SOA formation potential of emissions from soil and leaf litter

Unlocking the secrets: Volatile Organic Compounds (VOCs) and their devastating effects on lung cancer

Lung cancer (LCs) is still a serious health problem globally, with many incidences attributed to environmental triggers such as Volatile Organic Compounds (VOCs). VOCs are a broad class of compounds that can be released via various sources, including industrial operations, automobile emissions, and indoor air pollution. VOC exposure has been linked to an elevated risk of lung cancer via multiple routes. These chemicals can be chemically converted into hazardous intermediate molecules, resulting in DNA damage and genetic alterations. VOCs can also cause oxidative stress, inflammation, and a breakdown in the cellular protective antioxidant framework, all of which contribute to the growth of lung cancer. Moreover, VOCs have been reported to alter critical biological reactions such as cell growth, apoptosis, and angiogenesis, leading to tumor development and metastasis. Epidemiological investigations have found a link between certain VOCs and a higher probability of LCs. Benzene, formaldehyde, and polycyclic aromatic hydrocarbons (PAHs) are some of the most well-researched VOCs, with comprehensive data confirming their cancer-causing potential. Nevertheless, the possible health concerns linked with many more VOCs and their combined use remain unknown, necessitating further research. Identifying the toxicological consequences of VOCs in LCs is critical for establishing focused preventative tactics and therapeutic strategies. Better legislation and monitoring mechanisms can limit VOC contamination in occupational and environmental contexts, possibly reducing the prevalence of LCs. Developing VOC exposure indicators and analyzing their associations with genetic susceptibility characteristics may also aid in early identification and targeted therapies.

A review of the factors affecting the emission of the ozone chemical precursors VOCs and NOx from the soil

The soil environment is one of the main places for the generation, emission, and absorption of various atmospheric pollutants, including nitrogen oxides (NO_x) and volatile organic compounds (VOCs), which are the main chemical precursors for the formation of ground-level ozone. Ground-level ozone pollution has become a concerning environmental problem because of the harm it poses to human health and the surrounding ecological environment. However, current studies on chemical precursors of ozone mainly focus on emissions from industrial sources, forest vegetation, and urban vehicle exhaust; by contrast, few studies have examined the role of the soil environment on NO_x and VOCs emissions. In addition, the soil environment is complex and heterogeneous. Agricultural activities (fertilization) and atmospheric deposition provide nutrients for the soil environment, with a significant effect on NO_x and VOCs emissions. There is thus a need to study the environmental factors related to the release of NO_x and VOCs in the soil to enhance our understanding of emission fluxes and the types of NO_x and VOCs in the soil environment and aid efforts to control ground-level ozone pollution through appropriate measures such as management of agricultural activities. This paper reviews the generation of NO_x and VOCs in the soil environment and the effects of various environmental factors on this process. Some suggestions are provided for future research on the regulation of NO_x and VOCs emissions in the soil environment and the ability of the soil environment to contribute to ground-level ozone pollution.

Tracer-based characterization of fine carbonaceous aerosol in Beijing during a strict emission control period

Strict emission controls were implemented in Beijing and the surrounding regions in the North China Plain to guarantee good air quality during the 2014 Asia-Pacific Economic Cooperation (APEC) summit. Thus, the APEC period provides a good opportunity to study the sources and formation processes of atmospheric organic aerosol. Here, fine particles (PM_2.5, particulate matter with a diameter of 2.5 μm or less) collected in urban Beijing before and during the APEC period were analyzed for molecular tracers of primary and secondary organic aerosol (SOA). The primary organic carbon (POC) and secondary organic carbon (SOC) were also reconstructed using a tracer-based method. The concentrations of biogenic SOA tracers ranged from 1.09 to 34.5 ng m^-3 (mean 10.3 ± 8.51 ng m^-3). Monoterpene oxidation products were the largest contributor to biogenic SOA, followed by isoprene- and sesquiterpene-derived SOA. The concentrations of biogenic SOA tracers decreased by 50 % during the APEC, which was largely attributed to the implementation of emission controls by the Chinese government. The increasing mass fractions of biogenic SOA tracers from isoprene and sesquiterpene during the pollution episodes implied that their photooxidation processes contributed to the poor air quality in urban Beijing. The reconstructed biogenic and anthropogenic SOC and POC concentrations were 89.6 ± 96.8 ng m^-3, 570 ± 611 ng m^-3, and 2.49 ± 2.08 μg m^-3, respectively, accounting for 21.9 ± 11.4 % of OC in total. Biomass-burning derived OC was the largest contributor to carbonaceous aerosol over the North China Plain. By comparing the results before and during the APEC, the emission controls effectively mitigated about 34 % of the estimated OC and were more effective at reducing SOC than POC. This suggests that the reduction of the primary organic aerosol loading is harder than SOA over the North China Plain.

