Global Methyl Halide Emissions From Rapeseed (Brassica napus) Using Life Cycle Measurements

Global budgets of methyl halides are not balanced between currently identified sources and sinks. Among biological sources, rapeseed is regarded as the second largest terrestrial source of CH₃Br, extrapolated from laboratory-based incubations and limited field measurements. This study analyzes the CH₃Br budget from rapeseed (Brassica napus “Empire”), using field-based life cycle measurements, yielding a globally scaled emission rate of 2.8 ± 0.7 Gg year⁻¹. Though this verifies that rapeseed is a significant global source, it is just half of the previous estimation, even after accounting for the doubling of global annual rapeseed production since then. The ozone-depleting potential of rapeseed is further sustained through CH₃Cl and CH₃I emissions, which were measured for the first time and scaled to 5.3 ± 1.3 and 4.0 ± 0.8 Gg year⁻¹ globally.