Bromide and other ions in the snow, firn air, and atmospheric boundary layer at Summit during GSHOX

Measurements of gas phase soluble bromide in the boundary layer and in firn air, and Br− in aerosol and snow, were made at Summit, Greenland (72.5° N, 38.4° W, 3200 m a.s.l.) as part of a larger investigation into the influence of Br chemistry on HOx cycling. The soluble bromide measurements confirm that photochemical activation of Br− in the snow causes release of active Br to the overlying air despite trace concentrations of Br− in the snow (means 15 and 8 nmol Br− kg−1 of snow in 2007 and 2008, respectively). Mixing ratios of soluble bromide above the snow were also found to be very small (mean \u3c1 ppt both years, with maxima of 3 and 4 ppt in 2007 and 2008, respectively), but these levels clearly oxidize and deposit long-lived gaseous elemental mercury and may perturb HOx partitioning. Concentrations of Br− in surface snow tended to increase/decrease in parallel with the specific activities of the aerosol-associated radionuclides 7Be and 210Pb. Earlier work has shown that ventilation of the boundary layer causes simultaneous increases in 7Be and 210Pb at Summit, suggesting there is a pool of Br in the free troposphere above Summit in summer time. Speciation and the source of this free tropospheric Br− are not well constrained, but we suggest it may be linked to extensive regions of active Br chemistry in the Arctic basin which are known to cause ozone and mercury depletion events shortly after polar sunrise. If this hypothesis is correct, it implies persistence of the free troposphere Br− for several months after peak Br activation in March/April. Alternatively, there may be a ubiquitous pool of Br− in the free troposphere, sustained by currently unknown sources and processes

Aerosol major ion record at Mount Washington

This study examined the seasonal cycles and regional-scale meteorological controls on the chemical properties of bulk aerosols collected from 1999 to 2004 at Mount Washington, the highest peak in the northeastern United States. The concentrations of NH4+ and SO42− peaked during summer months. The pattern for aerosol NO3− was more complicated with relatively high median concentrations characterizing spring and summer months, but with major elevated events occurring during fall, winter, and spring. The seasonal relationship between NH4+ and SO42− indicated that during warmer months a mixture of (NH4)2SO4 and NH4HSO4 was present, while it was mainly the latter in winter. More acidity and higher concentrations of the major species were generally associated with winds from the southwest and west sectors. The highest (≥95th percentile) concentrations of SO42− and NH4+ were associated with air mass transport from major upwind source regions in the Midwest and along the eastern seaboard. The ionic composition and seasonal cycle observed at Mount Washington were similar to those measured at other northeastern sites, but the range and average concentrations were much lower. These differences were exaggerated during wintertime. Included in this paper are several Eulerian case studies of SO2 conversion to SO42− during transit from Whiteface Mountain, New York, to Mount Washington. The calculations suggest a gas-phase SO2 oxidation rate of ∼1–2% per hour and demonstrate the possibility of using these two sites to investigate the chemical evolution of air masses as they move from Midwestern source regions to northern New England

Characterization of aerosol associated with enhanced small particle number concentrations in a suburban forested environment

Two elevated particle number/mass growth events associated with Aitken‐mode particles were observed during a sampling campaign (13–29 September 2004) at the Duke University Free‐Air CO2 Enrichment facility, a forested field site located in suburban central North Carolina. Aerosol growth rates between 1.2 and 4.9 nm hr−1 were observed, resulting in net increases in geometric mean diameter of 21 and 37 nm during events. Growth was dominated by addition of oxidized organic compounds. Campaign‐average aerosol mass concentrations measured by an Aerodyne quadrupole aerosol mass spectrometer (Q‐AMS) were 1.9 ± 1.6 (σ), 1.6 ± 1.9, 0.1 ± 0.1, and 0.4 ± 0.4 μg m−3 for organic mass (OM), sulfate, nitrate, and ammonium, respectively. These values represent 47%, 40%, 3%, and 10%, respectively, of the measured submicron aerosol mass. Based on Q‐AMS spectra, OM was apportioned to hydrocarbon‐like organic aerosol (HOA, likely representing primary organic aerosol) and two types of oxidized organic aerosol (OOA‐1 and OOA‐2), which constituted on average 6%, 58%, and 36%, respectively, of the apportioned OM. OOA‐1 probably represents aged, regional secondary organic aerosol (SOA), while OOA‐2 likely reflects less aged SOA. Organic aerosol characteristics associated with the events are compared to the campaign averages. Particularly in one event, the contribution of OOA‐2 to overall OM levels was enhanced, indicating the likelihood of less aged SOA formation. Statistical analyses investigate the relationships between HOA, OOA‐1, OOA‐2, other aerosol components, gas‐phase species, and meteorological data during the campaign and individual events. No single variable clearly controls the occurrence of a particle growth event

