Uptake Of NO3 Research Articles

Enrichment, Isolation, and Characterization of High-Affinity N2O-Reducing Bacteria in a Gas-Permeable Membrane Reactor.

The recent discovery of nitrous oxide (N2O)-reducing bacteria suggests a potential biological sink for the potent greenhouse gas N2O. For an application toward N2O mitigation, characterization of more isolates will be required. Here, we describe the successful enrichment and isolation of high-affinity N2O-reducing bacteria using a N2O-fed reactor (N2OFR). Two N2OFRs, where N2O was continuously and directly supplied as the sole electron acceptor to a biofilm grown on a gas-permeable membrane, were operated with acetate or a mixture of peptone-based organic substrates as an electron donor. In parallel, a NO3- -fed reactor (NO3FR), filled with a nonwoven sheet substratum, was operated using the same inoculum. We hypothesized that supplying N2O vs NO3- would enhance the dominance of distinct N2O-reducing bacteria. Clade II type nosZ bacteria became rapidly enriched over clade I type nosZ bacteria in the N2OFRs, whereas the opposite held in the NO3FR. High-throughput sequencing of 16S rRNA gene amplicons revealed the dominance of Rhodocyclaceae in the N2OFRs. Strains of the Azospira and Dechloromonas genera, canonical denitrifiers harboring clade II type nosZ, were isolated with high frequency from the N2OFRs (132 out of 152 isolates). The isolates from the N2OFR demonstrated higher N2O uptake rates (Vmax: 4.23 × 10-3-1.80 × 10-2 pmol/h/cell) and lower N2O half-saturation coefficients (Km,N2O: 1.55-2.10 μM) than a clade I type nosZ isolate from the NO3FR. Furthermore, the clade II type nosZ isolates had higher specific growth rates on N2O than nitrite as an electron acceptor. Hence, continuously and exclusively supplying N2O in an N2OFR allows the enrichment and isolation of high-affinity N2O-reducing strains, which may be used as N2O sinks in bioaugmentation efforts.

Soil inorganic nitrogen composition and plant functional type determine forage crops nitrogen uptake preference in the temperate cultivated grassland, Inner Mongolia

ABSTRACT Plant nitrogen (N)-acquisition strategy affects soil N availability, community structure, and vegetation productivity. Cultivated grasslands are widely established to improve degraded pastures, but little information is available to evaluate the link between N uptake preference and forage crop biomass. Here an in-situ 15N labeling experiment was conducted in the four cultivated grasslands of Inner Mongolia, including two dicots (Medicago sativa and Brassica campestris) and two monocots (Bromus inermis and Leymus chinensis). Plant N uptake rate, shoot- and root biomass, and concentrations of soil inorganic-N and microbial biomass-N were measured. The results showed that the root/shoot ratios of the dicots were 2.6 to 16.4 fold those of the monocots. The shoot N concentrations of the dicots or legumes were 40.6% to 165% higher than those of the monocots or non-legumes. The four forage crops in the cultivated grassland preferred to uptake more NO3 −-N than NH4 +-N regardless of growth stages, and the NH4 +/NO3 − uptake ratios were significantly lower in the non-legumes than in the legumes (p < 0.05). Significant differences in the NH4 +-N rather than NO3 −-N uptake rate were observed among the four forages, related to plant functional types and growth stages. The NH4 + uptake rate in the perennial forages exponentially decreased with the increases in shoot-, root biomass, and root/shoot ratio. Also, the plant NH4 +/NO3 − uptake ratio was positively correlated with soil NH4 +/NO3 − ratio. Our results suggest that the major forage crops prefer to absorb soil NO3 −-N, depending on soil inorganic N composition and belowground C allocation. The preferential uptake of NO3 −-N by forages indicates that nitrate-N fertilizer could have a higher promotion on productivity than ammonium-N fertilizer in the semi-arid cultivated grassland.

