Low RH Conditions Research Articles

Cellulose-Based Crosslinked and Reinforced Sulfonated Poly(ether ether ketone) Membranes for Robust Proton Exchange Membranes in Fuel Cells

Proton exchange membrane fuel cells (PEMFCs) are a promising clean energy solution due to their high efficiency and eco-friendly operation. Central to their function is the proton exchange membrane (PEM), typically composed of perfluorosulfonic acid (PFSA) ionomers like Nafion and Aquivion. However, challenges such as cost, gas crossover, and limited temperature range persist. To address these, researchers explore hydrocarbon (HC)-based polymers like sulfonated poly(ether ether ketone) (SPEEK), prized for cost-effectiveness and stability. However, HC-based polymers suffer from issues like unstable mechanical behavior and reduced proton conductivity under low humidity, necessitating further development for practical application.In this study, we propose two approaches to overcome these drawbacks of HC-based PEMs. Firstly, we prepare crosslinked SPEEK membranes with cellulose acetate to enhance proton conduction under low RH conditions and stabilize membrane properties. The crosslinked structure of SPEEK/cellulose membranes is investigated using small-angle X-ray scattering, atomic force microscopy, and transmission electron microscopy. Additionally, we incorporate cellulose-based nanofibers obtained by electrospinning as a reinforcing substrate, enhancing the interaction between the SPEEK matrix and cellulose nanofiber filler. This results in a dense membrane without voids, effectively preventing gas crossover and improving membrane robustness. These investigations using cellulose-containing SPEEK membranes lead to enhanced power density and durable operation of fuel cells, particularly at low RH conditions.

Effect of Heat Treatment on Hygroscopicity of Chinese Fir (Cunninghamia lanceolata [Lamb.] Hook.) Wood

Chinese fir (Cunninghamia lanceolata [Lamb.] Hook.) is a widely planted species of plantation forest in China, and heat treatment can improve its dimensional stability defects and improve its performance. The wood samples were heat-treated at various temperatures (160, 180, 200, and 220 °C) for 2 h. To clarify the effect of heat treatment on wood hygroscopicity, the equilibrium moisture content (EMC) was measured, the moisture adsorption and desorption rates were determined, the hygroscopic hysteresis was examined, and the Guggenheim, Anderson, and de Boer (GAB) model was fitted to the experimental data. The moisture absorption isotherms of all samples belonged to the Type II adsorption isotherm, but the shape of the desorption isotherm was more linear for heat-treated wood samples, especially when the heat treatment temperature was higher. According to the results analyzed with ANOVA, there were significant differences in equilibrium moisture content between the control samples and the heat-treated samples under the conditions of 30%, 60%, and 95% relative humidity (RH, p < 0.05), and the results of multiple comparisons were similar. The decrease in hygroscopicity was more pronounced in wood treated at higher temperatures. The EMC of the 160–220 °C heat-treated samples of the control samples was 14.00%, 22.37%, 28.95%, and 39.63% lower than that of the control sample at 95% RH. Under low RH conditions (30%), water is taken up mainly via monolayer sorption, and multilayer sorption gradually predominates over monolayer sorption with the increase in RH. The dynamic vapor sorption (DVS) analysis indicated that the heat-treated wood revealed an increase in isotherm hysteresis, which was due to the change in cell wall chemical components and microstructure caused by heat treatment. In addition, the effective specific surface area of wood samples decreased significantly after heat treatment, and the change trend was similar to that of equilibrium moisture content.

