The capacity for volatile isoprenoid production under standardized environmental conditions at a certain time (ES, the emission factor) is a key characteristic in constructing isoprenoid emission ...inventories. However, there is large variation in published ES estimates for any given species partly driven by dynamic modifications in ES due to acclimation and stress responses. Here we review additional sources of variation in ES estimates that are due to measurement and analytical techniques and calculation and averaging procedures, and demonstrate that estimations of ES critically depend on applied experimental protocols and on data processing and reporting. A great variety of experimental setups has been used in the past, contributing to study-to-study variations in ES estimates. We suggest that past experimental data should be distributed into broad quality classes depending on whether the data can or cannot be considered quantitative based on rigorous experimental standards. Apart from analytical issues, the accuracy of ES values is strongly driven by extrapolation and integration errors introduced during data processing. Additional sources of error, especially in meta-database construction, can further arise from inconsistent use of units and expression bases of ES. We propose a standardized experimental protocol for BVOC estimations and highlight basic meta-information that we strongly recommend to report with any ES measurement. We conclude that standardization of experimental and calculation protocols and critical examination of past reports is essential for development of accurate emission factor databases.
During two field campaigns (OP3 and ACES), which ran in Borneo in 2008, we measured large emissions of estragole (methyl chavicol; IUPAC systematic name 1-allyl-4-methoxybenzene; CAS number 140-67-0) ...in ambient air above oil palm canopies (0.81 mg m−2 h−1 and 3.2 ppbv for mean midday fluxes and mixing ratios respectively) and subsequently from flower enclosures. However, we did not detect this compound at a nearby rainforest. Estragole is a known attractant of the African oil palm weevil (Elaeidobius kamerunicus), which pollinates oil palms (Elaeis guineensis). There has been recent interest in the biogenic emissions of estragole but it is normally not included in atmospheric models of biogenic emissions and atmospheric chemistry despite its relatively high potential for secondary organic aerosol formation from photooxidation and high reactivity with OH radical. We report the first direct canopy-scale measurements of estragole fluxes from tropical oil palms by the virtual disjunct eddy covariance technique and compare them with previously reported data for estragole emissions from Ponderosa pine. Flowers, rather than leaves, appear to be the main source of estragole from oil palms; we derive a global estimate of estragole emissions from oil palm plantations of ~0.5 Tg y−1. The observed ecosystem mean fluxes (0.44 mg m−2 h−1) and mean ambient volume mixing ratios (3.0 ppbv) of estragole are the highest reported so far. The value for midday mixing ratios is not much different from the total average as, unlike other VOCs (e.g. isoprene), the main peak occurred in the evening rather than in the middle of the day. Despite this, we show that the estragole flux can be parameterised using a modified G06 algorithm for emission. However, the model underestimates the afternoon peak even though a similar approach works well for isoprene. Our measurements suggest that this biogenic compound may have an impact on regional atmospheric chemistry that previously has not been accounted for in models and could become more important in the future due to expansion of the areas of oil palm plantation.
Fine particle matter with aerodynamic diameter <2.5 μm (PM2.5) and gas-phase emissions from open burning of six fine (foliar) fuels common to fire-prone U.S. ecosystems are investigated. PM2.5 ...distribution is unimodal within the 10−450 nm range, indicative of an accumulation mode. Smoldering relative to flaming combustion shows smaller particle number density per unit time and median size. Over 100 individual organic compounds in the primarily carbonaceous (>70% by mass) PM2.5 are chemically speciated by gas chromatography/mass spectrometry. Expressed as a percent of PM2.5 mass, emission ranges by organic compound class are as follows: n-alkane (0.1−2%), polycyclic aromatic hydrocarbon (PAH) (0.02−0.2%), n-alkanoic acid (1−3%), n-alkanedioic acid (0.06−0.3%), n-alkenoic acid (0.3−3%), resin acid (0.5−6%), triterpenoid (0.2−0.5%), methoxyphenol (0.5−3%), and phytosterol (0.2−0.6%). A molecular tracer of biomass combustion, the sugar levoglucosan is abundant and constitutes a remarkably narrow PM2.5 mass range (2.8−3.6%). Organic chemical signatures in PM2.5 from open combustion of fine fuels differ with those of residential wood combustion and other related sources, making them functional for source−receptor modeling of PM. Inorganic matter PM2.5 − (organic compounds + elemental carbon) on average is estimated to make up 8% of the PM2.5. Wavelength dispersive X-ray fluorescence spectroscopy and ion chromatography identify 3% of PM2.5 as elements and water-soluble ions, respectively. Compared with residential wood burning, the PM2.5 of fine fuel combustion is nitrate enriched but shows lower potassium levels. Gas-phase C2−C13 hydrocarbon and C2−C9 carbonyl emissions are speciated by respective EPA Methods TO-15 and TO-11A. They comprise mainly low molecular weight C2−C3 compounds and hazardous air pollutants (48 wt % of total quantified volatile organic carbon).
