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El presente artículo tiene por objetivo analizar la vigilancia colonial y su relación con el desarrollo policial. Para realizar este propósito se reconstruye la polisemia conceptual de la noción de policía y se relaciona con la introducción de los alcaldes de barrio en Santafé de Bogotá en 1774. Con base en un análisis amplio de fuentes primarias, se diferencia policía como concepto, práctica e incipiente institución (Policía). Solo con esta claridad se trazan sus diferentes articulaciones en las prácticas de vigilancia en la vida cotidiana en Santafé. El trabajo señala la importancia de historizar la policía en los siglos XVII, XVIII y el umbral del siglo XIX y describe el surgimiento de una cultura de la vigilancia policial fundada en la construcción del enemigo, la interiorización de las normas, la sectorización del espacio urbano, la investigación del crimen, la captura de sospechosos y el apoyo en la administración de justicia. Con este resultado, esta investigación invita a reflexionar sobre los alcaldes de barrio, en medio de diacronías, como una futura herencia colonial en cuerpo de la Policía moderna como garante de privilegios sistémicos.

Accurate airborne aerosol instrumentation is required to determine the spatial distribution of ambient aerosol particles, particularly when dealing with the complex vertical profiles and horizontal variations of atmospheric aerosols. A versatile water-based condensation particle counter (vWCPC) has been developed to provide aerosol concentration measurements under various environments with the advantage of reducing the health and safety concerns associated with using butanol or other chemicals as the working fluid. However, the airborne deployment of vWCPCs is relatively limited due to the lack of characterization of vWCPC performance at reduced pressures. Given the complex combinations of operating parameters in vWCPCs, modeling studies have advantages in mapping vWCPC performance. In this work, we thoroughly investigated the performance of a laminar-flow vWCPC using COMSOL Multiphysics® simulation coupled with MATLAB™. We compared it against a modified vWCPC (vWCPC model 3789, TSI, Shoreview, MN, USA). Our simulation determined the performance of particle activation and droplet growth in the vWCPC growth tube, including the supersaturation, Dp,kel,0 (smallest size of particle that can be activated), Dp,kel,50 (particle size activated with 50 % efficiency) profile, and final growth particle size Dd under wide operating temperatures, inlet pressures P (30–101 kPa), and growth tube geometry (diameter D and initiator length Lini). The effect of inlet pressure and conditioner temperature on vWCPC 3789 performance was also examined and compared with laboratory experiments. The COMSOL simulation result showed that increasing the temperature difference (ΔT) between conditioner temperature Tcon and initiator Tini will reduce Dp,kel,0 and the cut-off size Dp,kel,50 of the vWCPC. In addition, lowering the temperature midpoint (Tmid=Tcon+Tini2) increases the supersaturation and slightly decreases the Dp,kel. The droplet size at the end of the growth tube is not significantly dependent on raising or lowering the temperature midpoint but significantly decreases at reduced inlet pressure, which indirectly alters the vWCPC empirical cut-off size. Our study shows that the current simulated growth tube geometry (D=6.3 mm and Lini=30 mm) is an optimized choice for current vWCPC flow and temperature settings. The current simulation can more realistically represent the Dp,kel for 7 nm vWCPC and also achieved good agreement with the 2 nm setting. Using the new simulation approach, we provide an optimized operation setting for the 7 nm setting. This study will guide further vWCPC performance optimization for applications requiring precise particle detection and atmospheric aerosol monitoring.

Aerosol particle number concentration measurements are a crucial part of aerosol research. Vertical profile measurements and high-altitude/low-pressure performance of the respective instruments become more important for remote sensing validation and a vital tool for the observation of climate variables. This study tests the new, commercially available water condensation particle counter (MAGIC 210-LP) for the deployment at aircraft cruising pressure levels that the European research infrastructure IAGOS (In-service Aircraft for a Global Observing System; http://www.iagos.org, last access: 2 May 2023) is aiming for by operating measurement instrumentation onboard passenger aircraft. We conducted laboratory experiments for conditions to simulate passenger aircraft flight altitude at operation pressure. We demonstrate that this type of water condensation particle counter shows excellent agreement with a butanol-based instrument used in parallel. A Faraday cup aerosol electrometer serves as the reference instrument. Experiments are performed with test aerosol ammonium sulfate and fresh combustion soot at pressure levels ranging from 700 to 200 hPa. For soluble particles like ammonium sulfate, the 50 % detection efficiency cut-off diameter (D50) is around 5 nm and does not differ significantly for all performed experiments. For non-soluble fresh soot particles, the D50 cut-off diameter of approximately 10 nm does not vary substantially as a function of pressure, whereas the 90 % detection efficiency cut-off diameter D90 increases from 19 nm at 700 hPa to 37 nm at 200 hPa. The overall counting efficiency for particles larger than 40 nm reaches 100 % for working pressures of 200 hPa and higher.

