Evaluation of Intercontinental Transport of Ozone Using Full-tagged, Tagged-N and Sensitivity Methods

Monday, 15 December 2014
Yixin Guo1, Junfeng Liu1, Denise L Mauzerall2,3, Louisa K Emmons4, Larry Wayne Horowitz5, Songmiao Fan5, Xiaoyuan Li2 and Shu Tao1, (1)Peking University, Beijing, China, (2)Princeton University, Department of Civil and Environmental Engineering, Princeton, NJ, United States, (3)Princeton University, Woodrow Wilson School of Public and International Affairs, Princeton, NJ, United States, (4)NCAR, Boulder, CO, United States, (5)Princeton Univ-NOAA GFDL, Princeton, NJ, United States
Long-range transport of ozone is of great concern, yet the source-receptor relationships derived previously depend strongly on the source attribution techniques used. Here we describe a new tagged ozone mechanism (full-tagged), the design of which seeks to take into account the combined effects of emissions of ozone precursors, CO, NOx and VOCs, from a particular source, while keeping the current state of chemical equilibrium unchanged. We label emissions from the target source (A) and background (B). When two species from A and B sources react with each other, half of the resulting products are labeled A, and half B. Thus the impact of a given source on downwind regions is recorded through tagged chemistry. We then incorporate this mechanism into the Model for Ozone and Related chemical Tracers (MOZART-4) to examine the impact of anthropogenic emissions within North America, Europe, East Asia and South Asia on ground-level ozone downwind of source regions during 1999-2000. We compare our results with two previously used methods -- the sensitivity and tagged-N approaches. The ozone attributed to a given source by the full-tagged method is more widely distributed spatially, but has weaker seasonal variability than that estimated by the other methods. On a seasonal basis, for most source/receptor pairs, the full-tagged method estimates the largest amount of tagged ozone, followed by the sensitivity and tagged-N methods. In terms of trans-Pacific influence of ozone pollution, the full-tagged method estimates the strongest impact of East Asian (EA) emissions on the western U.S. (WUS) in MAM and JJA (~3 ppbv), which is substantially different in magnitude and seasonality from tagged-N and sensitivity studies. This difference results from the full-tagged method accounting for the maintenance of peroxy radicals (e.g., CH3O2, CH3CO3, and HO2), in addition to NOy, as effective reservoirs of EA source impact across the Pacific, allowing for a significant contribution to ozone formation over WUS (particularly in summer). Thus, the full-tagged method, with its clear discrimination of source and background contributions on a per-reaction basis, provides unique insights into the critical role of VOCs (and additional reactive nitrogen species) in determining the nonlinear inter-continental influence of ozone pollution.