[1] The global distribution of carbonaceous aerosols is simulated online in the Goddard Institute for Space Studies General Circulation Model II-prime (GISS GCM II-prime). Prognostic tracers include black carbon (BC), primary organic aerosol (POA), five groups of biogenic volatile organic compounds (BVOCs), and 14 semivolatile products of BVOC oxidation by O 3 , OH, and NO 3 , which condense to form secondary organic aerosols (SOA) based on an equilibrium partitioning model and experimental observations. Estimated global burdens of BC, organic carbon (OC), and SOA are 0.22, 1.2, and 0.19 Tg with lifetimes of 6.4, 5.3, and 6.2 days, respectively. The predicted global production of SOA is 11.2 Tg yr À1 , with 91% due to O 3 and OH oxidation. Globally averaged, top of the atmosphere (TOA) radiative forcing by anthropogenic BC is predicted as +0.51 to +0.8 W m À2 , the former being for BC in an external mixture and the latter for BC in an internal mixture of sulfate, OC, and BC. Globally averaged, anthropogenic BC, OC, and sulfate are predicted to exert a TOA radiative forcing of À0.39 to À0.78 W m À2 , depending on the exact assumptions of aerosol mixing and water uptake by OC. Forcing estimates are compared with those published previously.

[1] A single-particle soot photometer (SP2) was flown on a NASA WB-57F high-altitude research aircraft in November 2004 from Houston, Texas. The SP2 uses laser-induced incandescence to detect individual black carbon (BC) particles in an air sample in the mass range of $3-300 fg ($0.15-0.7 mm volume equivalent diameter). Scattered light is used to size the remaining non-BC aerosols in the range of $0.17-0.7 mm diameter. We present profiles of both aerosol types from the boundary layer to the lower stratosphere from two midlatitude flights. Results for total aerosol amounts in the size range detected by the SP2 are in good agreement with typical particle spectrometer measurements in the same region. All ambient incandescing particles were identified as BC because their incandescence properties matched those of laboratory-generated BC aerosol. Approximately 40% of these BC particles showed evidence of internal mixing (e.g., coating). Throughout profiles between 5 and 18.7 km, BC particles were less than a few percent of total aerosol number, and black carbon aerosol (BCA) mass mixing ratio showed a constant gradient with altitude above 5 km. SP2 data was compared to results from the ECHAM4/MADE and LmDzT-INCA global aerosol models. The comparison will help resolve the important systematic differences in model aerosol processes that determine BCA loadings. Further intercomparisons of models and measurements as presented here will improve the accuracy of the radiative forcing contribution from BCA.Citation: Schwarz, J. P., et al. (2006), Single-particle measurements of midlatitude black carbon and light-scattering aerosols from the boundary layer to the lower stratosphere,

[1] Soot aerosol particles (also called light-absorbing, black, or elemental carbon) are major contributors to global warming through their absorption of solar radiation. When embedded in organic matter or sulfate, as is common in polluted areas such as over Mexico City (MC) and other megacities, their optical properties are affected by their shapes and positions within their host particles. However, large uncertainties remain regarding those variables and how they affect warming by soot. Using electron tomography with a transmission electron microscope, three-dimensional (3-D) images of individual soot particles embedded within host particles collected from MC and its surroundings were obtained. From those 3-D images, we calculated the optical properties using a discrete dipole approximation. Many soot particles have open, chainlike shapes even after being surrounded by organic matter and are located in off-center positions within their host materials. Such embedded soot absorbs sunlight less efficiently than if compact and located near the center of its host particle. In the case of our MC samples, their contribution to direct radiative forcing is ∼20% less than if they had a simple core-shell shape, which is the shape assumed in many climate models. This study shows that the shapes and positions of soot within its host particles have an important effect on particle optical properties and should be recognized as potentially important variables when evaluating global climate change.

