Showing papers by "Leonard A. Barrie published in 2001"

Aerosols, their Direct and Indirect Effects

Abstract: Contributing Authors A. Ackerman, P. Adams, P. Austin, R. Boers, O. Boucher, M. Chin, C. Chuang, B. Collins, W. Cooke, P. DeMott, Y. Feng, H. Fischer, I. Fung, S. Ghan, P. Ginoux, S.-L. Gong, A. Guenther, M. Herzog, A. Higurashi, Y. Kaufman, A. Kettle, J. Kiehl, D. Koch, G. Lammel, C. Land, U. Lohmann, S. Madronich, E. Mancini, M. Mishchenko, T. Nakajima, P. Quinn, P. Rasch, D.L. Roberts, D. Savoie, S. Schwartz, J. Seinfeld, B. Soden, D. Tanre, K. Taylor, I. Tegen, X. Tie, G. Vali, R. Van Dingenen, M. van Weele, Y. Zhang

A comparison of large-scale atmospheric sulphate aerosol models (COSAM): overview and highlights

Abstract: The comparison of large-scale sulphate aerosol models study (COSAM) compared the performance of atmospheric models with each other and observations. It involved: (i) design of a standard model experiment for the world wide web, (ii) 10 model simulations of the cycles of sulphur and 222Rn/210Pb conforming to the experimental design, (iii) assemblage of the best available observations of atmospheric SO= ,S O 2 and MSA and (iv) a workshop in Halifax, Canada to analyze model performance and future model development needs. The analysis presented in this paper and two companion papers by Roelofs, and Lohmann and co-workers examines the variance between models and observations, discusses the sources of that variance and suggests ways to improve models. Variations between models in the export of SO x from Europe or North America are not suYcient to explain an order of magnitude variation in spatial distributions of SO x downwind in the northern hemisphere. On average, models predicted surface level seasonal mean SO= aerosol mixing ratios better (most within 20%) than SO 2 mixing ratios (over-prediction by factors of 2 or more). Results suggest that vertical mixing

Atmospheric methyl iodide: High correlation with surface seawater temperature and its implications on the sea-to-air flux

Abstract: Intensive measurements of atmospheric methyl iodide taken at high, middle, and low latitudes over a period of 3 years have provided evidence for its photochemical production in seawater and given new information that sea-to-air transport of CH3I is mainly controlled by surface seawater temperature (SST). These findings suggest a highly localized production and distribution of CH3I in the surface microlayer. As a result, the oceanic emission of CH3I is likely to be larger than previous estimates based on the classical two-layer model. Owing to the SST dependence of atmospheric CH3I concentration, its impact on tropospheric or stratospheric ozone depletion would be increased by El Nino or future global warming.

Analysis of regional budgets of sulfur species modeled for the COSAM exercise

Abstract: The COSAM intercomparison exercise (comparison of large-scale sulfur models) was organized to compare and evaluate the performance of global sulfur cycle models. Eleven models participated, and from these models the simulated surface concentrations, vertical profiles and budget terms were submitted. This study focuses on simulated budget terms for the sources and sinks of SO 2 and sulfate in three polluted regions in the Northern Hemisphere, i.e., eastern North America, Europe, and Southeast Asia. Qualitatively, features of the sulfur cycle are modeled quite consistently between models, such as the relative importance of dry deposition as a removal mechanism for SO 2 , the importance of aqueous phase oxidation over gas phase oxidation for SO 2 , and the importance of wet over dry deposition for removal of sulfate aerosol. Quantitatively, however, models may show large differences, especially for cloud-related processes, i.e., aqueous phase oxidation of SO 2 and sulfate wet deposition. In some cases a specific behavior can be related to the treatment of oxidants for aqueous phase SO 2 oxidation, or the vertical resolution applied in models. Generally, however, the differences between models appear to be related to simulated cloud (micro-)physics and distributions, whereas differences in vertical transport efficiencies related to convection play an additional role. The estimated sulfur column burdens, lifetimes and export budgets vary between models by about a factor of 2 or 3. It can be expected that uncertainties in related effects which are derived from global sulfur model calculations, such as direct and indirect climate forcing estimates by sulfate aerosol, are at least of similar magnitude. DOI: 10.1034/j.1600-0889.2001.530509.x

Vertical distributions of sulfur species simulated by large scale atmospheric models in COSAM: Comparison with observations

