Preprints
https://doi.org/10.5194/acp-2021-708
https://doi.org/10.5194/acp-2021-708

  20 Sep 2021

20 Sep 2021

Review status: this preprint is currently under review for the journal ACP.

Direct Measurements of Ozone Response to Emissions Perturbations in California

Shenglun Wu1, Hyung Joo Lee2, Andrea Rohrbacher3, Shang Liu2, Toshihiro Kuwayama2, John H. Seinfeld4, and Michael J. Kleeman1 Shenglun Wu et al.
  • 1Department of Civil and Environmental Engineering, University of California Davis, 1 Shields Ave, Davis, CA 95616, USA
  • 2Department of Chemistry, University of California Irvine, Irvine, CA 92697, USA
  • 3Research Division, California Air Resources Board, 1001 I Street, Sacramento, CA 95814, USA
  • 4Department of Chemical Engineering, California Institute of Technology, 1200 E. California Blvd, Pasadena, CA 91125, USA

Abstract. A new technique was used to directly measure O3 response to changes in precursor NOx and VOC concentrations in the atmosphere using three identical Teflon “smog chambers” equipped with UV lights. One chamber served as the baseline measurement for O3 formation, one chamber added NOx, and one chamber added surrogate VOCs (ethylene, m-xylene, n-hexane). Comparing the O3 formation between chambers over a three-hour UV cycle provides a direct measurement of O3 sensitivity to precursor concentrations. Measurements made with this system at Sacramento, California, between April 2020 – December 2020 revealed that the atmospheric chemical regime followed a seasonal cycle. O3 formation was VOC-limited (NOx – rich) during the early spring, transitioned to NOx-limited during the summer due to increased concentrations of ambient VOCs with high O3 formation potential, and then returned to VOC-limited (NOx-rich) during the fall season as the concentrations of ambient VOCs decreased and NOx increased. This seasonal pattern of O3 sensitivity is consistent with the cycle of biogenic emissions in California. The direct chamber O3 sensitivity measurements matched semi-direct measurements of HCHO / NO2 ratios from the TROPOspheric Monitoring Instrument (TROPOMI) onboard the Sentinel-5 Precursor (Sentinel-5P) satellite. Furthermore, the satellite observations showed that the same seasonal cycle in O3 sensitivity occurred over most of the entire state of California, with only the urban cores of the very large cities remaining VOC-limited across all seasons. Looking at the entire measurement period, days with baseline chamber O3 concentrations above 90 ppb had median O3 sensitivity that was NOx-limited, suggesting that a NOx emissions control strategy would be most effective at reducing these peak O3 concentrations. In contrast, days with O3 concentrations below 80 ppb had median O3 sensitivity that was VOC-limited, suggesting that an emissions control strategy focusing on NOx reduction would increase O3 concentrations. VOC controls on these intermediate days would be difficult, however, if biogenic VOCs account for the majority of the O3 formation. This challenging situation suggests that emissions control programs that focus on NOx reductions will immediately lower peak O3 concentrations, but slightly increase intermediate O3 concentrations until NOx levels fall far enough to re-enter the NOx-limited regime. The spatial pattern of increasing and decreasing O3 concentrations in response to a NOx emissions control strategy should be carefully mapped in order to fully understand the public health implications.

Shenglun Wu et al.

Status: open (until 01 Nov 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on acp-2021-708', Youwen Sun, 21 Sep 2021 reply
  • RC1: 'Comment on acp-2021-708', Anonymous Referee #1, 11 Oct 2021 reply
  • RC2: 'Comment on acp-2021-708', William Stockwell, 14 Oct 2021 reply
  • RC3: 'Comment on acp-2021-708', Anonymous Referee #3, 16 Oct 2021 reply

Shenglun Wu et al.

Shenglun Wu et al.

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Short summary
An ozone control experiment usually conducted in the laboratory was installed in a trailer and moved to the outdoor environment to directly confirm that we are controlling the right sources in order to lower ambient ozone concentrations. Adding small amounts of precursor oxides of nitrogen and volatile organic compounds to ambient air showed that the highest ozone concentrations are best controlled by reducing concentrations of oxides of nitrogen. The results confirm satellite measurements.
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