosols from China to global air quality,premature mortality and radiative forcing

Aerosols are harmful to human health and have both direct and indirect effects on climate. China is a major contributor to global emissions of sulfur dioxide (SO₂), a sulfate (SO₄^2?) precursor, organic carbon (OC), and black carbon (BC) aerosols. Although increasingly examined, the effect of present and potential future levels of these emissions on global premature mortality and climate change has not been well quantified. Through both direct radiative effects and indirect effects on clouds, SO₄^2? and OC exert negative radiative forcing (cooling) while BC exerts positive forcing (warming). We analyze the effect of China's emissions of SO₂, SO₄^2?, OC and BC in 2000 and for three emission scenarios in 2030 on global surface aerosol concentrations, premature mortality, and radiative forcing (RF). Using global models of chemical transport (MOZART-2) and radiative transfer (GFDL RTM), and combining simulation results with gridded population data, mortality rates, and concentration–response relationships from the epidemiological literature, we estimate the contribution of Chinese aerosols to global annual premature mortality and to RF in 2000 and 2030. In 2000, we estimate these aerosols cause approximately 470 000 premature deaths in China and an additional 30 000 deaths globally. In 2030, aggressive emission controls lead to a 50% reduction in premature deaths from the 2000 level to 240 000 in China and 10 000 elsewhere, while under a high emissions scenario premature deaths increase 50% from the 2000 level to 720 000 in China and to 40 000 elsewhere. Because the negative RF from SO₄^2? and OC is larger than the positive forcing from BC, Chinese aerosols lead to global net direct RF of ?74 mW m^?2 in 2000 and between ?15 and ?97 mW m^?2 in 2030 depending on the emissions scenario. Our analysis indicates that increased effort to reduce greenhouse gases is essential to address climate change as China's anticipated reduction of aerosols will result in the loss of net negative radiative forcing.     

Global emissions of HFC-23 estimated to year 2015

HFC-23 (trifluoromethane, fluoroform, CHF₃) is a powerful greenhouse gas that is formed at the reactor stage of the manufacture of HCFC-22 (chlorodifluoromethane, CHClF₂). The amount formed depends on the conditions used in the manufacturing process and, for individual plants, lies between 1% and 4% of the production of HCFC-22. While it is possible to reduce the formation of HFC-23 by optimising process conditions, it is not possible to eliminate its production. This requires destruction, generally by thermal oxidation. Under the Kyoto Protocol, developed countries have obligations to reduce greenhouse gas emissions and, in the developing world, there are projects under the Clean Development Mechanism for the incineration of HFC-23 waste streams. These should lead to a reduction in average global emission factors relative to production of HCFC-22. We present estimates of global production of HCFC-22 up to the year 2015 and also the calculated range of emissions of HFC-23 that may be consequences of this. In terms of the effect on climate change, the atmospheric burden of HFC-23 accumulated from emissions is calculated to contribute between 0.1% and 0.2% of the radiative forcing of climate in 2015. Annual emissions of HFC-23 would be equivalent to between 284 and 28 million tonnes of CO₂ in that year, when total anthropogenic greenhouse gas emissions are predicted to lie between 46,000 million and 59,000 million tonnes of CO₂ equivalent.     