Characterizing receptive field selectivity in area V2

The computations performed by neurons in area V1 are reasonably well understood, but computation in subsequent areas such as V2 have been more difficult to characterize. When stimulated with visual stimuli traditionally used to investigate V1, such as sinusoidal gratings, V2 neurons exhibit similar selectivity (but with larger receptive fields, and weaker responses) relative to V1 neurons. However, we find that V2 responses to synthetic stimuli designed to produce naturalistic patterns of joint activity in a model V1 population are more vigorous than responses to control stimuli that lacked this naturalistic structure (Freeman, et. al. 2013). Armed with this signature of V2 computation, we have been investigating how it might arise from canonical computational elements commonly used to explain V1 responses. The invariance of V1 complex cell responses to spatial phase has been previously captured by summing over multiple “subunits” (rectified responses of simple cell-like filters with the same orientation and spatial frequency selectivity, but differing in their receptive field locations). We modeled V2 responses using a similar architecture: V2 subunits were formed from the rectified responses of filters computing the derivatives of the V1 response map over frequencies, orientations, and spatial positions. A V2 complex cell” sums the output of such subunits across frequency, orientation, and position. This model can qualitatively account for much of the behavior of our sample of recorded V2 neurons, including their V1-like spectral tuning in response to sinusoidal gratings as well as the pattern of increased sensitivity to naturalistic images

Cockpit Text Communications: Evaluating the Efficiency and Accuracy

Non-voice data exchanges will become a primary method of communication between pilots and Air Traffic Controllers as the Federal Aviation Administration’s plan for the Next Generation Air Traffic Control System (NextGen) evolves. In support of this communication evolution, pilots will need the most efficient interface tools in order to accurately and quickly exchange text messages with Air Traffic Control. Keyboards, or similar input devices, will be become a necessity in the cockpit. This study aims to investigate and compare the typing speed and accuracy possible using three sizes of two-hand, QWERTY1 keyboards: a full size (100%), a medium size (92%), and a small size (thumb typing home theater PC keyboard) that could be used for aviation data exchanges. Each study participant was administered 15 typing tests having aviation specific content, on each keyboard, including 5 tests of short length, 5 tests of medium length, and 5 tests of long length. The results of this study suggest that in terms of words per minute typing speed, participants using the medium size keyboard had a slightly faster typing speed than with the large keyboard, while the small keyboard produced a considerably slower typing speed than either the medium or large keyboards. In terms of accuracy, participants using the small keyboard had the highest level of accuracy, followed by the medium keyboard, while the least accurate keyboard tended to be the large keyboard. Overall, findings suggest that the optimal size of two-handed, QWERTY keyboard for use in an aircraft cockpit was the medium keyboard

Cockpit Text Communications: Evaluating the Efficiency and Accuracy of Different Keyboards

Non-voice data exchanges will become a primary method of communication between pilots and Air Traffic Controllers as the Federal Aviation Administration’s plan for the Next Generation Air Traffic Control System (NextGen) evolves. In support of this communication evolution, pilots will need the most efficient interface tools in order to accurately and quickly exchange text messages with Air Traffic Control. Keyboards, or similar input devices, will be become a necessity in the cockpit. This study aims to investigate and compare the typing speed and accuracy possible using three sizes of two-hand, QWERTY1 keyboards: a full size (100%), a medium size (92%), and a small size (thumb typing home theater PC keyboard) that could be used for aviation data exchanges. Each study participant was administered 15 typing tests having aviation specific content, on each keyboard, including 5 tests of short length, 5 tests of medium length, and 5 tests of long length. The results of this study suggest that in terms of words per minute typing speed, participants using the medium size keyboard had a slightly faster typing speed than with the large keyboard, while the small keyboard produced a considerably slower typing speed than either the medium or large keyboards. In terms of accuracy, participants using the small keyboard had the highest level of accuracy, followed by the medium keyboard, while the least accurate keyboard tended to be the large keyboard. Overall, findings suggest that the optimal size of two-handed, QWERTY keyboard for use in an aircraft cockpit was the medium keyboard