Emissions of anthropogenic hydrogen to the atmosphere during the potential transition to an increasingly H2-intensive economy

In this study, current and future anthropogenic hydrogen (H2) emissions to the atmosphere from technological processes are assessed. Current emissions are dominated by the direct exhaust gas of road-based motor vehicles and losses during the industrial production of H2 from fossil-fuels. H2 emissions from transportation are estimated at 4.5 Tg for 2010. An additional ∼0.5–2 Tg H2 are estimated to be lost to the atmosphere from industrial processes in 2010. In 2020, emissions from transportation are estimated at approximately 50% of those in 2010. Future emissions will occur as losses along the entire production, distribution, and end-use chain, including emissions from H2 fuel cell vehicles (FCVs). In 2050, overall anthropogenic H2 emissions will only approach current levels at high-end loss rates; direct emissions from transportation are expected to be significantly lower than current levels. In 2100, an average loss rate of 0.5% would result in overall H2 emissions exceeding current levels even with no net H2 emissions from FCVs. However, based on an average loss rate of 0.1%, H2 emission factors from FCVs on the order to 120–170 mg km−1 are projected to result in overall anthropogenic H2 emissions similar to 2010 levels.