The new Aerosol hygroscopic growth plays an important role in atmospheric particle chemistry and the effects of aerosol on radiation and hence climate. The hygroscopic growth is often characterized by a growth factor probability density function (GF-PDF), where the growth factor is defined as the ratio of the particle size at a specified relative humidity to its dry size. Parametric, least-squares methods are the most widely used algorithms for inverting the GF-PDF from measurements of the humidified tandem differential mobility analyzer (HTDMA) and have been recently applied to the GF-PDF inversion from measurements of the humidity-controlled fast integrated mobility spectrometer (HFIMS). However, these least-squares methods suffer from noise amplification due to the lack of regularization in solving the ill-posed problem, resulting in significant fluctuations in the retrieved GF-PDF and even occasional failures of convergence. In this study, we introduce nonparametric, regularized methods to invert the aerosol GF-PDF and apply them to HFIMS measurements. Based on the HFIMS kernel function, the forward convolution is transformed into a matrix-based form, which facilitates the application of the nonparametric inversion methods with regularizations, including Tikhonov regularization and Twomey's iterative regularization. Inversions of the GF-PDF using the nonparameteric methods with regularization are demonstrated using HFIMS measurements simulated from representative GF-PDFs of ambient aerosols. The characteristics of reconstructed GF-PDFs resulting from different inversion methods, including previously developed least-squares methods, are quantitatively compared. The result shows that Twomey's method generally outperforms other inversion methods. The capabilities of Twomey's method in reconstructing the pre-defined GF-PDFs and recovering the mode parameters are validated.

Capturing the vertical profiles and horizontal variations of atmospheric aerosols often requires accurate airborne measurements. With the advantage of avoiding health and safety concerns related to the use of butanol or other chemicals, water-based condensation particle counters have emerged to provide measurements under various environments. However, airborne deployments are relatively rare due to the lack of instrument characterization under reduced pressure at flight altitudes. This study investigates the performance of a commercial “versatile” water-based condensation particle counter (vWCPC, model 3789, TSI, Shoreview, MN, USA) under various ambient pressure conditions (500–920 hPa) with a wide range of particle total number concentrations (1500–70 000 cm−3). The effect of conditioner temperature on vWCPC 3789 performance at low pressure is examined through numerical simulation and laboratory experiments. We show that the default instrument temperature setting of 30 ∘C for the conditioner is not suitable for airborne measurement and that the optimal conditioner temperature for low-pressure operation is 27∘. Under the optimal conditioner temperature (27∘), the 7 nm cut-off size is also maintained. Additionally, we show that insufficient droplet growth becomes more significant under the low-pressure operation. The counting efficiency of the vWCPC 3789 can vary up to 20 % for particles of different chemical compositions (e.g., ammonium sulfate and sucrose particles). However, such variation is independent of pressure.

Aerosols are a source of great uncertainty in radiative forcing predictions and have poorly understood health impacts. Most aerosol mass is formed in the atmosphere from reactive gas-phase organic precursors, forming secondary organic aerosol (SOA). Semivolatile organic compounds (SVOCs) (effective saturation concentration, C*, of 10−1–103 µg m−3) comprise a large fraction of organic aerosol, while intermediate-volatility organic compounds (IVOCs) (C* of 103–106 µg m−3) and volatile organic compounds (VOCs) (C* ≥ 106 µg m−3) are gas-phase precursors to SOA and ozone. The Comprehensive Thermal Desorption Aerosol Gas Chromatograph (cTAG) is the first single instrument simultaneously quantitative for a broad range of compound-specific VOCs, IVOCs and SVOCs. cTAG is a two-channel instrument which measures concentrations of C5–C16 alkane-equivalent-volatility VOCs and IVOCs on one channel and C14–C32 SVOCs on the other coupled to a single high-resolution time-of-flight mass spectrometer, achieving consistent quantification across 15 orders of magnitude of vapor pressure. cTAG obtains concentrations hourly and gas–particle partitioning for SVOCs every other hour, enabling observation of the evolution of these species through oxidation and partitioning into the particle phase. Online derivatization for the SVOC channel enables detection of more polar and oxidized species. In this work we present design details and data evaluating key parameters of instrument performance such as I/VOC collector design optimization, linearity and reproducibility of calibration curves obtained using a custom liquid evaporation system for I/VOCs and the effect of an ozone removal filter on instrument performance. Example timelines of precursors with secondary products are shown, and analysis of a subset of compounds detectable by cTAG demonstrates some of the analytical possibilities with this instrument.