Little information is currently available regarding emissions of biogenic volatile organic compounds (BVOCs) in southern Asia. To address the need for BVOC emission estimates in regional atmospheric ...chemistry simulations, 95 common plant species were screened for emissions of BVOC in and near the Xishuangbanna Tropical Biological Gardens in southern Yunnan Province, Peoples’ Republic of China in February 2003. In situ measurements with leaf cuvettes and branch bag enclosures were used in combination with portable gas chromatography, flame ionization, photoionization, and mass spectral detection to identify and quantify BVOC emissions. Forty-four of the species examined emitted isoprene at rates exceeding 20
μg C
g
−1 (leaf dry weight) h
−1. An emphasis was placed on the genus
Ficus, which is important in the region and occupies a wide range of ecological niches. Several species in the footprint of a nearby flux tower were also examined. Several palm species and an abundant fern (
Cyclosorus parasiticus) emitted substantial amounts of isoprene, and probably accounted for observed daytime mean isoprene fluxes from the understory of a
Hevea brasiliensis plantation of 1.0 and 0.15
mg
C
m
−2
h
−1 during the wet and dry seasons, respectively. These measurements verify that both the forest floor and canopy in this region can be sources of isoprene. Monoterpene emissions exceeded 1.0
μg-C
g
−1 (leaf dry weight) h
−1 from only 4 of 38 species surveyed, including some
Ficus species and
H. brasiliensis. However most of the trees of the latter species were sparsely foliated due to dry season senescence, and emission factors are approximately an order of magnitude lower than those reported during the wet season. BVOC emission rates and physiology of many species are impacted by reduced moisture availability, especially
Mangifera indica. South Asia is a region undergoing rapid landuse change and forest plantation establishment, with large increases in area of high BVOC-emitting species in the genera
Bambusa,
Elaeis,
Eucalyptus,
Hevea,
Pinus, and
Populus (among others). This could result in profound changes in atmospheric chemistry in these regions, for instance, terpene emissions from
H. brasiliensis could increase wet season biogenic organic aerosol burdens by approximately a factor of 2 in the Xishuangbanna region. Increases in plantation area established with high isoprene emitting species, (e.g.
Bambusa spp. and
Eucalyptus spp.) are also projected for China and other parts of Southeast Asia in the near future. Thus, landcover change in South Asian landscapes is usually associated with large increases in BVOC flux with the potential to alter the atmospheric chemical composition and air quality over this rapidly developing region.
Mixing ratios of isoprene, methyl vinyl ketone (MVK), and methacrolein (MACR) were determined continuously during an 8‐day period in the summer of 1998 at a rural forested site located within the ...University of Michigan Biological Station (UMBS). The measurements were obtained as part of the Program for Research on Oxidants: Photochemistry, Emissions, and Transport (PROPHET) study. Fluxes of isoprene were concurrently measured at a nearby tower (AmeriFlux, located 132 m north‐northeast of the PROPHET tower). Following the study, 1‐km‐resolution emission estimates were derived for isoprene within a 60‐km radius of the tower using forest density estimates (Biogenic Emissions Inventory System (BEIS3) model). Measured isoprene fluxes at the site compared well with modeled isoprene fluxes when using BEIS3 and a detailed leaf litter‐fall data set by tree species from the UMBS site. Mean midday (1000–1400 LT) mixing ratios for isoprene, MACR, and MVK were 1.90 ± 0.43, 0.07 ± 0.01, and 0.14 ± 0.04 ppbv, respectively. Median midday mixing ratios of these compounds were 1.96 ± 0.26, 0.06 ± 0.02, and 0.10 ± 0.02 ppbv, respectively. Ratios of the isoprene oxidation products to isoprene are understood in the context of previous laboratory and field measurement studies of these compounds and a simple consecutive reaction scheme model. Results of the model indicate that the air masses studied represented relatively fresh emissions with a photochemical age of measured isoprene between 3.6 and 18 min, which is significantly less than the photochemical lifetime of isoprene (τ = 45 min at OH = 3.35 × 106 molecules cm−3). Thus a large portion of the isoprene that reaches the manifold has not had time to react completely with OH, yielding lower than expected ratios based on model calculations that do not explicitly take this into account. A rapid decrease in isoprene mixing ratios was observed soon after sunset, followed by a slower decay throughout the rest of the night. Emission maps were generated indicating that isoprene fluxes are highest in the immediate vicinity of the tower compared to the surrounding area of the site. Thus vertical diffusion and advection from the surrounding region are postulated to cause the observed initial rapid decrease in isoprene at the site. The second isoprene decay may be due to chemistry and/or dynamics, but the effects cannot be separated with the available data.
