Tropospheric sulfate distribution during SUCCESS: Contributions from jet exhaust and surface sources

The distribution of SO4= aerosol over the central US during SUCCESS indicates that surface sources of SO4= and SO2 in the western US caused SO4= enhancements up to 10 km altitude. The mean (median) SO4= mixing ratio in the mid- and upper-troposphere increased from 24 (16) pptv over the Pacific ocean to 58 (29) pptv over the central plains. Above 10 km the SO4=mixing ratio was essentially the same in both regions, and also when the geographic classifications were further partitioned into upper tropospheric and lower stratospheric categories (mean near 40 pptv). No obvious enhancements of SO4= could be detected in jet exhaust plumes, but this may reflect the difficulty of keeping a large airborne sampling platform within a turbulent wake for time periods longer than a few seconds. Expected SO4=enhancements (based on observed CO2 enhancements and emission factors for these two species) were generally much smaller than the variability of ambient SO4= mixing ratios, so our null result does not mean that aircraft do not emit H2SO4

Influence of vertical transport on free tropospheric aerosols over the central USA in springtime

Measurements of the atmospheric aerosol chemical composition during the Subsonic Aircraft: Contrail and Cloud Effects Special Study (SUCCESS) indicate substantial vertical transport of boundary layer aerosol to the free troposphere over the south-central United States during springtime. Mixing ratios of water-soluble aerosol Ca 2+ at 6 - 12 km altitude exhibited a median mixing ratio of 20 pptv, with 15% of the measurements \u3e 100 pptv and a maximum of ! 235 pptv. In air parcels with enhanced Ca 2+, the ratios K+/Ca 2+, Mg2+/Ca 2+, and Na+/Ca 2+ in the bulk aerosol were distinctly characteristic of those in limestone and/or cement. Significantly enhanced mixing ratios of aerosol SO42-, NO3-, and NH4 + were also concomitant with the elevated Ca 2+, suggesting transport of both crustal and anthropogenic aerosols to the upper troposphere. The mass concentration of water-soluble aerosol material was in the range 0.1 - 6 pg m -3 STP, and estimated crustal dust levels were 7 - 160 pg m \u273 ST

Research opportunities on immunocompetence in space

The most significant of the available data on the effects of space flight on immunocompetences and the potential operational and clinical significance of reported changes are as follows: (1) reduced postflight blastogenic response of peripheral lymphocytes from space crew members; (2) postflight neutrophilia persisting up to 7 days; (3) gingival inflammation of the Skylab astronauts; (4) postflight lymphocytopenia, eosinopenia, and monocytopenia; (5) modifications and shifts in the microflora of space crews and spacecraft; and (6) microbial contamination of cabin air and drinking water. These responses and data disclose numerous gaps in the knowledge that is essential for an adequate understanding of space-related changes in immunocompetence

Soluble acidic species in air and snow at Summit, Greenland

Simultaneous measurements of the concentrations of soluble acidic species in the gas, aerosol and snow phases at Summit, Greenland were made during summer 1993. Mean concentrations of gas phase HCOOH, CH3COOH, and HNO3 (49±28, 32±17 and 0.9±0.6 nmol m−3 STP, respectively) exceeded the concentrations of aerosol-associated HCOO−, CH3COO−, and NO3−by 1–3 orders of magnitude. On average, SO2 concentrations (0.9±0.6 nmol m−3 STP) were approximately 1/3 those of aerosol SO4=, but this ratio varied widely due largely to changes in the concentration of aerosol SO4=. Concentrations of aerosol SO4= plus SO2 consistently exceeded the sum of aerosol NO3− plus HNO3, yet NO3− was 3–20 times as abundant as SO4=in surface snow. Gas phase concentrations of HCOOH and CH3COOH at Summit were unexpectedly as large as those previously reported for several high latitude continental sites. However, carboxylate concentrations in snow were lower than those of SO4=. Our observation of post-depositional loss of these carboxylic acids within hours after a snowfall must partially explain the low concentrations found in snow. The relative abundance of soluble acids in summer snow at Summit was opposite of that in the overlying atmosphere. Our results highlight the need for improved understanding of the processes controlling transfer of soluble atmospheric species between air and snow

Mercury deposition in southern New Hampshire, 2006–2009

The atmospheric deposition of mercury (Hg) occurs via several mechanisms including wet, dry, and occult processes. In an effort to understand the atmospheric cycling and seasonal depositional characteristics of Hg, event-based wet deposition samples and reactive gaseous Hg (RGM) measurements were collected for approximately 3 years at Thompson Farm (TF), a near-coastal rural site in Durham, NH, part of the University of New Hampshire AIRMAP Observing Network. Total aqueous mercury exhibited seasonal patterns in Hg wet deposition at TF. The lowest Hg wet deposition was measured in the winter with an average total seasonal deposition of 1.56 μg m−2compared to the summer average of 4.71 μg m−2. Inter-annual differences in total wet deposition are generally linked with precipitation volume, with the greatest deposition occurring in the wettest year. Relationships between surface level RGM and Hg wet deposition were also investigated based on continuous RGM measurements at TF from November 2006 to September 2009. No correlations were observed between RGM mixing ratios and Hg wet deposition, however the ineffective scavenging of RGM during winter precipitation events was evidenced by the less frequent depletion of RGM below the detection level. Seasonal dry deposition of reactive gaseous Hg (RGM) was estimated using an order-of-magnitude approach. RGM mixing ratios and dry deposition estimates were greatest during the winter and spring. The seasonal ratios of Hg wet deposition to RGM dry deposition vary by up to a factor of 80

High-frequency carbonate-siliciclastic cycles in the Miocene of the Lorca Basin (Western Mediterranean, SE Spain)

