VOLATILE ORGANIC MATERIAL OF PLANT ORIGIN IN THE ATMOSPHERE

Evolution and the critical role of the microbiota in the reduced mental and physical health associated with low socioeconomic status (SES)

The evolution of the gut-microbiota-brain axis in animals reveals that microbial inputs influence metabolism, the regulation of inflammation and the development of organs, including the brain. Inflammatory, neurodegenerative and psychiatric disorders are more prevalent in people of low socioeconomic status (SES). Many aspects of low SES reduce exposure to the microbial inputs on which we are in a state of evolved dependence, whereas the lifestyle of wealthy citizens maintains these exposures. This partially explains the health deficit of low SES, so focussing on our evolutionary history and on environmental and lifestyle factors that distort microbial exposures might help to mitigate that deficit. But the human microbiota is complex and we have poor understanding of its functions at the microbial and mechanistic levels, and in the brain. Perhaps its composition is more flexible than the microbiota of animals that have restricted habitats and less diverse diets? These uncertainties are discussed in relation to the encouraging but frustrating results of attempts to treat psychiatric disorders by modulating the microbiota.

The pinene scaffold: its occurrence, chemistry, synthetic utility, and pharmacological importance

This review provides insight into the utility of pinene in the synthetic building block and as reagent in asymmetric synthesis.

Review on plant terpenoid emissions worldwide and in China

Biogenic volatile organic compounds (BVOCs), particularly terpenoids, can significantly drive the formation of ozone (O₃) and secondary organic aerosols (SOA) in the atmosphere, as well as directly or indirectly affect global climate change. Understanding their emission mechanisms and the current progress in emission measurements and estimations are essential for the accurate determination of emission characteristics, as well as for evaluating their roles in atmospheric chemistry and climate change. This review summarizes the mechanisms of terpenoid synthesis and release, biotic and abiotic factors affecting their emissions, development of emission observation techniques, and emission estimations from hundreds of published papers. We provide a review of the main observations and estimations in China, which contributes a significant proportion to the total global BVOC emissions. The review suggests the need for further research on the comprehensive effects of environmental factors on terpenoid emissions, especially soil moisture and nitrogen content, which should be quantified in emission models to improve the accuracy of estimation. In China, it is necessary to conduct more accurate measurements for local plants in different regions using the dynamic enclosure technique to establish an accurate local emission rate database for dominant tree species. This will help improve the accuracy of both national and global emission inventories. This review provides a comprehensive understanding of terpenoid emissions as well as prospects for detailed research to accurately describe terpenoid emission characteristics worldwide and in China.

Forest Volatile Organic Compounds and Their Effects on Human Health: A State-of-the-Art Review

The aim of this research work is to analyze the chemistry and diversity of forest VOCs (volatile organic compounds) and to outline their evidence-based effects on health. This research work was designed as a narrative overview of the scientific literature. Inhaling forest VOCs like limonene and pinene can result in useful antioxidant and anti-inflammatory effects on the airways, and the pharmacological activity of some terpenes absorbed through inhalation may be also beneficial to promote brain functions by decreasing mental fatigue, inducing relaxation, and improving cognitive performance and mood. The tree composition can markedly influence the concentration of specific VOCs in the forest air, which also exhibits cyclic diurnal variations. Moreover, beneficial psychological and physiological effects of visiting a forest cannot be solely attributed to VOC inhalation but are due to a global and integrated stimulation of the five senses, induced by all specific characteristics of the natural environment, with the visual component probably playing a fundamental role in the overall effect. Globally, these findings can have useful implications for individual wellbeing, public health, and landscape design. Further clinical and environmental studies are advised, since the majority of the existing evidence is derived from laboratory findings.

