Abstract
Abstract. We use satellite observations from IASI (Infrared Atmospheric Sounding Interferometer) on board the MetOp-A satellite to evaluate the springtime daily variations in lower-tropospheric ozone over east Asia. The availability of semi-independent columns of ozone from the surface up to 12 km simultaneously with CO columns provides a powerful observational data set to diagnose the processes controlling tropospheric ozone enhancement on synoptic scales. By combining IASI observations with meteorological reanalyses from ERA-Interim, we develop an analysis method based only on IASI ozone and CO observations to identify the respective roles of the stratospheric source and the photochemical source in ozone distribution and variations over east Asia. The succession of low- and high-pressure systems drives the day-to-day variations in lower-tropospheric ozone. A case study analysis of one frontal system and one cut-off low system in May 2008 shows that reversible subsiding and ascending ozone transfers in the upper-troposphere–lower-stratosphere (UTLS) region, due to the tropopause perturbations occurring in the vicinity of low-pressure systems, impact free and lower-tropospheric ozone over large regions, especially north of 40° N, and largely explain the ozone enhancement observed with IASI for these latitudes. Irreversible stratosphere–troposphere exchanges of ozone-rich air masses occur more locally in the southern and southeastern flanks of the trough. The contribution to the lower-tropospheric ozone column is difficult to dissociate from the tropopause perturbations generated by weather systems. For regions south of 40° N, a significant correlation has been found between lower-tropospheric ozone and carbon monoxide (CO) observations from IASI, especially over the North China Plain (NCP). Considering carbon monoxide observations as a pollutant tracer, the O3–CO correlation indicates that the photochemical production of ozone from primary pollutants emitted over such large polluted regions significantly contributes to the ozone enhancements observed in the lower troposphere via IASI. When low-pressure systems circulate over the NCP, stratospheric and pollution sources play a concomitant role in the ozone enhancement. IASI's 3-D observational capability allows the areas in which each source dominates to be determined. Moreover, the studied cut-off low system has enough potential convective capacity to uplift pollutants (ozone and CO) and to transport them to Japan. The increase in the enhancement ratio of ozone to CO from 0.16 on 12 May over the North China Plain to 0.28 over the Sea of Japan on 14 May indicates photochemical processing during the plume transport.
Highlights
In addition to being an important greenhouse gas (Stevenson et al, 2013), tropospheric ozone (O3) plays a central role in atmospheric chemistry and air quality by controlling the oxidation processes through the formation of hydroxyl radicals (OH) (Monks, 2005; Monks et al, 2015)
Based on ozone and carbon monoxide (CO) retrieval from IASI, we develop an analysis method to diagnose which processes contribute to ozone enhancement in the lower troposphere
We demonstrate that ozone profiles and semi-independent ozone columns between the surface and 12 km associated with simultaneous CO measurements from IASI provide a powerful observational data set to identify the stratospheric and anthropogenic origin of the lower-tropospheric ozone
Summary
In addition to being an important greenhouse gas (Stevenson et al, 2013), tropospheric ozone (O3) plays a central role in atmospheric chemistry and air quality by controlling the oxidation processes through the formation of hydroxyl radicals (OH) (Monks, 2005; Monks et al, 2015). Bethan et al, 1998; Hannan et al, 2003; Miyazaki et al, 2003; Cooper et al, 2004, Ding et al, 2009, 2015; Foret et al, 2014, and references therein) One part of these processes, the warm conveyor belts (WCBs) associated with frontal activity and lifting have been studied mainly in the context of their role in the long-range transport of pollutants because they lift pollutants to levels where horizontal transport is more efficient. We demonstrate that semi-independent ozone columns between the surface and 12 km from IASI associated with simultaneous CO measurements provide a powerful observational data set to identify, at least partly, the stratospheric and anthropogenic origin of lower free-tropospheric ozone. The contributions made to the enhanced lower-tropospheric ozone columns by descending air from the UTLS in the vicinity of the weather systems and by the photochemical production of ozone are investigated for the two case studies.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