Implementation of the ISORROPIA-lite aerosol thermodynamics model into the EMAC chemistry climate model (based on MESSy v2.55): implications for aerosol composition and acidity

Abstract. This study explores the differences in performance and results by various versions of the ISORROPIA thermodynamic module implemented within the ECHAM/MESSy Atmospheric Chemistry (EMAC) model. Three different versions of the module were used, ISORROPIA II v1, ISORROPIA II v2.3, and ISORROPIA-lite. First, ISORROPIA II v2.3 replaced ISORROPIA II v1 in EMAC to improve pH predictions close to neutral conditions. The newly developed ISORROPIA-lite has been added to EMAC alongside ISORROPIA II v2.3. ISORROPIA-lite is more computationally efficient and assumes that atmospheric aerosols exist always as supersaturated aqueous (metastable) solutions, while ISORROPIA II includes the option to allow for the formation of solid salts at low RH conditions (stable state). The predictions of EMAC by employing all three aerosol thermodynamic models were compared to each other and evaluated against surface measurements from three regional observational networks in the polluted Northern Hemisphere (Interagency Monitoring of Protected Visual Environments (IMPROVE), European Monitoring and Evaluation Programme (EMEP), and Acid Deposition Monitoring Network of East Asia (EANET)). The differences between ISORROPIA II v2.3 and ISORROPIA-lite were minimal in all comparisons with the normalized mean absolute difference for the concentrations of all major aerosol components being less than 11 % even when different phase state assumptions were used. The most notable differences were lower aerosol concentrations predicted by ISORROPIA-lite in regions with relative humidity in the range of 20 % to 60 % compared to the predictions of ISORROPIA II v2.3 in stable mode. The comparison against observations yielded satisfactory agreement especially over the USA and Europe but higher deviations over East Asia, where the overprediction of EMAC for nitrate was as high as 4 µg m−3 (∼20 %). The mean annual aerosol pH predicted by ISORROPIA-lite was on average less than a unit lower than ISORROPIA II v2.3 in stable mode, mainly for coarse-mode aerosols over the Middle East. The use of ISORROPIA-lite accelerated EMAC by nearly 5 % compared to the use of ISORROPIA II v2.3 even if the aerosol thermodynamic calculations consume a relatively small fraction of the EMAC computational time. ISORROPIA-lite can therefore be a reliable and computationally efficient alternative to the previous thermodynamic module in EMAC.

Research on Thermal Insulation Performance and Impact on Indoor Air Quality of Cellulose-Based Thermal Insulation Materials.

Worldwide, the need for thermal insulation materials used to increase the energy performance of buildings and ensure indoor thermal comfort is constantly growing. There are several traditional, well-known and frequently used thermal insulation materials on the building materials market, but there is a growing trend towards innovative materials based on agro-industrial waste. This paper analyses the performance of 10 such innovative thermal insulation materials obtained by recycling cellulosic and/or animal waste, using standardised testing methods. More precisely, thermal insulation materials based on the following raw materials were analysed: cellulose acetate, cigarette filter manufacturing waste; cellulose acetate, cigarette filter manufacturing waste and cigarette paper waste; cellulose acetate, waste from cigarette filter manufacturing, waste cigarette paper and waste aluminised paper; cellulose from waste paper (two types made by two independent manufacturers); wood fibres; cellulose from cardboard waste; cellulose from waste cardboard, poor processing, inhomogeneous product; rice husk waste and composite based on sheep wool, recycled PET fibres and cellulosic fibres for the textile industry. The analysis followed the performance in terms of thermal insulating quality, evidenced by the thermal conductivity coefficient (used as a measurable indicator) determined for both dry and conditioned material at 50% RH, in several density variants, simulating the subsidence under its own weight or under various possible stresses arising in use. The results showed in most cases that an increase in material density has beneficial effects by reducing the coefficient of thermal conductivity, but exceptions were also reported. In conjunction with this parameter, the analysis of the 10 types of materials also looked at their moisture sorption/desorption capacity (using as a measurable indicator the amount of water stored by the material), concluding that, although they have a capacity to regulate the humidity of the indoor air, under low RH conditions the water loss is not complete, leaving a residual quantity of material that could favour the development of mould. Therefore, the impact on indoor air quality was also analysed by assessing the risk of mould growth (using as a measurable indicator the class and performance category of the material in terms of nutrient content conducive to the growth of microorganisms) under high humidity conditions but also the resistance to the action of two commonly encountered moulds, Aspergillus niger and Penicillium notatum. The results showed a relative resistance to the action of microbiological factors, indicating however the need for intensified biocidal treatment.

