Temperature-dependent emissions dominate aerosol and ozone formation in Los Angeles

Creators: Pfannerstill, Eva Y.; Arata, Caleb; Zhu, Qindan; Schulze, Benjamin C.; Ward, Ryan; Woods, Roy; Harkins, Colin; Schwantes, Rebecca H.; Seinfeld, John H.¹; Bucholtz, Anthony; Cohen, Ronald C.; Goldstein, Allen H.

1. California Institute of Technology

Abstract

Despite declines in transportation emissions, urban North America and Europe still face unhealthy air pollution levels. This has challenged conventional understanding of the sources of their volatile organic compound (VOC) precursors. Using airborne flux measurements to map emissions of a wide range of VOCs, we demonstrate that biogenic terpenoid emissions contribute ~60% of emitted VOC OH reactivity, ozone, and secondary organic aerosol formation potential in summertime Los Angeles and that this contribution strongly increases with temperature. This implies that control of nitrogen oxides is key to reducing ozone formation in Los Angeles. We also show some anthropogenic VOC emissions increase with temperature, which is an effect not represented in current inventories. Air pollution mitigation efforts must consider that climate warming will strongly change emission amounts and composition.

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Acknowledgement

The authors thank D. Baldocchi, G. Wolfe, E. Delaria, and T. Wang for insightful discussions about vertical flux divergence; A. Guenther for providing a tree cover inventory; B. McDonald for help with SOA formation potentials; M. Coggon, C. Stockwell, and C. Warneke for valuable discussions on PTR–time-of-flight mass spectrometry VOC corrections; the Regional Chemical Modeling Group of NOAA CSL for help with weather forecasting; and the Modeling and Meteorology Branch at CARB for providing their inventory. We gratefully acknowledge G. Cooper for excellent mission support; the pilots B. Kujat and G. Loudakis for their dedicated help in flight preparation, planning, and execution; and R. Weber and E. Katz for logistical support. We also thank NOAA’s High Performance Computing and Communications program.

Funding

California Air Resources Board contract nos. 20RD003 and 20AQP012 (to A.H.G. and R.C.C.); NOAA Climate Program Office’s Atmospheric Chemistry, Carbon Cycle, and Climate program, grant no. NA22OAR4310540 (UCB)/ NA22OAR4310541 (AD) (to A.H.G.); Office of Naval Research Defense University Research Instrumentation Program grant no. N00014-19-1-2108 (to A.H.G.); Presidential Early Career Award for Scientists and Engineers (PECASE) (to Brian McDonald); Alexander von Humboldt Foundation Feodor Lynen Fellowship (to E.Y.P.); EPA-STAR grant no. 84001001 (to R.H.S. and Q.Z.). The views expressed in this article are those of the authors and do not necessarily represent the views or policies of the US Environmental Protection Agency. The EPA does not endorse any products or commercial services mentioned in this publication.

Contributions

Conceptualization: A.H.G. and R.C.C.; Methodology: E.Y.P., C.A., Q.Z., and R.H.S.; Software: E.Y.P., C.A., and Q.Z.; Investigation: E.Y.P., C.A., B.C.S., A.B., and R. Wa., and R. Wo. Formal analysis: E.Y.P.; Visualization: E.Y.P.; Funding acquisition: A.H.G., R.C.C., and R.H.S.; Project administration: A.H.G., R.C.C., and A.B.; Supervision: A.H.G. and R.C.C.; Writing – original draft: E.Y.P.; Writing – review and editing: All authors.

Data Availability

All data used for this manuscript are available at https://csl.noaa.gov/projects/sunvex/. The codes used for wavelet flux analysis and footprint calculation are available online (54, 55).

Materials and Methods

Figs. S1 to S16

Table S1 and S2

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