Volatilome of Aleppo Pine litter over decomposition process

Biogenic Volatile Organic Compounds (BVOC) are largely accepted to contribute to both atmospheric chemistry and ecosystem functioning. While the forest canopy is recognized as a major source of BVOC, emissions from plant litter have scarcely been explored with just a couple of studies being focused on emission patterns over litter decomposition process. The aim of this study was to quantitatively and qualitatively characterize BVOC emissions (C1-C15) from Pinus halepensis litter, one of the major Mediterranean conifer species, over a 15-month litter decomposition experiment. Senescent needles of P. halepensis were collected and placed in 42 litterbags where they underwent in situ decomposition. Litterbags were collected every 3 months and litter BVOC emissions were studied in vitro using both online (PTR-ToF-MS) and offline analyses (GC-MS). Results showed a large diversity of BVOC (58 compounds detected), with a strong variation over time. Maximum total BVOC emissions were observed after 3 months of decomposition with 9.18 µg gDM -1 hr-1 mainly composed by terpene emissions (e.g., α-pinene, terpinolene, β-caryophyllene). At this stage, methanol, acetone, and acetic acid were the most important nonterpenic volatiles representing, respectively, up to 26%, 10%, and 26% of total emissions. This study gives an overview of the evolution of BVOC emissions from litter along with decomposition process and will thus contribute to better understand the dynamics and sources of BVOC emission in Mediterranean pine forests.

Vapor pressure deficit helps explain biogenic volatile organic compound fluxes from the forest floor and canopy of a temperate deciduous forest

Biogenic volatile organic compounds (BVOCs) play critical roles in ecological and earth-system processes. Ecosystem BVOC models rarely include soil and litter fluxes and their accuracy is often challenged by BVOC dynamics during periods of rapid ecosystem change like spring leaf out. We measured BVOC concentrations within the air space of a mixed deciduous forest and used a hybrid Lagrangian/Eulerian canopy transport model to estimate BVOC flux from the forest floor, canopy, and whole ecosystem during spring. Canopy flux measurements were dominated by a large methanol source and small isoprene source during the leaf-out period, consistent with past measurements of leaf ontogeny and theory, and indicative of a BVOC flux situation rarely used in emissions model testing. The contribution of the forest floor to whole-ecosystem BVOC flux is conditional on the compound of interest and is often non-trivial. We created linear models of forest floor, canopy, and whole-ecosystem flux for each study compound and used information criteria-based model selection to find the simplest model with the best fit. Most published BVOC flux models do not include vapor pressure deficit (VPD), but it entered the best canopy, forest floor, and whole-ecosystem BVOC flux model more than any other study variable in the present study. Since VPD is predicted to increase in the future, future studies should investigate how it contributes to BVOC flux through biophysical mechanisms like evaporative demand, leaf temperature and stomatal function.

Compartment specific chiral pinene emissions identified in a Maritime pine forest

To track unknown sources and sinks of volatile organic compounds (VOCs) inside forest canopies we measured diel cycles of VOC exchanges in a temperate maritime forest at the branch, stem and ground level with special focus on the chiral signatures of pinenes. All compartments released day and night α- and β-pinene as major compounds. In addition, strong light dependent emissions of ocimene and linalool from branches occurred during hot summer days. In all compartments the overall emission strength of pinenes varied from day to day spanning 1 to 2 orders of magnitude. The highest pinene emissions from ground and stem were observed during high moisture conditions. Despite this variability stem emissions consistently expressed a different chiral composition than branch emissions, the former containing a much larger fraction of (-)-enantiomers than the latter. Pinene emissions from dead needle litter and soil were mostly enriched in (-)-enantiomers, while the chiral signatures of the ambient air inside the forest showed mostly intermediate levels compared to the emission signatures. These findings suggest that different organ-specific pinene producing enzymes exist in Maritime pine, and indicate that emissions from ground and stem compartments essentially contribute to the canopy VOC flux. Overall the results open new perspectives to explore chirality as a possible marker to recognize shifts in the contributions of different VOC sources present within forest ecosystems and to explain observed temporal changes in the chiral signature of pinenes in the atmosphere.