A Modified Dent-Fractal Mathematical Model to Investigate the Water Vapor Adsorption on Nanopore Structure Heterogeneity from the Longmaxi Shale, Sichuan Basin, China

The study of water vapor adsorption (WVA) isotherms on shales is crucial to comprehend the adsorption–desorption behavior and deposit mechanism of water in shale pore systems. To systematically investigate the relationship between fractal dimension and WVA in shale reservoirs, a new Dent-fractal (DF) model was developed and the ability of different adsorption models to match with WVA experimental data was evaluated. The role of shale pore structure heterogeneity controlling the amount of WVA is also discussed. The results indicate that WVA on shale involves the monolayer–multilayer adsorption and capillary condensation. On the one hand, the GAB and Dent and DF models were found to be the best models for fitting and predicting WVA isotherms in Longmaxi shale. On the other hand, the DLP and DS models had the worst fitting qualities for WVA adsorption data. The pore structure of micropores has a more significant effect on WVA adsorption than that of meso-macropores. The larger surface and pore volume of micropores can provide more adsorption sites and space, which is favorable for WVA. In low-Rh conditions, the higher surface area, the pore surface complexity rises, resulting in higher water vapor monolayer adsorption. Under high-Rh conditions, for shale reservoirs with a highly heterogeneous pore structure, the relationship between the heterogeneous pore structure of the shale and the amount of water adsorbed in multiple layers is not obvious due to the formation of clusters of water molecules.

P(VDF-TrFE) reinforced composite membranes fabricated via sol-gel and dual-fiber electrospinning for reduced relative humidity operation of PEM fuel cells

In this study, dual-fiber electrospinning and sol-gel methods have been used to prepare membranes for low relative humidity conditions, with low dimensional change containing poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)), Nafion® and hygroscopic sulfonated-silica (S-SiO2) additive. This approach allowed us to finely tune the polymer ratios, additive contents, and ultimate homogeneous distribution to provide better water uptake, proton conductivity, and robustness. In this study, for the first time, S-SiO2 was synthesized using 3-(trihydroxysilyl) -1-propanesulfonic acid (TPS) and tetraethyl orthosilicate (TEOS) via the sol-gel method for the PEM fuel cell application at low humidity. We characterized our membranes in terms of morphology, ion exchange capacity, ionic conductivity, molecular structure, mechanical properties, hydrogen crossover, and fuel cell performance. To investigate the effect of reinforcing polymer, the results obtained from P(VDF-TrFE)-based membranes were compared with polyvinylidene fluoride (PVDF)-based membranes. Although Young's modules of PVDF-based membranes (324 MPa) are higher compared to the P(VDF-TrFE)-based membranes (228 MPa), the latter showed greater proton conductivity (132 mS/cm) and fuel cell performance, particularly at low RH conditions. Furthermore, P(VDF-TrFE)-based membranes provided a maximum power density of 344 mW/cm2 which is almost 2-times higher than that of PVDF-based membranes.

Capillary adhesion governs the friction behavior of electrochemically corroded polycrystalline diamond

The friction behavior of rough polycrystalline diamond (PCD) surfaces is important in many applications and devices that are required to operate in various harsh environments and it can be argued that a thorough understanding of the friction behavior is essential to the application performance. However, the interplay between electrochemical corrosion, capillary adhesion and friction behavior of PCD in multi-asperity contacts is still poorly understood. In this work, we quantify the interfacial capillary adhesion at contact interfaces and its effect on the friction response, between a colloidal microsphere and rough PCD films before and after electrochemical corrosion, for water-immersed, low RH, and humid air conditions. For these multi-asperity contacts, we demonstrate how electrochemical corrosion influences the surface hydrophilicity of the PCD surfaces, and how capillary adhesion due to water condensation contributes to the friction force. We estimate the capillary forces from both the microscopic lateral force experiments and elastoplastic boundary element method (BEM) contact calculations. The combined results indicate strongly that the observed increase in friction force on electrochemically-corroded PCD surfaces is governed by enhanced capillary adhesion at the contact interface, as affected by surface hydrophilicity and environmental humidity.