The ability of aerosol particles to uptake water (hygroscopic growth) is an important determinant of aerosol optical properties and radiative effects. Aerosol hygroscopic growth is traditionally measured by humidified tandem differential mobility analyzers (HTDMA), in which size-selected dry particles are exposed to elevated relative humidity (RH), and the size distribution of humidified particles is subsequently measured using a scanning mobility particle sizer. As a scanning mobility particle sizer can measure only one particle size at a time, HTDMA measurements are time consuming, and ambient measurements are often limited to a single RH level. Pinterich et al. (2017b) showed that fast measurements of aerosol hygroscopic growth are possible using a humidity-controlled fast integrated mobility spectrometer (HFIMS). In HFIMS, the size distribution of humidified particles is rapidly captured by a water-based fast integrated mobility spectrometer (WFIMS), leading to a factor of ∼10 increase in measurement time resolution. In this study we present a prototype HFIMS that extends fast hygroscopic growth measurements to a wide range of atmospherically relevant RH values, allowing for more comprehensive characterizations of aerosol hygroscopic growth. A dual-channel humidifier consisting of two humidity conditioners in parallel is employed such that aerosol RH can be quickly stepped among different RH levels by sampling from alternating conditioners. The measurement sequence is also optimized to minimize the transition time between different particle sizes. The HFIMS is capable of measuring aerosol hygroscopic growth of six particle diameters under five RH levels ranging from 20 % to 85 % (30 separate measurements) every 25 min. The performance of this HFIMS is characterized and validated using laboratory-generated ammonium sulfate aerosol standards. Measurements of ambient aerosols are shown to demonstrate the capability of HFIMS to capture the rapid evolution of aerosol hygroscopic growth and its dependence on both size and RH.

Objective/Context: The aim of this article is to discuss, in historical terms, the emotional tension between the desire for revenge and death, and the different ways in which the affective universe is interpreted. To this end, we study a threat of execution of political prisoners —known at the time as the prevención (prevention)— made by the Minister of War Aristides Fernández during the War of a Thousand Days (1899-1902) in Colombia. Methodology: The above is done from primary sources, with a micro view and from a regressive narrative, in which details reveal structural aspects. Originality: It is an episode named by historiography, but whose complexity has yet to be reconstructed, making the dense interpretation of the case epistemologically useful. More so, when emotions evidence how the emotional logics of violence permeate the State’s institutional framework, transform anomie, and law into governmental techniques and end up integrated into the interpretation of the law and State activity. Conclusions: The study of events surrounding the prevención reveals that state policy rationalized the feelings and emotional demand for revenge and the death of the enemy under cover of the legal rhetoric of a state of siege. With blood and passion being regulators of political interests; and that, under the cloak of exception, the State was able to promote and harness feelings of retaliation with yearnings for justice, co-opt public opinion through censorship, monopolize the interpretation of the law, regulate death, and shoot and execute the enemy. Thanks to the prevención, we thus learn of multiple ways of codifying a sensory world —hatred, lust for power, and fear— under the rhetoric of law and justice.

Un enemigo invisible puso en reposo a gran parte del sistema económico del mundo. Se trató del virus SARS-COV-2, que, para octubre de 2020, cobraba mundialmente ya más de treinta millones de contagiados, más de un millón de muertos y todavía estaba lejos de desaparecer. La pandemia, en sus inicios, generó una concentración temática tan fuerte en los medios de comunicación que todo lo que sucedía por fuera de sus lógicas tenía la posibilidad de pasar rápidamente al olvido o incluso desapercibido. Más allá del desastre humano, la pandemia produjo algo perverso: cálculo político. Y, en sintonía con esta lógica, todo aquello que durante la normalidad cotidiana ponía en jaque a la democracia, en plena pandemia, fue más extremo: una serie de acontecimientos destruía los principios democráticos como consecuencia del estado de emergencia sanitario.

