International Global Atmospheric Chemistry Research Articles

The ASTEX/MAGE Experiment

The Atlantic Stratocumulus Transition Experiment/Marine Aerosol and Gas Exchange (ASTEX/MAGE) was a multinational experiment designed to study the relationship between marine chemistry, aerosols, clouds, and air/sea exchange. Several aircraft, ships, and island sites supported measurements of marine boundary layer chemistry in both pristine and polluted North Atlantic air masses in the vicinity of the Azores in June of 1992. The International Global Atmospheric Chemistry (IGAC) Program's MAGE activity organized the chemical experiments in ASTEX because such experiments are beyond the capabilities of any one platform, discipline, or nation working alone. One highlight of ASTEX/MAGE was the development of a Lagrangian experimental strategy. It offered a unique way of constraining fluxes and reaction rates by observing the effect those processes have on a tagged parcel of air.

Pacific Exploratory Mission‐West A (PEM‐West A): September–October 1991

The NASA Pacific Exploratory Mission‐West (PEM‐West) is a major component of the East Asia/North Pacific Regional Study (APARE), a project within the International Global Atmospheric Chemistry (IGAC) program. The broad objective of the PEM‐West/APARE initiative is to study chemical processes and long‐range transport over the northwestern Pacific Ocean and to estimate the magnitude of the human impact on the oceanic atmosphere over this region particularly for tropospheric ozone and its precursors as well as for sulfur species. The first phase of this mission, PEM‐West A, was conducted during September–October 1991. The PEM‐West A included intensive airborne measurements of trace gases from the NASA DC‐8 aircraft coordinated with measurements at PEM‐West A surface sites as well as with measurements obtained from collaborating APARE ground and airborne platforms. This paper reports the experimental design for PEM‐West A with a brief summary of the general content and focus of companion papers in this special issue.

Atmospheric aerosol research in the U.S.: 1991–1994

A common theme underlying many aspects of recent atmospheric aerosol research is the role of particulate matter in climate and climate change. Aerosols influence climate directly, by scattering and absorbing solar radiation, and indirectly via their role as cloud condensation nuclei (CCN), by modifying optical properties and lifetimes of clouds. The atmospheric cycles of two radiatively‐important species—sulfate and soot—have been significantly perturbed by anthropogenic activities, and thus it is expected that anthropogenic aerosols will have significant effects on global mean radiative forcing.There is general agreement that, despite uncertainty in estimates, the averaged global direct effects of aerosols are not negligible and are probably comparable in magnitude but opposite in sign to anthropogenic greenhouse gas forcing. However, all estimates are subject to significant uncertainty, in part because of gaps in understanding of critical factors and relationships. To minimize these uncertainties, a combination of activities must be undertaken (NRC (National Research Council) [1993] and Penner et al. [1993a]): long‐term observations at fixed sites, to establish background conditions and trends; short‐term intensive observations, surface‐based and airborne; laboratory analyses and process studies; model development; and satellite observations to connect local observations to global measurements. There is also a need for new techniques for automated and real‐time measurements of aerosol chemical and physical properties. Components of IGAC (International Global Atmospheric Chemistry Program) and its U.S. component, GTCP (Global Tropospheric Chemistry Program) are focused on obtaining the data needed for quantifying the effects of aerosols on climate (NRC (National Research Council) [1993]), and indeed much of the research reported here reflects this priority.

Global emissions inventories of acid-related compounds

Computer assessments of the atmospheric chemistry and air quality of the past, present, and future rely in part on inventories of emissions constructed on appropriate spatial and temporal scales and with appropriate chemical species. Accurate inventories are also of substantial utility to field measurement scientists and the regulatory and policy communities. The production of global emissions inventories is the task of the Global Emissions Inventory Activity (GEIA) of the International Global Atmospheric Chemistry Project (IGAC). This paper presents a summary of recent emissions inventories from GEIA and other programs for reference year 1985, with special attention directed to emissions of the acid-related compounds CO2 (≈6.2 Pg C yr−1 anthropogenic), SOx (≈65 Tg S yr−1 anthropogenic and 15 Tg S yr−1 natural), NOx (≈21 Tg N yr−1 anthropogenic and 15–20 Tg N yr−1 natural), HCl (≈55 Tg Cl yr−1 total), and NH3 (≈45 Tg N yr−1 total). The global acid-equivalent flux of about 4.2 Teq H+yr−1 is about equally attributable to SOx and NOx emissions. For some of the acid-related species, historic inventories are available for a century or more; all show dramatic emissions increases over that period. IPCC scenario IS92a is used here as the basis for constructing global acid-related emissions estimates for selected years to 2100; among the results are that acid equivalent emissions are expected to more than double in the coming century.