Exploring the driving factors of haze events in Beijing during Chinese New Year holidays in 2020 and 2021 under the influence of COVID-19 pandemic

Unexpected outbreak of the 2019 novel coronavirus (COVID-19) has profoundly altered the way of human life and production activity, which posed visible impacts on PM2.5 and its chemical species. The abruptly emergency reduction in human activities provided an opportunity to explore the synergetic impacts of multi-factors on shaping PM2.5 pollution. Here, we conducted two comprehensive observation measurements of PM2.5 and its chemical species from 1 January to 16 February in Beijing 2020 and the same lunar date in 2021, to investigate temporal variations and reveal the driving factors of haze before and after Chinese New Year (CNY). Results show that mean PM2.5 concentrations during the whole observation were 63.83 and 66.86 μg/m3 in 2020 and 2021, respectively. Higher secondary inorganic species were observed after CNY, and K+, Cl− showed three prominent peaks which associated closely with fireworks burnings from suburb Beijing and surroundings, verifying that they could be used as two representative tracers of fireworks. Further, we explored the impacts of meteorological conditions, regional transportation as well as chemical reactions on PM2.5. We found that unfavorable meteorological conditions accounted for 11.0 % and 16.9 % of PM2.5 during CNY holidays in 2020 and 2021, respectively. Regional transport from southwest and southeast (south) played an important role on PM2.5 during the two observation periods. Higher ratio of NO3−/SO42− were observed under high OX and low RH conditions, suggesting the major pathway of NO3− and SO42− formation could be photochemical process and aqueous-phase reaction. Additionally, nocturnal chemistry facilitated the formation of secondary components of both inorganic and organic. This study promotes understandings of PM2.5 pollution in winter under the influence of COVID-19 pandemic and provides a well reference for haze and PM2.5 control in future.

Investigation into the differences and relationships between gasSOA and aqSOA in winter haze pollution on Chongming Island, Shanghai, based on VOCs observation

To investigate the formation of secondary organic aerosol (SOA) under current atmospheric conditions, we conducted a field observation of SOA precursors in the downwind region of the Yangtze River Delta (YRD) in winter 2019 using a variety of offline and online instruments. During the entire observation period, the averaged fine particulate SOA was 7.9 ± 2.3 μg m−3, with precursor concentrations of 31 ± 11 ppbv for the measured volatile organic compounds (VOCs) and 16 ± 12 ppbv for NOx. Compared to those on the clean days, SOA on the haze days increased by a factor of 1.6, while the VOC and NOx increased by a factor of 1.3 and 2.0, respectively. Aerosol liquid water content (ALWC) and oxygenated VOCs (OVOCs, including acetaldehyde, formic acid, acetone, acetic acid, methyl ethyl ketone, and methylglyoxal) relationships suggested that the gasSOA and aqSOA occurred simultaneously on Chongming Island in winter. The gasSOA was primarily formed by the oxidation of aromatics and NOx at low RH (RH < 80%) conditions. In contrast, the aqSOA was formed under higher RH (RH > 80%) conditions via a combination of daytime photochemical aqueous phase processes of water-soluble OVOCs and nocturnal dark aqueous phase processes of primary emissions from biomass. The inversed higher mass ratio of NACs to (benzene + toluene) and nitrogen oxidation ratio (NOR) in the daytime during the gasSOA-dominated haze periods indicated that gasSOA could be transformed to aqSOA at high NOx levels. Our results also suggested the importance of NOx and VOC reduction measures in directly mitigating gasSOA and indirectly mitigating aqSOA during winter haze pollution.

Phase State and Relative Humidity Regulate the Heterogeneous Oxidation Kinetics and Pathways of Organic-Inorganic Mixed Aerosols.