Abstract: A comparison of large-scale models simulating atmospheric sulfate aerosols (COSAM) was conducted to increase our understanding of global distributions of sulfate aerosols and precursors. Earlier model comparisons focused on wet deposition measurements and sulfate aerosol concentrations in source regions at the surface. They found that different models simulated the observed sulfate surface concentrations mostly within a factor of two, but that the simulated column burdens and vertical profiles were very different amongst different models. In the COSAM exercise, one aspect is the comparison of sulfate aerosol and precursor gases above the surface. Vertical profiles of SO 2 , SO 2− 4 , oxidants and cloud properties were measured by aircraft during the North Atlantic Regional Experiment (NARE) experiment in August/September 1993 off the coast of Nova Scotia and during the Second Eulerian Model Evaluation Field Study (EMEFSII), in central Ontario in March/April 1990. While no single model stands out as being best or worst, the general tendency is that those models simulating the full oxidant chemistry tend to agree best with observations although differences in transport and treatment of clouds are important as well. DOI: 10.1034/j.1600-0889.2001.530508.x

Toxaphene in the United States: 2. Emissions and residues

Abstract: Emission factors of toxaphene for spraying and tilling events are distributed for the United States on a 1°×1° latitude and longitude grid system. By using the gridded usage and emission factors, inventories of gridded toxaphene emissions and residues in agricultural soil in the United States with 1/6°×1/4° latitude and longitude resolution have been created. Total toxaphene emissions were around 190 kt between 1947 and 1999. At the beginning of 2000, almost 20 years after banning the use of toxaphene, there were still around 29 kt of toxaphene left in the agricultural soil, of which 360 t will emit to the air in 2000. The calculated toxaphene emissions and residues are in general consistent with published monitoring data. The trends of toxaphene emissions due to current use and residues in agricultural soil in the United States match both the historical atmospheric input function for toxaphene extending over the past 40 years derived from the composition of toxaphene in peat core from eastern Minnesota to Nova Scotia, and the trends of air concentration of toxaphene in the Arctic. This indicates that toxaphene residues in the United States agricultural soil could be a major source of toxaphene in the Canadian Arctic and the Great Lakes region.

Size-Segregated Aerosol Composition and Mass Loading of Atmospheric Particles as Part of the Pacific Northwest 2001 (PNW2001) Air Quality Study in Puget Sound, WA

Abstract: Size and composition are key factors in determining the impact aerosols have on global climate change and human health. The DELTA group at UC Davis has developed sampling techniques that allow continuous collection of aerosols separated into 8 different size fractions with 1-hour time resolution. Total aerosol mass determination: Scanning Transmission Ion Microscopy (STIM) with a 3 MeV proton beam can produce profiles of aerosol mass with an error limit of less than 10%. The aerosol collection strip is scanned with a proton beam of 50 micrometer spatial resolution while recording the proton mean energy loss as a function of position (Bench et al., 1992). A differential beta attenuation mass monitor (beta-gauge) is also used for mass determination. The beta-gauge consists of a 63Ni source and a surface barrier detector. This technique allows quantitative mass measurement by recording attenuation of beta particles through the sample and substrate (Chueinta and Hopke, 2001). Mineral mass and elemental composition: Synchrotron X-ray Fluorescence (s-XRF) is performed at the Advanced Light Source (ALS) at LBNL. The s-XRF technique is quantitative for elements Na through U. The ALS synchrotron provides an extraordinarily intense white beam of X-rays (4-20 KeV) that are 100% polarized. These properties provide more » us with a very high count rate and a reduced background, giving us exceptional sensitivity. Also, the beam can be focused to a spot on the order of 200 micons yielding time resolution on our sample strips of approximately 1 hour (Cahill et al., 1992). Organic mass determination: Proton Elastic Scattering Analysis (PESA) is performed at the Center for Accelerator Mass Spectrometry at the LLNL. PESA determines the concentration of particulate hydrogen, which is a surrogate for organic aerosol composition (Nejedly et al., 1997). Organic compound determination: Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (LDI-TOFMS) is used to characterize polycyclic aromatic hydrocarbons (PAHs) and their derivatives in aerosols, as well as sulfates and nitrates. We use a low laser power in order to minimize fragmentation, and a wavelength which is resonant for PAH photo-ionization (Bezabeh et al., 1999). Characterization of individual particles: Scanning electron microscopy (SEM) coupled with a state-of-the-art field emission gun (FEG) is used to provide imaging with a resolution capability better than 2 nm (magnifications greater than 600 kX). Single particle analysis by SEM provides elemental composition, heterogeneity information, shape, size, and morphology of individual particles. « less