Airborne surface characterization

Single Particle Analysis and Surface Characterization of Airborne Particles... 

Airborne contaminant movement in the building depends upon the type of heat and contaminant sources, which can be classified as (1) buoyant (e.g., heat) sources, (2) nonbuoyant (diffusion) sources, and (d) dynamic sources.- With the first type of sources, contaminants move in the space primarily due to the heat energy as buoyant plumes over the heated surfaces. The second type of sources is characterized by cimtaminant diffusion in the room in all directions due to the concentration gradient in all directions (e.g., in the case of emission from painted surfaces). The emission rare in this case is significantly affected by the intensity of the ambient air turbulence and air velocity, dhe third type of sources is characterized by contaminant movement in the space with an air jet (e.g., linear jet over the tank with a push-pull ventilation), or particle flow (e.g., from a grinding wheel). In some cases, the above factors influencing contaminant distribution in the room are combined. 

Vaccaro, J.R. et al., The use of unique study design to estimate exposure of adults and children to surface and airborne chemicals, in Tichenor, B.A., Ed., Characterizing Sources of Indoor Air Pollution and Related Sink Effects, ASTM STP1287, American Society of Testing Materials, 1996, pp. 166-183. 

There are chemical reactions between the released contaminant and ambient air or surfaces. If the released contaminant reacts, any reacted material can no longer be considered airborne (although the reaction products may also be hazardous), and so chemical reactions effectively reduce the rate or amount of airborne contaminant. Some reactions can be characterized as dry or wet deposition. 

The use of a passive sampler is characterized by long sampling times, which are needed to allow the airborne compounds to enter the sampler and become trapped on the sorbent surface. Sampling times often exceed several days. The long sampling times show a pitfall of this sampling technique because the sampler is in contact with the air to be sampled for a long time, very volatile compounds may have the chance not only to enter the sampler, but also to leave it on the same way, if their interaction with the sorbent is low. In this case an underestimation of the very volatile substances can be expected. 

A passing cold front is heralded by clouds, a drop in temperature, and precipitation cooler air and clear skies occur behind the cold front (see Fig. 4-15b). The slower moving warm front is characterized by a more gradual lowering of cloud heights, followed by rain or snow (Fig. 4-15a). As air masses pass, so do their burdens of airborne chemicals. The clouds and precipitation formed along the front act as sinks for certain atmospheric chemicals because of rainout and washout processes. These processes, which remove particles, gases, and dissolved chemicals from the atmosphere and deposit them on Earth s surface, are discussed in Section 4.5. 

The airborne particles differ significantly not only in size but also in chemical composition, depending primarily on the sources of the particles. Desert and other bare lands are sources of dust particles which are primarily made of mineral oxides. Sea salt originated from sea spray consists mainly of sodium chloride. Soil tillage in agriculture produces dust particles characterizing the land surface. In contrast, urban dust is often rich in cement powder, tire scraps, car exhaust particulate. Soot particles generated from various combustion processes are essentially elemental carbon. Combustion also produces fly ash which is rich in oxides and contains toxic metals. 

Welding that may release metal fumes such as those of zinc that can cause a condition of metal fume fever characterized by elevated temperature and chills Painting and coating, especially in surface preparation where cleaning old surfaces may release airborne lead, chromium, or other toxic substances Waste handling that may expose workers to toxic waste materials... 

More accurate determination of reflective radiative surface emissivity The radiative emissivity of the composite surface, similarly to the heat transfer coefficient (4), is a function of the resin-char composition of the surface at any point during the combustion process, and is also affected by the surface profile and roughness. Hence it is not sufficient to use one value for this parameter in the model for the duration of the exposure event. However, characterizing the in-situ dynamic behavior of this parameter in a turbulent combustive atmosphere in the presence of soot, flame and airborne particles is a particularly challenging task, so that modelers may well be forced to rely on binary before/after shifts in the emissivity based on measurements made on the virgin resin-fiber composite and char-fiber residue respectively. 

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