research

Does waterpipe smoke contain significant toxicants? To what extent are these absorbed by the user? Is waterpipe smoke biologically active? Does inhaling it lead to immediate measureable health consequences? Does smoking a waterpipe lead to addiction? Is second-hand waterpipe smoke hazardous? Should waterpipe smoking be exempted from public smoking bans?

Over the past decade, investigators at the Aerosol Lab have been working to elucidate the potential health consequences of smoking the narghile waterpipe (aka shisha, hookah), a centuries-old but little-studied tobacco use method prevalent in Southwest Asia and North Africa, and increasingly around the world. Through analytical, biological, and clinical investigations with our collaborators, we are learning what toxicants first-hand and second-hand waterpipe smokers inhale, the degree to which some of these toxicants are absorbed in the body (i.e. appear in blood and urine), and resulting acute physiological (e.g. heart rate variability, lung function) and subjective effects (e.g. desire to smoke). We are also studying the ability of waterpipe smoke to disrupt lifecycles and induce inflammatory responses in human cells, as well as effects of smoke exposure on animals. This multi-pronged approach is driven by a central goal of gathering converging lines of evidence that are needed to inform tobacco control policy. It will also inform design of long-term epidemiological studies of health outcomes, and make known to consumers potential hazards of waterpipe smoking.

In the course of conducting these investigations, we have developed several unique instruments including those used to measure waterpipe puff topography (the way people puff) and to automatically sample smoke from waterpipes when used in cafés and homes. We also developed a smoking robot that replicates human puffing behavior in detail resolved to 100 ms for chemical and biological assays in the laboratory, and an artificial-lung waterpipe smoking machine to study second-hand smoke from the waterpipe and its user. Some of these instruments are also being used by our collaborators at the Clinical Behavioral Pharmacology Lab at Virginia Commonwealth University, the Syrian Center for Tobacco Studies, Jordan University of Science and Technology, and other investigators in Europe and North America. We also developed the Beirut Method, a protocol for waterpipe smoking machine testing of waterpipe tobacco products which was validated against inhaled toxicant doses measured in waterpipe users in cafés.

Our work has been critical for informing public health and regulatory responses to the growing worldwide epidemic of waterpipe tobacco smoking, and is widely cited in the literature. The Aerosol Lab regularly advises international and local agencies on the health effects and applicability of tobacco control regulations to waterpipe tobacco smoking.

Current funding: US National Cancer Institute, R01 CA120142, R01 DA025659

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It has been widely recognized that regional air pollution models generally under-predict formation of aerosol particles in the atmosphere by a large margin, thereby hampering efforts to evaluate policy options aimed at improving air quality. One reason for this discrepancy is thought to be the poor state of knowledge regarding semi-volatile species that are important in atmospheric particle formation, a gap stemming from challenges of accurately measuring the vapor pressure and the molecular accommodation/evaporation coefficient of complex, time-varying, low vapor pressure materials.

In partnership with the Khlystov Aerosol Research Lab at Duke University we have developed from first principles thermodenuder-based methods (IV-TDMA and Equilibration Profile) to measure these properties in the lab. Our key methodological contribution to this field has been to experimentally decouple overlapping thermodynamic and kinetic constraints on particle evaporation. By doing so, we have been able to report first determinations of evaporation coefficient for a number of organic compounds and mixtures relevant to atmospheric air pollution, and have revised previously reported values of their vapor pressures. We have also reported first determinations of the effective evaporation coefficient of concentrated atmospheric particles sampled in Beirut in the summer of 2010. The data showed that these are of the order 10-1, indicating that ambient aerosol may be significantly more volatile than previously estimated from field measurements made under the assumption that the coefficient is unity. This difference would, at least in part, account for “missing aerosol” in ambient pollution models.

Using computational and experimental means we have also studied the problem of growth and evaporation of hygroscopic aerosol particles in bounded flows with wall heat and mass transfer, a problem fundamental to predicting the fraction and location inhaled particles deposit in the human respiratory system. This is relevant to understanding health effects of inhaled pollutants and to designing respiratory drug delivery devices.

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We have been active in a number of projects aimed at assessing urban air quality and human exposure to airborne particle pollutants. One ongoing project, funded by the Issam Fares Institute for Public Policy and International Affairs, focuses on assessing the role of diesel generators in human exposure to airborne carcinogens in Beirut. To compensate for electric power production shortages by the national provider, privately-owned diesel generator sets have become ubiquitous in Lebanon over the past decade. Even in dense urban areas it is common for every residential and commercial building to have its own generator. But, given the high background pollution levels here, do these generators actually represent a significant additional burden of inhaled toxicants? We have been measuring time-resolved particle-bound PAH concentrations on balconies of households in Beirut, and correlating these with the operating state of the nearest generator to estimate the added exposure due to generator operation. Measurements are analyzed using a Lagrangian particle dispersion model.

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