Climate Policy to Defeat the Green Paradox

Carbon dioxide emissions have accelerated since the signing of the Kyoto Protocol. This discouraging development may partly be blamed on accelerating world growth and on lags in policy instruments. However, it also raises serious question concerning whether policies to reduce CO₂ emissions are as effective as generally assumed. In recent years, a considerable number of studies have identified various feedback mechanisms of climate policies that often erode, and occasionally reinforce, their effectiveness. These studies generally focus on a few feedback mechanisms at a time, without capturing the entire effect. Partial accounting of policy feedbacks is common in many climate scenarios. The IPCC, for example, only accounts for direct leakage and rebound effects. This article attempts to map the aggregate effects of different types of climate policy feedback mechanisms in a cohesive framework. Controlling feedback effects is essential if the policy measures are to make any difference on a global level. A general conclusion is that aggregate policy feedback mechanisms tend to make current climate policies much less effective than is generally assumed. In fact, various policy measures involve a definite risk of ‘backfiring’ and actually increasing CO₂ emissions. This risk is particularly pronounced once effects of climate policies on the pace of innovation in climate technology are considered. To stand any chance of controlling carbon emissions, it is imperative that feedback mechanisms are integrated into emission scenarios, targets for emission reduction and implementation of climate policy. In many cases, this will reduce the scope for subsidies to renewable energy sources, but increase the scope for other measures such as schemes to return carbon dioxide to the ground and to mitigate emissions of greenhouse gases from wetlands and oceans. A framework that incorporates policy feedback effects necessitates rethinking the design of the national and regional emission targets. This leads us to a new way of formulating emission targets that include feedback effects, the global impact target. Once the full climate policy feedback mechanisms are accounted for, there are probably only three main routes in climate policy that stand a chance of mitigating global warming: (a) returning carbon to the ground, (b) technological leaps in zero-emission energy technology that make it profitable to leave much carbon in the ground even in Annex II countries and (c) international agreements that make it more profitable to leave carbon in the ground or in forests.     

Transport impacts on atmosphere and climate: Shipping

Emissions of exhaust gases and particles from oceangoing ships are a significant and growing contributor to the total emissions from the transportation sector. We present an assessment of the contribution of gaseous and particulate emissions from oceangoing shipping to anthropogenic emissions and air quality. We also assess the degradation in human health and climate change created by these emissions. Regulating ship emissions requires comprehensive knowledge of current fuel consumption and emissions, understanding of their impact on atmospheric composition and climate, and projections of potential future evolutions and mitigation options. Nearly 70% of ship emissions occur within 400 km of coastlines, causing air quality problems through the formation of ground-level ozone, sulphur emissions and particulate matter in coastal areas and harbours with heavy traffic. Furthermore, ozone and aerosol precursor emissions as well as their derivative species from ships may be transported in the atmosphere over several hundreds of kilometres, and thus contribute to air quality problems further inland, even though they are emitted at sea. In addition, ship emissions impact climate. Recent studies indicate that the cooling due to altered clouds far outweighs the warming effects from greenhouse gases such as carbon dioxide (CO₂) or ozone from shipping, overall causing a negative present-day radiative forcing (RF). Current efforts to reduce sulphur and other pollutants from shipping may modify this. However, given the short residence time of sulphate compared to CO₂, the climate response from sulphate is of the order decades while that of CO₂ is centuries. The climatic trade-off between positive and negative radiative forcing is still a topic of scientific research, but from what is currently known, a simple cancellation of global mean forcing components is potentially inappropriate and a more comprehensive assessment metric is required. The CO₂ equivalent emissions using the global temperature change potential (GTP) metric indicate that after 50 years the net global mean effect of current emissions is close to zero through cancellation of warming by CO₂ and cooling by sulphate and nitrogen oxides.     

Dynamic consistency problems behind the Kyoto Protocol

This paper examines the economic rationale behind both the quantitative targets and the flexibility mechanisms adopted in the Kyoto Protocol. It synthesises some theoretical dimensions of the debate about the socalled 'when flexibility' of climate policies, explaining the importance of the interplay between uncertainty and techno-economic inertia. Numerical results show that the aggregate Kyoto abatement target is consistent with a stochastic dynamic optimum in which a 450 ppm concentration ceiling is seriously considered. Turning to the EU-US debate about the interpretation of the 'supplemental to' condition in Article 3 of the Kyoto Protocol regarding the articulation between international trading systems and domestic policies and measures, this paper illuminates the risk of dynamic inconsistencies due to the heterogeneity of capital stocks in the economy, if price signals do not emerge in due time from greenhouse gas trading systems because of the 'hot air' in some countries and the discovery of low cost abatement potentials in Annex B countries. Numerical simulations show that a delay of action on sectors with large inertia of capital stocks may, under such circumstances, undermine the economic viability of climate policies beyond 2012. Some lessons are derived from the future of climate policies and negotiations about the implementation of the Kyoto Protocol.     