Deposition of α-pinene oxidation products on plant surfaces affects plant VOC emission and herbivore feeding and oviposition

White cabbage, Brassica oleracea, plants and artificial leaves covered with B. oleracea epicuticular wax were exposed to α-pinene and α-pinene oxidation products formed through the oxidation of α-pinene by ozone (O₃) and hydroxyl (OH) radicals. O₃ and OH-induced oxidation of α-pinene led to the formation of oxygenated volatile organic compounds (OVOCs) and secondary organic aerosol particles (SOA), referred to together as oxidation products (OP). Exposure of cabbage plants to O₃ and OH-induced α-pinene OP led to the deposition and re-emission of gas-phase OP by exposed cabbage plants. In a series of 2-choice bioassays, the specialist cruciferous herbivore, Plutella xylostella adults deposited less eggs on artificial leaves exposed to α-pinene OP than on control plants exposed to clean filtered air. P. xylostella larvae did not show a specific feeding preference when offered leaves from different exposure treatments. However, the generalist Indian stick insect, Carausius morosus, fed more on control filtered air-exposed plants than on those exposed to α-pinene OP. Taken together, our results show that exposure to α-pinene oxidation products affects VOC emissions of B. oleracea and alters P. xylostella oviposition and C. morosus feeding responses.

Observation and analysis of VOCs in nine prefecture-level cities of Sichuan Province, China

The observation and analysis of volatile organic compounds (VOCs) were conducted during January 2018 in nine prefecture-level cities of Sichuan, China, covering the period of heavily polluted weather. Air samples collected in nine prefecture-level cities were analyzed using a preconcentration method coupled with GC-MS/FID. The characteristics and ozone generation potential (OFP) of VOCs were analyzed. The relationship between air quality index (AQI) and VOCs and gross domestic product (GDP) and VOCs were also discussed, respectively. The results show that the characteristics of VOCs in cities are highly related to their industrial structure and GDP. Generally, areas with high AQI values are accompanied by high VOC concentrations. Alkanes and halocarbons were the most abundant VOCs in the atmospheric environment in the nine prefecture-level cities, accounting for 24.5~61.6% and 15.6~23.6% of total VOC concentration, respectively. The MIR method was used to analyze the OFP, and olefins contributed the most to ozone formation. Among the nine cities located in Sichuan, Dazhou was found to be the city with the highest OFP value (1191.49 μg/m³).

Analysis of Volatile Organic Compounds during the OCTAVE Campaign: Sources and Distributions of Formaldehyde on Reunion Island

The Oxygenated Compounds in the Tropical Atmosphere: Variability and Exchanges (OCTAVE) campaign aimed to improve the assessment of the budget and role of oxygenated volatile organic compounds (OVOCs) in tropical regions, and especially over oceans, relying on an integrated approach combining in situ measurements, satellite retrievals, and modeling. As part of OCTAVE, volatile organic compounds (VOCs) were measured using a comprehensive suite of instruments on Reunion Island (21.07° S, 55.38° E) from 7 March to 2 May 2018. VOCs were measured at a receptor site at the Maïdo observatory during the entire campaign and at two source sites: Le Port from 19 to 24 April 2018 (source of anthropogenic emissions) and Bélouve from 25 April to 2 May 2018 (source of biogenic emissions) within a mobile lab. The Maïdo observatory is a remote background site located at an altitude of 2200 m, whereas Bélouve is located in a tropical forest to the east of Maïdo and Le Port is an urban area located northwest of Maïdo. The major objective of this study was to understand the sources and distributions of atmospheric formaldehyde (HCHO) in the Maïdo observatory on Reunion Island. To address this objective, two different approaches were used to quantify and determine the main drivers of HCHO at Maïdo. First, a chemical-kinetics-based (CKB) calculation method was used to determine the sources and sinks (biogenic, anthropogenic/primary, or secondary) of HCHO at the Maïdo site. The CKB method shows that 9% of the formaldehyde formed from biogenic emissions and 89% of HCHO had an unknown source; that is, the sources cannot be explicitly described by this method. Next, a positive matrix factorization (PMF) model was applied to characterize the VOC source contributions at Maïdo. The PMF analysis including VOCs measured at the Maïdo observatory shows that the most robust solution was obtained with five factors: secondary biogenic accounting for 17%, primary anthropogenic/solvents (24%), primary biogenic (14%), primary anthropogenic/combustion (22%), and background (23%). The main contributions to formaldehyde sources as described by the PMF model are secondary biogenic (oxidation of biogenic VOCs with 37%) and background (32%). Some assumptions were necessary concerning the high percentage of unknown HCHO sources of the CKB calculation method such as the biogenic emission factor resulting in large discrepancies between the two methods.