Inorganic species always coexist with organic materials in atmospheric particles and may influence the heterogeneous oxidation of organic aerosols. However, very limited studies have explored the role of the inorganics in the chemical evolution of organic species in mixed aerosols. This study examines the heterogeneous oxidation of glutaric acid-ammonium sulfate and 1,2,6-hexanetriol-ammonium sulfate aerosols by hydroxyl radicals (OH) under varied organic mass fractions (forg) and relative humidity in a flow tube reactor. Coupling the oxidation kinetics and product measurements with kinetic model simulations, we found that under both low relative humidity (RH, 30-35%) and high RH conditions (85%), the decreased forg from 0.7 to 0.2 accelerates the oxidation of the organic materials by a factor of up to 11. We suggest that the faster oxidation kinetics under low-RH conditions is due to full or partial phase separation, with the organics greatly enriched at the particle outer region, while enhanced "salting-out" of the organics and OH adsorption caused by higher inorganics could explain the observations under high-RH conditions. Analysis of the oxidation products reveals that the dilution of organics by the inorganic salts and corresponding water uptake under high-RH conditions will favor alkoxy radical fragmentation by a factor of 3-4 and inhibit its secondary chain propagation chemistry. Our results suggest that atmospheric organic aerosol oxidation lifetime and composition are strongly impacted by the coexistent inorganic salts.

The effect of spider mite-pathogenic strains of Beauveria bassiana and humidity on the survival and feeding behavior of Neoseiulus predatory mite species

Predatory mites and invertebrate-pathogenic fungi have been used as biological control agents in a complementary way to suppress two-spotted spider mite (TSM) populations, which are a key pest of horticultural crops worldwide. However, their performance can be lowered by both biotic (e.g., intraguild interactions) and abiotic stress (especially relative humidity - RH). The present study evaluated the susceptibility of three predatory phytoseiid mite species in the genus Neoseiulus – N. californicus, N. idaeus, and N. barkeri – to infection by selected spider mite-pathogenic Beauveria bassiana strains as well as their predation capacity and resilience under simulated drought conditions. The two selected B. bassiana strains induced TSM mortality above 70 %. All three Neoseiulus mite species also showed susceptibility to both strains; however, N. barkeri was less susceptible to fungal infections than the other Neoseiulus species (with mortality < 65 % and without reduction of oviposition). All three Neoseiulus species were negatively affected by low RH conditions. Neoseiulus barkeri was the most affected with a drastic reduction in TSM egg consumption (about 40 %) and preventing the deposition of eggs by females. The egg consumption by N. californicus and N. idaeus was not affected by low RH conditions; however, both predatory mites reduced the number of eggs laid per female. Thus, the efficiency of the conversion of food into egg biomass for all three Neoseiulus species decreased under low RH conditions, dropping to zero for N. barkeri. We showed that the simultaneous use of B. bassiana and Neoseiulus had a detrimental effect on predatory mite survival and progeny, indicating the need for further development of new strategies which combine these biological control agents.

Thermal conductivity, heat capacity and thermal expansion of ettringite and metaettringite: Effects of the relative humidity and temperature

Thermal processes play a crucial role in the durability problems related to ettringite formation and the applications of ettringite for thermal energy storage. The complete characterization of the thermal response of ettringite requires the knowledge of how the thermoelastic properties of the materials evolve with the relative humidity and temperature. Here, molecular dynamics simulations are deployed to provide ettringite's thermoelastic properties, including the collapsing ettringite and metaettringite domains. The thermoelastic properties remain stable for RH ranging from 10 to 100 % at ambient temperature. The properties evolve linearly with the temperature in the range 278–328 K. Results from simulations show a good agreement with the experimental data available, building confidence in the use of molecular simulations to provide the property data in the conditions in which there is no experimental data available (as is the case of low RH conditions).

Hydrogen chloride (HCl) at ground sites during CalNex 2010 and insight into its thermodynamic properties.

