Reevaluating CFC-11 Emissions: Insights from the 3D GEOS-5 Model Analysis and the Recent NASA Aircraft Missions

As a result of successful regulation of the Montreal Protocol, atmospheric concentrations of the most important chlorofluorocarbon, CFCl₃ or CFC-11, has been declining at ~1.0%/yr [WMO, 2014]. Recent atmospheric observations from the ground-based networks suggest that the CFC-11 decline rate has slowed down significantly in 2015-2016. This slow-down in the global decline rate, together with an increase in the inter-hemispheric concentration gradient, points to likely increases in recent CFC-11 emissions. Strong episodic enhancements of CFC-11 above the background concentrations were observed during the recent NASA Korea-United States Air Quality (KORUS-AQ) and Atmospheric Tomography Mission (ATom) aircraft missions, confirming significant fresh emissions from the populated continents. We analyze these ground-based and airborne CFC-11 observations with the NASA GEOS-5 global chemistry model. Our analysis suggests that (i) global CFC-11 emissions have been decreasing steadily in the past two decades and increased again since 2013, and (ii) while emissions from developed countries have been much smaller than the inventory-based bottom-up estimates in the past two decades, emissions in developing countries, e.g., Article 5 and tropical countries, are much greater than the original inventory-based estimates from the Article 5 countries. These results imply that the emissions of CFC-11 from the past foam blowing uses into the atmosphere occur at a slower rate than originally expected, and the recent increases in CFC-11 emissions likely indicate illegal production and usages from the developing countries.