Isoprene research - 60 years later, the biology is still enigmatic

Isoprene emission is a major component of biosphere-atmosphere interactions. It is the single largest source of non-methane hydrocarbon in the atmosphere. The first report of isoprene emission from plants was published in 1957 by Professor Guivi Sanadze. While humans have smelled the monoterpene hydrocarbons made by coniferous trees since their earliest migrations, only in 1957 did the world became aware that other trees make a type of hydrocarbon in even greater amounts but one to which the human nose is much less sensitive. For this 60th anniversary of the first report of isoprene emission from leaves, we trace the discovery and development of the research field, highlighting some of the most seminal observations and theoretical interpretations. This is not an exhaustive review, and many important papers are not cited, but we hope it will be of general interest to read how research in this field developed, how new observations forced us to reevaluate our theories about the significance of isoprene biosynthesis to plant physiology and adaptation and how scientific serendipity can sometimes drive a topic forward.

Evolution of isoprene emission capacity in plants

Light-dependent de novo volatile isoprene emission by terrestrial plants (approximately 2% of carbon fixed during photosynthesis) contributes as much as 0.5 PgC/year to the global carbon cycle. Although most plant taxa exhibit either constitutive or inducible monoterpene emissions, the evolution of isoprene emission capacity in multiple lineages has remained unexplained. Based on the predominant occurrence of isoprene emission capacity in long-lived, fast-growing woody plants; the relationship between 'metabolic scope' of tree genera and their species richness; and the proposed role of high growth rates and long generation times in accelerating molecular evolution, we hypothesise that long-lived plant genera with inherently high speciation rates have repeatedly acquired and lost the capacity to emit isoprene in their evolutionary history.

Quantitative and qualitative sensing techniques for biogenic volatile organic compounds and their oxidation products

The physiological production mechanisms of some of the organics in plants, commonly known as biogenic volatile organic compounds (BVOCs), have been known for more than a century. Some BVOCs are emitted to the atmosphere and play a significant role in tropospheric photochemistry especially in ozone and secondary organic aerosol (SOA) productions as a result of interplays between BVOCs and atmospheric radicals such as hydroxyl radical (OH), ozone (O3) and NOX (NO + NO2). These findings have been drawn from comprehensive analysis of numerous field and laboratory studies that have characterized the ambient distribution of BVOCs and their oxidation products, and reaction kinetics between BVOCs and atmospheric oxidants. These investigations are limited by the capacity for identifying and quantifying these compounds. This review highlights the major analytical techniques that have been used to observe BVOCs and their oxidation products such as gas chromatography, mass spectrometry with hard and soft ionization methods, and optical techniques from laser induced fluorescence (LIF) to remote sensing. In addition, we discuss how new analytical techniques can advance our understanding of BVOC photochemical processes. The principles, advantages, and drawbacks of the analytical techniques are discussed along with specific examples of how the techniques were applied in field and laboratory measurements. Since a number of thorough review papers for each specific analytical technique are available, readers are referred to these publications rather than providing thorough descriptions of each technique. Therefore, the aim of this review is for readers to grasp the advantages and disadvantages of various sensing techniques for BVOCs and their oxidation products and to provide guidance for choosing the optimal technique for a specific research task.

Biological and Chemical Diversity of Biogenic Volatile Organic Emissions into the Atmosphere

Biogenic volatile organic compounds (BVOC) emitted by terrestrial ecosystems into the atmosphere play an important role in determining atmospheric constituents including the oxidants and aerosols that control air quality and climate. Accurate quantitative estimates of BVOC emissions are needed to understand the processes controlling the earth system and to develop effective air quality and climate management strategies. The large uncertainties associated with BVOC emission estimates must be reduced, but this is challenging due to the large number of compounds and biological sources. The information on the immense biological and chemical diversity of BVOC is reviewed with a focus on observations that have been incorporated into the MEGAN2.1 BVOC emission model. Strategies for improving current BVOC emission modeling approaches by better representations of this diversity are presented. The current gaps in the available data for parameterizing emission models and the priorities for future measurements are discussed.

