WHAT IS OZONE?

Ozone is a gas that forms in the atmosphere when three atoms of oxygen are combined (O₃). It is not emitted directly into the air, but at ground level is created by a chemical reaction between oxides of nitrogen (NO_X), and volatile organic compounds (VOC) in the presence of sunlight. Ozone occurs in two layers in the atmosphere. The layer surrounding the Earth is the troposphere which extends to a level of about ten miles up, where it meets the second layer, the stratosphere. Tropospheric ozone is not desired because of several harmful effects on health, vegetation, and many common materials. However, stratospheric ozone is helpful in protecting life on Earth from the sun's harmful ultraviolet rays (UV-b).

STAGE I VAPOR RECOVERY SYSTEMS:

Stage I Vapor Recovery is used during the refueling of underground gasoline storage tanks found wherever gasoline is dispensed (for example: gas stations). Hydrocarbon vapors in the tank are displaced by the incoming gasoline and then routed through a hose into the cargo tanker instead of being vented into the atmosphere. The truck then takes the vapors back to the bulk terminal where they are either recovered or destroyed. This is all done in an attempt to reduce hydrocarbon emissions.

One type of Stage I Vapor Recovery is dual point. This system utilizes two openings, one to deliver the fuel, and the other to remove the vapor from the tank. Dual point systems are designed as either TOP or BOTTOM filling.

The second type of Stage I Vapor Recovery is the COAXIAL system. It requires only one opening from the tank. The system utilizes two tubes, one inside the other. The inner tube delivers the fuel while the vapor is removed through the outer tube.

STAGE II VAPOR RECOVERY SYSTEMS:

The purpose of the Stage II Vapor Recovery System is to capture vapors emitted as vehicles are being refueled. These systems contain special nozzle spouts that are used to collect the vapors, which are returned through the nozzle and hose back into the underground gasoline storage tank. Estimated cost for the fitting of nozzles for Stage II Vapor Recovery is approximately five hundred dollars per nozzle.

According to the EPA, properly maintained Stage II Vapor Recovery Systems reduce refueling vapors by approximately forty-one percent. These systems undergo rigorous tests including maintenance of: Air to Liquid Volume Ratio, Pressure Decay, and Dynamic Back-Pressure (Blockage). Diagrams of these three procedures follow. The first is the Air to Liquid Volume Ratio test. This test is straight-forward, it measures the ratio of air to liquid in the fuel. The second diagram shows the Pressure Decay test. This test procedure is used to quantify the tightness of Vapor Recovery systems installed at any gasoline dispensing facility equipped with pressure/vacuum (P/V) valves. The third diagram is of the Dynamic Back-Pressure test. This test procedure is used to quantify the Dynamic Pressure (Back-Pressure) in the vapor path leading from the dispensing nozzle to the storage tank.

PRESSURE DECAY

DYNAMIC BACK- PRESSURE Courtesy of http://mtinternational.com/solu2.htm

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EFFECTIVENESS OF VAPOR RECOVERY SYSTEMS

The following calculations are based on an annual throughput of one million gallons and include emissions from underground storage tank filling and vehicle refueling operations. Refueling emissions for Spokane County, Washington were used as a basis for the entire United States. These records were scaled up according to population to predict the annual national refueling emissions.

• Total U.S. Emissions (without any recovery system):
• 16,028,105 lb/yr
• Emissions with Stage I Recovery:
• 8,655,177 lb/yr
• Emissions with Stage II Recovery:
• 9,616,863 lb/yr
• Emissions with Stage I and Stage II Recovery:
• 2,243,934 lb/yr

Facilities' total Volatile Organic Compound (VOC) emissions were reduced by 46% with Stage I Vapor Recovery Systems, 41% with Stage II Vapor Recovery Systems, and 87% with Stage I and Stage II.

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BENEFITS OF VAPOR RECOVERY SYSTEMS

Vapor Recovery Systems help to minimize the production of O₃ precursors, and in doing so, reduce the concentration of tropospheric ozone. This is beneficial since tropospheric ozone:

• Attacks cells and breaks down tissues
• Interferes with the ability of plants to produce and store food causing damage to crops, forests, and makes plants more susceptible to disease, insects, other pollutants, and harsh weather.
• Triggers a variety of human health problems such as nausea, chest pain, difficulty breathing, increased incidence of bronchitis, pneumonia, and lung damage

A second benefit of vapor recovery is the reduction of human exposure to gasoline fumes. These fumes contain over 150 chemicals, including benzene (very dangerous). Depending on the amount of gasoline fumes inhaled, and the sensitivity of the individual, gasoline can:

• Irritate the lungs
• Depress the central nervous system
• Cause dizziness and headaches

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REFERENCES

http://www.epa/gov/oar/oaqps/gooduphigh/#goodbad

http://www.daq.state.nc-us/offices/Technical/Mobile/Vapor/

http://www.deq.co.pima.az.us/airinfo/stage2/stge2faq.html

http://www.scapca.org/gas.html

http://www.census.gov/population/www/estimates/popest.html

http://www.ideo.columbia.edu/~psguest/eda/ozone_/ecl.html

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SITES THAT RELATE TO THIS STUFF

http://airq.ci.el-paso.tx.us/stageii4.htm

http://patent.womplex.ibm.com/details?patent_number=5345979

http://www.arb.ca.gov

http://www.deq.state.la.us/oarp/o3stage2.htm

http://www.dnr.state.mo.us/deq/apcp/stage1.htm#Quest

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Last Updated 12/10/99