Gas phase hydrogen chloride (HCl) was measured at Pasadena and San Joaquin Valley (SJV) ground sites in California during May and June 2010 as part of the CalNex study. Observed mixing ratios were on average 0.83 ppbv at Pasadena, ranging from below detection limit (0.055 ppbv) to 5.95 ppbv, and were on average 0.084 ppbv at SJV with a maximum value of 0.776 ppbv. At both sites, HCl levels were highest during midday and shared similar diurnal variations with HNO3. Coupled phase partitioning behavior was found between HCl/Cl- and HNO3/NO3 - using thermodynamic modelling and observations. Regional modeling of Cl- and HCl using CMAQ captures some of the observed relationships but underestimates measurements by a factor of 5 or more. Chloride in the 2.5-10 μm size range in Pasadena was sometimes higher than sea salt abundances, based on co-measured Na+, implying that sources other than sea salt are important. The acid-displacement of HCl/Cl- by HNO3/NO3 - (phase partitioning of semi-volatile acids) observed at the SJV site can only be explained by aqueous phase reaction despite low RH conditions and suggests the temperature dependence of HCl phase partitioning behavior was strongly impacted by the activity coefficient changes under relevant aerosol conditions (e.g., high ionic strength). Despite the influence from activity coefficients, the gas-particle system was found to be well constrained by other stronger buffers and charge balance so that HCl and Cl- concentrations were reproduced well by thermodynamic models.

Efflorescence kinetics of aerosols comprising internally-mixed ammonium sulfate and water-soluble organic compounds

Understanding the efflorescence process of atmospheric aerosols is a key step towards a complete description of their phase transition dynamics. Atmospheric aerosols comprise internally mixed organic and inorganic components, and the composition of the condensed phase strongly affects the overall efflorescence dynamics. Although the kinetics of efflorescence has been thoroughly investigated for aerosols containing inorganic salts, the influence of non-ideal mixing with water-soluble organic compounds (WSOCs) remains considerably controversial. In this work, we measure the efflorescence process of ammonium sulfate (AS) aerosol droplets mixed with four types of WSOCs – sucrose, glycerol, malonic acid, and citric acid – by using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. The absorbance band of ammonium ions (δ-NH4+ at 1441 cm−1) in the aqueous phase was used to calculate the crystallization ratio of AS and the heterogeneous nucleation rate. Adding WSOCs lowers the characteristic efflorescence relative humidity (ERH), broadens the ERH ranges, and reduces the terminal crystallization ratio of AS aerosol droplets. Amongst the various WSOCs studied here, the inhibiting effect on AS efflorescence decreases in the following order: sucrose > citric acid ≈ malonic acid > glycerol, mainly attributed to the mass transfer limitation caused by the viscosity of WSOCs. Sucrose and glycerol can completely suppress the crystallization of AS droplets at organic to inorganic ratio (OIR) of 1:1 and 4:1, respectively. This distinct observation suggests that atmospheric aerosols may skip efflorescence and evolve into a glassy state at low RH conditions.

Enhanced proton conductivity of poly(ether sulfone) multi-block copolymers grafted with densely pendant sulfoalkoxyl side chains for proton exchange membranes

A series of proton exchange membranes were prepared from poly(ether sulfone) multi-block copolymers grafted with densely pendent sulfoalkoxyl side chains for fuel cell applications. Each polymers contains four pendent sulfonic acids per unit. The chemical structures were confirmed by 1H NMR and FTIR spectroscopy, providing evidence of complete methoxy conversion and sulfobutylation. The introduction of densely grafted flexible pendent side chains to the block structure was effective to enhance phase separation and thus form broader hydrophilic channels. These membranes displayed considerably improved proton conductivities especially at low RH conditions. Furthermore, these membranes also showed promising fuel cell performance both at 20% and 80% RH conditions. In comparison to Nafion 212 membranes, the present membranes displayed enhanced swelling behavior, mechanical strength, proton conductivity, and fuel cell performance, demonstrating that they can be an alternative PEM to perfluorosulfonic acid polymers.

Superior Proton Exchange Membrane Fuel Cell (PEMFC) Performance Using Short-Side-Chain Perfluorosulfonic Acid (PFSA) Membrane and Ionomer.

