Global source attribution of tropospheric ozone: Long‐range transport from various source regions

Abstract

We examine contributions from various source regions to global distributions and budgets of tropospheric ozone (O3) in the context of intercontinental transport, using tagged tracer simulation with a global chemical transport model. For tagging O3, we consider regional separation of the model domain on the basis of the distributions of O3 chemical production. We define 14 polluted source regions (14 tracers) in the boundary layer (North America, Europe, China, etc.) and 8 regions (8 tracers) in the free troposphere; O3 production in the remaining (remote) tropospheric region and O3 transport from the stratosphere are also tagged as separate tracers. O3 transport from the polluted source regions like North America, Europe, and Asia generally accounts for more than 40% of ozone abundances even in remote locations. O3 exports from boundary layer in China and Asian free troposphere are discerned through much of the Northern Hemisphere, suggesting significant and extensive impacts of eastern Asian pollution. In particular, O3 from Asian free troposphere plays the most important roles in distribution and seasonal variation of O3 in the middle‐upper troposphere almost globally. In June–September, the model calculates a large O3 contribution (5–10 ppbv) from Asian free troposphere in the upper troposphere over the South Pacific associated with long‐range interhemispheric transport from Asia to the southern midlatitudes (via the western Indian Ocean, Africa, and Atlantic) in the upper troposphere. O3 transported from biomass burning regions such as South America, Africa, and Australia widely distributes in the Southern Hemisphere. Our simulation demonstrates that there is a significant interhemispheric O3 transport from South America to the northern midlatitudes in the upper troposphere which reaches Japan, North Pacific, and the United States in conjunction with O3 export from North Africa. Our tagged O3 simulation estimates that the annual mean global tropospheric O3 burden, as calculated to be 344 Tg in this study, comes from chemical production in the source regions (48%) and in the remote regions (29%) and from stratosphere‐troposphere exchange (23%).

Enhanced Mid-Latitude Tropospheric Column Ozone over East Asia: Coupled Effects of Stratospheric Ozone Intrusion and Anthropogenic Sources

“…In the tagged-tracer simulation used in this study, the concentration of ozone calculated by a stratospheric chemistry climate model was assimilated into CHASER above the tropopause. If we assimilated the ozone concentration only above 55 hPa (∼20 km) altitude as in Sudo and Akimoto (2007), stratospheric ozone input would be estimated to be about 560 Tg(O 3 ) year −1 , which well falls within the range shown in Stevenson et al (2006). However, comparisons between the calculated concentrations of ozone with the several ozonesonde observations revealed that the simulation limiting the assimilation of stratospheric ozone above 55 hPa obviously overestimated the concentration of ozone, particularly at the upper troposphere.…”

“…Stevenson et al (2006) summarized the stratospheretroposphere exchange (STE) of ozone calculated from 26 atmospheric chemistry models, and showed that there is a large variety in estimates for stratospheric ozone input fluxes ranging from 296 to 930 Tg(O 3 ) year −1 (see Table 5 in Stevenson et al (2006)). In their intercomparison and also in the analysis in Sudo and Akimoto (2007), CHASER was reported to give a value for stratospheric ozone input of about 500 Tg(O 3 ) year −1 . In the tagged-tracer simulation with CHASER used in this paper (Nagashima et al 2010), the stratospheric ozone input is estimated to be about 135 Tg(O 3 ) year −1 .…”

“…The observational data were compared with a tagged tracer simulation (Sudo and Akimoto 2007;Nagashima et al 2010) using the global chemical transport model CHASER (Sudo et al 2002). For this study, the horizontal resolution of T63 (∼1.9 × 1.9 degrees) was adopted with 32 vertical layers from the surface to an altitude of ∼40 km.…”

“…In addition to TCO data, we analyzed horizontal wind data from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis to investigate the correspondence between the E-TCO belt and the STJ. We also compared the observational data with tagged tracer simulation output from a global chemical transport model, the CHemical Atmospheric general circulation model for the Study of atmospheric Environment and Radiative forcing (CHASER) (Sudo and Akimoto 2007;Nagashima et al 2010), to assess the contribution of ozone of stratospheric and tropospheric origins.…”

“…Despite its relatively small quantity, however, tropospheric ozone is the primary precursor for hydroxyl (OH) radicals, which control the lifetimes of many gas species in the troposphere. Recently, chemical transport modeling studies have demonstrated that a significant amount of ozone is produced by photochemical processes in the troposphere from anthropogenic ozone precursors and is transported globally, and the roles of photochemical formation processes have been elucidated (Lelieveld and Dentener 2000;Sudo and Akimoto 2007). As a result of its enhancement, tropospheric ozone is the third most important anthropogenic greenhouse gas (Intergovernmental Panel on Climate Change (IPCC) report 2007), and because of its impact on climate change, there is an urgent need to clarify the global and regional behavior of tropospheric ozone.…”