NO and NO2 were simultaneously measured by photolytic conversion / chemiluminescence techniques during the Mauna Loa Observatory Photochemistry Experiment (MLOPEX). The field site, located at an ...elevation of 3.4 km on the north side of the Mauna Loa Volcano, was subject to two airflow regimes which typically corresponded to upslope (marine boundary layer plus island sources) conditions during the day and downslope (middle free tropospheric) conditions at night to mid‐morning. Median values of NOx (NOx = NO + NO2) were 37 and 31 pptv during upslope and downslope conditions, respectively, with the downslope measurements consistent with previous measurements made from aircraft in the middle free troposphere over the North Pacific. Although the difference in median NOx mixing ratios in the upslope and downslope regimes is small, the influence of island sources of NOx is apparent. Indeed, the median upslope values were approximately 2.5 times greater than measurements made previously in the remote marine boundary layer. The data have been examined according to downslope / free tropospheric and upslope air flow regimes for relationships between NOx and the various species that were measured simultaneously (e.g., peroxyacetyl nitrate (PAN), HNO3, NO3, NOy, O3, CO, and hydrocarbons). While positive correlations between NOx and O3 and PAN were typically observed in free tropospheric air, these correlations were considerably weaker than those observed during previous campaigns. This is likely primarily due to the lower sampling altitude during the MLOPEX study. NOx and dew point temperature were weakly anticorrelated in free tropospheric air masses. Linear correlations between NOx and the peroxides, formaldehyde, alkyl nitrates, and hydrocarbons were also weak in the free tropospheric air masses at the MLO. NOx/NOy was typically on the order of 0.1–0.2 in free tropospheric flow. Considerably higher values of NOx/NOy, were occasionally observed under upslope conditions. The NOx/NOy and HNO3/NOx values obtained under downslope conditions were similar to those previously obtained during aircraft measurements in the middle free troposphere over the northeast Pacific. On the whole, the downslope air masses sampled appear to be characteristic of well‐aged, marine free tropospheric air, and this conclusion is supported by 10‐day trajectory analyses.
Measurements of vertical profiles and level averages of ozone over the north central Atlantic near the Azores are presented. Lagrangian experiments were carried out in clean air and polluted air, and ...differences between the cases are discussed. Significant vertical structure was found in the profiles from both cases. Trajectory analysis indicates that the source regions for ozone in the marine boundary layer and in the air above the inversion capping the boundary layer were different. No significant production or destruction of ozone in the boundary layer was observed in the clean case. No substantial differences in ozone concentration between cloudy and clear air were observed, although cloud processes in the polluted case may have been partially responsible for an observed overall reduction in boundary layer ozone concentration.
As part of the Atlantic Stratocumulus Transition Experiment/Marine Aerosol and Gas Exchange (ASTEX/MAGE), ship‐based aerosol size distribution measurements have been carried out with a scanning ...electrical mobility spectrometer (SEMS) aboard the R/V Oceanus. The fast time resolution of these measurements illustrates some of the short‐timescale variability of both the marine background aerosol and the anthropogenically influenced continental air masses. The resulting total number concentrations are largely in agreement with those from a collocated condensation nucleus counter (CNC). The aerosol size distributions provide characteristic signatures for different atmospheric conditions, showing low‐concentration bimodal distributions in cleaner air masses and higher‐concentration single‐mode distributions in air masses with apparent recent continental influence.
In this study, a mixed porcine–human bioengineered liver (MPH-BEL) was used in a preclinical setup of extracorporeal liver support devices as a treatment for a model of post-resection liver failure ...(PRLF). The potential for human clinical application is further illustrated by comparing the functional capacity of MPH-BEL grafts as assessed using this porcine PRLF model with fully human (FH-BEL) grafts which were perfused and assessed in vitro. BEL grafts were produced by reseeding liver scaffolds with HUVEC and primary porcine hepatocytes (MPH-BEL) or primary human hepatocytes (FH-BEL). PRLF was induced by performing an 85% liver resection in domestic white pigs and randomized into the following three groups 24 h after resection: standard medical therapy (SMT) alone, SMT + extracorporeal circuit (ECC), and SMT + MPH-BEL. The detoxification and metabolic functions of the MPH-BEL grafts were compared to FH-BEL grafts which were perfused in vitro. During the 24 h treatment interval, INR values normalized within 18 h in the MPH-BEL therapy group and urea synthesis increased as compared to the SMT and SMT + ECC control groups. The MPH-BEL treatment was associated with more rapid decline in hematocrit and platelet count compared to both control groups. Histological analysis demonstrated platelet sequestration in the MPH-BEL grafts, possibly related to immune activation. Significantly higher rates of ammonia clearance and metabolic function were observed in the FH-BEL grafts perfused in vitro than in the MPH-BEL grafts. The MPH-BEL treatment was associated with improved markers of liver function in PRLF. Further improvement in liver function in the BEL grafts was observed by seeding the biomatrix with human hepatocytes. Methods to reduce platelet sequestration within BEL grafts is an area of ongoing research.
Measurements of nitric acid vapor and aerosol nitrate, sulfate, and ammonium were made at the Mauna Loa Observatory on Hawaii between October of 1984 and January of 1986 during 10‐day periods every 2 ...months. Nitric acid exhibited both a diurnal cycle (higher concentrations during the upslope wind hours of 0900 to 2100 LT) and a seasonal modulation (highest concentrations during the late summer). In August the daytime/nighttime average HNO3 concentrations were 97/79 parts per trillion by volume (pptv), while in February they were only 18/8 pptv. The ratio of summer/winter average HNO3 concentrations was 8. Dry deposition at the surface may be a major factor causing the diurnal variation, causing the measured surface values to be lower than the concentrations in the free troposphere above the surface. The long‐range transport of anthropogenic odd nitrogen from the west coast of North America is a likely cause of the higher summertime nitric acid concentrations. This suggests that there may be regular periods during which apparently “short‐lived” anthropogenic trace gases may be transported to remote parts of the atmosphere with relatively high efficiency. Aerosol NO3−, SO42−, and NH4+ also showed seasonal variations: summer/winter ratios were 3, 2, and 0.5, respectively.
From August 14 to September 5, 1991, we measured the mixing ratio of nitric acid vapor and several aerosol species (nitrate, sulfate, ammonium and sodium) at three heights (2 m, 10 m and 30 m) at the ...Mauna Loa Observatory. Well‐defined logarithmic gradients of temperature and HNO3 vapor were measured throughout the experiment, indicating rapid HNO3 vapor deposition to the ground. Measured dry deposition velocities for HNO3 vapor ranged from 0.27 to 4 cm s−1. The collection efficiency for HNO3 vapor varied with sampler location and orientation on the sampling tower, due to concentration depletion by the tower or the sampler itself. We found that our long‐term samplers at 8 m may underestimate free tropospheric HNO3 mixing ratios by about 20% due to dry deposition.
