ALBERT

Description: In a 1994 National Research Council report, "Atmospheric Effects of Stratospheric Aircraft: An Evaluation of NASA's Interim Assessment", the assessment panel's key issues for better determining the atmospheric effects of stratospheric aircraft, particularly on ozone, were presented.

Description: The primary objective of PEM Tropics B was to study the processes responsible for the production and loss of tropospheric ozone over the tropical Pacific. This region of the globe contains very clean air as well as aged, polluted air that was advected from both the Asian and American continents. Understanding ozone requires understanding of HO(x) (HO(x) = OH + HO2) chemistry, since the reaction between H02 and NO leads to ozone production and the production of OH often requires ozone loss. In addition, OH is the atmosphere's primary oxidant. Since most atmospheric oxidation is thought to occur in the tropical lower troposphere, measurements during PEM Tropics B should provide an important test of the OH abundances and distributions. Thus, understanding and thoroughly testing HO(x) processes was an important objective of PEM Tropics B. Several issues need to be tested, One is HO, production rates and sources, since HO,, production directly affects ozone production and loss. Another is HO(x) behavior in and around clouds, since HO(x) is lost to cloud particles, but convection may bring HO(x) precursors from near the surface to the upper troposphere. A third is the rise and fall of HO(x) at sunrise and sunset, since these variations give strong indications of the important sources and sinks of HO(x). Making and interpreting high-quality OH and H02 measurements from the NASA DC-8 during PEM Tropics B is the objective of this research effort.

Description: This report assesses the potential atmospheric impacts of a proposed fleet of high-speed civil transport (HSCT) aircraft. The purpose of the report is to assess the effects of HSCT's on atmospheric composition and climate in order to provide a scientific basis for making technical, commercial, and environmental policy decisions regarding the HSCT fleet. The work summarized here was carried out as part of NASA's Atmospheric Effects of Aviation Project (a component of the High-Speed Research Program) as well as other NASA, U.S., and international research programs. The principal focus is on change in stratospheric ozone concentrations. The impact on climate change is also a concern. The report describes progress in understanding atmospheric processes, the current state of understanding of HSCT emissions, numerical model predictions of HSCT impacts, the principal uncertainties in atmospheric predictions, and the associated sensitivities in predicted effects of HSCT's.

Description: This report assesses the potential atmospheric impacts of a proposed fleet of high-speed civil transport (HSCT) aircraft. The purpose of the report is to assess the effects of HSCT's on atmospheric composition and climate in order to provide a scientific basis for making technical, commercial, and environmental policy decisions regarding the HSCT fleet. The work summarized here was carried out as part of NASA's Atmospheric Effects of Aviation Project (a component of the High-Speed Research Program) as well as other NASA, U.S., and international research programs. The principal focus is on change in stratospheric ozone concentrations. The impact on climate change is also a concern. The report describes progress in understanding atmospheric processes, the current state of understanding of HSCT emissions, numerical model predictions of HSCT impacts, the principal uncertainties in atmospheric predictions, and the associated sensitivities in predicted effects of HSCT'S.

Description: OH and HO2 were measured with the Airborne Tropospheric Hydrogen Oxides Sensor (ATHOS) as part of a large measurement suite from the NASA DC-8 aircraft during the Intercontinental Chemical Transport Experiment - A (INTEX-A). This mission, which was conducted mainly over North America and the western Atlantic Ocean in summer 2004, was an excellent test of atmospheric oxidation chemistry. Throughout the troposphere, observed OH was generally 0.60 of the modeled OH; below 8 km, observed HO2 was generally 0.78 of modeled HO2. If the over-prediction of tropospheric OH is not due to an instrument calibration error, then it implied less global tropospheric oxidation capacity and longer lifetimes for gases like methane and methyl chloroform than currently thought. This discrepancy falls well outside uncertainties in both the OH measurement and rate coefficients for known reactions and points to a large unknown OH loss. If the modeled OH is forced to agree with observed values by introducing of an undefined OH loss that removed HOx (HOx=OH+HO2), the observed and modeled HO2 and HO2/OH ratios are largely reconciled within the measurement uncertainty. HO2 behavior above 8 km was markedly different. The observed-to-modeled ratio correlating with NO. The observed-to-modeled HO2 ratio increased from approximately 1 at 8 km to more than approximately 2.5 at 11 km with the observed-to-modeled ratio correlating with NO. The observed-to-modeled HO2 and NO were both considerably greater than observations from previous campaigns. In addition, the observed-to-modeled HO2/OH, which is sensitive to cycling reactions between OH and HO2, increased from approximately 1.2 at 8 km to almost 4 above 11 km. In contrast to the lower atmosphere, these discrepancies above 8 km suggest a large unknown HOx source and additional reactants that cycle HOx from OH to HO2. In the continental planetary boundary layer, the OH observed-to-modeled ratio increased from 0.6 when isoprene was less than 0.1 ppbv to over 3 when isoprene was greater than 2 ppbv, suggesting that forests throughout the United States are emitting unknown HOx sources. Progress in resolving these discrepancies requires further examinations of possible unknown OH sinks and HOx sources and a focused research activity devoted to ascertaining the accuracy of the OH and HO2 measurements.

