Abstract
Abstract. Surface ozone concentrations are observed to increase with rising temperatures, but the mechanisms responsible for this effect in rural and remote continental regions remain uncertain. Better understanding of the effects of temperature on ozone is crucial to understanding global air quality and how it may be affected by climate change. We combine measurements from a focused ground campaign in summer 2013 with a long-term record from a forested site in the rural southeastern United States, to examine how daily average temperature affects ozone production. We find that changes to local chemistry are key drivers of increased ozone concentrations on hotter days, with integrated daily ozone production increasing by 2.3 ppb ∘C−1. Nearly half of this increase is attributable to temperature-driven increases in emissions of nitrogen oxides (NOx), most likely by soil microbes. The increase of soil NOx emissions with temperature suggests that ozone will continue to increase with temperature in the future, even as direct anthropogenic NOx emissions decrease dramatically. The links between temperature, soil NOx, and ozone form a positive climate feedback.
Highlights
Elevated concentrations of tropospheric ozone are an important contributor to anthropogenic radiative forcing, and are associated with increased human mortality and decreased crop yields (Myhre et al, 2013; World Health Organization, 2005; Booker et al, 2009)
We find that changes in local chemistry are important drivers of the increase in ozone concentrations observed at this site, and that increased nitrogen oxides (NOx) emissions are responsible for 40 % of the temperature-dependent increase in daily integrated ozone production
VOC reactivity (VOCR) increases strongly with temperature, the RONO2-dominated NOx chemistry causes neither the ozone production rate nor Changes in NOx emissions with temperature have an outsized effect when considering the impacts of ozone on human health and climate
Summary
Elevated concentrations of tropospheric ozone are an important contributor to anthropogenic radiative forcing, and are associated with increased human mortality and decreased crop yields (Myhre et al, 2013; World Health Organization, 2005; Booker et al, 2009). Long-term monitoring from the SouthEastern Aerosol Research and CHaracterization (SEARCH) network shows that ozone increases significantly with temperature at this site (Fig. 1), despite being in a low-NOx environment where the predicted response of the instantaneous ozone production rate to temperature is small (Pusede et al, 2015). We combine this record with extensive measurements from the Southern Oxidant and Aerosol Study (SOAS) in summer 2013 to explicitly calculate daily integrated ozone production and NOx loss as a function of daily average tem-. We expect similar effects to be present in other low-NOx areas with high concentrations of VOCs, where the chemistry of alkyl and multifunctional nitrates is the majority pathway for permanent NOx loss
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