Global temperature change from the transport sectors: Historical development and future scenarios

Transport affects climate directly and indirectly through mechanisms that operate on very different timescales and cause both warming and cooling. We calculate contributions to the historical development in global mean temperature for the main transport sectors (road transport, aviation, shipping and rail) based on estimates of historical emissions and by applying knowledge about the various forcing mechanisms from detailed studies. We also calculate the development in future global mean temperature for four transport scenarios consistent with the IPCC SRES scenarios, one mitigation scenario and one sensitivity test scenario. There are large differences between the transport sectors in terms of sign and magnitude of temperature effects and with respect to the contributions from the long- and short-lived components. Since pre-industrial times, we calculate that transport in total has contributed 9% of total net man-made warming in the year 2000. The dominating contributor to warming is CO₂, followed by tropospheric O₃. By sector, road transport is the largest contributor; 11% of the warming in 2000 is due to this sector. Likewise, aviation has contributed 4% and rail ～1%. Shipping, on the other hand, has caused a net cooling up to year 2000, with a contribution of ?7%, due to the effects of SO₂ and NOx emissions. The total net contribution from the transport sectors to total man-made warming is ～15% in 2050, and reaches 20% in 2100 in the A1 and B1 scenarios. For all scenarios and throughout the century, road transport is the dominating contributor to warming. Due to the anticipated reduction in sulphur content of fuels, the net effect of shipping changes from cooling to warming by the end of the century. Significant uncertainties are related to the estimates of historical and future net warming mainly due to cirrus, contrails and aerosol effects, as well as uncertainty in climate sensitivity.     

Sensitivity of biogenic secondary organic aerosols to future climate change at regional scales: An online coupled simulation

Biogenic emissions and secondary organic aerosols (SOA) are strongly dependent on climatic conditions. To understand the SOA levels and their sensitivity to future climate change in the United States (U.S.), we present a modeling work with the consideration of SOA formation from the oxidation of biogenic emissions with atmospheric oxidants (e.g., OH, O₃, and NO₃). The model simulation for the present-day climate is evaluated against satellite and ground-based aerosol measurements. Although the model underestimates aerosol concentrations over the northwestern U.S. due to the lack of fire emissions in the model simulations, overall, the SOA results agree well with previous studies. Comparing with the available measurements of organic carbon (OC) concentrations, we found that the amount of SOA in OC is significant, with the ratio ranging from 0.1 to 0.5/0.6. The enhanced modeling system driven by global climate model output was also applied for two three-year one-month simulations (July, 2001–2003 and 2051–2053) to examine the sensitivity of SOA to future climate change. Under the future two emissions scenarios (A1B and A2), future temperature changes are predicted to increase everywhere in the U.S., but with different degrees of increase in different regions. As a result of climate change in the future, biogenic emissions are predicted to increase everywhere, with the largest increase (～20%) found in the southeastern and northwestern U.S. under the A1B scenario. Changes in SOA are not identical with those in biogenic emissions. Under the A1B scenario, the biggest increase in SOA is found over Texas, with isoprene emissions being the major contributor to SOA formation. The range of change varies from 5% over the southeast region to 26% over Texas. The changes in either biogenic emissions or SOA under the two climate scenarios are different due to the differences in climatic conditions. Our results also suggest that future SOA concentrations are also influenced by several other factors such as the partitioning coefficients, the atmospheric oxidative capability, primary organic carbon aerosols and anthropogenic emissions.     

Halogenated compounds and climate change: future emission levels and reduction costs

OBJECTIVES: This work assesses the contribution to climate change resulting from emissions of the group of halogenated greenhouse gases. METHODS: A bottom-up emission model covering 22 technological sectors in four major regions is described. Emission estimates for 1996 and projection for 2010 and 2020 are presented. The costs for deep cuts into projected emission levels are calculated. RESULTS: The substances covered by this study have contributed emissions of 1100 +/- 800 MT CO2 equivalents per year in 1996. In terms of their relative contribution to emissions of CO2 equivalents, this corresponds to 3 +/- 2% of global emissions of all anthropogenic greenhouse gases. The wide range of uncertainty is due to the poorly quantified net global warming potential of the ozone depleting substances, which have an indirect cooling effect on climate through the destruction of stratospheric ozone. For annual emissions of HFCs, PFCs and SF6 (which are regulated under the Kyoto Protocol and for which global warming potentials are well defined), the relative contribution is projected to increase to 2% (600 MT CO2 eq.) of global greenhouse gas emissions by 2010. This trend is expected to continue, emissions are projected to grow to a contribution of roughly 3% (870 MT CO2 eq.) in 2020 compared to 0.9% (300 MT CO2 eq.) in 1996. For HFCs, PFCs and SF6, this study identifies global emission reduction potentials of 260 MT CO2 eq. per year in 2010 and 640 MT CO2 eq. per year in 2020 at below US$ 50 per ton. These values correspond to roughly 40% and 75% of projected emissions in 2010 and 2020, respectively.     

