USA emissions estimates of CH3CHF2, CH2FCF3, CH3CF3 and CH2F2 based on in situ observations at Mace Head

We investigate the low level, surface-to-surface transport of five hydrofluorocarbons (HFC-152a, -134a, -143a, -125 and -32) from North America to the Advanced Global Atmospheric Gases Experiment (AGAGE) observing station at Mace Head, Ireland during 2005–2012. Using the UK Meteorological Office Numerical Atmospheric dispersion Modelling Environment (NAME) we select air masses, which are dominated by direct transport from the North American continent to Mace Head, thereby eliminating any significant influence from local or other regional sources. To estimate emissions of individual HFCs we use the interspecies correlation method with HFC-125 as the reference compound. We then compare these derived North American emissions with those reported to UNFCCC. Our results indicate an under-reporting of HFC-152a emissions by the USA to the UNFCCC, with an annual average difference of 24 Gg (9–36 Gg). For HFC-134a our estimated emissions indicate an over-reporting of USA reported emissions by 24 Gg (21–28 Gg). For HFC-143a USA reported emissions are lower than our estimates by 1.8 Gg (1–3.5 Gg); whereas for HFC-32 there is close agreement, within the uncertainties, between the USA emissions reported to UNFCCC and our emissions estimates. Combining our USA emissions estimates for HFC-152a, HFC-134a, HFC-143a and HFC-32 with the UNFCCC estimate for HFC-125 could contribute potentially 201 ± 36 Tg-CO2 eq yr−1 to atmospheric radiative forcing in 2011–2012. This compares with UNFCCC of 146 Tg-CO2 eq yr−1 for the same five HFCs.