Climate variability modulates western US ozone air quality in spring via deep stratospheric intrusions

Abstract

Evidence suggests deep stratospheric intrusions can elevate western US surface ozone to unhealthy levels during spring. These intrusions can be classified as ‘exceptional events', which are not counted towards non-attainment determinations. Understanding the factors driving the year-to-year variability of these intrusions is thus relevant for effective implementation of the US ozone air quality standard. Here we use observations and model simulations to link these events to modes of climate variability. We show more frequent late spring stratospheric intrusions when the polar jet meanders towards the western United States, such as occurs following strong La Niña winters (Niño3.4<−1.0 °C). While El Niño leads to enhancements of upper tropospheric ozone, we find this influence does not reach surface air. Fewer and weaker intrusion events follow in the two springs after the 1991 volcanic eruption of Mt. Pinatubo. The linkage between La Niña and western US stratospheric intrusions can be exploited to provide a few months of lead time during which preparations could be made to deploy targeted measurements aimed at identifying these exceptional events.

Climate-driven ground-level ozone extreme in the fall over the Southeast United States

“…Although the impact of stratospheric intrusion on surface ozone has been reported at elevated sites in the mountainous western United States (26)(27)(28), its effect on nearsurface ozone in the eastern United States is insignificant (29), especially considering that stratospheric intrusion is weakest in the fall season (30,31) …”

Tropospheric Ozone Assessment Report: Assessment of global-scale model performance for global and regional ozone distributions, variability, and trends

“…These models generate their own climate and weather variability, meaning that they will be unlikely to capture the decadal-scale (and shorter-term) variations and the timing of anomalous years seen in observations (e.g., the 1997/1998 El Niño). The lack of synchronized natural variability between the models and observations can then likely lead to a bias in their trends, even if sampled over the same time periods (e.g., Lamarque et al, 2010;Parrish et al, 2014), as discussed by recent studies (Lin et al, 2014;2015a, 2015bBarnes et al, 2016).…”

“…It is thought to have strong connections with several modes of climate variability, including ENSO (Langford, 1999;Zeng and Pyle, 2005;Neu et al, 2014;Lin et al, 2015b), the Arctic Oscillation (Hess and Lamarque, 2007), the North Atlantic Oscillation (Sprenger and Wernli, 2003;Pausata et al, 2012), and the stratospheric quasi-biennial oscillation (QBO) (Hsu and Prather, 2009;Neu et al, 2014), as well as (episodic) volcanic eruptions (Oltmans et al, 1998;Fusco and Logan, 2003;Tang et al, 2013;Lin et al, 2015b). The ability of global models to represent tropospheric ozone variability associated with the STT ozone flux varies depending on model representation of stratospheric chemistry and its dynamical coupling with the troposphere (see Table S1 of Lin et al, 2015b).…”

Reanalysis comparisons of upper tropospheric–lower stratospheric jets and multiple tropopauses

“…Moreover, transport processes that alter the extent and consequences of extratropical stratosphere-troposphere exchange (STE) are closely linked to the tropopause and jets, which are themselves sensitive to climate change and ozone depletion (e.g., Seidel and Randel, 2006;Lorenz and DeWeaver, 2007;Polvani et al, 2011;WMO, 2011;Hudson, 2012;Grise et al, 2013;Waugh et al, 2015). Both tropospheric and total column ozone vary with tropopause height and STE near the UTLS jets (e.g., Olsen et al, 2002;Neu et al, 2014), as well as with natural modes of variability such as ENSO that alter the jets (Hudson, 2012;Lin et al, 2014Lin et al, , 2015Olsen et al, 2016, and references therein). Thus, much of the variability in UTLS ozone is inextricably linked to that of the UTLS jets.…”