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Anthropogenic aerosols are composed of a variety of aerosol types and components including water-soluble inorganic species (e.g., sulfate, nitrate, ammonium), condensed organic species, elemental or black carbon, and mineral dust. Previous estimates of the clear sky forcing by anthropogenic sulfate aerosols and by organic biomass-burning aerosols indicate that this forcing is of sufficient magnitude to mask the effects of anthropogenic greenhouse gases over large regions. Here, the uncertainty in the forcing by these aerosol types is estimated. The clear sky forcing by other anthropogenic aerosol components cannot be estimated with confidence, although the forcing by these aerosol types appears to be smaller than that by sulfate and biomass-burning aerosols. The cloudy sky forcing by anthropogenic aerosols, wherein aerosol cloud condensation nuclei concentrations are increased, thereby increasing cloud droplet concentrations and cloud albedo and possibly influencing cloud persistence, may also be significant. In contrast to the situation with the clear sky forcing, estimates of the cloudy sky forcing by anthropogenic aerosols are little more than guesses, and it is not possible to quantify the uncertainty of the estimates. In view of present concerns over greenhouse gas-induced climate change, this situation dictates the need to quantify the forcing by anthropogenic aerosols and to define and minimize uncertainties in the calculated forcings. In this article, a research strategy for improving thq estimates of the clear sky forcing is defined. The strategy encompasses five major, and necessarily coordinated, activities: surface-based observations of aerosol chemical and physical properties and their influence on the radiation field; aircraft-based observations of the same properties; process studies to refine model treatments; satellite observations of aerosol abundance and size distribution; and modeling studies to demonstrate consistency between the observations, to provide guidance for determination of the most important parameters, and to allow extension of the limited set of observations to the global scale. Such a strategy, if aggressively implemented, should allow these effects to be incorporated into climate models in the next several years. A similar strategy for defining the magnitude of the cloudy sky forcing should also be possible, but the less firm understanding of this forcing suggests that research of a more exploratory nature be carried out before undertaking a research strategy of the magnitude recommended for the clear sky forcing.

Investigates the effects of target compliance on liquid drop impact. Studies of liquid/solid impact which show the difference between the predicted and observed times of jetting measured from the first impact; Advantage of a gel technique in the study of liquid/sold impacts; Procedures in preparing the gel.

Visible Multifilter Rotating Shadowband Radiometer (vis-MFRSR) data were collected at Storm Peak Laboratory (SPL), a mountain-top facility in northwest Colorado, from 1999 to 2011 and in 2013. From 2011 to 2014, in situ measurements of aerosol light scattering were also obtained. Using these data sets together, the seasonal impact of dust and biomass burning is considered for the western USA. Analysis indicates that the median contributions to spring and summer aerosol optical depth (AOD) from dust and biomass-burning aerosols across the data set are comparable. The mean AOD is slightly greater in the summer, with significantly more frequent and short-duration high AOD measurements due to biomass-burning episodes than in the spring. The Ångström exponent showed a significant increase in the summer for both the in situ and vis-MFRSR data, suggesting an increase in combustion aerosols. Spring dust events are less distinguishable in the in situ data than the column measurement, suggesting that a significant amount of dust may be found above the elevation of SPL, 3220ma.s.l. Twenty-two known case studies of intercontinental dust, regional dust, and biomass-burning events were investigated. These events were found to follow a similar pattern, in both aerosol loading and Ångström exponent, as the seasonal mean signal in both the vis-MFRSR and ground-based nephelometer. This data set highlights the wide-scale implications of a warmer, drier climate on visibility in the western USA. [ABSTRACT FROM AUTHOR]