Ante la insistente censura que vivió la prensa a finales del siglo XIX, en uno de los periódicos más populares, afamado por su sátira y el poder de sus caricaturas, se publicó una plancha sin contenido, es decir, una hoja en blanco como signo de protesta (El Barbero [Bogotá] abr. 24, 1892). La imagen en blanco, sin embargo, tenía algo que decir. Su título, “Un penitente”, problematizaba el hecho de los reiterados cierres y multas que padecía el gremio de impresores, publicistas e ideólogos políticos de oposición. A través de la metáfora visual de la “ausencia de voz” se representaba la cínica consecuencia de aquel artículo transitorio k de la Constitución de 1886 y, más adelante, del decreto 635 de 1886 y del decreto 151 de 1888, que hacían de la censura una práctica avalada por el derecho. Hoy en día, aunque estamos lejos de ser censurados y distantes de ser penitentes, en este post scriptum del editorial silencioso quisiera apropiarme y retomar esta forma simbólica de inconformidad para plantear una crítica al poder de la indexación como una forma de constricción a la hora de generar conocimiento histórico en nuestra sociedad. Entonces, más allá de la provocación, la hoja en blanco tiene su razón de ser porque de otra manera lo que pretendo señalar tal vez hubiese pasado inadvertido.

In this study we characterized the performance of three new particle counters able to detect particles smaller than 3 nm during the Helsinki condensation particle counter (CPC) workshop in summer 2016: the Aerosol Dynamics Inc. (ADI; Berkeley, USA) versatile water condensation particle counter (vWCPC), TSI 3777 nano enhancer (TSI Inc., Shoreview, USA) and modified and boosted TSI 3010-type CPC from Université Blaise Pascal called a B3010. The performance of all CPCs was first measured with charged tungsten oxide test particles at temperature settings which resulted in supersaturation low enough to not detect any ions produced by a radioactive source. Due to similar measured detection efficiencies, additional comparison between the 3777 and vWCPC were conducted using electrically neutral tungsten oxide test particles and with positively charged tetradodecylammonium bromide. Furthermore, the detection efficiencies of the 3777 and vWCPC were measured with boosted temperature settings yielding supersaturation which was at the onset of homogeneous nucleation for the 3777 or confined within the range of liquid water for the ADI vWCPC. Finally, CPC-specific tests were conducted to probe the response of the 3777 to various inlet flow relative humidities, of the B3010 to various inlet flow rates and of the vWCPC to various particle concentrations. For the 3777 and vWCPC the measured 50 % detection diameters (d50s) were in the range of 1.3–2.4 nm for the tungsten oxide particles, depending on the particle charging state and CPC temperature settings, between 2.5 and 3.3 nm for the organic test aerosol, and in the range of 3.2–3.4 nm for tungsten oxide for the B3010.

The capacity of airborne particulate matter to generate reactive oxygen species (ROS) has been correlated with the generation of oxidative stress both in vitro and in vivo. The cellular damage from oxidative stress, and by implication with ROS, is associated with several common diseases, such as asthma and chronic obstructive pulmonary disease (COPD), and some neurological diseases. Yet currently available chemical and in vitro assays to determine the oxidative capacity of ambient particles require large samples, analyses are typically done offline, and the results are not immediate.Here we report the development of an online monitor of the oxidative capacity of aerosols (o-MOCA) to provide online, time-resolved assessment of the capacity of airborne particles to generate ROS. Our approach combines the Liquid Spot Sampler (LSS), which collects particles directly into small volumes of liquid, and a chemical module optimized for online measurement of the oxidative capacity of aerosol using the dithiothreitol (DTT) assay. The LSS uses a three-stage, laminar-flow water condensation approach to enable the collection of particles as small as 5 nm into liquid. The DTT assay has been improved to allow the online, time-resolved analysis of samples collected with the LSS but could be adapted to other collection methods or offline analysis of liquid extracts.The o-MOCA was optimized and its performance evaluated using the 9,10-phenanthraquinone (PQ) as a standard redox-active compound. Laboratory testing shows minimum interferences or carryover between consecutive samples, low blanks, and a reproducible, linear response between the DTT consumption rate (nmol min−1) and PQ concentration (µM). The calculated limit of detection for o-MOCA was 0.15 nmol min−1. The system was validated with a diesel exhaust particle (DEP) extract, previously characterized and used for the development, improvement, and validation of the standard DTT analysis. The DTT consumption rates (nmol min−1) obtained with the o-MOCA were within experimental uncertainties of those previously reported for these DEP samples. In ambient air testing, the fully automated o-MOCA was run unattended for 3 days with 3 h time resolution and showed a diurnal and daily variability in the measured consumption rates (nmol min−1 m−3).