The upper Miocene Parilla Formation, Lorca Basin, Spain, provides an example of stacked high-frequency cycles of mixed carbonates and siliciclastics. Cycles developed on a steep carbonate ramp bordering an alluvialfan system. Three cycle variants are distinguished: siliciclastic-dominated cycles at the proximal part of the ramp, mid-ramp mixed carbonate - siliciclastic cycles, and carbonate-dominated cycles on the more distal parts of the ramp. The vertical thickness of these stacked simple sequences ranges from 0.7 up to 8 m. High-frequency changes in relative sea level resulted in a dynamic interplay between terrigenous sediment supply and carbonate production rates. During falling stage and lowstands, the alluvial system migrated basinwards and coarse-grained siliciclastics were deposited, whereas rising sea level and highstands provided optimal conditions for the production and accumulation of biogenic carbonates. Coral colonies up to 4 m thick provide a minimum measure of the magnitude of sea-level change involved in the development of the cycles. In contrast to previously documented simple carbonate sequences, this hybrid system of carbonates and siliciclastics preserves a more complete record of cyclic sea-level change, where terrigenous sediment supply compensated for the reduction in carbonate production during periods of falling and low sea level

A piloted simulator study on augmentation systems to improve helicopter flying qualities in terrain flight

Four basic single-rotor helicopters, one teetering, on articulated, and two hingeless, which were found to have a variety of major deficiencies in a previous fixed-based simulator study, were selected as baseline configurations. The stability and control augmentation systems (SCAS) include simple control augmentation systems to decouple pitch and yaw responses due to collective input and to quicken the pitch and roll control responses; SCAS of rate-command type designed to optimize the sensitivity and damping and to decouple the pitch-roll due to aircraft angular tate; and attitude-command type SCAS. Pilot ratings and commentary are presented as well as performance data related to the task. SCAS control usages and their gain levels associated with specific rotor types are also discussed

Effects of rotor parameter variations on handling qualities of unaugmented helicopters in simulated terrain flight

A coordinated analysis and ground simulator experiment was performed to investigate the effects on single rotor helicopter handling qualities of systematic variations in the main rotor hinge restraint, hub hinge offset, pitch-flap coupling, and blade lock number. Teetering rotor, articulated rotor, and hingeless rotor helicopters were evaluated by research pilots in special low level flying tasks involving obstacle avoidance at 60 to 100 knots airspeed. The results of the experiment are in the form of pilot ratings, pilot commentary, and some objective performance measures. Criteria for damping and sensitivity are reexamined when combined with the additional factors of cross coupling due to pitch and roll rates, pitch coupling with collective pitch, and longitudinal static stability. Ratings obtained with and without motion are compared. Acceptable flying qualities were obtained within each rotor type by suitable adjustment of the hub parameters, however, pure teetering rotors were found to lack control power for the tasks. A limit for the coupling parameter L sub q/L sub p of 0.35 is suggested

A temperate river estuary is a sink for methanotrophs adapted to extremes of pH, temperature and salinity

River Tyne (UK) estuarine sediments harbour a genetically and functionally diverse community of methane-oxidizing bacteria (methanotrophs), the composition and activity of which were directly influenced by imposed environmental conditions (pH, salinity, temperature) that extended far beyond those found in situ. In aerobic sediment slurries methane oxidation rates were monitored together with the diversity of a functional gene marker for methanotrophs (pmoA). Under near in situ conditions (4-30°C, pH 6-8, 1-15gl-1 NaCl), communities were enriched by sequences affiliated with Methylobacter and Methylomonas spp. and specifically a Methylobacter psychrophilus-related species at 4-21°C. More extreme conditions, namely high temperatures ≥40°C, high ≥9 and low ≤5 pH, and high salinities ≥35gl-1 selected for putative thermophiles (Methylocaldum), acidophiles (Methylosoma) and haloalkaliphiles (Methylomicrobium). The presence of these extreme methanotrophs (unlikely to be part of the active community in situ) indicates passive dispersal from surrounding environments into the estuary

Air-snow exchange of HNO3 and NOy at Summit, Greenland

Ice core records of NO3− deposition to polar glaciers could provide unrivaled information on past photochemical status and N cycling dynamics of the troposphere, if the ice core records could be inverted to yield concentrations of reactive N oxides in the atmosphere at past times. Limited previous investigations at Summit, Greenland, have suggested that this inversion may be difficult, since the levels of HNO3 and aerosol-associated NO3− over the snow are very low in comparison with those of NO3− in the snow. In addition, it appears that some fraction of the NO3− in snow may be reemitted to the atmosphere after deposition. Here we report on extensive measurements of HNO3, including vertical gradients between 1.5 and 7 m above the snow, made during the summers of 1994 and 1995 at Summit. These HNO3 data are compared with NO3− concentrations in surface snow and the first measurements of the concentrations and fluxes of total reactive nitrogen oxides (Ny) on a polar glacier. Our results confirm that HNO3 concentrations are quite low (mean 0.5 nmol m−3) during the summer, while NO3− is the dominant ion in snow. Daytime peaks in HNO3− appear to be due at least partly to emissions from the snow, an assertion supported by gradients indicating a surface source for HNO3− on many days. Observed short-term increases in NO3− inventory in the snow can be too large to be readily attributed to deposition of HNO3− suggesting that deposition of one or more other N oxides must be considered. We found that the apparent fluxes of HNO3 and NOy were in opposite directions during about half the intervals when both were measured, with more cases of HNO3 leaving the snow, against an NOy flux into the snow, than the reverse. The concentrations of NOy are generally about 2 orders of magnitude greater than those of HNO3; hence deposition of only a small, non-HNO3, fraction of this pool could dominate NO3− in snow, if the depositing species converted to NO3−, either in the snowpack or upon melting for analysis