Effects of land use conversion and fertilization on CH<Subscript>4</Subscript> and N<Subscript>2</Subscript>O fluxes from typical hilly red soil

Land use conversion and fertilization have been widely reported to be important managements affecting the exchanges of greenhouse gases between soil and atmosphere. For comprehensive assessment of methane (CH₄) and nitrous oxide (N₂O) fluxes from hilly red soil induced by land use conversion and fertilization, a 14-month continuous field measurement was conducted on the newly converted citrus orchard plots with fertilization (OF) and without fertilization (ONF) and the conventional paddy plots with fertilization (PF) and without fertilization (PNF). Our results showed that land use conversion from paddy to orchard reduced the CH₄ fluxes at the expense of increasing the N₂O fluxes. Furthermore, fertilization significantly decreased the CH₄ fluxes from paddy soils in the second stage after conversion, but it failed to affect the CH₄ fluxes from orchard soils, whereas fertilizer applied to orchard and paddy increased soil N₂O emissions by 68 and 113.9 %, respectively. Thus, cumulative CH₄ emissions from the OF were 100 % lower, and N₂O emissions were 421 % higher than those from the PF. Although cumulative N₂O emissions were stimulated in the newly converted orchard, the strong reduction of CH₄ led to lower global warming potentials (GWPs) as compared to the paddy. Besides, fertilization in orchard increased GWPs but decreased GWPs of paddy soils. In addition, measurement of soil moisture, temperature, dissolved carbon contents (DOCs), and ammonia (NH₄ ⁺-N) and nitrate (NO₃ ^?-N) contents indicated a significant variation in soil properties and contributed to variations in soil CH₄ and N₂O fluxes. Results of this study suggest that land use conversion from paddy to orchard would benefit for reconciling greenhouse gas mitigation and citrus orchard cultivation would be a better agricultural system in the hilly red soils in terms of greenhouse gas emission. Moreover, selected fertilizer rate applied to paddy would lead to lower GWPs of CH₄ and N₂O. Nevertheless, more field measurements from newly converted orchard are highly needed to gain an insight into national and global accounting of CH₄ and N₂O emissions.     

Sulfur processing in the marine atmospheric boundary layer: A review and critical assessment of modeling uncertainties

Sulfur is an extremely motile and vital element in the Earth's biogeochemical environment, one whose active redox chemistry maintains small reservoirs in the atmosphere and biosphere yet large fluxes through both. Essential for life, intimately linked to the climate state, and an important component of air quality, sulfur and its transport and processing in the atmosphere have been the subject of active research for several decades. This review article describes the current state of our understanding of the atmospheric sulfur cycle, focusing on the marine atmospheric boundary layer, with the aim of identifying the largest roots of uncertainty that most inhibit accurate simulation of sulfur cycling in the atmosphere. An overview of the emissions by phytoplankton and shipping, dispersion and entrainment in the marine boundary layer, and chemical processing by aerosols, clouds, and dry deposition is presented. Analysis of 20 contemporary modeling studies suggests that the greatest ambiguity in global sulfur cycling derives from (in descending order) wet deposition of aerosol sulfate, dry deposition of sulfur dioxide to the Earth's surface, and the heterogeneous oxidation of SO₂ in aerosols and clouds.     