El artículo tiene como objetivo discutir el rol de la Policía desde el cruce entre la antropometría, el detectivismo y la Policía Judicial en Colombia a principios del siglo xx. Con base en material inédito de archivo, prensa y revistas de la época, se reconstruye el caso de la deportación de Emilio Napoleón Ravalletty, un migrante francés, sospechoso de robo y presuntamente indocumentado. Dada la confluencia entre las políticas raciales de migración, las nociones de seguridad y los imaginarios de peligrosidad social, se analizan las prácticas de registro antropométrico, la construcción de prueba como ejercicio detectivesco y la administración de justicia a cargo de la Policía. Con este acercamiento se evidencian, primero, las estrategias con las cuales se fabrica la noción de sujeto pernicioso; segundo, cómo el prejuicio es objeto de racionalización; y, tercero, la fragilidad del límite entre positivo y falso positivo como parte constitutiva de la prevención y la anticipación.

En la escena, cuatro policías arrestan a un presunto delincuente y para ello se valen de tres sogas. Con una envuelven el cuello del sospechoso, con la otra ciñen su torso y sus brazos y con la tercera le inmovilizan las manos. Mientras tres de los agentes armados se esfuerzan por atar al sujeto, el cuarto sonríe, expectante. En un segundo plano se anuncia el destino inmediato del apresado: un carro de prisión tirado por un caballo, artefacto visto por primera vez en las calles de Bogotá desde 1914. La acción, además, parece destinada a proteger a quienes se representa en un tercer plano, una mujer que deambula desprevenida con su hija por el sardinel. La caricatura capta la intervención policial, el castigo ante el delito y el proyecto de protección. Captura, encierro y control son, entonces, los tópicos más evidentes de esta obra, una representación basada en la realidad de los carros-prisión introducidos en la capital —uno para hombres, otro para mujeres— y anunciados al público mediante el decreto 1449, publicado en la Revista de la Policía Nacional No. 39-40 (1914) junto con una foto ilustrativa y la siguiente acla- ración: “para conducción de ebrios y detenidos”.

Groundwater is a critical freshwater resource for irrigation in the California Central Valley, particularly in times of drought. Groundwater depth has dropped rapidly in California’s overdrafted basins, but irregular monitoring across space and time limits the accuracy of the groundwater depth projections in the Groundwater Sustainability Plans required by the California Sustainable Groundwater Management Act (SGMA). This work constructs a Bayesian hierarchical model for predicting groundwater depth from sparse monitoring data in three Central Valley counties. We apply this model to generate 300 m resolution monthly groundwater depth estimates for drought years 2013–2015, and compare our smoothed groundwater depth map to smoothed rasterized maps published by the CA Department of Water Resources. Finally, we quantify uncertainty in groundwater depth predictions that are made by imputing missing well data and interpolating predictions across the study domain, which is helpful in directing future sampling efforts towards areas with high uncertainty. The BHM model accurately captures the spatiotemporal pattern in groundwater depth, as evidenced by 94.54% of withheld test samples’ true depth being covered by the 95% prediction interval drawn from the BHM posterior distribution. The model converged despite a very sparse dataset, demonstrating broad applicability for evaluating changes in regional groundwater depth as required by SGMA. Depth prediction intervals can also help prioritize future groundwater depth sampling activity and increase the utility of groundwater depth maps in total storage predictions by enabling sensitivity analysis.

Despite recent efforts to record wind at finer spatial and temporal scales, stochastic realizations of wind are still important for many purposes and particularly for wind energy grid integration and reliability studies. Most instances of wind generation in the literature focus on simulating only wind speed, or power, or only the wind vector at a particular location and sampling frequency. In this work, we introduce a Markov-switching vector autoregressive (MSVAR) model, and we demonstrate its flexibility in simulating wind vectors for 10-min, hourly and daily time series and for individual, locally-averaged and regionally-averaged time series. In addition, we demonstrate how the model can be used to simulate wind vectors at multiple locations simultaneously for an hourly time step. The parameter estimation and simulation algorithm are presented along with a validation of the important statistical properties of each simulation scenario. We find the MSVAR to be very flexible in characterizing a wide range of properties in the wind vector, and we conclude with a discussion of extensions of this model and modeling choices that may be investigated for further improvements.

