03 May 2023
 | 03 May 2023
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Volatile organic compound fluxes in the San Joaquin Valley – spatial distribution, source attribution, and inventory comparison

Eva Y. Pfannerstill, Caleb Arata, Qindan Zhu, Benjamin C. Schulze, Roy Woods, John H. Seinfeld, Anthony Bucholtz, Ronald C. Cohen, and Allen H. Goldstein

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 landcover-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.

Eva Y. Pfannerstill et al.

Status: open (until 14 Jun 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-723', Anonymous Referee #2, 23 May 2023 reply

Eva Y. Pfannerstill et al.

Data sets

Meteorological and VOC flux data Eva Y. Pfannerstill, Caleb Arata, Roy Woods, Anthony Bucholtz, and Allen H. Goldstein

Citrus processing and ethanol manufacturing locations southern San Joaquin Valley Eva Y. Pfannerstill

Model code and software

VOC airborne eddy covariance code Eva Y. Pfannerstill, Caleb Arata, and Allen H. Goldstein

Footprint model code converted from R to Matlab (original: Natascha Kljun, Stefan Metzger) Qindan Zhu and Eva Y. Pfannerstill

Eva Y. Pfannerstill et al.


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Short summary
The San Joaquin Valley is an agricultural area with poor air quality. Organic gases drive the formation of hazardous air pollutants. Agricultural emissions of these gases are not well understood and have rarely been quantified at landscape scale. By combining aircraft-based emission measurements with land cover information, we found mis- or unrepresented emission sources. The results of this study help understand pollution sources and improve predictions of air quality in agricultural regions.