Combustion Aerosols: Factors Governing Their Size and Composition and Implications to Human Health

Nearly a decade of epidemiologic research has indicated that exposure to elevated concentrations of ambient particulate matter less than 2.5 µm in size (PM 2.5 ) can adversely impact human health.Despite this, plausible mechanistic pathways remain poorly understood.This limited understanding stems in part from the complexity of the PM itself.Although epidemiologic studies often treat PM 2.5 as a single entity, in reality, it is broadly distributed in particle size, particle morphology, and particle composition.All of these factors may plausibly influence the interaction of the particles with the human airway.In the Critical Review by Lighty, Veranth, and Sarofim, the authors provide a comprehensive review of these complexities associated with PM 2.5 .In their paper, PM 2.5 formation in combustion systems, measurement methods for PM 2.5 , and exposure studies associated with PM 2.5 are all discussed in an interrelated fashion.The synthesis of these three topics in one comprehensive review makes this paper a valuable resource for researchers in the field.The emphasis on following particles through their entire history, from formation to emissions and ultimately deposition and health effects, also makes this review particularly useful for researchers in one community seeking to understand the governing phenomena in another.One particularly valuable aspect of the review is the discussion of particle formation in combustion systems from a fundamental perspective, followed by more detailed discussions addressing phenomena specific to individual fuels or combustion devices.This discussion is useful for its identification of the factors that remain poorly characterized and in need of additional study.For example, the authors present a stark contrast between the relatively well-characterized emissions of coal-fired utility plants and the poorly characterized emissions of domestic biomass combustion.Their comments suggest that coupling epidemiologic studies in regions burning diverse fuels with detailed particle size and composition distribution measurements would be quite useful in understanding the importance of particle size and composition on PM 2.5 -induced health effects.