This paper summarizes and synthesizes the collective results that emerged from the series of papers published in this issue of J-NABS, and places these results in the context of previously published literature describing variation in aquatic biota at landscape spatial scales. Classifications based on landscape spatial scales are used or are being evaluated for use in several countries for aquatic bioassessment programs. Evaluation of the strength of classification of different approaches should provide insight for refinement of existing bioassessment programs and expedite the development of new programs. The papers in this series specifically addressed the degree to which descriptions and classification of landscape features allow us to account for, and thus predict, variation in the composition of biota among individual sites. In general, we found that although landscape classifications accounted for more biotic variation than would be expected by chance, the amount of variation related to landscape features was not large. Thus, large-scale regionalizations, if used alone to specify expected biotic conditions, will likely have limited use in aquatic bioassesments, where it is critical to specify expected conditions as accurately and precisely as possible. Landscape classifications can play an important additional role, however, by providing an initial stratification of site locations to ensure that different landscape features are adequately represented in a sampling program. In general, we believe a tiered classification based on both reach-level and larger-scale landscape features is needed to accurately predict the composition of freshwater fauna. One potential approach entails use of landscape classifications as a means of refining or augmenting classifications based on local habitat features, which appear to account for substantially more biotic variation than larger-scale environmental features. These results have significant implications for how assessment and monitoring programs at local, state/province, and national levels should be designed.

[1] The temporal and spatial variations of ozone (O 3 ) in polluted continental outflow over the North Atlantic were investigated during the International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) field campaign in July-August 2004. Our analysis utilized measurements of O 3 from three smart balloons traveling at 0.5-3 km altitude in combination with simulations using the MM5/SMOKE/CMAQ air quality modeling system. Model results for over and within 300 km off North America were corroborated by comparison to a suite of measurements from ground stations, ozonesondes, and the NOAA ship Ronald H. Brown cruising in the Gulf of Maine. A prominent feature of the O 3 distribution was the high mixing ratios over the North Atlantic, reaching a peak value of 171 ppbv, compared to the northeastern United States (<$100 ppbv). The enhanced O 3 levels over ocean, mostly observed at night, appeared to be the result of four factors: (1) a supply of precursors in prevailing flow off the polluted U.S. east coast, (2) significant daytime in situ chemical production, (3) minimal depositional loss to the ocean at the balloon altitudes, and (4) small nighttime chemical loss. An important implication is that quantification of O 3 export from the United States must include estimation of downwind chemical processing in polluted air masses. Balloons 3 and 4 were launched within 18 hours of each other, and their tracks allowed examination of horizontal gradients in O 3 across distances varying from 200 to 400 km. In air masses influenced by recent outflow (<2 days) the O 3 gradient was À0.2 to 0.2 ppbv km À1 , while by distant source regions (>2 days) it exhibited only À0.05-0.05 ppbv km À1 . These same two balloons encountered Hurricane Alex at different times, but both measured O 3 mixing ratios >100 ppbv. Our model results show clearly that polluted air from the mid-Atlantic states was channeled directly into Alex's inflow region. Overall, variations in O 3 on timescales of tens of minutes to hours are attributed to its highly heterogeneous distribution in urban plumes, with variations over hours to days caused by changing source regions related to cyclonic activity.

The history of constant‐level balloons as observational platforms for atmospheric research is reviewed. Recent experience in using simple tetroons with Global Positioning System transponders for long‐range tracking during the Atlantic Stratocumulus Transition Experiment (ASTEX) is presented, along with an overview of the results of the ASTEX/Marine Aerosol and Gas Exchange Lagrangian strategy experiments. Progress in balloon materials and tracking capabilities is discussed, and a design is presented for an economical, lightweight “smart balloon” for use in future Lagrangian strategy, atmospheric chemistry experiments.

One of the primary aims of the North Atlantic regional Aerosol Characterisation Experiment (ACE-2) was to quantify the physical and chemical processes affecting the evolution of the major aerosol types over the North Atlantic. The best, practical way of doing this is in a Lagrangian framework where a parcel of air is sampled over several tens of hours and its physical and chemical properties are intensively measured. During the intensive observational phase of ACE-2, between 15 June 1997 and 24 July 1997, 3 cloudy Lagrangian experiments and 3 cloud-free, Lagrangian experiments were undertaken between the south west tip of the Iberian Peninsula and the Canary Islands. This paper gives an overview of the aims and logistics of all of the Lagrangian experiments and compares and contrasts them to provide a framework for the more focused Lagrangian papers in this issue and future process modelling studies and parametrisation development. The characteristics of the cloudy Lagrangian experiments were remarkably different, enabling a wide range of different physical and chemical processes to be studied. In the 1st Lagrangian, a clean maritime air mass was sampled in which salt particle production, due to increased wind speed, dominated the change in the accumulation mode concentrations. In the 2nd Lagrangian, extensive cloud cover resulted in cloud processing of the aerosol in a polluted air mass, and entrainment of air from the free troposphere influenced the overall decrease in aerosol concentrations in the marine boundary layer (MBL). Very little change in aerosol characteristics was measured in the 3rd Lagrangian, where the pollution in the MBL was continually being topped up by entraining air from a residual continental boundary layer (CBL) above. From the analysis of all the Lagrangian experiments, it has been possible to formulate, and present here, a generalised description of a European continental outbreak of pollution over the sub-tropical North Atlantic.

This paper provides an overview of the trials and successes in the development of an autonomous balloon instrument platform (smart balloon) and reviews scientific insights gained through its employment as a marker in a Lagrangian strategy during recent field experiments. The smart balloons are designed and constructed at the National Oceanic and Atmospheric Administration Air Resources Laboratory Field Research Division in collaboration with the University of Hawaii. In a 2004 field deployment a smart balloon carrying a miniature ozone sensor successfully crossed the Atlantic Ocean from Long Island, New York, to the African coast of Morocco. Significant progress has been made through field experiments such as this in our understanding of the relationships between the evolution of marine boundary layers and the chemistry of aerosol and gaseous constituents in clean and polluted air masses. Innovation in design and advances in instrument and communication technology have opened a dramatic new range of applications for the smart balloon in atmospheric research, including, for example, the interesting prospect of making observations very near the ocean surface in hurricanes and typhoons, which are not possible with research aircraft.