14.10.2013

Quantitative Analysis of Odors and Pollutants

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Industrial facilities, power stations, vehicles with internal combustion engines and a whole range of other human activities can all cause emissions of air pollutants. Taken together, different industrial sectors produce a broad array of pollutants. Examples include metals, volatile organic compounds (VOC) such as aldehydes and ketones, dioxins and furans, volatile inorganic materials such as ammonia, hydrochloric acid, carbon monoxide carbon, and particulate pollution. The term "pollution" reflects the fact that these agents are harmful, to some degree, to living things. Human exposure to polluted air can compromise health. Certain populations—such as children, the elderly, and asthma sufferers—are at greater risk than others.

Gases emitted from various sources might also produce various odors. Odor might also be defined as air/environmental pollution and a nuisance. It can impair the quality of people's lives, affecting their health and the value of their property.

Minute amounts or only a brief presence of pollutants in the air may be all it takes for air pollution and odor nuisances to occur. Such nuisances may be further compounded due to reactions between substances in midair. As a result, discovering these materials using chemical or physical analytical methods can be quite expensive and sometimes impossible.

In order to analyze the amount of odors and pollutants in the air, the relevant processes and emission sources must first be identified. Pollution sources are divided into centralized sources—vents, chimneys and stalks and non-centralized sources— sewage ponds, piles, open piles, etc.

     pollution dispersion               smell sample

The next step is to identify the types of air pollutants and odor substances that might be emitted into the air as a result of the manufacturing processes. These depend on the types of processes and materials used.

Once the identification of pollutants that may be emitted into the air is completed, the air emissions need to be sampled. This is done by collecting the air emitted from each emission source using appropriate sampling equipment that measures the concentration of the gases.

Due to the difficulty in defining odor quantitatively and in setting standards for determining what constitutes reasonable or unreasonable odor, criteria are needed that will enable those in charge to decide the existence of an odor hazard in order to handle smell-related complaints as well as odor problems that may arise in future installations. Thus, in addition to checking the concentration of known odorous materials in the air, smell tests are sometimes carried out by a smelling team on site, namely a group of people trained to identify smells and determine their characteristics. Alternatively, samples can be sent to an olfactrometric lab, where a team of smellers can analyze diluted samples at varying concentrations to assess the smell-detection threshold.

After sampling the emitted gases at the source, their environmental impact is analyzed and assessed using a pollutant dispersion model. Several models are used to predict dispersion of pollutants in the environment. One such model is the AERMOD- Gaussian plume model, which is used in the U.S. and Europe and is likewise recognized and recommended by the Ministry of Environmental Protection in Israel.
The data entered into the model are: the characteristics of emission sources (size, height, and flow rates), the type and concentration of the gases, meteorological and geographic data in the contaminating site and its surroundings.

After entering the required input data, an area is selected—a certain radius around the site—within which the pollutant dispersal is to be examined. A network of receptors is set up within this radius, a receptor is a point at which the model calculates the concentration of pollutants over time. The receptors network is generally denser closer to the site, where the highest concentrations are expected, as well as in areas of special importance such as populated areas, nature reserves and other points of interest.

Once the setup is complete, the model can be run to work out the dispersion of pollutants in the network defined around the site over time. Results are available numerically or graphically.

The final step in the process of environmental impact assessment is the analysis of the results:
• Which receptor points around the site will the pollutants reach, and at what level of odor concentration?
• Where is the maximum concentration of each contaminant recorded, and what is its value?
• What are the maximum and average concentrations at each one of the network receptors?
• Do the values obtained exceed the standards required by the Ministry of Environmental Protection?
• What steps can be taken at the source to minimize excessive contamination?

Summary-
The process of modeling/sampling and performing quantitative analysis of odors and pollutants provides a comprehensive picture of the environmental impact of different emission sites in both present and future circumstances, taking into account various data and the contribution of nearby emission sites. Understanding the impact of different emission sources is of great importance, both because of the growing awareness of the impact of human activity on both the local and global environment, and in light of the need to meet appropriate standards as set by the authorities.
 

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