John F. Karlik

Active atmosphere-ecosystem exchange of the vast majority of detected volatile organic compounds.

Two-Way Street Most studies of volatile organic compounds (VOCs) found in the atmosphere, which play important roles in atmospheric chemistry, have concentrated on dominant species such as isoprene. There are thousands of other classes of VOCs, and how they are exchanged between the biosphere and the atmosphere is unclear. Park et al. (p. 643) measured the fluxes of more than 500 types of VOCs using a highly sensitive type of mass spectrometry and an absolute value eddy covariance method. The majority of these species were actively exchanged between the atmosphere and the biosphere, with more than a quarter showing net deposition. These results should help to improve air quality and global climate models, and strengthen our understanding of atmospheric VOC chemistry. Many volatile organic compounds emitted by vegetation are actively exchanged between plants and the atmosphere. Numerous volatile organic compounds (VOCs) exist in Earth’s atmosphere, most of which originate from biogenic emissions. Despite VOCs’ critical role in tropospheric chemistry, studies for evaluating their atmosphere-ecosystem exchange (emission and deposition) have been limited to a few dominant compounds owing to a lack of appropriate measurement techniques. Using a high–mass resolution proton transfer reaction–time of flight–mass spectrometer and an absolute value eddy-covariance method, we directly measured 186 organic ions with net deposition, and 494 that have bidirectional flux. This observation of active atmosphere-ecosystem exchange of the vast majority of detected VOCs poses a challenge to current emission, air quality, and global climate models, which do not account for this extremely large range of compounds. This observation also provides new insight for understanding the atmospheric VOC budget.

Ozone deposition to an orange orchard: Partitioning between stomatal and non-stomatal sinks

Orange trees are widely cultivated in regions with high concentrations of tropospheric ozone. Citrus absorb ozone through their stomata and emit volatile organic compounds (VOC), which, together with soil emissions of NO, contribute to non-stomatal ozone removal. In a Valencia orange orchard in Exeter, California, we used fast sensors and eddy covariance to characterize water and ozone fluxes. We also measured meteorological parameters necessary to model other important sinks of ozone deposition. We present changes in magnitude of these ozone deposition sinks over the year in response to environmental parameters. Within the plant canopy, the orchard constitutes a sink for ozone, with non-stomatal ozone deposition larger than stomatal uptake. In particular, soil deposition and reactions between ozone, VOC and NO represented the major sinks of ozone. This research aims to help the development of metrics for ozone-risk assessment and advance our understanding of citrus in biosphere-atmosphere exchange.

Sesquiterpenoid emissions from agricultural crops: correlations to monoterpenoid emissions and leaf terpene content.

Emissions of biogenic volatile organic compounds (BVOCs) are important precursors to both ozone and secondary organic aerosol formation. In this study, we identify and quantify volatile (C(10)) and intermediate-volatility (C(15)) BVOCs stored in and emitted from 22 prominent woody and herbaceous crops with a particular focus on sesquiterpenoids (SQTs), which have presented measurement challenges in previous studies. Monoterpenoids (MNTs) and SQTs were simultaneously emitted from all the crops studied; there were significant correlations between emission rates and leaf content for both MNTs and SQTs and additional correlations between MNTs and SQTs in both emissions and leaf content. Our results suggest that species with high concentrations of stored terpenoids in their leaves, such as those grown commercially for their essential oil content, are likely high BVOC emitters. Emissions from agricultural species were dominated by SQTs at low MNT emission rates (on the order of several tens of ng/(g(DM)*h)), while at higher MNT levels (on the order of several hundreds of ng/(g(DM)*h)), SQT emissions were approximately equivalent. Based on our empirical correlations, we estimate that global SQT emissions are similar to MNT emissions and on the order of 100 Tg yr(-1), which justifies the need for better representation of SQTs in both BVOC emission and atmospheric models.

