## 2 Materials and Methods
### Environmental Assessment Using the Waste Reduction Algorithm (WAR)
#### 2.2.2 Atmospheric Impact Categories  
Global Warning Potential (GWP) is determined by comparing the extent to which a unit mass of a chemical absorbs infrared radiation over its atmospheric lifetime to the extent that CO2 absorbs infrared radiation over its respective lifetimes [17]:  
\[GWP=\frac{\int_{0}^{t}a_{c}i_{i}(t)dt}{\int_{0}^{t}a_{CO_{2}}c_{CO_{2}}(t)dt}m_ {i} \tag{5}\]  
where \(a_{i}\) and \(a_{CO_{2}}\) are the radiation heat absorption per unit of greenhouse gas \(i\) and per unit of carbon dioxide; \(c_{i}(t)\) and \(c_{CO_{2}}(t)\) is the greenhouse gas \(i\) concentration and the carbon dioxide concentration in a time t after being released; \(t\) is the number of years over which GWP will be evaluated; and \(m_{i}\) is the mass (kg) of the emitted gas. Ozone Depletion Potential (ODP) is determined by comparing the rate at which a unit mass of chemical reacts with ozone to form molecular oxygen to the rate at which a unit mass of CFC-11 (trichlorofluoromethane) reacts with ozone to form molecular oxygen [17]:  
\[ODP=\frac{\delta[O_{3}]_{i}}{\delta[O_{3}]FCKW-11}m_{i} \tag{6}\]  
where \(\delta[O_{3}]_{i}\) and \(\delta[O_{3}]FCKW-11\) refers to the depletion of global ozone produced by a gas \(i\) and CFC-11 unit; and \(m_{i}\) is the mass (kg) of the emitted gas. Photochemical Oxidation Potential (PCOP) is determined by comparing the rate at which a unit mass of chemical reacts with a hydroxyl radical (OH-) to the rate at which a unit mass of ethylene reacts with OH- [17]:  
\[PCOP=\frac{\frac{a_{i}}{b_{i}(t)}}{\frac{a_{C_{2}H_{4}}}{b_{C_{2}H_{4}}(t)}m_ {i}} \tag{7}\]  
where \(a_{i}\) and \(a_{C_{2}H_{4}}\) is the change in ozone concentration due to the change in a volatile organic compound emission and due to the change in ethylene emission; \(b_{i}(t)\) and \(b_{C_{2}H_{4}}(t)\) is the integrated emission of a volatile organic compound \(i\) up to a time t and the integrated emission of ethylene at the same time; and \(m_{i}\) is the mass (kg) of the emitted gas. Acidification Potential (AP) is determined by comparing the rate of release of H\({}^{+}\) in the atmosphere as promoted by a chemical to the rate of release of H\({}^{+}\) in the atmosphere as promoted by SO2 [17]:  
\[AP=\frac{\frac{V_{i}}{M_{i}}}{\frac{V_{SO_{2}}}{M_{SO_{2}}}}m_{i} \tag{8}\]  
where \(V_{i}\) and \(V_{SO_{2}}\) are the acidification potential of component \(i\) and SO\({}_{2}\); \(M_{i}\) and \(M_{SO_{2}}\) is the mass unit of substance \(i\) and SO\({}_{2}\); and \(m_{i}\) is the mass (kg) of the emitted substance \(i\). The WAR algorithm relates the PEI to the flow of an environmental impact across the boundaries of the system as a consequence of the mass and energy that crosses these limits. This algorithm handles two types of indices to assess the environmental impact of a chemical industry. The first class measures the PEI emitted by the process and the other class measures the PEI generated. Within each class, two indices are defined: total output impact indices expressed as the impact potential per unit of time and impact indices per product mass. The main objective of the PEI output is to assess the external environmental efficiency of the process, that is, the capacity of the process to obtain final products at a minimum discharge potential. Regarding the PEI generated, the most important thing is to know the internal environmental efficiency of the process. The total output rate of PEI is calculated using Equation (9); the total mass output rate is calculated by Equation (10); the total generation rate is calculated by Equation (11); and the total mass generation rate is calculated using Equation (12).