Dos mujeres bajo un parasol rojo. Una de ellas, blanca; la otra, negra. La esclava porta la sombrilla para proteger a su ama de los efectos del sol. Todo ocurre en un mercado, en medio de la vida cotidiana en las Antillas. Esta circunstancia hace parte de algo más amplio. En un primer plano aparecen seres de diferentes colores, mercancías de consumo, textiles, arte, animales y, nuevamente, esclavos o pardos libres. En un segundo plano, incluso más extenso, se divisa el mar insinuando una red de comercio transatlántico. En medio de ese acontecimiento congelado se intuyen aspectos, aunque sin representación evidente. Muchos los sentían y vivían: prejuicios, estereotipos y jerarquías sociales que juntos formaban una poderosa matriz social del mundo colonial. La imagen es sin duda solo un fragmento del día a día. No hace falta decirlo, se trata de la portada del presente número, una pintura de Agostino Brunias de finales del siglo xviii que comentamos como abrebocas para el nuevo dossier en manos del lector.

Los protagonistas esta vez: los cerdos. Y con seguridad también un “negro” llamado Pasos, su verdugo. Con esta trama de Mauricio A. Gómez Gómez abre el presente número, resultado de la convocatoria Tema Libre. Indudablemente existen varios clásicos sobre la historia de los animales. Por ejemplo, son muy conocidos el análisis simbólico sobre las peleas de gallos en Bali de Clifford Geertz y la matanza de gatos en París de Robert Darnton. Pero, esta vez, el presente número nos remite a otro lugar, a otro tiempo y a otros animales: los porcinos en la provincia de Antioquia, en el siglo XVIII.

This article provides both an historical basis as well as a theoretical-methodological proposal with which to analyze processes of racialization before the modern period. To do so, the proposal is framed within the debate about the possible racial-ized character of the purity of blood laws, taking into account the power of discourse and everyday practices. After an historical overview both in Spain and in the New Kingdom of Granada (fifteenth to eighteenth centuries), the article argues that, starting from a racial antisemitism in the Iberian peninsula, the purity of blood became, in Hispanic America, a strategy of colonial racialization because it codified social relations hierarchially through corporeal and cultural symbols.

In recent decades, the Rocky Mountains (RM) have undergone significant changes associated with anthropogenic activities and natural disturbances. These changes have the potential to alter primary productivity and biomass carbon storage. In particular, dissolved organic carbon (DOC) in RM streams can affect heterotrophic processes, act as a source for the nutrient cycle, absorb sunlight radiation, alter metal transport, and can promote the production of carcinogenic byproducts during water treatment. Recent studies have focused on the relationship between bark beetle infestations and stream organic matter but have reached conflicting conclusions. Consequently, here we compile and process multiple datasets representing features of the RM for the period 1983–2012 with the purpose of assessing their relative influence on stream DOC concentrations using spatial statistical modeling. Features representing climate, land cover, forest disturbances, topography, soil types, and anthropogenic activities are included. We focus on DOC during base-flow conditions in RM streams because base-flow concentrations are more representative of the longer-term (annual to decadal) impacts and are less dependent on episodic, short-term storm and runoff/erosion events. To predict DOC throughout the network, we use a stream network model in a 56,550 km2 area to address the intrinsic connectivity and hydrologic directionality of the stream network. Natural forest disturbances are positively correlated with increased DOC concentrations; however, the effect of urbanization is far greater. Similarly, higher maximum temperatures, which can be exacerbated by climate change, are also associated with elevated DOC concentrations. Overall, DOC concentrations present an increasing trend over time in the RM region.

The relationship between cloud condensation nuclei (CCN) number and the physical and chemical properties of the atmospheric aerosol distribution is explored for a polluted urban data set from the Study of Organic Aerosols at Riverside I (SOAR-1) campaign conducted at Riverside, California, USA during summer 2005. The mixing state and, to a lesser degree, the average chemical composition are shown to be important parameters in determining the activation properties of those particles around the critical activation diameters for atmospherically-realistic supersaturation values. Closure between predictions and measurements of CCN number at several supersaturations is attempted by modeling a number of aerosol chemical composition and mixing state cases of increasing complexity. It is shown that a realistic treatment of the state of mixing of the urban aerosol distribution is critical in order to eliminate model bias. Fresh emissions such as elemental carbon and small organic particles must be treated as non-activating and explicitly accounted for in the model. The relative number concentration of these particles compared to inorganics and oxygenated organic compounds of limited hygroscopicity plays an important role in determining the CCN number. Furthermore, expanding the different composition/mixing state cases to predictions of cloud droplet number concentration in a cloud parcel model highlights the dependence of cloud optical properties on the state of mixing and hygroscopic properties of the different aerosol modes, but shows that the relative differences between the different cases are reduced compared to those from the CCN model.