Profiles of volatile organic compound emissions from soils amended with organic waste products

Volatile Organic Compounds (VOCs) are reactive compounds essential to atmospheric chemistry. They are mainly emitted by living organisms, and mostly by plants. Soil microbes also contribute to emissions of VOCs. However, these emissions have not yet been characterised in terms of quality and quantity. Furthermore, long-term organic matter amendments are known to affect the microbial content of soils, and hence the quantity and quality of VOC emissions. This study investigates which and how much of these VOCs are emitted from soil amended with organic waste products (OWPs). Four OWPs were investigated: municipal solid waste compost (MSW), green waste and sludge co-compost (GWS), bio-waste compost (BIOW) and farmyard manure (FYM). These OWPs have been amended every two years since 1998 until now at a rate of ~4 tC ha^-1. A soil receiving no organic inputs was used as a reference (CN). VOCs emissions were measured under laboratory conditions using a Proton Transfer Reaction-Quadrupole ion guide Time of Flight-Mass Spectrometry (PTR-QiToF-MS). A laboratory system was set up made of two Pyrex chambers, one for samples and the second empty, to be used as a blank. Our results showed that total VOC emissions were higher in BIOW than in MSW. Further findings outlined that the most emitted compounds were acetone, butanone and acetaldehyde in all treatments, suggesting a common production mechanism for these compounds, meaning they were not affected by the OWP amendment. We isolated 21 VOCs that had statistically different emissions between the treatments and could therefore be considered as good markers of soil biological functioning. Our results suggest that organic matter and pH jointly influenced total VOC emissions. In conclusion, OWPs in soil affect the type of VOC emissions and the total flux also depends on the pH of the soil and the quantity of organic matter.

Secondary compounds of Pinus massoniana alter decomposers' effects on Quercus variabilis litter decomposition

A major gap to understand the effects of plant secondary compounds on litter decomposition in the brown food web is lack of information about how these secondary compounds modify the activities of soil decomposers. To address this question, we conducted an experiment where aqueous extracts and tannins prepared from Pinus massoniana needles were added to soils collected either from P. massoniana (pine soil) or Quercus variabilis (oak soil). Our objective was to investigate the cascading effects of the two compounds on isopod (Armadillidium vulgare) activity and subsequent change in Q. variabilis litter decomposition. We found that in pine soil, both aqueous extracts and tannins (especially at high concentrations) had positive effects on litter decomposition rates when isopods were present. While without isopods, litter decomposition was enhanced only by high concentrations of aqueous extracts, and tannins had no significant effect on decomposition. In oak soil, high concentrations of aqueous extracts and tannins inhibited litter decomposition and soil microbial biomass, regardless of whether isopods were present or not. Low concentrations of aqueous extracts increased litter decomposition rates and soil microbial biomass in oak soil in the absence of isopods. Based on our results, we suggest that the high concentration of secondary compounds in P. massoniana is a key factor influencing the effects of decomposers on litter decomposition rates, and tannins form a major part of secondary compounds. These funding particularly provide insight into form- and concentration-oriented effects of secondary compounds and promote our understanding of litter decomposition and soil nutrient cycling in forest ecosystem.

