Use of Ozone Depleting Substances by Plastics Industry

Both ground-based and satellite measurements have unambiguously established that the stratospheric ozone concentrations have been slowly falling since the mid-1980s (see Appendix B for a discussion of Stratospheric Ozone Depletion). The ozone concentrations in the stratosphere are latitude dependent and the decline in concentrations is uneven. The Antarctic winter ozone hole (with about a 50% loss in ozone within it) in the 1990s is an extreme case of the depletion exacerbated by the polar meteorological features. A similar seasonal loss has been seen in the Arctic as well. In midlatitudes (25°N to 60°N) average total ozone was lower by 4-6% in the 1990s compared to 1980. While meteorological factors also contribute to the phenomenon of stratospheric ozone loss in midlatitudes, this depletion is believed to be mainly related to halogen-catalyzed photochemical destruction of ozone in the stratosphere.

The emission of CFCs into the atmosphere is believed to be primarily responsible for the occurrence of atmospheric chlorine. CFCs were used as physical blowing agents in the production of polyurethane and polystyrene foams used in building insulation applications and in aerosol spray cans. The excellent thermal insulation properties of the gas and its nonflammability made it a good candidate for these purposes. These gases diffuse out of the foam and into the environment over the years of product use or once the foam is destroyed. CFCs persist long enough in the environment37 to reach the stratosphere and once there interfere with the photochemical reactions responsible for maintaining the ozone layer (see Appendix B on Ozone Layer Depletion). The loss of stratospheric ozone directly affects the UV-B content of terrestrial sunlight. The increase in the terrestrial UV-B (290-315 nm) radiation has far-reaching effects on the biosphere. Adverse impacts of increased UV-B include threats to public health, loss of yield in key agricultural crops, and possible damage to aquatic ecosystems. (On the positive side, ozone depletion has a cooling effect on the stratosphere and can offset as much as 30% of the radiative forcing due to increased greenhouse gases).

The Montreal Protocol (1987) has restricted the production and use of several classes of ozone-depleting compounds (ODS) including the original suspect, the CFCs. In July of 1992, the EPA issued its final rule implementing section 604 of the Clean Air Act Amendments of 1990, which limit the production and consumption of ozone-depleting substances. The rule requires industry to reduce production of Class I ODSs and to phase them out completely by January 1, 2000

37 The fact that CFCs are denser than air does not result in their settling to ground level and away from the stratosphere. Such settling though possible in undisturbed masses of air will be short lived, and air currents will readily carry the CFCs into the stratosphere.

(2002 for methyl chloroform). The combined abundance of chlorine and bromine in the stratosphere is expected to peak out around the year 2000, and the rate of decline in ozone at midlatitudes is already apparent. Taking the anticipated reductions about in ODSs into account, the ozone layer is expected to undergo photochemical self-repair, reaching the pre-1980 levels by the about year 2050.

Ozone-Depleting Substances in Polymer Foams Expanded polystyrene and polyurethane foams are popularly used as insulation materials in the refrigeration industry as well as in the building industry. Polyurethane foams are also used as floatation aids in marine vessels. These applications typically use polyisocya-nurate board stock (PIR), expanded polystyrene (XPS), and sprayed polyurethane foam (PU-S). Because of the demand for low thermal conductivity, CFC-11 and CFC-12 (mostly in XPS) was used in these foam applications. In 1988-1999, the use of CFCs in foam blowing was at an all-time high, about 200,000 Mt globally. Post-Montreal Protocol manufacturing relies on less polluting substitutes in place of these ODSs. Nearly all of the CFC blowing agents has now been replaced with HCFCs. In the transitional period following the 1995 restrictions on ODSs, HCFC 141b and HCFC 142b, with somewhat similar insulating potentials might be used. But the international agreements ultimately require the use of non-ODS blowing agents in these applications (e.g., CO2, cyclopentanes, and certain HFCs; see Table 1.4).

A U.S. EPA study in 1993 estimated the U.S. production of flexible polyurethane foam slabstock at 600,000 tons. The 25 companies that manufactured foam at the time were estimated to emit 15,000 tons of methylene chloride (CH2Cl2) into the atmosphere. This amounted to 10% of the total emission of this hazardous air pollutant (HAP) into the air nationwide. The volatile emissions from the industry (estimated by industry sources in 1992) is summarized in Table 1.5 (note: no process water is used in flexible polyurethane manufacture, so only air emissions are considered.)

A majority of (HAPs) release is from the use of methylene chloride (or methyl chloroform) as an auxiliary blowing agent (ABA) in the manufacture of foam. These compounds were used for that purpose long before the popular CFC-11 chlorofluorocarbon was phased out. The primary foaming agent in polyurethane is CO2 formed in the reaction between isocyanate and water. Auxiliary blowing agents mixed in with the reactants vaporize during the exothermic reaction of

Table 1.4 Common Classes of ODSs and Their Chemical Composition

Class

Chemical Name

Atoms

Example

Was this article helpful?

0 0
Building Your Own Greenhouse

Building Your Own Greenhouse

You Might Just End Up Spending More Time In Planning Your Greenhouse Than Your Home Don’t Blame Us If Your Wife Gets Mad. Don't Be A Conventional Greenhouse Dreamer! Come Out Of The Mould, Build Your Own And Let Your Greenhouse Give A Better Yield Than Any Other In Town! Discover How You Can Start Your Own Greenhouse With Healthier Plants… Anytime Of The Year!

Get My Free Ebook


Post a comment