This overview summarizes the objectives of the Aerosol Characterization Experiments (ACEs) of the International Global Atmospheric Chemistry (IGAC) project and the research strategy implemented in the second of this series of experiments (ACE‐2). ACE‐2 took place from 16 June to 24 July 1997, over the sub‐tropical North‐East Atlantic. It provided an opportunity to study the properties, processes and effects of contrasting aerosol types in this region, including background marine and anthropogenic pollution aerosol in the marine boundary layer (MBL), and background aerosol and mineral dust in the overlaying free troposphere (FT). The major achievements of ACE‐2 include:(a) identification of entrainment, in‐cloud scavenging and coagulation as the major processes transforming a pollution aerosol transported within the MBL; (b) the first documentation of the indirect radiative effect of aerosols at the scale of a cloud ensemble in continental pollution outflow; (c) observation of a wide range in the contribution of organic material to the sub‐micron aerosol mass, with possibly the highest contribution in the free tropospheric; (d) improved understanding of the role of condensing HCl, HNO3 and NH3 as a growth mechanism of sub‐micron aerosols in polluted air masses advecting over the ocean. A close connection was observed between meteorological factors (such as horizontal and vertical wind speed, boundary layer development, entrainment, humidity fields) and aerosol and cloud characteristics. In the ACE‐2 region, these meteorological factors, rather than aerosol microphysics and chemistry, often dominated the shaping of the aerosol size distribution and/or their effect on radiation and clouds. The ACE‐2 data presently analyzed provide a qualitative, and in many cases a quantitative understanding of the complex gas/aerosol/cloud system in the sub‐tropical marine environment. This will guide future model development. Some major data sets are still to be analyzed.

This overview summarizes the objectives of the Aerosol Characterization Experiments (ACEs) of the International Global Atmospheric Chemistry (IGAC) project and the research strategy implemented in the second of this series of experiments (ACE-2). ACE-2 took place from 16 June to 24 July 1997, over the sub-tropical North-East Atlantic. It provided an opportunity to study the properties, processes and effects of contrasting aerosol types in this region, including background marine and anthropogenic pollution aerosol in the marine boundary layer (MBL), and background aerosol and mineral dust in the overlaying free troposphere (FT). The major achievements of ACE-2 include: (a) identification of entrainment, in-cloud scavenging and coagulation as the major processes transforming a pollution aerosol transported within the MBL; (b) the first documentation of the indirect radiative effect of aerosols at the scale of a cloud ensemble in continental pollution outflow; (c) observation of a wide range in the contribution of organic material to the sub-micron aerosol mass, with possibly the highest contribution in the free tropospheric; (d) improved understanding of the role of condensing HCl, HNO 3 and NH 3 as a growth mechanism of sub-micron aerosols in polluted air masses advecting over the ocean. A close connection was observed between meteorological factors (such as horizontal and vertical wind speed, boundary layer development, entrainment, humidity fields) and aerosol and cloud characteristics. In the ACE-2 region, these meteorological factors, rather than aerosol microphysics and chemistry, often dominated the shaping of the aerosol size distribution and/or their effect on radiation and clouds. The ACE-2 data presently analyzed provide a qualitative, and in many cases a quantitative understanding of the complex gas/aerosol/cloud system in the sub-tropical marine environment. This will guide future model development. Some major data sets are still to be analyzed.

Enriched stable isotope immersion techniques were used to mark the otoliths of larval golden perch (Macquaria ambigua) immediately post-hatch. Two experiments were undertaken: the first involved rearing larvae in water enriched with three concentrations of 137 Ba for 1-5 days. Marks were produced in as little as 1 day; however, otolith isotope ratios reached equilibrium with the water in 5 days at 90 lgAEl )1 . The second experiment involved rearing larvae in isotope enriched water with combinations of stable isotopes of Ba and Mg for 4 days after hatching. Seven significantly different isotopic signatures were produced using three Ba isotopes, which were reflective of the water. Only slight differences were found in otoliths of larvae that were reared in combinations of Mg isotopes, which did not reflect the water chemistry. The length of golden perch at 3 weeks of age showed that isotope immersion did not negatively affect early growth.