Transcriptome profiling of Puccinellia tenuiflora during seed germination under a long-term saline-alkali stress

BackgroundPuccinellia tenuiflora is the most saline-alkali tolerant plant in the Songnen Plain, one of the three largest soda saline-alkali lands worldwide. Here, we investigated the physicochemical properties of saline-alkali soils from the Songnen Plain and sequenced the transcriptomes of germinated P. tenuiflora seedlings under long-term treatment (from seed soaking) with saline-alkali soil extracts.ResultsWe found that the soils from Songnen Plain were reasonably rich in salts and alkali; moreover, the soils were severely deficient in nitrogen [N], phosphorus [P], potassium [K] and several other mineral elements. This finding demonstrated that P. tenuiflora can survive from not only high saline-alkali stress but also a lack of essential mineral elements. To explore the saline-alkali tolerance mechanism, transcriptional analyses of P. tenuiflora plants treated with water extracts from the saline-alkali soils was performed. Interestingly, unigenes involved in the uptake of N, P, K and the micronutrients were found to be significantly upregulated, which indicated the existence of an efficient nutrition-uptake system in P. tenuiflora. Compared with P. tenuiflora, the rice Oryza sativa was hypersensitive to saline-alkali stress. The results obtained using a noninvasive microtest techniques confirmed that the uptake of NO3- and NH4+ and the regulatory flux of Na+ and H+ were significantly higher in the roots of P. tenuiflora than in those of O. sativa. In the corresponding physiological experiments, the application of additional nutrition elements significantly eliminated the sensitive symptoms of rice to saline-alkali soil extracts.ConclusionsOur results imply that the survival of P. tenuiflora in saline-alkali soils is due to a combination of at least two regulatory mechanisms and the high nutrient uptake capacity of P. tenuiflora plays a pivotal role in its adaptation to those stress. Taken together, our results highlight the role of nutrition uptake in saline-alkali stress tolerance in plants.

Biochar application and summer temperatures reduce N2O and enhance CH4 emissions in a Mediterranean agroecosystem: Role of biologically-induced anoxic microsites

Biochar applications have been proposed for mitigating some soil greenhouse gas (GHG) emissions. However, results can range from mitigation to no effects. To explain these differences, mechanisms have been proposed but their reliability depends on biochar type, soil and climatic conditions. Furthermore, it is found that the mitigation capacity is dependent on how the biochar is aging under field conditions.The effects on N2O, CH4 and CO2 emission rates of a gasification pine biochar (applied as 0, 5, and 30 t ha−1) were studied between 8 and 21 months of the application in an alkaline soil cropped to barley under Mediterranean climate. Together with GHG, soil chemical and biological properties were assessed, namely, changes in labile organic matter content and nutrient status, and pH, as well as microbial abundance, activity, and functional composition.During the 2 years of the application, significant changes were observed at the highest rate of biochar application such as higher contents of water, K+, Mg2+, SO42−, higher basal respiration, and with non-significant changes in microbial community, though with some temporal effects. Regarding GHG, N2O decreases coupled with CH4 increases in the summer sampling were measured, although only for the highest application rate scenario. Such effects were unrelated to pH, bioavailable nitrogen status, or bulk soil microbial community shifts. We hypothesized that the key is the porous structure of our wood biochar, which is able to provide more and diversified microbial microhabitats in comparison to bulk soil. At higher temperatures in summer, biologically-induced anoxic conditions in biochar pores acting as microsites may be promoted, where total denitrification to N2 occurs which leads to N2O uptake, while CH4 production is promoted.

Optimization of Macroalgal Density and Salinity for Nutrient Removal by Caulerpa lentillifera from Aquaculture Effluent

Determining the optimum levels of macroalgal density and salinity for removing aquaculture effluent has gained increasing research interest in recent years because of the growing concerns over environmental sustainability. Here, we determined the effects of macroalgal density and salinity on the uptake of NO2−, NO3−, NH3, and PO43− by Caulerpa lentillifera from the effluent of Poecilia latipinna using spectrophotometry. Laboratory experiments were conducted to measure nutrient uptake at five different macroalgal density levels (10, 20, 30, 40, and 50 g/L) and three salinity levels (20, 30, and 40 ppt) with and without aeration. Quadratic regression analysis revealed significant nonlinear and linear effects of macroalgal density on the uptake of NO2−, NO3−, NH3, and PO43−, where the maximum uptake was predicted to occur at the macroalgal densities of 31.6, 33.3, 50.0, and 20.0 g/L, respectively. Likewise, the effects of salinity on the uptake of NO2−, NO3−, NH3, and PO43− were significant and nonlinear where the maximum uptake was predicted to occur at the salinity levels of 29.1, 30.7, 29.5, and 29.5 ppt, respectively. The result of the effects of aeration was mixed but somewhat indicated a positive effect on the nutrient uptake within the 24 h period. Our results could help aquaculturists to minimize the excessive nutrients by C. lentillifera from aquaculture effluent while achieving long-term sustainable aquaculture production.