Description: Concentrations of atmospheric trace species in the United States have changed dramatically over the past several decades in response to pollution control strategies, shifts in domestic energy policy and economics, and economic development (and resulting emission changes) elsewhere in the world. Reliable projections of the future atmosphere require models to not only accurately describe current atmospheric concentrations, but to do so by representing chemical, physical and biological processes with conceptual and quantitative fidelity. Only through incorporation of the processes controlling emissions and chemical mechanisms that represent the key transformations among reactive molecules can models reliably project the impacts of future policy, energy and climate scenarios. Efforts to properly identify and implement the fundamental and controlling mechanisms in atmospheric models benefit from intensive observation periods, during which collocated measurements of diverse, speciated chemicals in both the gas and condensed phases are obtained. The Southeast Atmosphere Studies (SAS, including SENEX, SOAS, NOMADSS and SEAC4RS) conducted during the summer of 2013 provided an unprecedented opportunity for the atmospheric modeling community to come together to evaluate, diagnose and improve the representation of fundamental climate and air quality processes in models of varying temporal and spatial scales. This paper is aimed at discussing progress in evaluating, diagnosing and improving air quality and climate modeling using comparisons to SAS observations as a guide to thinking about improvements to mechanisms and parameterizations in models. The effort focused primarily on model representation of fundamental atmospheric processes that are essential to the formation of ozone, secondary organic aerosol (SOA) and other trace species in the troposphere, with the ultimate goal of understanding the radiative impacts of these species in the southeast and elsewhere. Here we address questions surrounding four key themes: gas-phase chemistry, aerosol chemistry, regional climate and chemistry interactions, and natural and anthropogenic emissions. We expect this review to serve as a guidance for future modeling efforts.

Description: The Photochemistry of Ozone Loss in the Arctic Region In Summer (POLARIS) mission was designed to investigate the natural summer decrease of stratospheric ozone levels. Both polar regions have large and distinct annual cycles of ozone column amounts. In northern spring, the average level is over 450 Dobson units (DU), decreasing to less than 275 DU by September. In order to cover this period of ozone decrease, POLARIS was conducted in three deployment phases from Fairbanks, Alaska, (650N) during the summer of 1997. The principal measurement platforms were the NASA ER-2 high-altitude aircraft and stratospheric balloons. Additional measurements were provided by ground-based instruments, sondes, and satellites. POLARIS observations included ozone, meteorological variables, particles, long-lived chemicals, and short-lived radicals. During the field deployments, several modeling and theoretical groups participated in flight planning and data evaluation activities. The interpretive studies in this Special Section of the Journal of Geophysical Research are a first comprehensive examination of the POLARIS data set, addressing stratospheric ozone abundances and its changes; the role of aerosols; details of the photochemistry of reactive species; transport of stratospheric air and the correlations of long-lived species; and measurement intercomparisons.

Description: Between November 1999 and April 2000, two major field experiments, the SAGE III Ozone Loss and Validation Experiment (SOLVE) and the Third European Stratospheric Experiment on Ozone (THESEO 2000), collaborated to form the largest field campaign yet mounted to study Arctic ozone loss. This international campaign involved more than 500 scientists from over 20 countries spread across the high and mid-latitudes of the northern hemisphere. The main scientific aims of SOLVE-THESEO 2000 were to study (a) the processes leading to ozone loss in the Arctic vortex and (b) the effect on ozone amounts over northern mid-latitudes. The campaign included satellites, heavy lift balloon launches, 6 different aircraft, ground stations, and scores of ozone-sonde. Campaign activities were principally conducted in 3 intensive measurement phases centered on early December 1999, late January 2000, and early March 2000. Observations made during the campaign showed that temperatures were unusually cold in the polar lower stratosphere over the course of the 1999-2000 winter. These cold temperatures resulted in the formation of extensive polar stratospheric clouds (PSCs) across the Arctic. Heterogeneous chemical reactions on the surfaces of the PSC particles produced high levels of reactive chlorine within the polar vortex by early January. This reactive chlorine catalytically destroyed about 60% of the ozone in a layer near 20 km between late January and mid-March 2000.