Global emissions inventories to aid atmospheric modelers

Computer projections of changes in global atmospheric chemistry could become more accurate and more easily compared with the availability of standard global emissions inventories. Starting in 1994, the Global Emissions Inventory Activity (GEIA) began to finalize gridded global emissions inventories and distribute them to atmospheric scientists. GEIA operates under the auspices of the International Global Atmospheric Chemistry (IGAC) Project, a cooperative effort of several hundred atmospheric scientists from more than 30 countries. The purpose of the IGAC Project is to measure, understand, and predict changes in global atmospheric chemistry, particularly those contributing to global problems such as acid rain, depletion of stratospheric ozone, greenhouse warming, and increased oxidant levels that damage biota.A 1992 survey by participants in the GEIA project [Graedel et al., 1993] showed that suitable emissions inventories are rarely available. The chlorofluorocarbon inventory, regarded as well quantified, was unavailable in gridded form. Inventories for CO2, CH4, NOx, SO2, reduced sulfur, and radon were regarded as having excess uncertainty, inadequate spatial resolution, or both; inventories for other chemical species were sketchy or nonexistent. Temporal resolution was almost uniformly poor. The survey made it clear that internally consistent, rigorously developed, gridded inventories with adequate spatial and temporal resolution would be valuable.

Critical Issues for Understanding Global Change Effects on Terrestrial Ecosystems.

Marked alterations in the Earth's environment have already been observed, and these presage even greater changes as the impact of human (i.e., land use and industrial) activities increases. Direct and indirect feedbacks link terrestrial ecosystems with global change, and include interactions affecting fluxes of water, energy, nutrients, and "greenhouse" gases and affecting ecosystem structure and composition. Community development can affect ecosystem dynamics by altering resource partitioning among biotic components and through changes in structural characteristics, thereby affecting feedbacks to global change. The response of terrestrial ecosystems to the climate-weather system is dependent on the spatial scale of the interactions between these systems and the temporal scale that links the various components. The International Geosphere-Biosphere Programme (IGBP), which was initiated by the International Council of Scientific Unions (ICSU) in 1986, has undertaken to develop a research plan to address a predictive understanding of how terrestrial ecosystem will be impacted by global changes in the environment and the potential feedbacks. The IGBP science plan, which incorporates established Core Projects and activities related to research on terrestrial ecosystem linkages to global change, includes the International Global Atmospheric Chemistry Project (IGAC); the Biospheric Aspects of the Hydrological Cycle (BAHC); the Global Change and Terrestrial Ecosystems (GCTE); Global Analysis, Integration, and Modelling (GAIM); IGBP Data and Information System (DIS); and IGBP Regional Research Centers (RRC). The coupling of research and policy communities for the purpose of developing mechanisms to adapt to these impending changes urgently needs to be established.

Planning for chemical air‐sea exchange research

The International Global Atmospheric Chemistry (IGAC) Programme has been created in response to growing international concern about rapid atmospheric chemical changes and their impact on mankind. This program, while emphasizing atmospheric composition and chemistry, recognizes that the Earth's atmosphere, oceans, land, and biota form an interacting system that collectively determine the global environment and its susceptibility to change. The IGAC Programme is intended to be a vital contributor to the broader interdisciplinary program of the International Geosphere Biosphere Programme (IGBP), providing the important atmospheric chemistry component and recognizing its linkages with the biosphere and human activities. The IGAC Programme is building on existing national programs by providing the international cooperation whereby essential scientific endeavors can be accomplished, even though they involve large demands for man power, technology, geographic coverage, or monetary resources beyond the capability of a single nation.