No abstract

There is a growing recognition of the risks to health, fire hazard, and air quality from cooking emissions. Recent research has identified what is emitted when foods are cooked. Some of the emitted mass is captured in the exhaust system. The balance is expelled into the atmosphere. The outlet of the exhaust system is a demarcation point-upstream the captured mass is the operator or building owner's concern, whereas downstream into the atmosphere, it affects air quality. Building codes have long required operators to deal with the upstream section. More recently, regulations are being placed on what kitchens can emit to the atmosphere. The industry is responding to this challenge with product innovations. Recently gained understanding of cooking emissions supports much of the innovation-but not all. This paper evaluates the purported benefit of adding better filtration and ultraviolet C (UVC) bulbs in kitchen hoods. A "UV hood" claims a two-step process to reduce emissions: better filters capture more emitted mass, and UVC photons and ozone drive photo-decomposition and oxidation reactions of some of the remaining greasy constituents. Adding UV to a hood at least doubles the cost compared to an equivalent non-UV hood. There is evidence that UV hoods do reduce some emissions. The essential question is whether improved performance is due to UV or relatively inexpensive, improved filters. Experimentation exposed an oleic acid aerosol, representative of cooking emissions, to UVC energy and ozone at higher concentrations and for longer exposure times than can occur in a UV hood. Particle-size and chemical changes were measured on samples collected with UV bulbs off and on. Results strongly indicate little change is happening and most emission reductions are caused by better filtration and not UV. The conclusion is that UV hoods fall short of claimed performance, and unreacted ozone may increase air pollution.

No abstract

The enthalpy of lnteractlon between test solutes and swollen polystyrene has been measured for toluene and tetrahydrofuran (THF) moblle phases. All solutes thermodynarnlcally prefer the statlonary phase when toluene Is the mobile phase, and pure slze-exciusion chromatography (SEC) never occurs. This surprislng result contradicts the "iike~issolves-like" approach to choosing moblie phase systems for size-excluslon chromatography. Tetrahydrofuran functions well for SEC, probably due to hydrogen-bonding effects In the mobile phase. However, nitromethane prefers the statlonary phase in this system. As wlth earlier work uslng a chloroform mobile phase, a deuterated moblie phase ylelds van't Hoff plots wlth nonzero slopes. The enthalplc contrlbutlon to retention Is different for each of the three mobile phases.The polystyrene-divinylbenzene (PS-DVB) gels are undergoing a period of renewed interest as alternative stationary phases to silica. These materials offer several advantages, including chemical stability and utility for a much wider spectrum of mobile phases than silica. The PS-DVB gels may be used as stationary phases for either normal-phase, reversed-phase, or size-exclusion chromatography (SEC).The latter application represents the traditional use for PS-DVB gels and has received considerable attention. This is supported by the amount of material devoted to gel stationary phases in recent monographs (1,2). However, a clear understanding of the total separation mechanism has yet to be elucidated. In addition to the conventional size-exclusion effects, other interactions such as adsorption or partitioning have been proposed, but only empirical information is available.Much of the attention has centered around the solventswollen gels. The use of "good" solvents should produce liquid chromatography systems where SEC is the dominating mechanism. We recently reported a study of the good solvent chloroform (3), where it was shown that the system separated most solutes by SEC. However, phenols and carboxylic acids interacted with the PS-DVB stationary phase, as evidenced by nonzero slopes from van't Hoff plots. Furthermore, the magnitude of the interaction between chloroform and the gel represented the threshold interaction energy necessary for a solute to interact with the gel.We report here an extension of this thermodynamic investigation to two other good solvents, toluene and tetrahydrofuran. Nonexclusion (enthalpic) effects are identified from the slope of van't Hoff plots, according to the equation (4)Ink=---.-+ --l n P z [is ]

No abstract