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Christopher Potter, Steven Klooster, David Bubenheim, Hanwant B. Singh, and Ranga Myneni

Abstract

In recent years, oxygenated volatile organic chemicals (OVOCs) likeacetone have been recognized as important atmospheric constituents due to their ability to sequester reactive nitrogen in the form peroxyacetyl nitrate (PAN) and to be a source of hydroxyl radicals (HOx) in critical regions of the atmosphere. The potential biogenic sources of acetone include terrestrial plant canopies, oxidation of dead plant material, harvest of cultivated plants, biomass burning, and the oceans. These sources are poorly constrained at present in budgets of atmospheric chemistry. Based on reported laboratory, field, and satellite observations to date, an approach is presented for a biosphere model to estimate monthly emissions of acetone from the terrestrial surface to the atmosphere. The approach is driven by observed land surface climate and estimates of vegetation leaf area index (LAI), which are generated at 0.5o spatial resolution from the NOAA satellite Advanced Very High Resolution Radiometer (AVHRR). Seasonal changes in LAI are estimated using the Moderate Resolution Imaging Spectroradiometer (MODIS) radiative transfer algorithms to identify the probable times and locations of crop harvest in cultivated areas and leaf fall of newly dead plant material in noncultivated areas. Temperature-dependent emission factors are applied to derive global budgets of acetone fluxes from terrestrial plant canopies, oxidation of dead plant material, and harvest of cropland plants. The predicted global distribution of acetone emissions from live foliage is strongly weighted toward the moist tropical zones, where relatively warm temperatures and high LAI are observed in rain forest areas year-round. Predicted acetone emissions are estimated at between 54 and 172 Tg yr–1 from live foliage sources and between 7 and 22 Tg yr–1 from decay of dead foliage. These flux totals from vegetation are large enough to account for the majority of postulated biogenic acetone sources in models of global atmospheric chemistry, but our model predictions are subject to verification in subsequent flux control experiments using a variety of plant species, particularly those from humid tropical zones.

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Katharine S. Law, Andreas Stohl, Patricia K. Quinn, Charles A. Brock, John F. Burkhart, Jean-Daniel Paris, Gerard Ancellet, Hanwant B. Singh, Anke Roiger, Hans Schlager, Jack Dibb, Daniel J. Jacob, Steve R. Arnold, Jacques Pelon, and Jennie L. Thomas

Given the rapid nature of climate change occurring in the Arctic and the difficulty climate models have in quantitatively reproducing observed changes such as sea ice loss, it is important to improve understanding of the processes leading to climate change in this region, including the role of short-lived climate pollutants such as aerosols and ozone. It has long been known that pollution produced from emissions at midlatitudes can be transported to the Arctic, resulting in a winter/spring aerosol maximum known as Arctic haze. However, many uncertainties remain about the composition and origin of Arctic pollution throughout the troposphere; for example, many climate–chemistry models fail to reproduce the strong seasonality of aerosol abundance observed at Arctic surface sites, the origin and deposition mechanisms of black carbon (soot) particles that darken the snow and ice surface in the Arctic is poorly understood, and chemical processes controlling the abundance of tropospheric ozone are not well quantified. The International Polar Year (IPY) Polar Study using Aircraft, Remote Sensing, Surface Measurements and Models, Climate, Chemistry, Aerosols and Transport (POLARCAT) core project had the goal to improve understanding about the origins of pollutants transported to the Arctic; to detail the chemical composition, optical properties, and climate forcing potential of Arctic aerosols; to evaluate the processes governing tropospheric ozone; and to quantify the role of boreal forest fires. This article provides a review of the many results now available based on analysis of data collected during the POLARCAT aircraft-, ship-, and ground-based field campaigns in spring and summer 2008. Major findings are highlighted and areas requiring further investigation are discussed.

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Eric J. Jensen, Leonhard Pfister, David E. Jordan, Thaopaul V. Bui, Rei Ueyama, Hanwant B. Singh, Troy D. Thornberry, Andrew W. Rollins, Ru-Shan Gao, David W. Fahey, Karen H. Rosenlof, James W. Elkins, Glenn S. Diskin, Joshua P. DiGangi, R. Paul Lawson, Sarah Woods, Elliot L. Atlas, Maria A. Navarro Rodriguez, Steven C. Wofsy, Jasna Pittman, Charles G. Bardeen, Owen B. Toon, Bruce C. Kindel, Paul A. Newman, Matthew J. McGill, Dennis L. Hlavka, Leslie R. Lait, Mark R. Schoeberl, John W. Bergman, Henry B. Selkirk, M. Joan Alexander, Ji-Eun Kim, Boon H. Lim, Jochen Stutz, and Klaus Pfeilsticker

Abstract

The February–March 2014 deployment of the National Aeronautics and Space Administration (NASA) Airborne Tropical Tropopause Experiment (ATTREX) provided unique in situ measurements in the western Pacific tropical tropopause layer (TTL). Six flights were conducted from Guam with the long-range, high-altitude, unmanned Global Hawk aircraft. The ATTREX Global Hawk payload provided measurements of water vapor, meteorological conditions, cloud properties, tracer and chemical radical concentrations, and radiative fluxes. The campaign was partially coincident with the Convective Transport of Active Species in the Tropics (CONTRAST) and the Coordinated Airborne Studies in the Tropics (CAST) airborne campaigns based in Guam using lower-altitude aircraft (see companion articles in this issue). The ATTREX dataset is being used for investigations of TTL cloud, transport, dynamical, and chemical processes, as well as for evaluation and improvement of global-model representations of TTL processes. The ATTREX data are publicly available online (at https://espoarchive.nasa.gov/).

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