Volatile organic compound fluxes in the agricultural San Joaquin Valley – spatial distribution, source attribution, and inventory comparison
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1.
University of California, Berkeley
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2.
Massachusetts Institute of Technology
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3.
California Institute of Technology
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4.
Naval Postgraduate School
Abstract
The San Joaquin Valley is an agricultural region in California that suffers from poor air quality. Since traffic emissions are decreasing, other sources of volatile organic compounds (VOCs) are gaining importance in the formation of secondary air pollutants. Using airborne eddy covariance, we conducted direct, spatially resolved flux observations of a wide range of VOCs in the San Joaquin Valley during June 2021 at 23–36 ∘C. Through land-cover-informed footprint disaggregation, we were able to attribute emissions to sources and identify tracers for distinct source types. VOC mass fluxes were dominated by alcohols, mainly from dairy farms, while oak isoprene and citrus monoterpenes were important sources of reactivity. Comparisons with two commonly used inventories showed that isoprene emissions in the croplands were overestimated, while dairy and highway VOC emissions were generally underestimated in the inventories, and important citrus and biofuel VOC point sources were missing from the inventories. This study thus presents unprecedented insights into the VOC sources in an intensive agricultural region and provides much needed information for the improvement of inventories, air quality predictions, and regulations.
Copyright and License
© Author(s) 2023. This work is distributed under the Creative Commons Attribution 4.0 License.
Published by Copernicus Publications on behalf of the European Geosciences Union.
Acknowledgement
The authors thank Dennis Baldocchi, Glenn Wolfe, Erin Delaria, and Tianxin Wang for insightful discussions about vertical flux divergence; Brian McDonald for help with SOA formation potentials; Matthew Coggon, Chelsea Stockwell, and Carsten Warneke for valuable discussions on PTR-ToF-MS VOC corrections; Pawel Misztal for providing initial airborne flux code; the Regional Chemical Modeling Group of NOAA CSL for providing their inventory and help with weather forecasting; and the Modeling and Meteorology Branch at CARB for providing their inventory. We gratefully acknowledge Greg Cooper for excellent mission support; the pilots Bryce Kujat and George Loudakis for their flight preparation, planning, and execution; and Robert Weber and Erin Katz for logistical support.
Funding
This research has been supported by the California Air Resources Board (grant nos. 20RD003 and 20AQP012); the US Department of Commerce, National Oceanic and Atmospheric Administration (Presidential Early Career Award for Scientists and Engineers); the National Oceanic and Atmospheric Administration, Climate Program Office (grant nos. NA22OAR4310540 and NA22OAR4310541 and Climate & Global Change Postdoctoral Fellowship); the Office of Naval Research (grant no. N00014-19-1-2108); the US Environmental Protection Agency (grant no. 84001001); and the Alexander von Humboldt-Stiftung (Feodor Lynen Research Fellowship).
Data Availability
The meteorological and VOC (flux) data used for this paper can be found at https://csl.noaa.gov/projects/sunvex/ (Pfannerstill et al., 2022).
Code Availability
The VOC airborne eddy covariance code and the footprint code are available online (https://doi.org/10.5281/ZENODO.8411339, Pfannerstill, 2023; https://doi.org/10.5281/zenodo.8279594, Zhu et al., 2023b).
Conflict of Interest
At least one of the co-authors is a member of the editorial board of Atmospheric Chemistry and Physics. The peer-review process was guided by an independent editor, and the authors also have no other competing interests to declare.
Ethics
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. EPA does not endorse any products or commercial services mentioned in this publication.
Publisher’s note: Copernicus Publications remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Additional Information
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Additional details
- Alternative title
- Volatile organic compound fluxes in the San Joaquin Valley – spatial distribution, source attribution, and inventory comparison
- California Air Resources Board
- 20RD003
- California Air Resources Board
- 20AQP012
- National Oceanic and Atmospheric Administration
- Presidential Early Career Award for Scientists and Engineers
- National Oceanic and Atmospheric Administration
- NA22OAR4310540
- National Oceanic and Atmospheric Administration
- NA22OAR4310541
- National Oceanic and Atmospheric Administration
- Climate & Global Change Postdoctoral Fellowship
- Office of Naval Research
- N00014-19-1-2108
- Environmental Protection Agency
- 84001001
- Alexander von Humboldt Foundation
- Feodor Lynen Fellowship
- Accepted
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2023-08-15
- Caltech groups
- Division of Chemistry and Chemical Engineering (CCE), Division of Geological and Planetary Sciences (GPS)
- Publication Status
- Published