Optimization of the ionomer materials in catalyst layers (CLs) which sometimes is overlooked has been equally crucial as selection of the membranes in membrane electrode assembly (MEA) for achieving a superior performance in proton exchange membrane fuel cells (PEMFCs). Four combinations of the MEAs composed of short-side-chain (SSC) and long-side-chain (LSC) perfluorosulfonic acid (PFSA) polymers as membrane and ionomer materials have been prepared and tested under various temperatures and humidity conditions, aiming to investigate the effects of different side chain polymer in membranes and CLs on fuel cell performance. It is discovered that SSC PFSA polymer used as membrane and ionomer in CL yields better fuel cell performance than LSC PFSA polymer, especially at high temperature and low RH conditions. The MEA with the SSC PFSA employed both as a membrane and as an ionomer in cathode CL demonstrates the best cell performance amongst the investigated MEAs. Furthermore, various electrochemical diagnoses have been applied to fundamentally understand the contributions of the different resistances to the overall cell performance. It is illustrated that the charge transfer resistance (Rct) made the greatest contribution to the overall cell resistance and then membrane resistance (Rm), implying that the use of the advanced ionomer in CL could lead to more noticeable improvement in cell performance than only the substitution as the membrane.

Smog Chamber Study on the Ozone Formation Potential of Acetaldehyde

Acetaldehyde is one of the important VOC species of O3 precursors in the atmospheric environment. The influences of relative humidity (RH) and initial VOC/NOx ratio (RCN) on the formation of O3 are studied in smog chamber experiments, and the MCM v3.3.1 mechanism of acetaldehyde is modified based on the experimental results. In low-RH conditions (RH = 11.6%±1.1%), the O3 concentration at 6 h increases first and then decreases with the increase of RCN, and the RCN at the inflection point of O3 concentrations is 3.2. In high-RH experiments (RH = 78.8%±1.0%), variation of the O3 concentration at 6 h with RCN is similar to that in low-RH experiments, but the RCN at the inflection point is 2.8. RH has no significant effect on the O3 concentrations under low RCN ( 3). Compared with the experimental results, original MCM v3.3.1 greatly underestimates the O3 concentrations. Addition of both the photolysis process of peroxyacetyl nitrate and the photolysis process of HNO3 on the reactor surface into the original MCM can reduce the difference between the simulated O3 concentrations and the experimental results at 6 h from 24%−35% and 17%−49% to 6%−26% and 10%−42% under low- and high-RH conditions, respectively. The maximum incremental reactivity (MIR) of acetaldehyde simulated with the modified MCM is 4.0 ppb ppb−1 without considering the effect of other VOCs.

Germination, viability and dormancy of 47 species from threatened tropical montane grassland in southeast Brazil: Implications for ex situ conservation.

To mitigate anthropogenic impacts on plant diversity in tropical montane grasslands, one of the most threatened ecosystems in Brazil, it will be essential to develop ex situ conservation strategies to preserve wild species. The lack of basic research on the seed storage behaviour of grassland species may, however, limit their use for reintroduction and restoration projects. We investigated seed storage behaviour at the community level by comparing the effects of cold-low RH (10 °C; 10% RH) and freezing-low RH (20 °C; 10% RH) conditions on seed viability, germination and dormancy of 47 species. Fresh seeds of 43% of the species showed primary dormancy. More than half of the species showed high seed survival responses (viability >60%) under both storage temperatures. Despite a variety of dormancy responses among the different species, the low RH storage conditions tested released dormancy for most species during 12- and 30-month storage times. Multivariate analysis of the best (freezing-low RH, 30 months) storage condition evidenced the formation of five distinct groups, three with species having high conservation potential in seed banks. Although further studies are needed to test dormancy-breaking treatments and improve seed conservation practices, this first approach to assessing seed banking techniques could contribute to demand for locally adapted seeds for ecological restoration projects in tropical montane grasslands.

