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Wetlands cover only 3g% of the global land surface area, but boreal wetlands are experiencing an unprecedented warming of four times the global average. These wetlands emit isoprene and terpenes (including monoterpenes (MT), sesquiterpenes (SQT), and diterpenes (DT)), which are climate-relevant highly reactive biogenic volatile organic compounds (BVOCs) with an exponential dependence on temperature. In this study, we present ecosystem-scale eddy covariance (EC) fluxes of isoprene, MT, SQT, and DT (hereafter referred to together as terpenes) at Siikaneva, a boreal fen in southern Finland, from the start to the peak of the growing season of 2021 (19 May 2021 to 28 June 2021). These are the first EC fluxes reported using the novel state-of-the-art Vocus proton transfer reaction mass spectrometer (Vocus-PTR) and the first-ever fluxes reported for DTs from a wetland. Isoprene was the dominant compound emitted by the wetland, followed by MTs, SQTs, and DTs, and they all exhibited a strong exponential temperature dependence. The Q10 values, the factor by which terpene emissions increases for every 10gg C rise in temperature, were up to five times higher than those used in most BVOC models. During the campaign, the air temperature peaked above 31gg C on 21-22 June 2021, which is abnormally high for boreal environments, and the maximum flux for all terpenes coincided with this period. We observed that terpene emissions were elevated after this abnormally "high-temperature stress period", indicating that past temperatures alter emissions significantly. The standardized emission factor (EF) of the fen for isoprene (EFiso) was 11.1g±g 0.3gnmolgm-2gs-1, which is at least two times higher than in previous studies and as high as the emission factors typical for broadleaf and other forests in the lower latitudes. We observed EFMT of 2.4g±g 0.1gnmolgm-2gs-1, EFSQT of 1.3g±g0.03gnmolgm-2gs-1, higher than typical for needle leaf and broadleaf tree functional types, and EFDT of 0.011g±g0.001gnmolgm-2gs-1. We also compared the landscape average emissions to the model of emissions of gases and aerosols from nature (MEGAN) v2.1 and found that the emissions were underestimated by over 9 times for isoprene, over 300 times for MTs, and 800 times for SQTs. Our results show that due to very high EFs and high sensitivity to increasing temperatures, these high-latitude ecosystems can be a large source of terpenes to the atmosphere, and anthropogenic global warming could induce much higher BVOC emissions from wetlands in the future., Lejish Vettikkat was financially supported by the UEF EPHB doctoral degree program. This work was financially supported by the Academy of Finland Flagship program (grant nos. 337550 and 337549) and Academy of Finland project no. 310682. Simon Schallhart was supported by Academy of Finland project no. 323255. Tuukka Petäjä was supported by Academy of Finland project nos. 1325681 and 1328616. Elisa Männistö and Eeva-Stiina Tuittila were supported by Academy of Finland project no. 330840. Roger Seco was supported by a Ramón y Cajal grant (RYC2020-029216-I) funded by MCIN/AEI/10.13039/501100011033 and by “ESF Investing in your future”, as well as project PID2021-122892NA-I00 funded by MCIN/AEI and by “ERDF A way of making Europe”. IDAEA-CSIC is a Severo Ochoa Centre of Research Excellence (MCIN/AEI, Project CEX2018-000794-S). Alex B. Guenther was supported by the US National Science Foundation award ANS-2041250.

We introduce two new drought stress algorithms designed to simulate isoprene emission with the Model of Emissions of Gases and Aerosols from Nature (MEGAN) model. The two approaches include the representation of the impact of drought on isoprene emission with a simple empirical approach for offline MEGAN applications and a more process-based approach for online MEGAN in Community Land Model (CLM) simulations. The two versions differ in their implementation of leaf-temperature impacts of mild drought. For the online version of MEGAN that is coupled to CLM, the impact of drought on leaf temperature is simulated directly and the calculated leaf temperature is considered for the estimation of isoprene emission. For the offline version, we apply an empirical algorithm derived from whole-canopy flux measurements for simulating the impact of drought ranging from mild to severe stage. In addition, the offline approach adopts the ratio (fPET) of actual evapotranspiration to potential evapotranspiration to quantify the severity of drought instead of using soil moisture. We applied the two algorithms in the CLM-CAM-chem (the Community Atmosphere Model with Chemistry) model to simulate the impact of drought on isoprene emission and found that drought can decrease isoprene emission globally by 11% in 2012. We further compared the formaldehyde (HCHO) vertical column density simulated by CAM-chem to satellite HCHO observations. We found that the proposed drought algorithm can improve the match with the HCHO observations during droughts, but the performance of the drought algorithm is limited by the capacity of the model to capture the severity of drought., H. Wang, X. Jiang and A. Guenther were supported by the U.S. National Science Foundation (NSF) Atmospheric Chemistry program award AGS-1643042, the National Aeronautics and Space Administration (NASA) and the Atmospheric Composition Modeling and Analysis Program (ACMAP) program award 80NSSC19K0986. R. Seco acknowledges Grants RYC2020-029216-I and CEX2018-000794-S funded by MCIN/AEI/10.13039/501100011033 and by “ESF Investing in your future.” T. Stavrakou and A. Guenther were partly supported by the ALBERI project, funded by the Belgian Science Policy Office via the STEREO II programme (SR/00/373). T. Karl received support from projects FWF P30600-NBL and FWF P33701. The authors would like to acknowledge high-performance computing support from Cheyenne (https://doi.org/10.5065/D6RX99HX) provided by NCAR's Computational and Information Systems Laboratory, sponsored by the National Science Foundation.

