Heterogeneity and chemical reactivity of the remote troposphere defined by...

Guo, H., C. M. Flynn, M. Prather, S. Strode, S. Steenrod, L. Emmons, F. Lacey, J. Lamarque, A. M. Fiore, G. Correa, L. Murray, G. M. Wolfe, J. M. St. Clair, M. Kim, J. D. Crounse, G. S. Diskin, J. P. DiGangi, B. Daube, R. Commane, K. McKain, J. Peischl, T. B. Ryerson, C. Thompson, T. F. Hanisco, D. R. Blake, N. J. Blake, E. Apel, R. S. Hornbrook, J. W. Elkins, E. Hintsa, F. Moore, and S. C. Wofsy (2021), Heterogeneity and chemical reactivity of the remote troposphere defined by aircraft measurements, Atmos. Chem. Phys., 21, 13729-13746, doi:10.5194/acp-21-13729-2021.

The NASA Atmospheric Tomography (ATom) mission built a photochemical climatology of air parcels based on in situ measurements with the NASA DC-8 aircraft along objectively planned profiling transects through the middle of the Pacific and Atlantic oceans. In this paper we present and analyze a data set of 10 s (2 km) merged and gap-filled observations of the key reactive species driving the chemical budgets of O3 and CH4 (O3 , CH4 , CO, H2 O, HCHO, H2 O2 , CH3 OOH, C2 H6 , higher alkanes, alkenes, aromatics, NOx , HNO3 , HNO4 , peroxyacetyl nitrate, other organic nitrates), consisting of 146 494 distinct air parcels from ATom deployments 1 through 4. Six models calculated the O3 and CH4 photochemical tendencies from this modeling data stream for ATom 1. We find that 80 %–90 % of the total reactivity lies in the top 50 % of the parcels and 25 %– 35 % in the top 10 %, supporting previous model-only studies that tropospheric chemistry is driven by a fraction of all the air. In other words, accurate simulation of the least reactive 50 % of the troposphere is unimportant for global budgets. Surprisingly, the probability densities of species and reactiv-

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Tropospheric Composition Program (TCP)