Indian Ocean Experiment: An integrated analysis of the climate forcing and effects of the great Indo-Asian haze

Every year, from December to April, anthropogenic haze spreads over most of the North Indian Ocean, and South and Southeast Asia. The Indian Ocean Experiment (INDOEX) documented this Indo-Asian haze at scales ranging from individual particles to its contribution to the regional climate forcing. This study integrates the multiplatform observations (satellites, aircraft, ships, surface stations, and balloons) with one- and four-dimensional models to derive the regional aerosol forcing resulting from the direct, the semidirect and the two indirect effects. The haze particles consisted of several inorganic and carbonaceous species, including absorbing black carbon clusters, fly ash, and mineral dust. The most striking result was the large loading of aerosols over most of the South Asian region and the North Indian Ocean. The January to March 1999 visible optical depths were about 0.5 over most of the continent and reached values as large as 0.2 over the equatorial Indian ocean due to long-range transport. The aerosol layer extended as high as 3 km. Black carbon contributed about 14% to the fine particle mass and 11% to the visible optical depth. The single-scattering albedo estimated by several independent methods was consistently around 0.9 both inland and over the open ocean. Anthropogenic sources contributed as much as 80% (±10%) to the aerosol loading and the optical depth. The in situ data, which clearly support the existence of the first indirect effect (increased aerosol concentration producing more cloud drops with smaller effective radii), are used to develop a composite indirect effect scheme. The Indo-Asian aerosols impact the radiative forcing through a complex set of heating (positive forcing) and cooling (negative forcing) processes. Clouds and black carbon emerge as the major players. The dominant factor, however, is the large negative forcing (-20±4 W m^(−2)) at the surface and the comparably large atmospheric heating. Regionally, the absorbing haze decreased the surface solar radiation by an amount comparable to 50% of the total ocean heat flux and nearly doubled the lower tropospheric solar heating. We demonstrate with a general circulation model how this additional heating significantly perturbs the tropical rainfall patterns and the hydrological cycle with implications to global climate

Source-oriented model for air pollutant effects on visibility

A source-oriented model for air pollutant effects on visibility has been developed that can compute light scattering, light extinction, and estimated visual range directly from data on gas phase and primary particle phase air pollutant emissions from sources. The importance of such a model is that it can be used to compute the effect of emission control proposals on visibility-related parameters in advance of the adoption of such control programs. The model has been assembled by embedding several aerosol process modules within the photochemical trajectory model previously developed for aerosol nitrate concentration predictions by Russell et al. [1983] and Russell and Cass [1986]. These modules describe the size distribution and chemical composition of primary particle emissions, the speciation of organic vapor emissions, atmospheric chemical reactions, transport of condensible material between the gas and the particle phases, fog chemistry, dry deposition, and atmospheric light scattering and light absorption. Model predictions have been compared to observed values using 48-hour trajectories arriving at Claremont, California, at each hour of August 28, 1987, during the Southern California Air Quality Study. The predicted fine particle concentration averages 62 μg m^(−3) compared to an observed value of 61 μg m^(−3), while predicted PM_(10) concentrations average 102 μg m^(−3) compared to an observed average of 97 μg m^(−3). The size distribution and chemical composition predictions for elemental carbon, sulfate, and sodium ion agree with observations to within plus or minus a few micrograms per cubic meter, while ammonium and nitrate concentrations are underpredicted by the base case model by 3 to 7 μg m^(−3) on average. Light-scattering coefficient values are calculated from the predicted aerosol size distribution and refractive index, and the model predictions agree with measured values on average to within 19%. The advantages and limitations of the modeling procedure are discussed

Sensitivity studies for r-process nucleosynthesis in three astrophysical scenarios

In rapid neutron capture, or r-process, nucleosynthesis, heavy elements are built up via a sequence of neutron captures and beta decays that involves thousands of nuclei far from stability. Though we understand the basics of how the r-process proceeds, its astrophysical site is still not conclusively known. The nuclear network simulations we use to test potential astrophysical scenarios require nuclear physics data (masses, beta decay lifetimes, neutron capture rates, fission probabilities) for all of the nuclei on the neutron-rich side of the nuclear chart, from the valley of stability to the neutron drip line. Here we discuss recent sensitivity studies that aim to determine which individual pieces of nuclear data are the most crucial for r-process calculations. We consider three types of astrophysical scenarios: a traditional hot r-process, a cold r-process in which the temperature and density drop rapidly, and a neutron star merger trajectory.Comment: 8 pages, 4 figures, submitted to the Proceedings of the International Nuclear Physics Conference (INPC) 201

Verification of a mathematical model for aerosol nitrate and nitric acid formation and its use for control measure evaluation