A survey of California plant species with a portable VOC analyzer for biogenic emission inventory development

Abstract An accurate estimate of the magnitude of biogenic volatile organic compound (BVOC) emissions in Californias airsheds is critical for formulating effective strategies to reduce concentrations of fine particles, ozone, and other secondary air pollutants which affect human health and reduce yields of agricultural crops. However, Californias natural and urban landscapes contain more than 6000 species, and the BVOC emissions from only a small fraction of these species have been characterized by quantitative measurements. A taxonomic method has been proposed to assign BVOC emission rate measurements to unmeasured species, but data are needed for additional plant families and genera to further develop and test this taxonomic approach. In the present study, BVOC emissions from more than 250 plant species were measured through a semi-quantitative method employing calibrated portable analyzers with photoionization detectors (PID). Replicate samples of live foliage were placed in plastic bags, in both light and darkened conditions, and the BVOC emissions categorized as low, medium or high. To validate our approach, for 63 plant species we compared our PID-measured BVOC emissions with published values, based on gas chromatography (GC) or GC–mass spectrometry, and found them to be well correlated. The method employed was more suited for detecting compounds with relatively higher emission rates, such as isoprene, than compounds with low emission rates, which could include monoterpenes and oxygenated compounds. For approximately 200 plant species not previously measured, the results provide further evidence that plant taxonomy can serve as a useful guide for generalizing the emissions behavior of many, but not all, plant families and genera.

Plant species composition, calculated leaf masses and estimated biogenic emissions of urban landscape types from a field survey in Phoenix, Arizona

Vegetation in the Phoenix, Arizona, metropolitan area was surveyed using a modified stratified random sampling design to identify plant species and to measure foliar volumes for species-specific calculation of leaf mass. We identified the genus and species and measured the crown dimensions of plants located in a park and parking lot, and in three types of urban landscapes: flood-irrigated, mesic and xeric. Species compositions of these landscape types were compared quantitatively using a Sorenson index of similarity and the landscape types were found to be dissimilar. The three landscape types varied in calculated leaf masses and the respective identities of the dominant species, and relatively few plant species accounted for the majority of the leaf mass. Plant species and leaf mass data were used to estimate relative contributions from each landscape type of the biogenic volatile organic compounds isoprene and monoterpenes. Results from this study have implications for future plant surveys taken for biogenic emissions inventory development, and for plant species selection for urban landscapes, especially large-scale tree planting programs.

COMPARISON OF CALCULATED AND MEASURED LEAF MASSES OF URBAN TREES

Accurate leaf-mass determination is a critical factor in estimating the magnitude of biogenic hydrocarbon (BHC) emissions from green plants. In several past studies that developed BHC emissions estimates for urban areas, a volumetric approach was used to estimate leaf masses of urban trees. Crown volumes were modeled by geometric solids and then multiplied by species-specific leaf-mass constants (experimentally determined leaf mass-to-volume ratios) to obtain leaf mass, although associated uncertainties were not well characterized. The purpose of the present study was to examine the precision and accuracy of a volumetric approach using geometric solids to compare estimated leaf masses to measured whole-tree leaf masses, and to compare leaf-mass constants derived from selective sampling within crowns to whole-tree values. Accordingly, total leaf masses obtained through tree harvest and leaf removal of 21 urban trees were compared to leaf masses calculated using geometric solids to model the shapes of tree ...

Biogenic emission inventory development: field assessment of the GAP vegetation database in California

Abstract Given the key role played by biogenic volatile organic compounds (BVOC) in tropospheric chemistry and regional air quality, it is critical to generate accurate BVOC emission inventories. Indeed, formulating effective air quality attainment strategies for formation of ozone, fine particles, and other secondary air pollutants may depend in some regions upon the strength of biogenic emissions, requiring the geolocated characterization of plant species and their areal coverages. Vegetation databases developed through remote sensing methods require calibration and validation from ground-based measurements to be reliably used for BVOC modeling. A recent GIS-based description of vegetation coverage in the natural areas of the US is provided by the Gap Analysis Program (GAP) database. We conducted an assessment of this database in central California through quantitative ground-based vegetation surveys in 18 polygons, using a modified stratified randomized sampling design, to evaluate the use of GAP for developing BVOC emission inventories. The plant species listed by GAP accounted for between 0% and 88% of the relative cover in the polygons, with a mean of 43%. Of the 76 species listed by GAP for which data were collected, 33 were found to be correctly listed within their respective assemblages, 13 were found to be listed for the wrong assemblage, and 30 were below percentages of co-dominants of any assemblage. Summed over all 18 polygons, BVOC emission indices based on field data were 20% less than those based on GAP, but for individual polygons differences ranged from −100% to more than +100%.

Describing California's rose plant production in the San Joaquin Valley: a short economic history.

Kern County, in the southern San Joaquin Valley of California, USA, is well suited climatically for growing rose (Rosa xhybrida) plants and many other crops, and during the later decades of the 20 th century was home to about half of U.S. rose plant production. At the industrys peak about 2000 ha of rose plants were in various stages of production. We trace through statistical data the beginnings of the industry, harvested area, and crop value. Recent data indicate a downsizing of the industry in California.