Intercontinental transport of aerosols and photochemical oxidants from Asia and its consequences

The intercontinental transport of aerosols and photochemical oxidants from Asia is a crucial issue for air quality concerns in countries downwind of the significant emissions and concentrations of pollutants occurring in this important region of the world. Since the lifetimes of some important pollutants are long enough to be transported over long distance in the troposphere, regional control strategies for air pollution in downwind countries might be ineffective without considering the effects of long-range transport of pollutants from Asia. Field campaigns provide strong evidence for the intercontinental transport of Asian pollutants. They, together with ground-based observations and model simulations, show that the air quality over parts of North America is being affected by the pollutants transported from Asia. This paper examines the current understanding of the intercontinental transport of gases and aerosols from Asia and resulting effects on air quality, and on the regional and global climate system.     

Use of a vehicle-modelling tool for predicting CO2 emissions in the framework of European regulations for light goods vehicles

The reduction of CO₂ emissions and fuel consumption from road transportation constitutes an important pillar of the EU commitment for implementing the Kyoto Protocol. Efforts to monitor and limit CO₂ emissions from vehicles can effectively be supported by the use of vehicle modelling tools. This paper presents the application of such a tool for predicting CO₂ emissions of vehicles under different operating conditions and shows how the results from simulations can be used for supporting policy analysis and design aiming at further reductions of the CO₂ emissions. For this purpose, the case of light duty goods (N1 category) vehicle CO₂ emissions control measures adopted by the EU is analysed. In order to understand how certain design and operating aspects affect fuel consumption, a number of N1 vehicles were simulated with ADVISOR for various operating conditions and the numerical results were validated against chassis dynamometer tests. The model was then employed for analysing and evaluating the new EU legislative framework that addresses CO₂ emissions from this vehicle class. The results of this analysis have shown the weaknesses of the current regulations and revealed new potential in CO₂ emissions control. Finally the TREMOVE model was used for simulating a possible scenario for reducing CO₂ emissions at fleet level.     

Cloud Albedo,Greenhouse Effects,Atmospheric Chemistry,and Climate Change

Changes in global atmospheric chemistry and climate are taking place as a result of observed trends in long-lived species such as CO₂, CH₄, N₂O, and the CFCs. The continuation of these trends is expected to eventually lead to a major atmospheric warming that might profoundly affect the society we live in. Trends in short-lived species such as NOx and SOx are also suspected. These trends are not as well established, because the shorter-lived species vary spatially and temporally. Trends in NOx would be expected to lead to increases in tropospheric ozone that would add to the warming created by the other greenhouse gases. Trends in NOx could also alter tropospheric OH concentrations that could lead to changes in CH₄ and some of the CFCs. On the other hand, increases in sulfur emissions may alter cloud optical properties. The changes in cloud optical properties could possibly offset the warming expected from increases in greenhouse gases, depending on the role of natural oceanic sulfur emissions. This paper summarizes recent research in these areas and the interactions of climate and atmospheric chemistry.     

Local Arctic air pollution: Sources and impacts

Local emissions of Arctic air pollutants and their impacts on climate, ecosystems and health are poorly understood. Future increases due to Arctic warming or economic drivers may put additional pressures on the fragile Arctic environment already affected by mid-latitude air pollution. Aircraft data were collected, for the first time, downwind of shipping and petroleum extraction facilities in the European Arctic. Data analysis reveals discrepancies compared to commonly used emission inventories, highlighting missing emissions (e.g. drilling rigs) and the intermittent nature of certain emissions (e.g. flaring, shipping). Present-day shipping/petroleum extraction emissions already appear to be impacting pollutant (ozone, aerosols) levels along the Norwegian coast and are estimated to cool and warm the Arctic climate, respectively. Future increases in shipping may lead to short-term (long-term) warming (cooling) due to reduced sulphur (CO₂) emissions, and be detrimental to regional air quality (ozone). Further quantification of local Arctic emission impacts is needed.     