[1] A unified tropospheric chemistry-aerosol model has been developed within the Goddard Institute for Space Studies general circulation model (GCM). The model includes a detailed simulation of tropospheric ozone-NO x -hydrocarbon chemistry as well as aerosols and aerosol precursors. Predicted aerosol species include sulfate, nitrate, ammonium, black carbon, primary organic carbon, and secondary organic carbon. The partitioning of ammonia and nitrate between gas and aerosol phases is determined by online thermodynamic equilibrium, and the formation of secondary organic aerosols is based on equilibrium partitioning and experimentally determined parameters. Two-way coupling between aerosols and chemistry provides consistent chemical fields for aerosol dynamics and aerosol mass for heterogeneous processes and calculations of gas-phase photolysis rates. Although the current version of the unified model does not include a prognostic treatment of mineral dust, we include its effects on photolysis and heterogeneous processes by using three-dimensional off-line fields. We also simulate sulfate and nitrate aerosols that are associated with mineral dust based on currently available chemical understanding. Considering both mineral dust uptake of HNO 3 and wet scavenging of HNO 3 on ice leads to closer agreement between predicted gas-phase HNO 3 concentrations and measurements than in previous global chemical transport model simulations, especially in the middle to upper troposphere. As a result of the coupling between chemistry and aerosols, global burdens of both gas-phase and aerosol species are predicted to respond nonlinearly to changing emissions of NO x , NH 3 , and sulfur.

[1] The equilibrium climate effect of direct radiative forcing of anthropogenic black carbon (BC) is examined by 100-year simulations in the Goddard Institute for Space Studies General Circulation Model II-prime coupled to a mixed-layer ocean model. Anthropogenic BC is predicted to raise globally and annually averaged equilibrium surface air temperature by 0.20 K if BC is assumed to be externally mixed. The predicted increase is significantly greater in the Northern Hemisphere (0.29 K) than in the Southern Hemisphere (0.11 K). If BC is assumed to be internally mixed with the present-day level of sulfate aerosol, the predicted annual mean surface temperature increase rises to 0.37 K globally, 0.54 K for the Northern Hemisphere, and 0.20 K for the Southern Hemisphere. The climate sensitivity of BC direct radiative forcing is calculated to be 0.6 K W À1 m 2 , which is about 70% of that of CO 2 , independent of the assumption of BC mixing state. The largest surface temperature response occurs over the northern high latitudes during winter and early spring. In the tropics and midlatitudes, the largest temperature increase is predicted to occur in the upper troposphere. Direct radiative forcing of anthropogenic BC is also predicted to lead to a change of precipitation patterns in the tropics; precipitation is predicted to increase between 0 and 20°N and decrease between 0 and 20°S, shifting the intertropical convergence zone northward. If BC is assumed to be internally mixed with sulfate instead of externally mixed, the change in precipitation pattern is enhanced. The change in precipitation pattern is not predicted to alter the global burden of BC significantly because the change occurs predominantly in regions removed from BC sources.Citation: Chung, S. H., and J. H. Seinfeld (2005), Climate response of direct radiative forcing of anthropogenic black carbon,

[1] The morphologies of soot particles are both complex and important. They influence soot atmospheric lifetimes, global distributions, and climate impacts. Particles can have complex geometries with overlapping projecting parts and pores that are difficult to infer from the conventional techniques used to study them. We used electron tomography with a transmission electron microscope (TEM) to determine three-dimensional (3D) properties such as fractal dimension (D f ), radius of gyration (R g ), volume (V), surface area (A s ), and structural coefficient (k a ) for individual soot particles from the ambient air of an Asian dust (AD) episode and from a U.S. traffic source. The respective median values of D f are 2.4 and 2.2, of R g are 274 and 251 nm, of A s /V are 9.2 and 13.7 Â 10 7 m À1 , and of k a are 0.67 and 0.71. The corresponding parameters, when calculated from 2D projections such as TEM images, are considerably less precise and commonly erroneous. Unlike other methods that have been used to derive fractal parameters, our method is applicable to particles of any D f . Using the 3D data, we estimate that mass-normalized scattering cross sections of our AD and traffic soot particles are respectively about 15 and 30 times greater than those of unaggregated spheres, which is the shape assumed in global models to estimate radiative forcing. Accurate 3D information can be used to compute more precise optical properties, which are important for estimating direct radiative forcing and improving our understanding of the climate impact of soot.Citation: Adachi, K., S. H. Chung, H. Friedrich, and P. R. , Fractal parameters of individual soot particles determined using electron tomography: Implications for optical properties,

