Inferring the diurnal variability of OH radical concentrations over the Amazon from BVOC measurements

The atmospheric oxidation of biogenic volatile organic compounds (BVOC) by OH radicals over tropical rainforests impacts local particle production and the lifetime of globally distributed chemically and radiatively active gases. For the pristine Amazon rainforest during the dry season, we empirically determined the diurnal OH radical variability at the forest-atmosphere interface region between 80 and 325 m from 07:00 to 15:00 LT using BVOC measurements. A dynamic time warping approach was applied showing that median averaged mixing times between 80 to 325 m decrease from 105 to 15 min over this time period. The inferred OH concentrations show evidence for an early morning OH peak (07:00-08:00 LT) and an OH maximum (14:00 LT) reaching 2.2 (0.2, 3.8) × 106 molecules cm-3 controlled by the coupling between BVOC emission fluxes, nocturnal NOx accumulation, convective turbulence, air chemistry and photolysis rates. The results were evaluated with a turbulence resolving transport (DALES), a regional scale (WRF-Chem) and a global (EMAC) atmospheric chemistry model.

Ozone Impact on Emission of Biogenic Volatile Organic Compounds in Three Tropical Tree Species From the Atlantic Forest Remnants in Southeast Brazil

Plants emit a broad number of Biogenic Volatile Organic Compounds (BVOCs) that can impact urban ozone (O₃) production. Conversely, the O₃ is a phytotoxic pollutant that causes unknown alterations in BVOC emissions from native plants. In this sense, here, we characterized the constitutive and O₃-induced BVOCs for two (2dO₃) and four (4dO₃) days of exposure (O₃ dose 80 ppb) and evaluated the O₃ response by histochemical techniques to detect programmed cell death (PCD) and hydrogen peroxide (H₂O₂) in three Brazilian native species. Croton floribundus Spreng, Astronium graveolens Jacq, and Piptadenia gonoacantha (Mart.) JF Macbr, from different groups of ecological succession (acquisitive and conservative), different carbon-saving defense strategies, and specific BVOC emissions. The three species emitted a very diverse BVOC composition: monoterpenes (MON), sesquiterpenes (SEQ), green leaf volatiles (GLV), and other compounds (OTC). C. floribundus is more acquisitive than A. graveolens. Their most representative BVOCs were methyl salicylate-MeSA (OTC), (Z) 3-hexenal, and (E)-2-hexenal (GLV), γ-elemene and (-)-β-bourbonene (SEQ) β-phellandrene and D-limonene (MON), while in A. graveolens were nonanal and decanal (OTC), and α-pinene (MON). Piptadenia gonoachanta is more conservative, and the BVOC blend was limited to MeSA (OTC), (E)-2-hexenal (GLV), and β-Phellandrene (MON). The O₃ affected BVOCs and histochemical traits of the three species in different ways. Croton floribundus was the most O₃ tolerant species and considered as an SEQ emitter. It efficiently reacted to O₃ stress after 2dO_3, verified by a high alteration of BVOC emission, the emergence of the compounds such as α-Ionone and trans-ß-Ionone, and the absence of H₂O₂ detection. On the contrary, A. graveolens, a MON-emitter, was affected by 2dO₃ and 4dO₃, showing increasing emissions of α-pinene and β-myrcene, (MON), γ-muurolene and β-cadinene (SEQ) and H₂O₂ accumulation. Piptadenia gonoachanta was the most sensitive and did not respond to BVOCs emission, but PCD and H₂O₂ were highly evidenced. Our results indicate that the BVOC blend emission, combined with histochemical observations, is a powerful tool to confirm the species' tolerance to O₃. Furthermore, our findings suggest that BVOC emission is a trade-off associated with different resource strategies of species indicated by the changes in the quality and quantity of BVOC emission for each species.

CO2 -responsiveness of leaf isoprene emission: Why do species differ?

Leaf isoprene emission rate, I, decreases with increasing atmospheric CO₂ concentration with major implications for global change. There is a significant interspecific variability in [CO₂ ]-responsiveness of I, but the extent of this variation is unknown and its reasons are not understood. We hypothesized that the magnitude of emission reduction reflects the size and changeability of precursor pools responsible for isoprene emission (dimethylallyl diphosphate, DMADP and 2-methyl-erythritol 2,4-cyclodiphosphate, MEcDP). Changes in I and intermediate pool sizes upon increase of [CO₂ ] from 400 to 1500 μmol/mol were studied in nine woody species spanning boreal to tropical ecosystems. I varied 10-fold, total substrate pool size 37-fold and the ratio of DMADP/MEcDP pool sizes 57-fold. At higher [CO₂ ], I was reduced on average by 65%, but [CO₂ ]-responsiveness varied an order of magnitude across species. The increase in [CO₂ ] resulted in concomitant reductions in both substrate pools. The variation in [CO₂ ]-responsiveness across species scaled with the reduction in pool sizes, the substrate pool size supported and the share of DMADP in total substrate pool. This study highlights a major interspecific variation in [CO₂ ]-responsiveness of isoprene emission and conclusively links this variation to interspecific variability in [CO₂ ] effects on substrate availability and intermediate pool size.