Volatile organic compounds (VOCs) emitted from forests are important chemical components that affect ecosystem functioning, atmospheric chemistry, and regional climate. Temperature differences between a forest and an adjacent river can induce winds that influence VOC fate and transport. Quantitative observations and scientific understanding, however, remain lacking. Herein, daytime VOC datasets were collected from the surface up to 500 m over the “Rio Negro” river in Amazonia. During time periods of river winds, isoprene, α-pinene, and β-pinene concentrations increased by 50, 60, and 80% over the river, respectively. The concentrations at 500 m were up to 80% greater compared to those at 100 m because of the transport path of river winds. By comparison, the concentration of methacrolein, a VOC oxidation product, did not depend on river winds or height. The differing observations for primary emissions and oxidation products can be explained by the coupling of timescales among emission, reaction, and transport. This behavior was captured in large-eddy simulations with a coupled chemistry model. The observed and simulated roles of river winds in VOC fate and transport highlight the need for improved representation of these processes in regional models of air quality and chemistry–climate coupling.

Biogenic volatile organic compound (BVOC) emissions have long been known to play vital roles in modulating the formation of ozone and secondary organic aerosols (SOAs). While early studies have evaluated their impact globally or regionally, the BVOC emissions emitted from urban green spaces (denoted as U-BVOC emissions) have been largely ignored primarily due to the failure of low-resolution land cover in resolving such processes, but also because their important contribution to urban BVOCs was previously unrecognized. In this study, by utilizing a recently released high-resolution land cover dataset, we develop the first set of emission inventories of U-BVOCs in China at spatial resolutions as high as 1 km. This new dataset resolved densely distributed U-BVOCs in urban core areas. The U-BVOC emissions in megacities could account for a large fraction of total BVOC emissions, and the good agreement of the interannual variations between the U-BVOC emissions and ozone concentrations over certain regions stresses their potentially crucial role in influencing ozone variations. The newly constructed U-BVOC emission inventory is expected to provide an improved dataset to enable the research community to re-examine the modulation of BVOCs on the formation of ozone, SOA, and atmospheric chemistry in urban environments.

Natural emissions play a key role in modulating the formation of ground-level ozone (O

Mitigation of ambient ozone (O

Biogenic volatile organic compounds (BVOCs) from terrestrial vegetation and marine organisms contribute to photochemical pollution and affect the radiation budget, cloud properties and precipitation via secondary organic aerosol formation. Their emission from both marine and terrestrial ecosystems is substantially affected by climate change in ways that are currently not well characterized. The Eastern Mediterranean Sea was identified as a hotspot for climate change, making it a natural laboratory for investigating the impact of climate change on BVOC emission from both terrestrial and marine vegetation. We quantified the mixing ratios of a suite of volatile organic compounds (VOCs), including isoprene, dimethyl sulfide (DMS), acetone, acetaldehyde and monoterpenes, at a mixed vegetation site ~ 4 km from the southeastern tip of the Levantine Basin, where the sea surface temperature maximizes and ultra-oligotrophic conditions prevail. The measurements were performed between July and October, 2015, using a proton-transfer-reaction–time-of-flight mass spectrometer. The analyses were supported by the Model of Emissions of Gases and Aerosols from Nature (MEGAN 2.1). For isoprene and DMS mixing ratios, we identified a dominant contribution from the seawater. Our analyses further suggest a major contribution at least for monoterpenes from the seawater. Our results indicate that the Levantine Basin greatly contributes to isoprene emission, corresponding with mixing ratios of up to ~ 9 ppbv. This highlights the need to update air-quality and climate models to account for the impact of sea surface temperature (SST) on marine isoprene emission. The DMS mixing ratios were one-to-two orders of magnitude lower than those measured in 1995 in the same area, suggesting a dramatic decrease in emission due to changes in the species composition induced by the rise in SST.