[1] Real-time forecasts of PM 2.5 aerosol mass from seven air quality forecast models (AQFMs) are statistically evaluated against observations collected in the northeastern United States and southeastern Canada from two surface networks and aircraft data during the summer of 2004 International Consortium for Atmospheric Research on Transport and Transformation (ICARTT)/New England Air Quality Study (NEAQS) field campaign. The AIRNOW surface network is used to evaluate PM 2.5 aerosol mass, the U.S. EPA STN network is used for PM 2.5 aerosol composition comparisons, and aerosol size distribution and composition measured from the NOAA P-3 aircraft are also compared. Statistics based on midday 8-hour averages, as well as 24-hour averages are evaluated against the AIRNOW surface network. When the 8-hour average PM 2.5 statistics are compared against equivalent ozone statistics for each model, the analysis shows that PM 2.5 forecasts possess nearly equivalent correlation, less bias, and better skill relative to the corresponding ozone forecasts. An analysis of the diurnal variability shows that most models do not reproduce the observed diurnal cycle at urban and suburban monitor locations, particularly during the nighttime to early morning transition. While observations show median rural PM 2.5 levels similar to urban and suburban values, the models display noticeably smaller rural/urban PM 2.5 ratios. The ensemble PM 2.5 forecast, created by combining six separate forecasts with equal weighting, is also evaluated and shown to yield the best possible forecast in terms of the statistical measures considered. The comparisons of PM 2.5 composition with NOAA P-3 aircraft data reveals two important features: (1) The organic component of PM 2.5 is significantly underpredicted by all the AQFMs and (2) those models that include aqueous phase oxidation of SO 2 to sulfate in clouds overpredict sulfate levels while those AQFMs that do not include this transformation mechanism underpredict sulfate. Errors in PM 2.5 ammonium levels tend to correlate directly with errors in sulfate. Comparisons of PM 2.5 composition with the U.S. EPA STN network for three of the AQFMs show that sulfate biases are consistently lower at the surface than aloft. Recommendations for further research and analysis to help improve PM 2.5 forecasts are also provided.

This is the first comprehensive study on the optimization of seed distribution in a crystallization process. For a batch crystallizer, a dynamic programming formulation optimizes a property of the product crystals over the supersaturation profile and the seed characteristics, namely the mean size of the seed crystals, the seed mass, and the width of the seed distribution. Three optimization objectives are considered: ( I ) weight mean size, (2) coefficient of variation, and (3) the ratio of the nucleated crystal mass to seed crystal mass. Different objectives lead to substantially different optimal seed distributions. It is shown that optimizing over the seed distribution can have a larger effect on the product crystal size distribution than optimizing over the supersaturation profile.C'est la premikre Ctude complkte sur I'optimisation de la distribution des semences dans un prockdk de cristallisation. Pour un cristalliseur discontinu, une formulation de programmation dynamique optimise une propriktk des cristaux du produit en fonction du profil de sursaturation et des caractkristiques des semences, B savoir la taille moyenne des cristaux de semences, la masse des semences et la largeur de la distribution des semences. Trois objectifs d'optimisation sont considkrks : ( I ) le poids moyen, ( 2 ) le coefficient de variation et (3) le rapport entre la masse de cristaux nuclkCdgerminks et la masse de cristaux de semences. Diffkrents objectifs conduisent B des distributions de semences optimales substantiellement diffkrentes. On montre que I'otpimisation de la distribution de semences peut avoir un effet plus important sur la distribution de taille des cristaux de produit que I'optimisation en fonction du profil de sursaturation.Keywords: crystallization, optimal control, dynamic programming, batch control rystallization from solution is an industrially important C unit operation due to its ability to provide high purity separations. The crystal size distribution (CSD) is a critically important factor in the production of high quality products and for determining the efficiency of downstream operations, such as filtration and washing. Batch crystallizers are heavily used in industry, and a large proportion of these crystallizers are seeded. While it is well-known that the optimal supersaturation profile and the seed characteristics have a strong influence on the crystal size distribution in batch crystallizers (Chianese et al., 1984; Bohlin & Rasmuson, 1992; Rawlings et al., 1993), optimal control studies have only optimized over the supersaturation profile (Ajinkya & Ray, 1974; Chang & Epstein, 1982;Jones, 1974; Jones & Mullin,, 1974; Morari, 1980; Miller & Rawlings, 1994; Mullin & N'yvlt, 1971).This study is the first comprehensive investigation of the effect of the seed distribution on the final CSD properties for a crystallization process. The model equations are based on the moment equations. The seed distribution is parameterized in terms of its width, the mean size, and the seed mass. A dynamic programming f...