Two Decades of Changes in Summertime Ozone Production in California’s South Coast Air Basin

Abstract

Tropospheric ozone (O 3 ) continues to be a threat to human health and agricultural productivity. While O 3 control is challenging, tracking underlying formation mechanisms provides insights for regulatory directions.Here, we describe a comprehensive analysis of the effects of changing emissions on O 3 formation mechanisms with observational evidence. We present a new approach that provides a quantitative metric for the ozone production rate (OPR) and its sensitivity to precursor levels by interpreting two decades of in situ observations of the six criteria air pollutants (2001−2018). Applying to the South Coast Air Basin (SoCAB), California, we show that by 2016−2018, the basin was at the transition region between nitrogen oxide (NO x )-limited and volatile organic compound (VOC)-limited chemical regimes. Assuming future weather conditions are similar to 2016−2018, we predict that NO x -focused reduction is required to reduce the number of summer days the SoCAB is in violation of the National Ambient Air Quality Standard (70 ppbv) for O 3 . Roughly, ∼40% (∼60%) NO x reductions are required to reduce the OPR by ∼1.8 ppb/h (∼3.3 ppb/h). This change would reduce the number of violation days from 28 to 20% (10%) in a year, mostly in summertime. Concurrent VOC reductions which reduce the production rate of HO x radicals would also be beneficial.

O3 Sensitivity to NOx and VOC During RECAP-CA: Implication for Emissions Control Strategies

“…47 The O 3 sensitivity pattern observed in Pasadena and Redlands reflects the transition from a VOC-limited urban core towards a more NO x -limited downwind area. 7,21,48,49 Overall, the trends in the O 3 chemical regime observed in Pasadena and Redlands are consistent with recent observations of O 3 chemistry in urban and downwind suburban areas. 7,50 The days with the highest measured O 3 concentrations are of particular interest in the current study since emissions control programs are traditionally tailored to reduce the O 3 design value, which is determined by the 4th highest MDA8 O 3 averaged over a three-year period.…”

Acute Ozone-Induced Transcriptional Changes in Markers of Oxidative Stress and Glucocorticoid Signaling in the Rat Hippocampus and Hypothalamus Are Sex-Specific

“…This observational study comparing sex differences in O 3 -induced OS and glucocorticoid-mediated transcriptional changes neither assessed potential protein levels of markers or functional effects, and rather associated changes to our prior publications related to neural and glucocorticoid changes. The O 3 concentrations used are several folds higher than what is encountered environmentally in tropical atmospheres, however, they are comparable to human clinical studies performed during intermittent exercise with O 3 concentrations ranging from 0.2 to 0.4 ppm [ 77 , 78 , 79 , 80 ]. Humans exposed during intermittent exercise retain 4–5 times the inhaled dose of O 3 compared to rodents exposed during rest [ 81 ].…”

“…Exposure began at ~0615 h each day and necropsies were performed after completion of second day exposure. The selected O 3 concentration of 0.8 ppm is several folds higher than what has been achieved in the areas of the United States [ 79 ]. However, 0.8 ppm O 3 exposure in resting rats is comparable to clinical studies using 0.2–0.3 ppm O 3 exposure in humans during intermittent exercise based on the airway dose deposition [ 81 ].…”

Multi-tissue transcriptomic and serum metabolomic assessment reveals systemic implications of acute ozone-induced stress response in male Wistar Kyoto rats

“…Exposure chamber conditions, including temperature, relative humidity, and air ow, along with actual ozone concentrations achieved have been previously described . Ozone concentrations are an order of magnitude higher than encountered in non-attainment areas in the US (Perdigones et al, 2022), but this concentration in resting rats is comparable to levels used in human clinical experiments during intermittent exercise based on airway dose deposition (Hatch et al, 1994).…”