The impacts of combustion emissions on air quality and climate – From coal to biofuels and beyond

Combustion processes have inherent characteristics that lead to the release in the environment of both gaseous and particulate pollutants that have primary and secondary impacts on air quality, human health, and climate. The emissions from the combustion of fossil fuels and biofuels and their atmospheric impacts are reviewed here with attention given to the emissions of the currently regulated pollutant gasses, primary aerosols, and secondary aerosol precursors as well as the emissions of non-regulated pollutants. Fuels ranging from coal, petroleum, liquefied petroleum gas (LPG), natural gas, as well as the biofuels; ethanol, methanol, methyl tertiary-butyl ether (MTBE), ethyl tertiary-butyl ether (ETBE), and biodiesel, are discussed in terms of the known air quality and climate impacts of the currently regulated pollutants. The potential importance of the non-regulated emissions of both gasses and aerosols in air quality issues and climate is also discussed with principal focus on aldehydes and other oxygenated organics, polycyclic aromatic hydrocarbons (PAHs), and nitrated organics. The connection between air quality and climate change is also addressed with attention given to ozone and aerosols as potentially important greenhouse species.     

Climate forcing by the on-road transportation and power generation sectors

The on-road transportation (ORT) and power generation (PG) sectors are major contributors to carbon dioxide (CO₂) emissions and a host of short-lived radiatively-active air pollutants, including tropospheric ozone and fine aerosol particles, that exert complex influences on global climate. Effective mitigation of global climate change necessitates action in these sectors for which technology change options exist or are being developed. Most assessments of possible energy change options to date have neglected non-CO₂ air pollutant impacts on radiative forcing (RF). In a multi-pollutant approach, we apply a global atmospheric composition-climate model to quantify the total RF from the global and United States (U.S.) ORT and PG sectors. We assess the RF for 2 time horizons: 20- and 100-year that are relevant for understanding near-term and longer-term impacts of climate change, respectively. ORT is a key target sector to mitigate global climate change because the net non-CO₂ RF is positive and acts to enhance considerably the CO₂ warming impacts. We perform further sensitivity studies to assess the RF impacts of a potential major technology shift that would reduce ORT emissions by 50% with the replacement energy supplied either by a clean zero-emissions source (S1) or by the PG sector, which results in an estimated 20% penalty increase in emissions from this sector (S2). We examine cases where the technology shift is applied globally and in the U.S. only. The resultant RF relative to the present day control is negative (cooling) in all cases for both S1 and S2 scenarios, global and U.S. emissions, and 20- and 100-year time horizons. The net non-CO₂ RF is always important relative to the CO₂ RF and outweighs the CO₂ RF response in the S2 scenario for both time horizons. Assessment of the full impacts of technology and policy strategies designed to mitigate global climate change must consider the climate effects of ozone and fine aerosol particles.     

Evaluating inter-continental transport of fine aerosols: (1) Methodology,global aerosol distribution and optical depth

Our objectives are to evaluate inter-continental source-receptor relationships for fine aerosols and to identify the regions whose emissions have dominant influence on receptor continents. We simulate sulfate, black carbon (BC), organic carbon (OC), and mineral dust aerosols using a global coupled chemistry-aerosol model (MOZART-2) driven with NCEP/NCAR reanalysis meteorology for 1997–2003 and emissions approximately representing year 2000. The concentrations of simulated aerosol species in general agree within a factor of 2 with observations, except that the model tends to overestimate sulfate over Europe in summer, underestimate BC and OC over the western and southeastern (SE) U.S. and Europe, and underestimate dust over the SE U.S. By tagging emissions from ten continental regions, we quantify the contribution of each region's emissions on surface aerosol concentrations (relevant for air quality) and aerosol optical depth (AOD, relevant for visibility and climate) globally. We find that domestic emissions contribute substantially to surface aerosol concentrations (57–95%) over all regions, but are responsible for a smaller fraction of AOD (26–76%). We define “background” aerosols as those aerosols over a region that result from inter-continental transport, DMS oxidation, and emissions from ships or volcanoes. Transport from other continental source regions accounts for a substantial portion of background aerosol concentrations: 36–97% for surface concentrations and 38–89% for AOD. We identify the Region of Primary Influence (RPI) as the source region with the largest contribution to the receptor's background aerosol concentrations (or AOD). We find that for dust Africa is the RPI for both aerosol concentrations and AOD over all other receptor regions. For non-dust aerosols (particularly for sulfate and BC), the RPIs for aerosol concentrations and AOD are identical for most receptor regions. These findings indicate that the reduction of the emission of non-dust aerosols and their precursors from an RPI will simultaneously improve both air quality and visibility over a receptor region.