Flux measurements of biogenic precursors to ozone and particulate matter in the central valley

Abstract The Central Valley of California is out of compliance with current air quality standards for ozone and particulate matter (PM). Ozone and PM air quality model simulations focused on the Central Valley are critical for State Implementation Plan development for ozone and particulate matter (PM). Model simulations are sensitive to emission sources, deposition/sinks, chemical reactions, and meteorology. Biogenic volatile organic compounds (BVOCs) participate in ozone and PM formation, and comprise a substantial fraction of ARB VOC emission inventories. Also, as regulatory controls are extended to agriculture, there is a renewed focus on crop biogenic emissions as well as ozone deposition to crops. While inputs to the ARB’s BVOC emission inventory model have been evaluated using field measurements, modeled emissions have not been evaluated using in-situ micrometeorological flux measurements for important valley floor crop environments, nor have emissions from native and naturalized plants frequently found in the Central Valley been characterized with recent measurement methods. Enclosure and landscapescale BVOC flux measurements are both critical for emission model performance evaluation, and for reducing uncertainties in emission inventories. In addition, recent field measurements suggest that emissions of fast reacting terpene species may be significantly underestimated (Kurpius and Goldstein, 2003), and no measurements of emissions from crops are available to evaluate this potential emission for modeling purposes. Crops cultivated on the valley floor may comprise a large source of monoterpenes, sesquiterpenes, and other compounds, but their emission potentials have not been measured extensively nor with recent measurement techniques. A two phase study has been conducted. In phase I, BVOC emissions at the branch or whole plant scale were characterized for more than 20 key crop species in a greenhouse. All crops studied had very low emission rates of isoprene. These results are consistent with previous studies in California for several of the same crop species. Emissions of terpenes and oxygenated hydrocarbons (particularly methanol, but also acetaldehyde, and acetone) represented the dominant fraction of the total BVOC emission for the crops studied. Oxygenated VOC dominated emissions for some crops such as tomato, grape, potato, miscanthus, mandarins, and lemon. All crops studied, with the exception of orange, fall in the category of low monoterpene emitters. The ‘Parent Navel’ orange tree emitted more terpenes than the other crop plants studied, and emissions of terpenoids and many other BVOC increased dramatically during the flowering event. However, emissions from orange per g dry leaf are still far less than emissions from the major BVOC emitting California plant species occurring in the natural environment.The Central Valley of California is out of compliance with current air quality standards for ozone and particulate matter (PM). Ozone and PM air quality model simulations focused on the Central Valley are critical for State Implementation Plan development for ozone and particulate matter (PM). Model simulations are sensitive to emission sources, deposition/sinks, chemical reactions, and meteorology. Biogenic volatile organic compounds (BVOCs) participate in ozone and PM formation, and comprise a substantial fraction of ARB VOC emission inventories. Also, as regulatory controls are extended to agriculture, there is a renewed focus on crop biogenic emissions as well as ozone deposition to crops. While inputs to the ARB’s BVOC emission inventory model have been evaluated using field measurements, modeled emissions have not been evaluated using in-situ micrometeorological flux measurements for important valley floor crop environments, nor have emissions from native and naturalized plants frequently found in the Central Valley been characterized with recent measurement methods. Enclosure and landscapescale BVOC flux measurements are both critical for emission model performance evaluation, and for reducing uncertainties in emission inventories. In addition, recent field measurements suggest that emissions of fast reacting terpene species may be significantly underestimated (Kurpius and Goldstein, 2003), and no measurements of emissions from crops are available to evaluate this potential emission for modeling purposes. Crops cultivated on the valley floor may comprise a large source of monoterpenes, sesquiterpenes, and other compounds, but their emission potentials have not been measured extensively nor with recent measurement techniques. A two phase study has been conducted. In phase I, BVOC emissions at the branch or whole plant scale were characterized for more than 20 key crop species in a greenhouse. All crops studied had very low emission rates of isoprene. These results are consistent with previous studies in California for several of the same crop species. Emissions of terpenes and oxygenated hydrocarbons (particularly methanol, but also acetaldehyde, and acetone) represented the dominant fraction of the total BVOC emission for the crops studied. Oxygenated VOC dominated emissions for some crops such as tomato, grape, potato, miscanthus, mandarins, and lemon. All crops studied, with the exception of orange, fall in the category of low monoterpene emitters. The ‘Parent Navel’ orange tree emitted more terpenes than the other crop plants studied, and emissions of terpenoids and many other BVOC increased dramatically during the flowering event. However, emissions from orange per g dry leaf are still far less than emissions from the major BVOC emitting California plant species occurring in the natural environment. Based on the species we measured, we conclude that the agricultural crops studied generally have low emission rates of isoprene and other terpenoid compounds compared to many plants found in natural or urban landscapes. Based on these phase I data and crop coverage data, a citrus orchard was selected to conduct landscape-scale, micrometeorological BVOC flux measurements.