Monoterpenes of Salvia leucophylla

The “ Salvia phenomenon” is one of the most famous examples of allelopathic interaction between higher plants. The Salvia thickets are surrounded by zones of bare soil (“bare zone”, 1-3 m in width), which merge into areas of inhibited grassland (“zone of inhibition”) and finally undisturbed grassland at a distance of 3-9 m. This characteristic vegetation pattern was attributed to monoterpenes, especially 1,8-cineole and camphor, which volatilized from S. leucophylla leaves, got adsorbed in the soil around the Salvia thickets, and inhibited germination and seedling growth of annual herbs. Initially, continuity of hydrophobic environment (clay soil particles – cuticular waxes on the seed/seedling surfaces – plasmodesmata - plasma membrane) was regarded to be important for the lipophilic compounds to enter the target cells. However, monoterpenes can reach the target cells via aqueous route as well. Because monoterpenes produced by S. leucophylla all induce similar symptoms in the seedlings of target plants, their mode of action appears to be essentially common. They exert various deteriorating effects on the cells of target plants, which might be totally explained if the primary point of action resides in mitochondrial function (respiratory ATP synthesis) and/or generation of reactive oxygen species. In contrast to the previous belief that cuticular waxes act as the pathway of lipophilic monoterpene to enter the site of action or reservoir of the inhibitors, they may act as “adsorptive barrier” to prevent the entering of monoterpenes inside the cell wall.

Summer time haze characteristics of the urban atmosphere of Gwangju and the rural atmosphere of Anmyon, Korea

An extensive visibility monitoring was carried out simultaneously in the urban area of Gwangju and the rural area of Anmyon, Korea. This study examines patterns of visibility impairment and haze-forming pollutant concentrations on both sites resulting from natural and anthropogenic sources of gases and particles. Optical visibility measurements by a transmissometer, a nephelometer and an aethalometer provide aerosol light extinction, scattering, and absorption coefficients for both sites. In order to investigate the physico-chemical characteristics of atmospheric aerosols, aerosol samples were collected by various aerosol samplers at GJVMS (Gwangju Visibility Monitoring Station) and at KGAWO (Korea Global Atmosphere Watch Observatory), respectively. In addition, haze characteristics causing visibility impairment at those two sites were analyzed to obtain source contributions by regionally transported aerosols using grid analysis and display system (GrADS) from NECP reanalysis data. During the intensive monitoring period, ammonium sulfate was dominantly responsible for the fine particle mass loading at GJVMS, whereas organic carbon was the largest contributor at KGAWO. Light scattering by particles accounted for 52.8 to 81.3% of the range at the urban site, GJVMS and for 72.1 to 94.2% of the range at the rural site, KGAWO. Light absorption by the EC and NO2 was between 14.5 and 34.8% at GJVMS, which was higher than the observed 1.1 approximately 6.8% at KGAWO, respectively. Light scattering by aerosol was higher in the rural area than in the urban area. And organic carbon concentration was observed to be significantly higher than the concentration of elemental carbon at KGAWO. These haze-forming carbonaceous particles originate from anthropogenic pollutants at the urban atmosphere but they can be produced by natural environments such as marine and forest at the rural atmosphere.

ISOPRENE EMISSION FROM PLANTS

Very large amounts of isoprene are emitted from vegetation, especially from mosses, ferns, and trees. This hydrocarbon flux to the atmosphere, roughly equal to the flux of methane, has a large effect on the oxidizing potential of the atmosphere. Isoprene emission results from de novo synthesis by the deoxyxylulose phosphate/methyl erythritol 4-phosphate pathway in plastids. Dimethylallyl pyrophosphate made by this pathway is converted to isoprene by isoprene synthase. Isoprene synthase activity in plants has a high pH optimum and requirement for Mg2+ that is consistent with its location inside chloroplasts. Isoprene emission costs the plant significant amounts of carbon, ATP, and reducing power. Researchers hypothesize that plants benefit from isoprene emission because it helps photosynthesis recover from short high-temperature episodes. The evolution of isoprene emission may have been important in allowing plants to survive the rapid temperature changes that can occur in air because of the very low heat capacity of isoprene relative to water.