Foliar uptake of atmospheric nitrate by two dominant subalpine plants: insights from in situ triple-isotope analysis.

The significance of foliar uptake of nitrogen (N) compounds in natural conditions is not well understood, despite growing evidence of its importance to plant nutrition. In subalpine meadows, N-limitation fosters the dominance of specific subalpine plant species, which in turn ensures the provision of essential ecosystems services. Understanding how these plants absorb N and from which sources is important in predicting ecological consequences of increasing N deposition. Here, we investigate the sources of N to plants from subalpine meadows with distinct land-use history in the French Alps, using the triple isotopes (Δ17 O, δ18 O, and δ15 N) of plant tissue nitrate (NO3- ). We use this approach to evaluate the significance of foliar uptake of atmospheric NO3- (NO3-atm ). The foliar uptake of NO3-atm accounted for 4-16% of the leaf NO3- content, and contributed more to the leaf NO3- pool after peak biomass. Additionally, the gradual 15 N enrichment of NO3- from the soil to the leaves reflected the contribution of NO3-atm assimilation to plants' metabolism. The present study confirms that foliar uptake is a potentially important pathway for NO3-atm into subalpine plants. This is of major significance as N emissions (and deposition) are predicted to increase globally in the future.

Dual nitrogen species involved in foliar uptake of nitrogen dioxide in Arabidopsis thaliana

ABSTRACTFoliar uptake of nitrogen dioxide (NO2) is governed by its reactive absorption mechanism, by which NO2 molecules diffuse through cell wall layers and simultaneously react with apoplastic ascorbate to form nitrous acid, which freely diffuses across plasmalemma. However, whether free diffusion of nitrous acid is the sole mechanism of foliar uptake of NO2 remains unknown. The involvement of ammonia-inhibitable nitrite transporters in the foliar uptake of NO2, as reported in nitrite transport in Arabidopsis roots, is also unknown. In this study, we treated Arabidopsis thaliana leaves with methionine sulfoximine (MSX) to inhibit incorporation of ammonia into glutamate and exposed them to 4 ppm 15N-labeled NO2 for 4 h in light followed by quantification of total nitrogen, reduced nitrogen, and ammonia nitrogen derived from NO2 using mass spectrometry and capillary electrophoresis. The total nitrogen derived from NO2 in leaves without MSX treatment was 587.0 nmol NO2/g fresh weight, of which more than 65% was recovered as reduced nitrogen. In comparison, MSX treatment decreased the total nitrogen and reduced nitrogen derived from NO2 by half. Thus, half of the foliar uptake of NO2 is not attributable to passive diffusion of nitrous acid but to ammonia-inhibitable nitrite transport. Foliar uptake of NO2 is mediated by a dual mechanism in A. thaliana: nitrous acid-free diffusion and nitrite transporter-mediated transport.

Developing a sustainable route to environmentally relevant metal–organic frameworks: ultra-rapid synthesis of MFM-300(Al) using microwave heating

The synthesis of MFM-300(Al) in aqueous conditions and 10 minutes using microwave heating is reported. The material produced exhibits significantly enhanced uptake of CO2, SO2, and NO2 compared to the 3-day solvothermal route.

Solid Products of NO3 Uptake on Methane Soot

A soot coating was treated with NO3 radicals using a flow reactor having a movable insert and coupled to a mass spectrometer for kinetic studies; the treatment was performed until the surface completely stopped to trap the radicals. The chromatographic and mass spectrometry analyses of the composition of the original methane soot and the solid products of its reaction with the gas-phase NO3 oxidant showed that the main products of this heterogeneous reaction were phthalic acid derivatives, paraffins, and acetophenones. The untreated soot contained arenes (up to four-membered aromatic molecules). The nitro compounds were not detected in the original soot and the products of its treatment with NO3 radicals.

