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One of the greatest sources of uncertainty in simulations of climate and climate change is the influence of aerosols on the optical properties of clouds. The root of this influence is the droplet nucleation process, which involves the spontaneous growth of aerosol into cloud droplets at cloud edges, during the early stages of cloud formation, and in some cases within the interior of mature clouds. Numerical models of droplet nucleation represent much of the complexity of the process, but at a computational cost that limits their application to simulations of hours or days. Physically‐based parameterizations of droplet nucleation are designed to quickly estimate the number nucleated as a function of the primary controlling parameters: the aerosol number size distribution, hygroscopicity and cooling rate. Here we compare and contrast the key assumptions used in developing each of the most popular parameterizations and compare their performances under a variety of conditions. We find that the more complex parameterizations perform well under a wider variety of nucleation conditions, but all parameterizations perform well under the most common conditions. We then discuss the various applications of the parameterizations to cloud‐resolving, regional and global models to study aerosol effects on clouds at a wide range of spatial and temporal scales. We compare estimates of anthropogenic aerosol indirect effects using two different parameterizations applied to the same global climate model, and find that the estimates of indirect effects differ by only 10%. We conclude with a summary of the outstanding challenges remaining for further development and application.

The influence of sea salt on the cloud droplet activation of sulfate particles is investigated using a size-resolving model of the aerosol activation process. The authors found that the total number concentration of activated cloud droplets increases with increasing sea salt concentration if the sulfate number concentrations are relatively low and updrafts are strong, but it decreases with higher sea salt if sulfate number concentrations are high and cloud updrafts are weak.

To contribute to the understanding of the sources, sinks, and radiative properties of black carbon (BC), the Department of Energy Atmospheric Science Program conducted a field experiment in 2006 in and around Mexico City. As a precursor to this experiment, measurements of BC and other aerosols were taken in Mexico City during 2003. In this study, analysis of these measurements were performed to understand the sources of the BC aerosols and to evaluate the significance of a primary sink. These issues were addressed using measurements of BC and related species from the following: measurements from the El Centro Nacional de Investigacion y Capacitacion Ambiental site, backward air-parcel trajectory calculations using HYSPLIT 4 model, and Fire Map derived from satellite datasets. Black carbon absorption measurements ranged from the IR band to the UV band. The dependence of the absorption on wavelength were hypothesized to be from (a) the BC during these periods were chemically different from the rest of the time series i.e. had a different source or (b) high values of relative humidity modified the locally emitted BC giving its absorption a dependence on wavelength. When comparing the backwards trajectories to the satellite pictures of the Yucatan Peninsula forest fires, the analysis showed that BC in the air was due to the forest fires during some of these times. The results of the correlation analysis between relative humidity and concentration of BC indicated only a few time periods with strong correlations. The correlation was not consistent enough to conclude that relative humidity was the only factor affecting the BC behavior. The analysis also showed that the rain events did not wash out all the BC in the air. Aerosol emission inventories in general do not include information resulting from burning of biomass or forest fires. Therefore, it is important to continue this study by analyzing the expanded data set provided by the DOE ASP 2006 field experiment. Studying the air quality in a megacity like Mexico City will help us understand more about the air pollution problems that exist throughout the world.

This thesis develops thermoeconomic (second law and present worth) analysis and investigates the feasibility of employing thermal storage for cogenerated refuse energy recovery using mass-burning water-wall incinerators and topping steam turbines. A typical design is envisioned to be modular in nature so that it may be applied to various size loads without major engineering modifications. Each module is rated at 150 tpd of refuse capacity, 750 kW of electrical power, and 26,200 lbm/hr (11,900 kg/hr) of 150 psig (1140 kPa absolute) steam. As an option, condensing turbines are considered to receive unused process steam in the case of reduced steam load. The results indicate that this option is not economically feasible for a typical off-peak utility-purchase rate which leads to the idea of storing the excess energy during off-peak periods and recuperating it during peak periods. Sensible thermal storage is considered in rectangular cross-sectional channels through which is passed unused process steam during the storage period and feedwater during the recovery period. In determining the optimum storage configuration, it is found that the economic feasibility is a function of of mass and specific heat of the material and surface area of the channel as well as cost of material and fabrication. Economic considerations included typical cash flows of capital charges, steam and electrical energy revenues, refuse tipping fee, operation and maintenance costs, and income taxes. Cast concrete is determined to be a potentially attractive storage medium.

Correction to “Droplet nucleation: Physically-based parameterizations and comparative evaluation”

Background: Repeated teenage pregnancy is a major burden on the healthcare system worldwide. Objective: We aimed to compare teenagers with their first and third pregnancies and to evaluate the likelihood of neonatal complications. Materials and Methods: This cross-sectional study was performed on female teenagers (aged ≤ 19 yr) with singleton pregnancies. The subjects (n = 298) were screened over 12 months. Ninety-six women were excluded, based on the exclusion criteria. The remaining subjects (n = 202) were divided into two groups: teenagers with first pregnancy (n = 96) and teenagers with third pregnancy (n = 47). The subjects were observed throughout pregnancy and delivery. The final sample size of the first and third pregnancy groups was 96 and 47, respectively. Results: There was a significant risk of preeclampsia in the first pregnancy group (p = 0.01). Low birth weight, five-min Apgar score < 7, and neonatal intensive care unit admission were the most significant neonatal outcomes in the first pregnancy group. In the third pregnancy group, significant predictors of neonatal complications included very young age in the first pregnancy (≤ 15 yr), an inter-pregnancy interval < 2 yr, current anemia, and history of obstetric and/or neonatal complications in previous pregnancies. Conclusion: Based on the results, teenagers with their first pregnancy had comparable obstetric outcomes (except for preeclampsia) as teenagers with their third pregnancy, whereas neonatal complications occurred more frequently in the first pregnancy group. Overall, we can predict high-risk neonates in the third pregnancy, based on the abovementioned parameters. Key words: Teenage pregnancy, Complications, Neonate.