O3 Concentration and Its Relation with BVOC Emissions in a Subtropical Plantation

An empirical model of O3 is developed using the measurements of emissions of biogenic volatile organic compounds (BVOCs), O3 concentration, global solar radiation, photosynthetically active radiation (PAR) and meteorological variables in a subtropical Pinus plantation, China, during 2013–2016. In view of the different structures of isoprene and monoterpenes, two empirical models of O3 concentration are developed, considering PAR absorption and scattering due to gases, liquids and particles (GLPs), as well as PAR attenuation caused by O3 and BVOCs. The estimated O3 is in agreement with the observations, and validation of the O3 empirical model is conducted. O3 concentrations are more sensitive to changes in PAR and water vapor than S/Q (horizontal diffuse to global solar radiation) and BVOC emissions. O3 is positive to changes in isoprene emission at low light and high GLPs, or negative at high light and low GLPs; O3 is negative to changes in monoterpene emissions. O3 are positive with the changes of PAR, water vapor and S/Q. It is suggested to control human-induced high BVOC emissions, regulate plant cutting, and reduce NOx and SO2 emissions more strictly than ever before. There are inverted U-shape interactions between O3 and its driving factors, and S/Q controls their turning points.

Using highly time-resolved online mass spectrometry to examine biogenic and anthropogenic contributions to organic aerosol in Beijing

Organic aerosols, a major constituent of fine particulate mass in megacities, can be directly emitted or formed from secondary processing of biogenic and anthropogenic volatile organic compound emissions. The complexity of volatile organic compound emission sources, speciation and oxidation pathways leads to uncertainties in the key sources and chemistry leading to formation of organic aerosol in urban areas. Historically, online measurements of organic aerosol composition have been unable to resolve specific markers of volatile organic compound oxidation, while offline analysis of markers focus on a small proportion of organic aerosol and lack the time resolution to carry out detailed statistical analysis required to study the dynamic changes in aerosol sources and chemistry. Here we use data collected as part of the joint UK-China Air Pollution and Human Health (APHH-Beijing) collaboration during a field campaign in urban Beijing in the summer of 2017 alongside laboratory measurements of secondary organic aerosol from oxidation of key aromatic precursors (1,3,5-trimethyl benzene, 1,2,4-trimethyl benzene, propyl benzene, isopropyl benzene and 1-methyl naphthalene) to study the anthropogenic and biogenic contributions to organic aerosol. For the first time in Beijing, this study applies positive matrix factorisation to online measurements of organic aerosol composition from a time-of-flight iodide chemical ionisation mass spectrometer fitted with a filter inlet for gases and aerosols (FIGAERO-ToF-I-CIMS). This approach identifies the real-time variations in sources and oxidation processes influencing aerosol composition at a near-molecular level. We identify eight factors with distinct temporal variability, highlighting episodic differences in OA composition attributed to regional influences and in situ formation. These have average carbon numbers ranging from C₅-C₉ and can be associated with oxidation of anthropogenic aromatic hydrocarbons alongside biogenic emissions of isoprene, α-pinene and sesquiterpenes.

Biogenic Volatile Organic Compounds Emission of Brazilian Atlantic Tree Grown Under Elevated Ozone in Ambient Controlled and Field Conditions

Croton floribundus (L.) Spreng trees were exposed to accumulated ozone (O₃) levels under laboratory and field conditions and monitored the foliar visible symptoms and BVOC emissions. Plants exposed to O₃ in the laboratory presented more substantial damage and significant increase in the BVOC emissions than plants in the field. Caryophyllene and 3-hexen-1-ol emissions were significantly increased in plants exposed to O₃ in the laboratory. Under field conditions, methyl salicylate (MeSA) was the majority compound emitted. A positive correlation among the meteorological conditions, O₃ and MeSA emission was observed in the field conditions, which may represent a mechanism of tolerance by C. floribundus to deal with long-term exposure to O₃.

