Chemical characteristics of ice residual nuclei in anvil cirrus clouds: evidence for homogeneous and heterogeneous ice formation

International audienceA counterflow virtual impactor was used to collect and analyze residual particles from anvil cirrus clouds generated over the state of Florida in the southern United States. A wide variety of particle types were found, including salts, crustal material, industrial metals, carbonaceous particles, and sulfates. Ambient aerosol particles near the anvils were found to have similar compositions, indicating that anvils act to redistribute particles over large regions of the atmosphere. Sampling occurred at a range of altitudes spanning temperatures from ?21 to ?56°C. More insoluble (crustal and metallic) particles typical of heterogeneous ice nuclei were found in ice crystals at warmer temperatures, while more soluble salts and sulfates were present at cold temperatures. At temperatures below about ?35 to ?40°C, soluble nuclei outnumbered insoluble nuclei, reflecting the transition from primarily heterogeneous to primarily homogeneous freezing as a source of anvil ice

Evidence of nitric acid uptake in warm cirrus anvil clouds during the NASA TC4 campaign

Uptake of HNO3 onto cirrus ice may play an important role in tropospheric NOx cycling. Discrepancies between modeled and in situ measurements of gas-phase HNO3 in the troposphere suggest that redistribution and removal mechanisms by cirrus ice have been poorly constrained. Limited in situ measurements have provided somewhat differing results and are not fully compatible with theory developed from laboratory studies. We present new airborne measurements of HNO3 in cirrus clouds from anvil outflow made during the Tropical Composition, Cloud, and Climate Coupling Experiment (TC4). Upper tropospheric (\u3e9 km) measurements made during three flights while repeatedly traversing the same cloud region revealed depletions of gas-phase HNO3 in regions characterized by higher ice water content and surface area. We hypothesize that adsorption of HNO3 onto cirrus ice surfaces could explain this. Using measurements of cirrus ice surface area density and some assumptions about background mixing ratios of gas-phase HNO3, we estimate molecular coverages of HNO 3 on cirrus ice surface in the tropical upper troposphere during the TC4 racetracks to be about 1 × 1013 molecules cm-2. This likely reflects an upper limit because potential dilution by recently convected, scavenged air is ignored. Also presented is an observation of considerably enhanced gas-phase HNO3 at the base of a cirrus anvil suggesting vertical redistribution of HNO3 by sedimenting cirrus particles and subsequent particle sublimation and HNO3 evaporation. The impact of released HNO3, however, appears to be restricted to a very thin layer just below the cloud. Copyright 2010 by the American Geophysical Union

Particle production in the outflow of a midlatitude storm

The concentrations of atmospheric gases and condensation nuclei (CN) or aerosol in the outflow of a storm were measured aboard a NASA DC-8 aircraft, as described in a companion paper [Twohy et al., 2002]. The data are used here to study the production of the aerosol. Major fluctuations in CN concentration are observed, in correlation with gas-phase species, but these are shown to arise as the result of the mixing of two distinct air masses. It is deduced that the CN originated in a storm outflow air mass and that its concentration before mixing was approximately uniform over a flight distance of about 200 km. The formation of the aerosol by nucleation followed by growth and coagulation is analyzed assuming that it consists of water and sulphuric acid produced locally by the oxidation of SO2. The analysis uses analytic models, and it is concluded that a 5 min burst of nucleation was followed by growth and coagulation over a period of about 5 hours. Both the mass and number concentrations of the observed aerosol can be reproduced by this analysis within a timescale consistent with that of the storm. The final number concentration is very insensitive to the initial SO2 concentration

Measurements of the light-absorbing material inside cloud droplets and its effect on cloud albedo

Most of the measurements of light-absorbing aerosol particles made previously have been in non-cloudy air and therefore provide no insight into aerosol effects on cloud properties. Here, researchers describe an experiment designed to measure light absorption exclusively due to substances inside cloud droplets, compare the results to related light absorption measurements, and evaluate possible effects on the albedo of clouds. The results of this study validate those of Twomey and Cocks and show that the measured levels of light-absorbing material are negligible for the radiative properties of realistic clouds. For the measured clouds, which appear to have been moderately polluted, the amount of elemental carbon (EC) present was insufficient to affect albedo. Much higher contaminant levels or much larger droplets than those measured would be necessary to significantly alter the radiative properties. The effect of the concentrations of EC actually measured on the albedo of snow, however, would be much more pronounced since, in contrast to clouds, snowpacks are usually optically semi-infinite and have large particle sizes

Relationships of Biomass-Burning Aerosols to Ice in Orographic Wave Clouds

Ice concentrations in orographic wave clouds at temperatures between −24° and −29°C were shown to be related to aerosol characteristics in nearby clear air during five research flights over the Rocky Mountains. When clouds with influence from colder temperatures were excluded from the dataset, mean ice nuclei and cloud ice number concentrations were very low, on the order of 1–5 L^(−1). In this environment, ice number concentrations were found to be significantly correlated with the number concentration of larger particles, those larger than both 0.1- and 0.5-μm diameter. A variety of complementary techniques was used to measure aerosol size distributions and chemical composition. Strong correlations were also observed between ice concentrations and the number concentrations of soot and biomass-burning aerosols. Ice nuclei concentrations directly measured in biomass-burning plumes were the highest detected during the project. Taken together, this evidence indicates a potential role for biomass-burning aerosols in ice formation, particularly in regions with relatively low concentrations of other ice nucleating aerosols

The Role Of Western Art In Lewis And Clark County Fifth Grade Classrooms And The Instructional Potential Of The Art Of Tucker Smith