Hourly averaged aerosol optical properties (AOPs) measured over the years 2010-2013 at four continental North American NOAA Earth System Research Laboratory (NOAA/ESRL) cooperative aerosol network sites -- Southern Great Plains near Lamont, OK (SGP), Bondville, IL (BND), Appalachian State University in Boone, NC (APP), and Egbert, Ontario, Canada (EGB) are analyzed. Aerosol optical properties measured over 1996-2009 at BND and 1997- 2009 at SGP are also presented. The aerosol sources and types in the four regions differ enough so as to collectively represent rural, anthropogenically perturbed air conditions over much of eastern continental North America. Temporal AOP variability on monthly, weekly, and diurnal timescales is presented for each site. Differences in annually averaged AOPs and those for individual months at the four sites are used to examine regional AOP variability. Temporal and regional variability are placed in the context of reported aerosol chemistry at the sites, meteorological measurements (wind direction, temperature), and reported regional mixing layer heights. Basic trend analysis is conducted for selected AOPs at the long-term sites (BND and SGP). Systematic relationships among AOPs are also presented. Seasonal variability in PM1 (sub-1 μm particulate matter) scattering and absorption coefficients at 550 nm (σsp and σap, respectively) and most of the other PM1 AOPs is much larger than day of week and diurnal variability at all sites. All sites demonstrate summer σsp and σap peaks. Scattering coefficient decreases by a factor of 2-4 in September-October and coincides with minimum single-scattering albedo (ω0) and maximum hemispheric backscatter fraction (b). The covariation of ω0 and b lead to insignificant annual cycles in top-of-atmosphere direct radiative forcing efficiency (DRFE) at APP and SGP. Much larger annual DRFE cycle amplitudes are observed at EGB (~40 %) and BND (~25 %), with least negative DRFE in September-October at both sites. Secondary winter peaks in σsp are observed at all sites except APP. Amplitudes of diurnal and weekly cycles in σap at the sites are larger for all seasons than those of σsp, with the largest differences occurring in summer. The weekly and diurnal cycle amplitudes of most intensive AOPs (e.g., those derived from ratios of measured σsp and σap) are minimal in most cases, especially those related to parameterizations of aerosol size distribution. Statistically significant trends in σsp (decreasing), PM1 scattering fraction (decreasing), and b (increasing) are found at BND from 1996 to 2013 and at SGP from 1997 to 2013. A statistically significant decreasing trend in PM10 scattering Ångström exponent is also observed for SGP but not BND. Most systematic relationships among AOPs are similar for the four sites and are adequately described for individual seasons by annually averaged relationships, although relationships involving absorption Ångström exponent vary with site and season. [ABSTRACT FROM AUTHOR]

S Scattering of solar radiation by aerosol particles is highly dependent on relative humidity (RH) as hygroscopic particles take up water with increasing RH. To achieve a better understanding of the effect of aerosol hygroscopic growth on light scattering properties and radiative forcing, the aerosol scattering coefficients at RH in the range of 40 to ~ 90% were measured using a humidified nephelometer system in the Yangtze River Delta of China in March 2013. In addition, the aerosol size distribution and chemical composition were measured. During the observation period, the mean and standard deviation (SD) of enhancement factors at RH = 85% for the scattering coefficient (f(85%)), backscattering coefficient (fb(85%)), and hemispheric backscatter fraction (fβ(85%)) were 1.58 ± 0.12, 1.25 ± 0.07, and 0.79 ± 0.04, respectively, i.e., aerosol scattering coefficient and backscattering coefficient increased by 58 and 25% as the RH increased from 40 to 85%. Concurrently, the aerosol hemispheric backscatter fraction decreased by 21%. The relative amount of organic matter (OM) or inorganics in PM1 was found to be a main factor determining the magnitude of f(RH). The highest values of f(RH) corresponded to the aerosols with a small fraction of OM, and vice versa. The relative amount of NO3â' in fine particles was strongly correlated with f(85%), which suggests that NO3â' played a vital role in aerosol hygroscopic growth during this study. The mass fraction of nitrate also had a close relationship to the curvature of the humidograms; higher mass fractions of nitrate were associated with humidograms that had the least curvature. Aerosol hygroscopic growth caused a 47% increase in the calculated aerosol direct radiative forcing at 85% RH, compared to the forcing at 40% RH [ABSTRACT FROM AUTHOR]

A detailed analysis of optical and microphysical properties of aerosol particles during the dry winter monsoon season above the northern Indian Ocean is presented. The Cloud Aerosol Radiative Forcing Experiment (CARDEX), conducted in February and March 2012 at the Maldives Climate Observatory on Hanimaadhoo island (MCOH) in the Republic of the Maldives, used autonomous unmanned aerial vehicles (AUAV) to perform vertical in-situ measurements of particle number concentration, particle number size distribution as well as particle absorption. These measurements were used together with surface-based Mini Micro Pulse Lidar (MiniMPL) observations and aerosol in-situ and off-line measurements to investigate the vertical distribution of aerosol particles. Air masses were mainly advected over the Indian subcontinent and the Arabian Peninsula. Mean surface aerosol number concentration was 1717±604cm-3 and the highest values were found in air masses from the Bay of Bengal and Indo-Gangetic Plain (2247±370cm-3). Investigations of the free tropospheric air showed that elevated aerosol layers with up to 3 times higher aerosol number concentrations than at the surface occurred mainly during periods with air masses originating from the Bay of Bengal and the Indo-Gangetic Plain. Compared to the Indian Ocean Experiment (INDOEX) conducted in winter 1999, elevated aerosol layers with increased aerosol number concentration were observed more frequently in 2012. However, lower particle absorption at the surface (σabs(520nm) = 8.5±4.2Wm-1) was found during CARDEX compared to INDOEX 1999. By combining vertical in-situ measured particle absorption with scattering calculated with Mie-theory, layers with single-scattering albedo (SSA) values of specific source regions were derived and utilized to calculate vertical particle absorption profiles from MiniMPL profiles. SSA surface values for dry conditions were found to be 0.94±0.02 and 0.91±0.02 for air masses from the Arabian Sea (and Middle East countries) and India (and Bay of Bengal), respectively. Lidar-derived particle absorption profiles showed both a similar magnitude and structure as the in-situ profiles measured with the AUAV. However, primarily due to insuffcient accuracy in the SSA estimates, the lidar-derived absorption profiles have large uncertainties and are generally weakly correlated to vertically in-situ measured particle absorption. Furthermore, the mass absorption effciency (MAE) for the northern Indian Ocean during the dry monsoon season was calculated to determine equivalent black carbon (EBC) concentrations from particle absorption measurements. A mean MAE of 11.6 and 6.9m2 g-1 for 520 and 880 nm, respectively, was found, likely representing internally mixed BC containing particles. Lower MAE values for 880nm were found for air masses originating from dust regions such as the Arabian Peninsula and western Asia (5.6m2 g-1) or from closer source regions as southern India (4.3m2 g-1). [ABSTRACT FROM AUTHOR]