A fast two-dimensional gas chromatography (GC-MS) method that uses heart-cutting and thermal extraction (TE) and requires no chemical derivatization was developed for the determination of ...anhydro-sugars in fine aerosols. Evaluation of the TE-GC-GC-MS method shows high average relative accuracy (≥90%), reproducibility (≤10% relative standard deviation), detection limits of less than 3 ng/μL, and negligible carryover for levoglucosan, mannosan, and galactosan markers. TE-GC-GC-MS- and solvent extraction (SE)-GC-MS-measured levoglucosan concentrations correlate across several diverse types of biomass burning aerosols. Because the SE-GC-MS measurements were taken 8 years prior to the TE-GC-GC-MS ones, the stability of levoglucosan is established for quartz filter-collected biomass burning aerosol samples stored at ultra-low temperature (−50 °C). Levoglucosan concentrations (w/w) in aerosols collected following atmospheric dilution near open fires of varying intensity are similar to those in biomass burning aerosols produced in a laboratory enclosure. An average levoglucosan-mannosan-galactosan ratio of 15:2:1 is observed for these two aerosol sets. TE-GC-GC-MS analysis of atmospheric aerosols from the US and Africa produced levoglucosan concentrations (0.01–1.6 μg/m3) well within those reported for aerosols collected globally and examined using different analytical techniques (0.004–7.6 μg/m3). Further comparisons among techniques suggest that fast TE-GC-GC-MS is among the most sensitive, accurate, and precise methods for compound-specific quantification of anhydro-sugars. In addition, an approximately twofold increase in anhydro-sugar determination may be realized when combining TE with fast chromatography.
Nonmethane hydrocarbons are ubiquitous trace atmospheric constituents yet they control the oxidation capacity of the atmosphere. Both anthropogenic and biogenic processes contribute to the release of ...hydrocarbons to the atmosphere. In this manuscript, the state of the science concerning biosynthesis, transport, and chemical transformation of hydrocarbons emitted by the terrestrial biosphere is reviewed. In particular, the focus is on isoprene, monoterpenes, and oxygenated hydrocarbons. The generated science during the last 10 years is reviewed to explain and quantify hydrocarbon emissions from vegetation and to discern impacts of biogenic hydrocarbons on local and regional atmospheric chemistry. Furthermore, the physiological and environmental processes controlling biosynthesis and production of hydrocarbon compounds are reported on. Many advances have been made on measurement and modeling approaches developed to quantify hydrocarbon emissions from leaves and forest ecosystems. A synthesis of the atmospheric chemistry of biogenic hydrocarbons and their role in the formation of oxidants and aerosols is presented. The integration of biogenic hydrocarbon kinetics and atmospheric physics into mathematical modeling systems is examined to assess the contribution of biogenic hydrocarbons to the formation of oxidants and aerosols, thereby allowing us to study their impacts on the earth’s climate system and to develop strategies to reduce oxidant precursors in affected regions.
MONTES (“Woodlands”) was a multidisciplinary international field campaign aimed at measuring energy, water and especially gas exchange between vegetation and atmosphere in a gradient from short ...semi-desertic shrublands to tall wet temperate forests in NE Spain in the North Western Mediterranean Basin (WMB). The measurements were performed at a semidesertic area (Monegros), at a coastal Mediterranean shrubland area (Garraf), at a typical Mediterranean holm oak forest area (Prades) and at a wet temperate beech forest (Montseny) during spring (April 2010) under optimal plant physiological conditions in driest-warmest sites and during summer (July 2010) with drought and heat stresses in the driest–warmest sites and optimal conditions in the wettest–coolest site. The objective of this campaign was to study the differences in gas, water and energy exchange occurring at different vegetation coverages and biomasses. Particular attention was devoted to quantitatively understand the exchange of biogenic volatile organic compounds (BVOCs) because of their biological and environmental effects in the WMB. A wide range of instruments (GC–MS, PTR-MS, meteorological sensors, O3 monitors,…) and vertical platforms such as masts, tethered balloons and aircraft were used to characterize the gas, water and energy exchange at increasing footprint areas by measuring vertical profiles. In this paper we provide an overview of the MONTES campaign: the objectives, the characterization of the biomass and gas, water and energy exchange in the 4 sites-areas using satellite data, the estimation of isoprene and monoterpene emissions using MEGAN model, the measurements performed and the first results. The isoprene and monoterpene emission rates estimated with MEGAN and emission factors measured at the foliar level for the dominant species ranged from about 0 to 0.2 mg m−2 h−1 in April. The warmer temperature in July resulted in higher model estimates from about 0 to ca. 1.6 mg m−2 h−1 for isoprene and ca. 4.5 mg m−2 h−1 for monoterpenes, depending on the site vegetation and footprint area considered. There were clear daily and seasonal patterns with higher emission rates and mixing ratios at midday and summer relative to early morning and early spring. There was a significant trend in CO2 fixation (from 1 to 10 mg C m−2 d−1), transpiration (from 1–5 kg C m−2 d−1), and sensible and latent heat from the warmest–driest to the coolest–wettest site. The results showed the strong land-cover-specific influence on emissions of BVOCs, gas, energy and water exchange, and therefore demonstrate the potential for feed-back to atmospheric chemistry and climate.
•We present a multidisciplinary biosphere-atmosphere field campaign.•We measured a gradient from semi-desertic shrublands to wet temperate forests.•A wide range of instruments and vertical platforms were used.•Land cover strongly influenced emissions of BVOCs and gas, energy and water exchange.•Vegetation has strong potential for feed-back to atmospheric chemistry and climate.
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