The purpose of this project was three-fold. The first was to determine the extent to which Western art is used in fifth grade classrooms in Lewis and Clark County. The second was to determine the possibility of expanded use of Western art as a tool for teaching art, art history, and Western history. And thirdly, the work of Tucker Smith was examined in detail as a representative artist of the American West for potential usefulness of this type of work as an aid in teaching art, art history and Western history. In order to discuss the extent to which Western art does or may fit into a classroom, it is necessary to have a brief understanding of Western art itself; therefore, Chapter One defines this area of art in terms of characteristic style, subject matter, regional identity and artistic committment. In Chapter Two , the historical origins of Western art will be discussed in terms of significant contributions by outstanding artists in the field and stylistic trends over the decades. In Chapter Three, the current status of Western art will be discussed by examining modern trends as they differ from the traditional notion of what Western art is. This has been done by looking at a few of the more outstanding contemporary Western artists and concluding with a regional examination of the work of Tucker Smith. In order to determine the level of fine art, art history and Western art taught in Lewis and Clark County classrooms, a brief poll was conducted of fifth grade classroom teachers. This poll served as an aid and point of departure in discussing the potential usefulness of Western art. Along with this poll, a review was made of each social studies text used in the polled population to determine how much, if any, Western art or Western history is covered in the textbooks. Chapter Four includes a description of the textbook review and information found by this search. Chapter Five includes a discussion of the survey question, and Chapter Six describes the results. Chapter Seven evaluates the survey results by pointing out the general consensus among instructors in the polled population regarding: 1) what is actually taught and 2) what they see in the way of potential for increased discussion of Western art in the classroom. These two items are compared in Chapter Seven and discussed in terms of identifiable differences between what is actually being done and what the respondents believe could be done. Identification of the current standing of Western art's role in the classroom and any indicated areas of possible expanded use will be made. In Chapter Eight the art of Tucker Smith and other selected artists will be examined for their potential usefulness as instructional aids in areas where the research indicates a place or a need exists. (After a brief examinaton of local Western artists, the work of Tucker Smith was chosen as a representative sample of contemporary Western art because of his local impact in this particular region and his reputation as a well-known Wes tern artist)

Observation of playa salts as nuclei in orographic wave clouds

During the Ice in Clouds Experiment-Layer Clouds (ICE-L), dry lakebed, or playa, salts from the Great Basin region of the United States were observed as cloud nuclei in orographic wave clouds over Wyoming. Using a counterflow virtual impactor in series with a single-particle mass spectrometer, sodium-potassium-magnesium-calcium-chloride salts were identified as residues of cloud droplets. Importantly, these salts produced similar mass spectral signatures to playa salts with elevated cloud condensation nuclei (CCN) efficiencies close to sea salt. Using a suite of chemical characterization instrumentation, the playa salts were observed to be internally mixed with oxidized organics, presumably produced by cloud processing, as well as carbonate. These salt particles were enriched as residues of large droplets (>19 μm) compared to smaller droplets (>7 μm). In addition, a small fraction of silicate-containing playa salts were hypothesized to be important in the observed heterogeneous ice nucleation processes. While the high CCN activity of sea salt has been demonstrated to play an important role in cloud formation in marine environments, this study provides direct evidence of the importance of playa salts in cloud formation in continental North America has not been shown previously. Studies are needed to model and quantify the impact of playas on climate globally, particularly because of the abundance of playas and expected increases in the frequency and intensity of dust storms in the future due to climate and land use changes

Working Conditions for Erotic Dancers: A Review of Health and Safety Concerns from a Minneapolis Based Needs Assessment

The present studies utilizes data from a needs assessment for dancers in Minneapolis-based strip clubs focusing on structural and in-club safety concerns as well as levels of cleanliness within the club. Research was conducted utilizing Participatory Action Research with help from the Sex Workers Outreach Project: Minneapolis. The assessment consisted of an online survey utilizing both quantitative and qualitative questions (n = 62) with follow-up interviews for willing participants (n = 33). Questions regarding personal safety, structural safety, cleanliness levels, and exposure to diseases were reported using descriptive statistics, and qualitative responses were examined with thematic analysis. Data indicated that primary concerns among dancers were damaged club structures (stages, stairs, etc.), poor security measures within clubs, and frequency and quality of club cleaning practices. Potential interventions are discussed

Ice Initiation by Aerosol Particles: Measured and Predicted Ice Nuclei Concentrations versus Measured Ice Crystal Concentrations in an Orographic Wave Cloud

The initiation of ice in an isolated orographic wave cloud was compared with expectations based on ice nucleating aerosol concentrations and with predictions from new ice nucleation parameterizations applied in a cloud parcel model. Measurements of ice crystal number concentrations were found to be in good agreement both with measured number concentrations of ice nuclei feeding the clouds and with ice nuclei number concentrations determined from the residual nuclei of cloud particles collected by a counterflow virtual impactor. Using lognormal distributions fitted to measured aerosol size distributions and measured aerosol chemical compositions, ice nuclei and ice crystal concentrations in the wave cloud were reasonably well predicted in a 1D parcel model framework. Two different empirical parameterizations were used in the parcel model: a parameterization based on aerosol chemical type and surface area and a parameterization that links ice nuclei number concentrations to the number concentrations of particles with diameters larger than 0.5 μm. This study shows that aerosol size distribution and composition measurements can be used to constrain ice initiation by primary nucleation in models. The data and model results also suggest the likelihood that the dust particle mode of the aerosol size distribution controls the number concentrations of the heterogeneous ice nuclei, at least for the lower temperatures examined in this case