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Biofuels are evolving in complex systems of interrelating environmental, economic and social issues. For this reason a number of sustainability criteria covering these issues have been developed. However, there has been little effort given to the development of a mechanism to evaluate compliance of biofuel systems with the sustainability criteria available. Grounded in the theoretical and practical insights from systems thinking and literature on indicator selection processes, this paper intends to extend the existing discussions on the sustainability of biofuels by providing a critical review of biofuels sustainability literature and providing a conceptual framework to guide thinking about measuring, monitoring and evaluating sustainability of biofuel systems. The paper focuses on the integration of social, economic and environmental issues to establish holistically the sustainability of biofuel systems. The paper established that monitoring and evaluation indicators should reflect: (i) all the processes involved in the life cycle of biofuels; (ii) interrelationships of subsystems and related impacts; (iii) different subsystem perspectives (economic, environmental, and social); and (iv) a process of continual learning, which facilitates improved functioning of the entire biofuel system.

Few panel studies have investigated the relationships between air pollutants and air spora and lung function change in asthmatic subjects. This article examines the association of outdoor air pollutant concentrations and air spora with the decrease in lung function (measured by morning peak expiratory flow) of two groups of asthmatic subjects in the subtropical environment of South East Queensland, Australia. Lung function responses were stratified by age, allergy status, and location, and seasonal effects were examined. Allergy status and age were found to be important, with air pollutants such as ozone and particles associated with decreases in lung function in allergic individuals older than 15 years. Fungal spore counts were strongly associated with a decrease in lung function in allergic adults, especially in those over 54 years, only in seasons when these air spora peak. Analysis for the entire study period indicates that the effect of ozone on peak expiratory flow in the allergic group can sometimes be confounded by air spora effects, indicating that in a subtropical climate the impact of ozone on asthma severity can be accurately estimated only when the confounding effects of air spora are included.