Amazonian biogenic volatile organic compounds under global change

Biogenic volatile organic compounds (BVOCs) play important roles at cellular, foliar, ecosystem and atmospheric levels. The Amazonian rainforest represents one of the major global sources of BVOCs, so its study is essential for understanding BVOC dynamics. It also provides insights into the role of such large and biodiverse forest ecosystem in regional and global atmospheric chemistry and climate. We review the current information on Amazonian BVOCs and identify future research priorities exploring biogenic emissions and drivers, ecological interactions, atmospheric impacts, depositional processes and modifications to BVOC dynamics due to changes in climate and land cover. A feedback loop between Amazonian BVOCs and the trends of climate and land-use changes in Amazonia is then constructed. Satellite observations and model simulation time series demonstrate the validity of the proposed loop showing a combined effect of climate change and deforestation on BVOC emission in Amazonia. A decreasing trend of isoprene during the wet season, most likely due to forest biomass loss, and an increasing trend of the sesquiterpene to isoprene ratio during the dry season suggest increasing temperature stress-induced emissions due to climate change.

Characterization of Total OH Reactivity in a Rapeseed Field: Results from the COV3ER Experiment in April 2017

Croplands remain poorly studied ecosystems in terms of total hydroxyl radical (OH) reactivity, especially when compared to forests. As part of the COV3ER project, total OH reactivity (ROH), defined as the total loss rate of OH due to its reaction with reactive species in the atmosphere, was characterized in a rapeseed field (Grignon, France) during the blooming season in April 2017. Measurements were performed in a dynamic chamber as well as in ambient air using the Comparative Reactivity Method (CRM). Complementary measurements of organic (including a proton transfer reaction quadrupole ion–time of flight mass spectrometry, PTRQi-ToFMS) and inorganic compounds were also performed in order to calculate the expected OH reactivity and evaluate the missing fraction. Measured ROH varied diurnally in the dynamic chamber (mROHchamber) with maxima around 20 to 30 s−1 at midday and minima during dark hours, following the variability of the enclosed branch VOCsrapeseed, which is light- and temperature-dependent. Oxygenated VOCs were the major compounds emitted by the rapeseed crop. However, in terms of contribution to OH reactivity, isoprene accounted for 40% during the daytime, followed by acetaldehyde (21%) and monoterpenes (18%). The comparison between mROHchamber and calculated ROH (cROHchamber) exhibited little or no difference during dark hours, whereas a maximum difference appeared around midday, highlighting a significant missing fraction (46% on average during daytime) mainly related to biogenic temperature- and/or light-dependent emissions.

Origin of volatile organic compound emissions from subarctic tundra under global warming

Warming occurs in the Arctic twice as fast as the global average, which in turn leads to a large enhancement in terpenoid emissions from vegetation. Volatile terpenoids are the main class of biogenic volatile organic compounds (VOCs) that play crucial roles in atmospheric chemistry and climate. However, the biochemical mechanisms behind the temperature-dependent increase in VOC emissions from subarctic ecosystems are largely unexplored. Using ¹³ CO₂ -labeling, we studied the origin of VOCs and the carbon (C) allocation under global warming in the soil-plant-atmosphere system of contrasting subarctic heath tundra vegetation communities characterized by dwarf shrubs of the genera Salix or Betula. The projected temperature rise of the subarctic summer by 5°C was realistically simulated in sophisticated climate chambers. VOC emissions strongly depended on the plant species composition of the heath tundra. Warming caused increased VOC emissions and significant changes in the pattern of volatiles toward more reactive hydrocarbons. The ¹³ C was incorporated to varying degrees in different monoterpene and sesquiterpene isomers. We found that de novo monoterpene biosynthesis contributed to 40%-44% (Salix) and 60%-68% (Betula) of total monoterpene emissions under the current climate, and that warming increased the contribution to 50%-58% (Salix) and 87%-95% (Betula). Analyses of above- and belowground ^12/13 C showed shifts of C allocation in the plant-soil systems and negative effects of warming on C sequestration by lowering net ecosystem exchange of CO₂ and increasing C loss as VOCs. This comprehensive analysis provides the scientific basis for mechanistically understanding the processes controlling terpenoid emissions, required for modeling VOC emissions from terrestrial ecosystems and predicting the future chemistry of the arctic atmosphere. By changing the chemical composition and loads of VOCs into the atmosphere, the current data indicate that global warming in the Arctic may have implications for regional and global climate and for the delicate tundra ecosystems.

