Observed suppression of ozone formation at extremely high temperatures due to chemical and biophysical feedbacks

Abstract

Ground level ozone concentrations ([O 3 ]) typically show a direct linear relationship with surface air temperature. Three decades of California measurements provide evidence of a statistically significant change in the ozone-temperature slope (Δm O3-T ) under extremely high temperatures (>312 K). This Δm O3-T leads to a plateau or decrease in [O 3 ], reflecting the diminished role of nitrogen oxide sequestration by peroxyacetyl nitrates and reduced biogenic isoprene emissions at high temperatures. Despite inclusion of these processes in global and regional chemistry-climate models, a statistically significant change in Δm O3-T has not been noted in prior studies. Future climate projections suggest a more frequent and spatially widespread occurrence of this Δm O3-T response, confounding predictions of extreme ozone events based on the historically observed linear relationship. (4-10), and several studies have attempted to isolate the drivers of this relationship, as summarized in ref. 11. Early studies investigating the ozone-temperature relationship noted the impact of peroxyacetyl nitrate (PAN) decomposition on ozone formation (4, 12). The PAN sink for NO x and odd hydrogen (HO x ) decreases exponentially as temperatures increase, implying a saturation of ozone formation from PAN decomposition as temperatures increase above ∼310 K. Sillman and Samson (10) found that m O3-T is a function of multiple chemical processes, including the reaction rate of PAN, emissions of biogenic volatile organic compounds (VOC), photolysis rates, and water vapor concentrations. Therefore whereas absolute temperature is a strong predictor of the effects of incremental temperature change on ozone (2), chemical kinetics and temperature-dependent emission rates further complicate this relationship. For example, prior studies have noted that m O3-T varies between regions with different NO x ∕VOC ratios (13), and can decrease following significant NO x emissions reductions (6). The m O3-T relationship has been called a climate change "penalty," signifying that emissions reductions will need to be more stringent to counteract the effects of warming temperatures (6,14). However, the stationarity of this ozone-temperature relationship has yet to be evaluated using observations over a broad range of temperatures.High concentrations of tropospheric ozone ([O 3 ]) are an indicator of poor air quality, and adversely affect the health of humans and ecosystems (15,16). A suite of chemical and meteorological factors contributes to the formation of ozone. Photochemically driven reactions of VOC in the presence of nitrogen oxides (NO x ) can form ozone at the surface (17), whereas stagnant meteorological conditions promote and maintain ozone events.Changes in the frequency of certain meteorological features such as fewer midlatitude cyclones (18,19) or shallower boundary layer depths (20) (Fig. S1). Daily maximum surface air temperature (T max ) data are obtained from a statistically interpolated gridded product of ground-based National Oceanic a...

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

“…The observations in the past three decades demonstrated that October ozone in the SE did not decrease like in July despite anthropogenic emission reductions in the region and that the two October high ozone extremes both occurred in the 2000s, implying higher ozone sensitivity to climate variation in October than July in the region. However, current discussion on the ozone climate penalty (the response of ground-level ozone to climate change) tends to focus on the ozone-temperature relationship (3,4,(6)(7)(8)(9)16). In this study, we find that a significant impact of VPD variation on the climate-chemistry interaction in the SE during the fall.…”

“…High ground-level ozone events are typically found in the summer when the formation of ozone is active through photochemical reactions involving nitrogen oxides (NO x = NO + NO 2 ) and volatile organic compounds (VOCs). However, ozone concentrations are sensitive to weather and climate (3)(4)(5)(6)(7)(8), and the high-ozone season could extend beyond summer in the future (9)(10)(11)(12)(13). Previous climate-chemistry model studies have estimated the change of ground-level ozone (ΔO 3 ) in the United States resulting only from meteorological changes.…”

Co-occurrence of extremes in surface ozone, particulate matter, and temperature over eastern North America

“…To the north, we may be seeing quicker activated photochemistry with respect to temperature or evidence of suppression of O 3 by high temperatures. This suppression has been identified previously, with one study implicating enhanced PAN decomposition and reduced isoprene emissions (48), and another study finding that the suppression is caused not by temperature-dependent effects on chemistry or emissions, but rather by a breakdown in the linearity of meteorology-O 3 correlations (44). In any case, it is not clear why this relationship changes at 40°N.…”

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

“…By extension, such methods can also provide insight into a model's usefulness for a range of possible (future) environmental conditions. However, care needs to be exercised when employing process-oriented model evaluation approaches because the observed relationships between ozone and the co-measured meteorological field or tracer may be complicated by other competing influences (e.g., Steiner et al, 2010;BrownSteiner et al, 2015;Shen et al, 2016)., or may change over time (e.g., Hassler et al, 2016).…”