Hydrochlorofluorocarbons (HCFCs) are human-made chemicals that have been used as temporary replacements for chlorofluorocarbons (CFCs) in refrigerants because they decompose more readily in the atmosphere and thus pose less of a threat to Earth’s protective ozone layer. Levels of HCFCs have been measured in the stratosphere, and the concentrations of many different HCFCs have been steadily increasing since the mid- to late 1990s. HCFCs were originally introduced as a solution to help phase out the use of CFCs . Which of the following most likely contributed to the increased levels of HCFCs in the stratosphere over the past 30 years?