1Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720, USA
2Department of Environmental Science, Policy and Management, University of California, Berkeley, CA 94720, USA
3Aix-Marseille Université – Institut méditerranéen de biodiversité et écologie IMBE CNRS UMR 7263, France
4Consiglio per la Ricerca e la sperimentazione in Agricoltura (CRA)- Research Centre for the Soil-Plant System, Rome, Italy
5Department of Chemistry University of California, Berkeley, CA 94720, USA
6Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309, USA
7Chemical Sciences Division, Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO 80305, USA
8University of California Cooperative Extension, Kern County, CA, USA
*now at: Department of Chemical & Environmental Engineering, Yale University, New Haven, CT 06511, USA
Received: 09 Sep 2013 – Discussion started: 01 Nov 2013
Abstract. Agriculture comprises a substantial, and increasing, fraction of land use in many regions of the world. Emissions from agricultural vegetation and other biogenic and anthropogenic sources react in the atmosphere to produce ozone and secondary organic aerosol, which comprises a substantial fraction of particulate matter (PM2.5). Using data from three measurement campaigns, we examine the magnitude and composition of reactive gas-phase organic carbon emissions from agricultural crops and their potential to impact regional air quality relative to anthropogenic emissions from motor vehicles in California's San Joaquin Valley, which is out of compliance with state and federal standards for tropospheric ozone PM2.5. Emission rates for a suite of terpenoid compounds were measured in a greenhouse for 25 representative crops from California in 2008. Ambient measurements of terpenoids and other biogenic compounds in the volatile and intermediate-volatility organic compound ranges were made in the urban area of Bakersfield and over an orange orchard in a rural area of the San Joaquin Valley during two 2010 seasons: summer and spring flowering. We combined measurements from the orchard site with ozone modeling methods to assess the net effect of the orange trees on regional ozone. When accounting for both emissions of reactive precursors and the deposition of ozone to the orchard, the orange trees are a net source of ozone in the springtime during flowering, and relatively neutral for most of the summer until the fall, when it becomes a sink. Flowering was a major emission event and caused a large increase in emissions including a suite of compounds that had not been measured in the atmosphere before. Such biogenic emission events need to be better parameterized in models as they have significant potential to impact regional air quality since emissions increase by several factors to over an order of magnitude. In regions like the San Joaquin Valley, the mass of biogenic emissions from agricultural crops during the summer (without flowering) and the potential ozone and secondary organic aerosol formation from these emissions are on the same order as anthropogenic emissions from motor vehicles and must be considered in air quality models and secondary pollution control strategies.
Revised: 28 Mar 2014 – Accepted: 11 Apr 2014 – Published: 03 Jun 2014
Gentner, D. R., Ormeño, E., Fares, S., Ford, T. B., Weber, R., Park, J.-H., Brioude, J., Angevine, W. M., Karlik, J. F., and Goldstein, A. H.: Emissions of terpenoids, benzenoids, and other biogenic gas-phase organic compounds from agricultural crops and their potential implications for air quality, Atmos. Chem. Phys., 14, 5393-5413, doi:10.5194/acp-14-5393-2014, 2014.