Ecosystem feedbacks on climate at the landscape scale

Vegetation controls aspects of climate at all scales. These controls operate through fluxes of mass (water vapour, particulates, trace gases, condensation nuclei, and ice nuclei) and energy (latent and sensible heat, radiative exchanges, and momentum dissipation) between the biosphere and the atmosphere. The role these fluxes play in controlling minimum and maximum temperature, temperature range, rainfall, and precipitation processes are detailed. On the hemispheric scale, the importance of evapotranspiration, vegetation surface roughness, and vegetation albedo in the current generation of atmospheric general circulation models is reviewed. Finally, I assess at the planetary scale the global climate effects of biogenic emissions that are well mixed throughout the troposphere. I show that daily maximum and minimum temperatures are, in part, controlled by the emission of non–methane hydrocarbons and transpired water vapour. In many regions, a substantial fraction of the rainfall arises from upstream evapotranspiration rather than from oceanic evaporation. Biosphere evapotranspiration, surface roughness, and albedo are key controls in the general circulation of the atmosphere: climate models that lack adequate specifications for these biosphere attributes fail. The biosphere modulates climate at all scales.

Factors Affecting the Emission of Monoterpenes from Red Pine (Pinus densiflora)

The mechanism of monoterpene emission from Pinus densiflora was studied using an environmentally controlled gas cabinet. It was found that monoterpene emission rate increases exponentially with temperature and is also influenced by light. These observations were explained reasonably by a mechanism whereby monoterpene emission rate depends on the monoterpene amount in the leaf oil and its saturated vapor pressure.

Influence of light and temperature on monoterpene emission rates from slash pine

There is a growing awareness of vegetation's role as a source of potentially reactive hydrocarbons that may serve as photochemical oxidant precursors. This study assessed the influence of light and temperature, independently, on monoterpene emissions from slash pine (Pinus elliottii Engelm.). Plants were preconditioned in a growth chamber, then transferred to an environmentally controlled gas exchange chamber. Samples of the chamber atmosphere were collected; the monoterpenes were concentrated cryogenically and measured by gas chromatography. Five monoterpenes (alpha-pinene, beta-pinene, myrcene, limonene, and beta-phellandrene) were present in the vapor phase surrounding the plants in sufficient quantity for reliable measurement. Light did not directly influence monoterpene emission rates since the emissions were similar in both the dark and at various light intensities. Monoterpene emission rates increased exponentially with temperature (i. e. emissions depend on temperature in a log-linear manner). The summed emissions of the five monoterpenes ranged from 3 to 21 micrograms C per gram dry weight per hour as temperature was increased from 20 to 46 C. Initially, emission rates from heat-stressed needles were similar to healthy needles, but rates decreased 11% per day. Daily carbon loss through monoterpene emissions accounted for approximately 0.4% of the carbon fixed during photosynthesis.

Sulfate Aerosol: Its Geographical Extent in the Midwestern and Southern United States

Sulfate particles (sulfuric acid and its neutralization products with ammonia) dominate the submicrometer-sized, light-scattering component of the aerosol in more than 90 percent of 2850 pairs of humidographic measurements made over a 3-month period at three rural midwestern and southern sites. The nearly continuous optical dominance by sulfate in the aerosol at these spatially varied locations, particularly in the Ozark Mountains, suggests that sulfate is a component of the submicrometer-sized aerosol that is distributed over a large geographical region and is not due to local sources.

Gas chromatographic-mass spectrometric evaluation of exhaled tobacco smoke

The impact of cigarette smoking on the distribution of organic substances in ambient air has been determined for the intermediate volatility range. A simple sampling procedure was employed, involving gas-solid adsorption onto an organic polymer followed by direct thermal elution onto a glass capillary column. Aliphatic and substituted aromatic hydrocarbons are predominant in urban atmospheres. Depending on location and weather conditions the total concentration of such volatiles can differ by as much as a factor of 20. This high background variation makes it difficult to analyze for trace substances with low odor threshold values, such as encountered in cigarette smoke. Standard cigarettes were smoked in a relatively small room, having no air filtration system. Air samples of approximately 3.51 were taken. The amount of volatiles added to air by cigarette smoking is unsignificant. Substances were analyzed and identified by gas chromatography and gas chromatography-mass spectrometry with glass capillary columns. Many compounds reported in cigarette smoke condensate have been confirmed.