Convective Transport of Short-Lived Hydrocarbons and Bromocarbons from the Surface to the Upper Troposphere and Lower Stratosphere

Deep convection is the primary mechanism that delivers important chemical trace gases into the upper troposphere and the lower stratosphere (UT/LS), where they exert significant impacts on atmospheric O₃ and OH. The Western Pacific has been viewed traditionally as the primary convective lofting region for air to enter the tropical tropopause layer (TTL), although deep convective injection over the continental U.S. has also been proposed as a potential pathway. Aircraft measurements of atmospheric trace gases from the NASA SEAC⁴RS and ATTREX missions and the NSF CONTRAST mission provide useful UT/LS observations to examine how convective transport differ between the N. American continental sub-tropics and the Western Pacific. We have analyzed aircraft measurements of CO₂, NMHCs (CO, ethyne, ethane, HCHO), and very-short-lived bromocarbons from multiple aircraft missions with trace gas simulations from the NASA GEOS-5 chemistry climate model. We found that the Western Pacific is convectively efficient with rapid vertical transport from the surface to 365K within 60 days. Convective transport over the continental N. America is less frequent and much slower (120 days from surface to 365K), but sporadic injection can be as high as 400K during some occasions. While CO has been commonly used a convective tracer, our analysis of all observed VOCs suggested that C₂H₆ is a better convective tracer to track transport from the surface polluted continents into the lower stratosphere, particularly in the N. American sub-tropics. The intense convective lofting over the subtropical N. America and the very high levels of very-short-lived bromine (~15 ppt, compared to mean 5-6 ppt throughout the tropics) observed in the Gulf of Mexico can potentially deliver abundant amount of the VSL-Br into the stratosphere and impact the stratospheric ozone depletion.