We present a characterization of the chemical composition of the atmosphere of the Brazilian Amazon rainforest based on trace gases measurements carried out during the South American Biomass Burning Analysis (SAMBBA) airborne experiment in September 2012. We analyzed the observations of primary biomass burning emission tracers, i.e., carbon monoxide (CO) and nitrogen oxides (NOx), ozone (O3), isoprene, and its main oxidation products, methyl vinyl ketone (MVK), methacrolein (MACR), and hydroxyhydroperoxides (ISOPOOH). The focus of SAMBBA was primarily on biomass burning emissions, but there were also several flights in areas of the Amazon forest not directly affected by biomass burning, revealing a background with a signature of biomass burning in the chemical composition due to long-range transport of biomass burning tracers from both Africa and the eastern part of Amazonia. We used the [MVK + MACR + ISOPOOH] / [Isoprene] ratio and the hydroxyl radical (OH) indirect calculation to assess the oxidative capacity of the Amazon forest atmosphere. We compared the background regions (CO

Alkenes are reactive hydrocarbons that influence local and regional atmospheric chemistry by playing important roles in the photochemical production of tropospheric ozone and in the formation of secondary organic aerosols. The simplest alkene, ethene (ethylene), is a major plant hormone and ripening agent for agricultural commodities. The group of light alkenes (C2-C4) originates from both biogenic and anthropogenic sources, but their biogenic sources are poorly characterized, with limited field-based flux observations. Here we report net ecosystem fluxes of light alkenes and isoprene from a semiarid ponderosa pine forest in the Rocky Mountains of Colorado, USA using the relaxed eddy accumulation (REA) technique during the summer of 2014. Ethene, propene, butene and isoprene emissions have strong diurnal cycles, with median daytime fluxes of 123, 95, 39 and 17 μg mg-2 hg-1, respectively. The fluxes were correlated with each other, followed general ecosystem trends of CO2 and water vapor, and showed similar sunlight and temperature response curves as other biogenic VOCs. The May through October flux, based on measurements and modeling, averaged 62, 52, 24 and 18 μg mg-2 hg-1 for ethene, propene, butene and isoprene, respectively. The light alkenes contribute significantly to the overall biogenic source of reactive hydrocarbons: roughly 18 % of the dominant biogenic VOC, 2-methyl-3-buten-2-ol. The measured ecosystem scale fluxes are 40-80 % larger than estimates used for global emissions models for this type of ecosystem.

The focus of the studies presented in the preceding companion paper (Part A: Review) and here (Part B: Applications) is on defining representative emission rates from vegetation for determining the roles of biogenic volatile organic compound (BVOC) emissions in atmospheric chemistry and aerosol processes. The review of previously published procedures for identifying and quantifying BVOC emissions has revealed a wide variety of experimental methods used by various researchers. Experimental details become increasingly critical for quantitative emission measurements of low volatility monoterpenes (MT) and sesquiterpenes (SQT). These compounds are prone to be lost inadvertently by uptake to materials in contact with the sample air or by reactions with atmospheric oxidants. These losses become more prominent with higher molecular weight compounds, potentially leading to an underestimation of their emission rates. We present MT and SQT emission rate data from numerous experiments that include 23 deciduous tree species, 14 coniferous tree species, 8 crops, and 2 shrubs. These data indicate total, normalized (30 degrees C) basal emission rates from10 to 5600ngCg(-1)h(-1) for MT, and from10 to 1150ngCg(-1)h(-1) for SQT compounds. Both MT and SQT emissions have exponential dependencies on temperature (i.e. rates are proportional to e(betaT)). The inter-quartile range of beta-values for MT was between 0.12 and 0.17K(-1), which is higher than the value commonly used in models (0.09K(-1)). However many of the MT emissions also exhibited light dependencies, making it difficult to separate light and temperature influences. The primary light-dependent MT was ocimene, whose emissions were up to a factor of 10 higher than light-independent MT emissions. The inner-quartile range of beta-values for SQT was between 0.15 and 0.21K(-1).