The comparison of large-scale sulphate aerosol models study (COSAM) compared the performance of atmospheric models with each other and observations. It involved: (i) design of a standard model experiment for the world wide web, (ii) 10 model simulations of the cycles of sulphur and 222Rn/210Pb conforming to the experimental design, (iii) assemblage of the best available observations of atmospheric SO= 4 , SO 2 and MSA and (iv) a workshop in Halifax, Canada to analyze model performance and future model development needs. The analysis presented in this paper and two companion papers by Roelofs, and Lohmann and co-workers examines the variance between models and observations, discusses the sources of that variance and suggests ways to improve models. Variations between models in the export of SO x from Europe or North America are not sufficient to explain an order of magnitude variation in spatial distributions of SO x downwind in the northern hemisphere. On average, models predicted surface level seasonal mean SO= 4 aerosol mixing ratios better (most within 20%) than SO 2 mixing ratios (over-prediction by factors of 2 or more . .   . 616 from the planetary boundary layer into the free troposphere in source regions is a major source of uncertainty in predicting the global distribution of SO= 4 aerosols in climate models today. For improvement, it is essential that globally coordinated research efforts continue to address emissions of all atmospheric species that affect the distribution and optical properties of ambient aerosols in models and that a global network of observations be established that will ultimately produce a world aerosol chemistry climatology.

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The present study was conducted to examine the effects of offering a single diet rationed to 80% (80% ME), 100% (100% ME), or 120% (120% ME) of recommended ME requirements from d 119 of gestation to lambing, with concurrent changes in other dietary nutrients. The effects on pre- and postpartum ewe performance, including estimated milk yield and milk fatty acid concentrations, were monitored. Sixty twin-bearing ewes were allocated to 1 of 3 dietary treatments ( = 20 per treatment) and individually fed for the final 4 wk of gestation. Metabolizable energy requirements were individually calculated for each ewe and amended according to treatment. Ewes were rationed daily on the basis of their treatment ME allocation, which led to concurrent alterations in other nutrient intakes. Diets were grass silage based and supplemented with concentrates to meet treatment ME allocation on an individual ewe basis. Ewes offered the 80% ME treatment had a lower liveweight ( = 0.04) and BCS ( = 0.03) at 24 h postpartum when compared with ewes offered the 120% ME diet. Although there was no difference in liveweight at either d 40 ( = 0.18) or 98 postpartum ( = 0.20), the difference in BCS persisted until d 40 postpartum ( = 0.02). Colostrum yield at 1 h postpartum ( = 0.03) and total yield up to 18 h postpartum ( = 0.04) was greater for ewes offered the 120% ME diet than either of the other treatment groups. Similarly, these ewes had a greater estimated milk yield during wk 3 of lactation ( = 0.04) and elevated concentrations of short-chain SFA ( = 0.02) and long-chain SFA ( ≤ 0.05) from wk 2 through 6 of lactation. In summary, the negative impact of applying a dietary insult to ewes in late gestation is reflected in colostrum and estimated milk yield and fatty acid composition, thus potentially influencing postpartum growth and development of the offspring.

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Lameness has a major negative impact on sheep production. The objective of this study was to 1) quantify the repeatability of sheep hoof temperatures estimated using infrared thermography (IRT); 2) determine the relationship between ambient temperature, sheep hoof temperature, and sheep hoof health status; and 3) validate the use of IRT to detect infection in sheep hooves. Three experiments (a repeatability, exploratory, and validation experiment) were conducted over 10 distinct nonconsecutive days. In the repeatability experiment, 30 replicate thermal images were captured from each of the front and back hooves of nine ewes on a single day. In the exploratory experiment, hoof lesion scores, locomotion scores, and hoof thermal images were recorded every day from the same cohort of 18 healthy ewes in addition to a group of lame ewes, which ranged from one to nine ewes on each day. Hoof lesion and locomotion scores were blindly recorded by three independent operators. In the validation experiment, all of the same procedures from the exploratory experiment were applied to a new cohort of 40 ewes across 2 d. The maximum and average temperature of each hoof was extracted from the thermal images. Repeatability of IRT measurements was assessed by partitioning the variance because of ewe and error using mixed models. The relationship between ambient temperature, hoof temperature, and hoof health status was quantified using mixed models. The percentage of hooves correctly classified as healthy (i.e., specificity) and infected (i.e., sensitivity) was calculated for a range of temperature thresholds. Results showed that a small-to-moderate proportion of the IRT-estimated temperature variability in a given hoof was due to error (1.6% to 20.7%). A large temperature difference (8.5 °C) between healthy and infected hooves was also detected. The maximum temperature of infected hooves was unaffected by ambient temperature (P > 0.05), whereas the temperature of healthy hooves was associated with ambient temperature. The best sensitivity (92%) and specificity (91%) results in the exploratory experiment were observed when infected hooves were defined as having a maximum hoof temperature ≥9 °C above the average of the five coldest hooves in the flock on that day. When the same threshold was applied to the validation dataset, a sensitivity of 77% and specificity of 78% was achieved, indicating that IRT could have the potential to detect infection in sheep hooves.