Modeling emissions for three-dimensional atmospheric chemistry transport models

Poor air quality is still a threat for human health in many parts of the world. In order to assess measures for emission reductions and improved air quality, three-dimensional atmospheric chemistry transport modeling systems are used in numerous research institutions and public authorities. These models need accurate emission data in appropriate spatial and temporal resolution as input. This paper reviews the most widely used emission inventories on global and regional scales and looks into the methods used to make the inventory data model ready. Shortcomings of using standard temporal profiles for each emission sector are discussed, and new methods to improve the spatiotemporal distribution of the emissions are presented. These methods are often neither top-down nor bottom-up approaches but can be seen as hybrid methods that use detailed information about the emission process to derive spatially varying temporal emission profiles. These profiles are subsequently used to distribute bulk emissions such as national totals on appropriate grids. The wide area of natural emissions is also summarized, and the calculation methods are described. Almost all types of natural emissions depend on meteorological information, which is why they are highly variable in time and space and frequently calculated within the chemistry transport models themselves. The paper closes with an outlook for new ways to improve model ready emission data, for example, by using external databases about road traffic flow or satellite data to determine actual land use or leaf area. In a world where emission patterns change rapidly, it seems appropriate to use new types of statistical and observational data to create detailed emission data sets and keep emission inventories up-to-date.

IMPLICATIONS

Emission data are probably the most important input for chemistry transport model (CTM) systems. They need to be provided in high spatial and temporal resolution and on a grid that is in agreement with the CTM grid. Simple methods to distribute the emissions in time and space need to be replaced by sophisticated emission models in order to improve the CTM results. New methods, e.g., for ammonia emissions, provide grid cell-dependent temporal profiles. In the future, large data fields from traffic observations or satellite observations could be used for more detailed emission data.

Chronic Drought Decreases Anabolic and Catabolic BVOC Emissions of Quercus pubescens in a Mediterranean Forest

Biogenic volatile organic compounds (BVOC) emitted by plants can originate from both anabolism (metabolite production through anabolic processes) and catabolism (metabolite degradation by oxidative reactions). Drought can favor leaf oxidation by increasing the oxidative pressure in plant cells. Thus, under the precipitation decline predicted for the Mediterranean region, it can be expected both strong oxidation of anabolic BVOC within leaves and, as a result, enhanced catabolic BVOC emissions. Using an experimental rain exclusion device in a natural forest, we compared the seasonal course of the emissions of the main anabolic BVOC released by Q. pubescens (isoprene and methanol) and their catabolic products (MACR+MVK+ISOPOOH and formaldehyde, respectively) after 3 years of precipitation restriction (-30% of rain). Thus, we assume that this repetitive amplified drought promoted a chronic drought. BVOC emissions were monitored, on-line, with a PTR-ToF-MS. Amplified drought decreased all BVOC emissions rates in spring and summer by around 40-50 %, especially through stomatal closure, with no effect in autumn. Moreover, ratios between catabolic and anabolic BVOC remained unchanged with amplified drought, suggesting a relative stable oxidative pressure in Q. pubescens under the water stress applied. Moreover, these results suggest a quite good resilience of this species under the most severe climate change scenario in the Mediterranean region.

Sesquiterpene emissions from Alternaria alternata and Fusarium oxysporum: Effects of age, nutrient availability, and co-cultivation

Alternaria alternata is one of the most studied fungi to date because of its impact on human life – from plant pathogenicity to allergenicity. However, its sesquiterpene emissions have not been systematically explored. Alternaria regularly co-occurs with Fusarium fungi, which are common plant pathogens, on withering plants. We analyzed the diversity and determined the absolute quantities of volatile organic compounds (VOCs) in the headspace above mycelial cultures of A. alternata and Fusarium oxysporum under different conditions (nutrient rich and poor, single cultures and co-cultivation) and at different mycelial ages. Using stir bar sorptive extraction and gas chromatography–mass spectrometry, we observed A. alternata to strongly emit sesquiterpenes, particularly during the early growth stages, while emissions from F. oxysporum consistently remained comparatively low. The emission profile characterizing A. alternata comprised over 20 sesquiterpenes with few effects from nutrient quality and age on the overall emission profile. Co-cultivation with F. oxysporum resulted in reduced amounts of VOCs emitted from A. alternata although its profile remained similar. Both fungi showed distinct emission profiles, rendering them suitable biomarkers for growth-detection of their phylotype in ambient air. The study highlights the importance of thorough and quantitative evaluations of fungal emissions of volatile infochemicals such as sesquiterpenes.