A mathematical model for the formation of atmospheric nitric acid and aerosol nitrate has been developed and employed to study the effect of emission controls. Based on a Lagrangian formulation of the atmospheric diffusion equation, the model computes nitric acid concentrations from a description of daytime photochemical reactions and night-time reactions involving NO_3 and N_2O_5. Ammonium nitrate formation is computed at a thermodynamic equilibrium between HNO_3 and NH_3, and heterogeneous reactions between HNO_3 and preexisting aerosol are considered. The accuracy of the air quality model's predictions is verified by comparison to O_3, NO_2, HNO_3, NH_3, aerosol nitrate and PAN measurements made for this purpose in California's South Coast Air Basin during the period of 30–31 August 1982. Examination of emission control alternatives shows that reduction in NO_x emissions yields a nearly proportional decrease in total inorganic nitrate levels (HNO_3 + aerosol nitrates). Reduction in NH_3 emissions suppresses aerosol nitrate formation, resulting in higher HNO_3 levels. Control of organic species emissions by the amounts expected in Los Angeles in future years causes a partial shift away from PAN formation toward greater production of HNO_3. Emission control strategies can be formulated that include a combination of controls on NO_x organic gases and NH_3 emissions that will achieve a greater reduction in HNO_3, aerosol nitrate and O_3 levels than a strategy predicated on control of only a single precursor species

Doxycycline alters metabolism and proliferation of human cell lines.

The tetracycline antibiotics are widely used in biomedical research as mediators of inducible gene expression systems. Despite many known effects of tetracyclines on mammalian cells-including inhibition of the mitochondrial ribosome-there have been few reports on potential off-target effects at concentrations commonly used in inducible systems. Here, we report that in human cell lines, commonly used concentrations of doxycycline change gene expression patterns and concomitantly shift metabolism towards a more glycolytic phenotype, evidenced by increased lactate secretion and reduced oxygen consumption. We also show that these concentrations are sufficient to slow proliferation. These findings suggest that researchers using doxycycline in inducible expression systems should design appropriate controls to account for potential confounding effects of the drug on cellular metabolism

The dynamics of nitric acid production and the fate of nitrogen oxides

A mathematical model is used to study the fate of nitrogen oxides (NO_x) emissions and the reactions responsible for the formation of nitric acid (HNO_3). Model results indicate that the majority of the NO_x inserted into an air parcel in the Los Angeles basin is removed by dry deposition at the ground during the first 24 h of travel, and that HNO_3 is the largest single contributor to this deposition flux. A significant amount of the nitric acid is produced at night by N_2O_5 hydrolysis. Perturbation of the N_2O_5 hydrolysis rate constant within the chemical mechanism results in redistribution of the pathway by which HNO_3 is formed, but does not greatly affect the total amount of HNO_3 produced. Inclusion of NO_3-aerosol and N_2O_5-aerosol reactions does not affect the system greatly at collision efficiencies, α, of 0.001, but at α = 0.1 or α = 1.0, a great deal of nitric acid could be produced by heterogeneous chemical processes. Ability to account for the observed nitrate radical (NO_3) concentrations in the atmosphere provides a key test of the air quality modeling procedure. Predicted NO_3 concentrations compare well with those measured by Platt et al. (Geophys. Res. Lett.7, 89–92, 1980). Analysis shows that transport, deposition and emissions, as well as chemistry, are important in explaining the behavior of NO_3 in the atmosphere

A reevaluation of achromatic spatio-temporal vision: nonoriented filters are monocular, they adapt, and can be used for decision making at high flicker speeds

Masking, adaptation, and summation paradigms have been used to investigate the characteristics of early spatio-temporal vision. Each has been taken to provide evidence for (i) oriented and (ii) nonoriented spatial-filtering mechanisms. However, subsequent findings suggest that the evidence for nonoriented mechanisms has been misinterpreted: those experiments might have revealed the characteristics of suppression (eg, gain control), not excitation, or merely the isotropic subunits of the oriented detecting mechanisms. To shed light on this, we used all three paradigms to focus on the ‘high-speed’ corner of spatio-temporal vision (low spatial frequency, high temporal frequency), where cross-oriented achromatic effects are greatest. We used flickering Gabor patches as targets and a 2IFC procedure for monocular, binocular, and dichoptic stimulus presentations. To account for our results, we devised a simple model involving an isotropic monocular filter-stage feeding orientation-tuned binocular filters. Both filter stages are adaptable, and their outputs are available to the decision stage following nonlinear contrast transduction. However, the monocular isotropic filters (i) adapt only to high-speed stimuli—consistent with a magnocellular subcortical substrate—and (ii) benefit decision making only for high-speed stimuli (ie, isotropic monocular outputs are available only for high-speed stimuli). According to this model, the visual processes revealed by masking, adaptation, and summation are related but not identical