Effects of halogens on European air-quality

Halogens (Cl, Br) have a profound influence on stratospheric ozone (O₃). They (Cl, Br and I) have recently also been shown to impact the troposphere, notably by reducing the mixing ratios of O₃ and OH. Their potential for impacting regional air-quality is less well understood. We explore the impact of halogens on regional pollutants (focussing on O₃) with the European grid of the GEOS-Chem model (0.25° × 0.3125°). It has recently been updated to include a representation of halogen chemistry. We focus on the summer of 2015 during the ICOZA campaign at the Weybourne Atmospheric Observatory on the North Sea coast of the UK. Comparisons between these observations together with those from the UK air-quality network show that the model has some skill in representing the mixing ratios/concentration of pollutants during this period. Although the model has some success in simulating the Weybourne ClNO₂ observations, it significantly underestimates ClNO₂ observations reported at inland locations. It also underestimates mixing ratios of IO, OIO, I₂ and BrO, but this may reflect the coastal nature of these observations. Model simulations, with and without halogens, highlight the processes by which halogens can impact O₃. Throughout the domain O₃ mixing ratios are reduced by halogens. In northern Europe this is due to a change in the background O₃ advected into the region, whereas in southern Europe this is due to local chemistry driven by Mediterranean emissions. The proportion of hourly O₃ above 50 nmol mol^-1 in Europe is reduced from 46% to 18% by halogens. ClNO₂ from N₂O₅ uptake onto sea-salt leads to increases in O₃ mixing ratio, but these are smaller than the decreases caused by the bromine and iodine. 12% of ethane and 16% of acetone within the boundary layer is oxidised by Cl. Aerosol response to halogens is complex with small (∼10%) reductions in PM_2.5 in most locations. A lack of observational constraints coupled to large uncertainties in emissions and chemical processing of halogens make these conclusions tentative at best. However, the results here point to the potential for halogen chemistry to influence air quality policy in Europe and other parts of the world.

Small scale structure in the atmosphere: implications for chemical composition and observational methods

Non-linearities in chemical processes are recognised as being important in a number of areas of atmospheric science. In this paper we show simulations using an idealised plume model which describes the relaxation of an urban plume into the background atmosphere. As might be anticipated, the initial conditions of NOx, O3 and VOCs within the plume and background are important in determining the chemistry downstream of the source, but crucially for this study, the rate of mixing (on timescales appropriate to the real atmosphere) is found to alter the composition of the atmosphere significantly. The model shows that NO3 chemistry can play a major role in the oxidation of biogenic VOCs present in the background atmosphere. In addition, the reaction of hydrocarbons with NO3 potentially has important implications for NOy speciation because a significant fraction of organic nitrates thus formed are sufficiently long-lived to leave the planetary boundary layer. A particularly critical result of the model is that under certain NOx conditions, O3 surface deposition can be significantly inhibited, with consequent effects on the O3 budget.

Assessment of a polyester-covered nitinol stent in an atherosclerotic swine model

PURPOSE

To evaluate the short-term patency and healing characteristics of the Cragg EndoPro covered stent in an atherosclerotic model as one of the Food and Drug Administration requirements before possible approval of the device for human use in the United States.

MATERIALS AND METHODS

Seventeen self-expanding stent-grafts were placed in the aorta and right and left iliac arteries of six Yucatan microswine exposed to a regimen of accelerated atherosclerosis. The stent-grafts were constructed from nitinol wire formed into a tubular zigzag configuration. The stent frame was covered by a thin woven polyester fabric tube, with medium permeability, available in multiple diameters and lengths. The animals were killed at 24 hours, 3 months, and 6 months. Assessment was done by angiography and histology.

RESULTS

All stents were patent immediately after deployment. Two stents were occluded at follow-up, indicating an 88% patency rate. Minor lumen narrowing was found at the follow-up intervals. Histologic examination revealed a mixture of mature and immature endothelial cells lining both the native and stented regions in all vessels examined. The new endoluminal surface was composed primarily of fibrocollagen and elastic fibers and smooth muscle cells. Intimal thickness was inversely correlated to medial thickness. Medial compression with atrophy was observed routinely with rare necrosis. Complete tissue ingrowth was seen by 3 months. The degree of vascular inflammation increased over time, as well as the foreign body giant cell reaction to the polyester fabric.

CONCLUSION

The patency rate does not appear to be better than that with angioplasty or noncovered stent placement in the studied time frame. The progressive vascular inflammatory changes noted should be further investigated in longer-term animal trials to ensure its safety in humans because this device is meant to be permanent.

The development of the terminal end bud in the prepubertal-pubertal mouse mammary gland

BACKGROUND

The mammary gland is one of the few organ systems in mammals that completes its morphologic development postnatally. Due to this unique developmental property, it serves as an excellent model for studying ductal morphogenesis beyond embryonic life. The primary objective of this study was to investigate the development of terminal end bud (TEB) structure in the prepubertal-pubertal mouse mammary gland.

METHODS

Seventy-five mice, weaned at 21 days of age, were fed a high fat, nonrestricted intake diet for optimum mammary gland growth. Whole-mount preparations and a computer-assisted image analyzer were used to record the size and number of TEB structures in the thoracic and inguinal mammary glands. Alight microscope was used to determine the number of cap cells present in select TEB structures.

RESULTS

In the prepubertal age group, the size and number (No.) of TEBs in the No. 2 and No. 3 thoracic glands were significantly greater than those in the No. 4 inguinal gland. In the pubertal age group, the size and number of TEBs in the No. 2 gland significantly decreased, indicating that for this particular gland the largest size and greatest number of TEBs are present during the prepubertal growth period. In contrast, the size and number of TEBs in the No. 3 and No. 4 glands remained relatively constant throughout the prepubertal-pubertal growth period.

CONCLUSIONS

The results of this study show: (1) like the rat mammary gland, there is asynchronous growth among the mouse mammary glands, (2) the maximum size and number of TEBs in the prepubertal-pubertal mouse mammary glands are a function of the gland of origin and the age of the mouse, and (3) the number of cap cells per TEB structure is directly correlated with the size of the TEB structure.