Tempered AISI 4340 steel was hydrogen charged and tested for impact energy. It was found that samples tempered above 468 °C (875 °F) and subjected to hydrogen charging exhibited lower impact energy values when compared to uncharged samples. No significant difference between charged and uncharged samples tempered below 468 °C (875 °F) was observed. Neither exposure nor bake time had any significant effect on impact energy within the tested ranges. [ABSTRACT FROM AUTHOR]

This article investigates the annual cycle observed in the Antarctic baseline aerosol scattering coefficient, total particle number concentration, and particle number size distribution (PNSD) as measured at Troll Atmospheric Observatory. Mie-theory shows that the annual cycles in microphysical and optical aerosol properties have a common cause. By comparison with observations at other Antarctic stations, it is shown that the annual cycle is not a local phenomenon, but common to Central Antarctic baseline air masses. Observations of ground-level ozone at Troll as well as backward plume calculations for the air masses arriving at Troll demonstrate that the baseline air masses originate from the free troposphere and lower stratosphere region, and descend over the Central Antarctic continent. The Antarctic summer PNSD is dominated by particles with diameters < 100 nm recently formed from the gas-phase despite the absence of external sources of condensible gases. The total particle volume in Antarctic baseline aerosol is linearly correlated with the integral insolation the aerosol received on its transport pathway, and the photooxidative production of particle volume is mostly limited by photooxidative capacity, not availability of aerosol precursor gases. The photooxidative particle volume formation rate in Central Antarctic baseline air is quantified to 207±4 μm³/(MJ m). Further research is proposed to investigate the applicability of this number to other atmospheric reservoirs, and to use the observed annual cycle in Antarctic baseline aerosol properties as a benchmark for the representation of natural atmospheric aerosol processes in climate models. [ABSTRACT FROM AUTHOR]

Although black carbon (BC) is one of the key atmospheric particulate components driving climate change and air quality, there is no agreement on the terminology that considers all aspects of specific properties, definitions, measurement methods, and related uncertainties. As a result, there is much ambiguity in the scientific literature of measurements and numerical models that refer to BC with different names and based on different properties of the particles, with no clear definition of the terms. The authors present here a recommended terminology to clarify the terms used for BC in atmospheric research, with the goal of establishing unambiguous links between terms, targeted material properties and associated measurement techniques. [ABSTRACT FROM AUTHOR]

Although black carbon (BC) is one of the key atmospheric particulate components driving climate change and air quality, there is no agreement on the terminology that considers all aspects of specific properties, definitions, measurement methods, and related uncertainties. As a result, there is much ambiguity in the scientific literature of measurements and numerical models that refer to BC with different names and based on different properties of the particles, with no clear definition of the terms. The authors present here a recommended terminology to clarify the terms used for BC in atmospheric research, with the goal of establishing unambiguous links between terms, targeted material properties and associated measurement techniques. [ABSTRACT FROM AUTHOR]

We have analysed the trends of total aerosol particle number concentrations (N) measured at long-term measurement stations involved either in the Global Atmosphere Watch (GAW) and/or EU infrastructure project ACTRIS. The sites are located in Europe, North America, Antarctica, and on Pacific Ocean islands. The majority of the sites showed clear decreasing trends both in the full-length time series, and in the intra-site comparison period of 2001-2010, especially during the winter months. Several potential driving processes for the observed trends were studied, and even though there are some similarities between N trends and air temperature changes, the most likely cause of many northern hemisphere trends was found to be decreases in the anthropogenic emissions of primary particles, SO2 or some coemitted species. We could not find a consistent agreement between the trends of N and particle optical properties in the few stations with long time series of all of these properties. The trends of N and the proxies for cloud condensation nuclei (CCN) were generally consistent in the few European stations where the measurements were available. This work provides a useful comparison analysis for modelling studies of trends in aerosol number concentrations. [ABSTRACT FROM AUTHOR]