Airborne Measurements Suggest That Halocarbon Emissions from the New York City Urban Region Have Comparable Climate Impacts to Its Methane Emissions

Urban centers concentrate high usage of halocarbons largely for refrigeration, air conditioning (A/C), heat pumps, and fire suppression. Loss of these gases to the atmosphere has a large climate impact. Here, we quantify halocarbon emissions from the New York City region during the East Coast Outflow airborne campaigns in 2018 and 2020. We quantify urban-scale emissions using discrete airborne flask samples collected during downwind plume sampling. We find that inventories of the urban region underestimate halocarbon emissions. For A/C species, higher emissions in 2018 correspond with higher temperatures, suggesting emissions may vary with appliance usage. The climate impact (100-year time horizon) of our observed halocarbon emissions is comparable to coincident methane emissions, equal to ∼10% of urban CO₂ emissions. Without leakage mitigation and effective phase-down efforts, high halocarbon emissions could undercut the benefits of switching to heat pumps and present a positive warming feedback with increasing air conditioning demand.