Exam Question

(a) Ozone Depleting Substances (ODS) are gases that, upon release into the atmosphere and reaching the stratosphere, interact with and destroy ozone molecules. The ozone layer is crucial for filtering harmful ultraviolet (UV) radiation from the sun, protecting life on Earth. Different ODS have varying capacities for ozone depletion. Ozone Depleting Potential (ODP) quantifies this relative depletion. ODP is calculated as the ratio of ozone depletion caused by a unit mass of a given gas to that caused by the same mass of CFC-11 (which has an ODP of 1). Conventional refrigerants, such as CFCs (chlorofluorocarbons) and some HCFCs (hydrochlorofluorocarbons), possess significant ODP values, meaning they substantially contribute to ozone layer damage. For example, while a gas like HCFC-22 has a lower ODP (0.05) compared to CFC-11 (1.0), it still contributes to ozone depletion, albeit to a lesser extent. The long atmospheric lifetime of these molecules (100-400 years) exacerbates their impact
(b) Alternative refrigerant gases with zero ODP are now available and used onboard vessels. These include:
R-134a: Suitable for medium and high-temperature applications, serving as a long-term replacement for R-12.
R-404A: Suitable for low and medium-temperature applications.