Evidence of a reduction in cloud condensation nuclei activity of water-soluble aerosols caused by biogenic emissions in a cool-temperate forest

Biogenic organic aerosols can affect cloud condensation nuclei (CCN) properties, and subsequently impact climate change. Large uncertainties exist in how the difference in the types of terrestrial biogenic sources and the abundance of organics relative to sulfate affect CCN properties. For the submicron water-soluble aerosols collected for two years in a cool-temperate forest in northern Japan, we show that the hygroscopicity parameter κ_CCN (0.44 ± 0.07) exhibited a distinct seasonal trend with a minimum in autumn (κ_CCN = 0.32-0.37); these κ_CCN values were generally larger than that of ambient particles, including water-insoluble fractions. The temporal variability of κ_CCN was controlled by the water-soluble organic matter (WSOM)-to-sulfate ratio (R² > 0.60), where the significant reduction of κ_CCN in autumn was linked to the increased WSOM/sulfate ratio. Positive matrix factorization analysis indicates that α-pinene-derived secondary organic aerosol (SOA) substantially contributed to the WSOM mass (~75%) in autumn, the majority of which was attributable to emissions from litter/soil microbial activity near the forest floor. These findings suggest that WSOM, most likely α-pinene SOA, originated from the forest floor can significantly suppress the aerosol CCN activity in cool-temperate forests, which have implications for predicting climate effects by changes in biogenic emissions in future.

Monoterpene emissions in response to long-term night-time warming, elevated CO2 and extended summer drought in a temperate heath ecosystem

Monoterpenes emitted from plants have an important role in atmospheric chemistry through changing atmospheric oxidative capacity, forming new particles and secondary organic aerosols. The emission rates and patterns can be affected by changing climate. In this study, emission responses to six years of climatic manipulations (elevated CO₂, extended summer drought and night-time warming) were investigated in a temperate semi-natural heath ecosystem. Samples for monoterpene analysis were collected in seven campaigns during an entire growing season (April-November, 2011). The results showed that the temperate heath ecosystem was a considerable source of monoterpenes to the atmosphere, with the emission averaged over the 8month measurement period of 21.7±6.8μgm^-2groundareah^-1 for the untreated heath. Altogether, 16 monoterpenes were detected, of which the most abundant were α-pinene, δ-3-carene and limonene. The emissions of these three compounds were positively correlated with light, chamber temperature and litter abundance, but negatively correlated with soil temperature. Elevated CO₂ tended to decrease the average monoterpene emissions by 40% over the whole growing season, and significantly reduced emissions in August. Extended summer drought significantly decreased the emission right after the drought treatment period, but also in the late growing season. Night-time warming significantly increased the total emissions (mainly α-pinene) in April, and tended to mitigate the decrease caused by drought. The inhibition effects of elevated CO₂ on emissions were diminished when the treatment was combined with drought or warming. The emission responses to different treatments were not explained by vegetation changes, and the monoterpene emission profile was only moderately related to plant species coverage. The emission responses to these long-term climate manipulations varied over the growing season (with strong correlation with litter abundance) and the observed antagonistic effects in the combined treatments underlie the importance of long-term studies with multiple factors acting in concert.

OH- and O3-initiated atmospheric degradation of camphene: temperature dependent rate coefficients, product yields and mechanisms

Gas-phase rate coefficients for the reactions of OH and O₃ with camphene have been measured over the temperature range 288–311 K using the relative rate method.

There's no place like home? An exploration of the mechanisms behind plant litter-decomposer affinity in terrestrial ecosystems

Litter decomposition in terrestrial ecosystems is an important first step for carbon and nutrient cycling, as senescent plant material is degraded and consequently incorporated, along with microbial products, into soil organic matter. The identification of litter affinity effects, whereby decomposition is accelerated in its home environment (home-field advantage, HFA), highlights the importance of plant-soil interactions that have consequences for biogeochemical cycling. While not universal, these affinity effects have been identified in a range of ecosystems, particularly in forests without disturbance. The optimization of the local decomposer community to degrade a particular combination of litter traits is the most oft-cited explanation for HFA effects, but the ways in which this specialized community can develop are only beginning to be understood. We explore ways in which HFA, or more broadly litter affinity effects, could arise in terrestrial ecosystems. Plant-herbivore interactions, microbial symbiosis, legacies from phyllosphere communities and attractors of specific soil fauna could contribute to spatially defined affinity effects for litter decomposition. Pyrosequencing soil communities and functional linkages of soil fauna provide great promise in advancing our mechanistic understanding of these interactions, and could lead to a greater appreciation of the role of litter-decomposer affinity in the maintenance of soil functional diversity.