Tropospheric Ozone Assessment Report: Present-day distribution and trends of tropospheric ozone relevant to climate and global atmospheric chemistry model evaluation

Abstract

The Tropospheric Ozone Assessment Report (TOAR) is an activity of the International Global Atmospheric Chemistry Project. This paper is a component of the report, focusing on the present-day distribution and trends of tropospheric ozone relevant to climate and global atmospheric chemistry model evaluation. Utilizing the TOAR surface ozone database, several figures present the global distribution and trends of daytime average ozone at 2702 non-urban monitoring sites, highlighting the regions and seasons of the world with the greatest ozone levels. Similarly, ozonesonde and commercial aircraft observations reveal ozone’s distribution throughout the depth of the free troposphere. Long-term surface observations are limited in their global spatial coverage, but data from remote locations indicate that ozone in the 21st century is greater than during the 1970s and 1980s. While some remote sites and many sites in the heavily polluted regions of East Asia show ozone increases since 2000, many others show decreases and there is no clear global pattern for surface ozone changes since 2000. Two new satellite products provide detailed views of ozone in the lower troposphere across East Asia and Europe, revealing the full spatial extent of the spring and summer ozone enhancements across eastern China that cannot be assessed from limited surface observations. Sufficient data are now available (ozonesondes, satellite, aircraft) across the tropics from South America eastwards to the western Pacific Ocean, to indicate a likely tropospheric column ozone increase since the 1990s. The 2014–2016 mean tropospheric ozone burden (TOB) between 60˚N–60˚S from five satellite products is 300 Tg ± 4%. While this agreement is excellent, the products differ in their quantification of TOB trends and further work is required to reconcile the differences. Satellites can now estimate ozone’s global long-wave radiative effect, but evaluation is difficult due to limited in situ observations where the radiative effect is greatest.

Twenty‐Five Years of Lower Tropospheric Ozone Observations in Tropical East Asia: The Influence of Emissions and Weather Patterns

“…The new data for 2008–2018 at HT reveal no obvious change during the past decade in these air masses ( p = 0.83 to 0.85), suggesting that the ozone levels in the outflow from eastern China may have reached or is reaching its peak. In Southeast Asia, previous analyses of vertical profiles from IAGOS aircraft and ozonesondes indicated an increase of about 20 ppbv in the boundary layer during summer from 1994–2004 to 2005–2014 (Gaudel et al, ). Our data suggest that the effect of ozone precursors from Southeast Asia can be detected on the south China coast after the air masses have traveled over 1,000 km (Figure a).…”

“…The tropospheric ozone burden is influenced by emissions of ozone precursors-oxides of nitrogen (NO x ), carbon monoxide (CO), and volatile organic compounds (VOCs)-and by meteorological conditions that affect the emission and chemistry of the precursors and atmospheric transport patterns (Jacob & Winner, 2009;Monks et al, 2015). Ozone levels in urban and rural areas in North America and Europe have mostly decreased in recent decades due to reductions in anthropogenic emissions (Akimoto, 2003;Gaudel et al, 2018;Parrish et al, 2014), but the ozone trend and drivers in some regions are quite complicated. Despite the decreases in the regional emission of ozone precursors, the ozone levels in rural areas of the western United States showed upward trends during 1980-2014 (Lin et al, 2017), which were attributed to increases in Asian emissions (Cooper et al, 2010;Gaudel et al, 2018;Jacob et al, 1999;Lin et al, 2017) and increased frequency of biomass burning (Jaffe et al, 2008;Lin et al, 2017;Westerling et al, 2006).…”

Tropospheric Ozone Assessment Report: Present-day tropospheric ozone distribution and trends relevant to vegetation

“…Whilst W126 and AOT40 have been decreasing at many sites in NAM and EUR, at some sites in these regions the M12 values have been increasing. Further research is needed to understand the basis of these changes in relation to hemispheric transport of precursors (Gaudel et al, 2018) and changes in NO titration of ozone, as well as the consequences for vegetation.…”

“…Local controls on precursor emissions have partially reduced peak ozone levels in regions such as the USA and Europe in the last two decades (CLRTAP, 2016;Cooper et al, 2012;Derwent et al, 2010;Simon et al, 2015). However, trends in daytime average ozone values are more varied with general decreases across North America during the growing season, weaker decreases across Europe and increases across Asia (see Gaudel et al, 2017, hereinafter referred to as TOAR-Climate for more details, and Chang et al, 2017).…”

The NASA Wallops Flight Facility Digital Ozonesonde Record: Reprocessing, Uncertainties, and Dual Launches

“…Journal of Geophysical Research: Atmospheres variability in the ozone structure. This presents a challenge to satellite-derived tropospheric ozone products that attempt to height-resolve vertical ozone distributions (Gaudel et al, 2018).…”