Secondary aerosol formation alters CCN activity in the North China Plain

Abstract. Secondary aerosols (SAs, including secondary organic and inorganic aerosols, SOAs and SIAs) are predominant components of aerosol particles in the North China Plain (NCP), and their formation has significant impacts on the evolution of particle size distribution (PNSD) and hygroscopicity. Previous studies have shown that distinct SA formation mechanisms can dominate under different relative humidity (RH). This would lead to different influences of SA formation on the aerosol hygroscopicity and PNSD under different RH conditions. Based on the measurements of size-resolved particle activation ratio (SPAR), hygroscopicity distribution (GF-PDF), PM2.5 chemical composition, PNSD, meteorology and gaseous pollutants in a recent field campaign, McFAN (Multiphase chemistry experiment in Fogs and Aerosols in the North China Plain), conducted during the autumn–winter transition period in 2018 at a polluted rural site in the NCP, the influences of SA formation on cloud condensation nuclei (CCN) activity and CCN number concentration (NCCN) calculation under different RH conditions were studied. Results suggest that during daytime, SA formation could lead to a significant increase in NCCN and a strong diurnal variation in SPAR at supersaturations lower than 0.07 %. During periods with daytime minimum RH exceeding 50 % (high RH conditions), SA formation significantly contributed to the particle mass and size changes in a broad size range of 150 to 1000 nm, leading to NCCN (0.05 %) increases within the size range of 200 to 500 nm and mass concentration growth mainly for particles larger than 300 nm. During periods with daytime minimum RH below 30 % (low RH conditions), SA formation mainly contributed to the particle mass and size and NCCN changes for particles smaller than 300 nm. As a result, under the same amount of mass increase induced by SA formation, the increase of NCCN (0.05 %) was stronger under low RH conditions and weaker under high RH conditions. Moreover, the diurnal variations of the SPAR parameter (inferred from CCN measurements) due to SA formation varied with RH conditions, which was one of the largest uncertainties within NCCN predictions. After considering the SPAR parameter (estimated through the number fraction of hygroscopic particles or mass fraction of SA), the relative deviation of NCCN (0.05 %) predictions was reduced to within 30 %. This study highlights the impact of SA formation on CCN activity and NCCN calculation and provides guidance for future improvements of CCN predictions in chemical-transport models and climate models.

Deleterious Effects of Storage Environmental Conditions on The Seed Quality of Two Varieties of Tomato (Solanum lycopersicum L.) Stored in Triple Laminated Aluminum Packing in Sri Lanka

Tomato is one of the most commonly growing vegetable crops among the farmers in Sri Lanka. Standard laboratory germination of tomato seeds fulfills the regulatory requirements of seed marketing. However, poor field performance is an overwhelming problem to farmers. Present study was focused on the longevity of two varieties of tomato seeds as affected by their quality characters (percentage germination, moisture, field emergence and vigour index, seed protein and carbohydrate contents) including seed health (exposure of Clavibacter michiganensis subsp. Michiganensis (CMMV), Spotted wilt virus (TSWV) and Leaf curly top virus (LCTV)) under four different storage environmental conditions during a one-year long storage study. Seeds were packed in triple-laminated aluminum packets (TLA) and stored in low temperature storage conditions (17±1 °C and 65% RH) and in ambient conditions in Gannoruwa, Kundasale, and MahaIlluppallama that represent the three agro-ecologically zones; Mid Country Wet Zone (MCWZ), Mid Country Intermediate Zone (MCIZ) and Low Country Dry Zone (LCDZ) respectively. Seed quality parameters displayed varied responses depending on the variety. Physiological changes that occur in seeds due to temperature, RH, changes in proteins and carbohydrate content, CMMV and TSWV during storage were manifested as reduction in seed germination, field emergence and vigour index. However, none of the seedling carried LCTV and therefore its effect on seed quality parameters could not be assessed. The seeds could be stored for ca. 29 months at low and constant temperatures and RH conditions without compromising local seed germination standards compared to ambient storage in the three environments. CMMV and TSWV detected in all seed samples indicated potential threats to tomato farmers in Sri Lanka.&#x0D;