Plant organic N uptake maintains species dominance under long-term warming

There is ample experimental evidence for shifts in plant community composition under climate warming. To date, however, the underlying mechanisms driving these compositional shifts remain poorly understood. The amount and form of nitrogen (N) available to plants are among the primary factors limiting productivity and plant coexistence in terrestrial ecosystems. We conducted a short-term 15N tracer experiment in a ten-year warming and grazing experiment in an alpine grassland to investigate the effects of warming and grazing on plant uptake of NO3−-N, NH4+-N, and glycine-N. Four dominant plant species (Kobresia humilis, Potentilla anseria, Elymus nutans, Poa annua) were selected. Results We found that 10-years of warming decreased plant uptake of inorganic N by up to 80% in all species. In contrast, warming increased the uptake of organic N in K. humilis, P. anseria, and E. nutans but not in P. annua. Results showed that plant relative biomass increased hyperbolically with the ratio of the plant species total uptake of available N and plant community uptake of available N. And a significant positive correlation between plant species uptake of soil glycine-N and the uptake of total available N. The stable relative biomass of plant species is largely dependent on organic N uptake by plants. We conclude that plant organic N uptake maintains species dominance under long-term warming.

Evidence of heterogeneous HONO formation from aerosols and the regional photochemical impact of this HONO source

Large missing daytime HONO sources have been reported by many previous studies around the world. Possible HONO sources include ground heterogeneous conversion, aerosol heterogeneous formation, soil emission, and photochemical production. In this study, a consistent 1D framework based on regional and 3D chemical transport models (CTMs) was used to analyze the unknown daytime HONO sources in 14 cases worldwide. We assume that the source of HONO from aerosols is through NO2 hydrolysis (not including its oxidation products) and that non-local mixing effect is negligible. Assuming all the missing unknown HONO source is from the ground, it would imply a NO2-to-HONO ground heterogeneous conversion exceeding 100% in daytime, which is unphysical. In contrast, a strong R2 reaching up to 0.92 is found between the unknown HONO sources and the products of aerosol wet surface area and short-wave radiation. Because the largest unknown daytime HONO sources are found in China due to high concentrations of aerosols and NO2, we derive an optimized NO2 uptake coefficient on the basis of these measurements. The 3D CTM simulations suggest that in some regions of central, eastern, and southwestern (e.g. SiChuan province) China, the aerosol HONO source has the greatest effects on ozone (>10 ppbv) and OH (>200%) in winter. In January, the simulated particulate sulfate level over these three regions increases by 6–10 μg m−3 after including the aerosol-HONO source, which helps reduce the previous model underestimation of sulfate production in winter. Additional measurement studies that target the daytime HONO sources will be essential to a better understanding of the mechanisms and resulting effects on atmospheric oxidants.

Measurements of NO and NO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; exchange between the atmosphere and &amp;lt;i&amp;gt;Quercus agrifolia&amp;lt;/i&amp;gt;

Abstract. NO2 foliar deposition through the stomata of leaves has been identified as a significant sink of NOx within a forest canopy. In this study, we investigated NO2 and NO exchange between the atmosphere and the leaves of the native California oak tree Quercus agrifolia using a branch enclosure system. NO2 detection was performed with laser-induced fluorescence (LIF), which excludes biases from other reactive nitrogen compounds and has a low detection limit of 5–50 ppt. We performed both light and dark experiments with concentrations between 0.5 and 10 ppb NO2 and NO under constant ambient conditions. Deposition velocities for NO2 during light and dark experiments were 0.123±0.009 and 0.015±0.001 cm s−1, respectively. Much slower deposition was seen for NO, with deposition velocities of 0.012±0.002 and 0.005±0.002 cm s−1 measured during light and dark experiments, respectively. This corresponded to a summed resistance of the stomata and mesophyll of 6.9±0.9 s cm−1 for NO2 and 140±40 s cm−1 for NO. No significant compensation point was detected for NO2 uptake, but compensation points ranging from 0.74 to 3.8 ppb were observed for NO. NO2 and NO deposition velocities reported here are comparable both with previous leaf-level chamber studies and inferences from canopy-level field measurements. In parallel with these laboratory experiments, we have constructed a detailed 1-D atmospheric model to assess the contribution of leaf-level NOx deposition to the total NOx loss and NOx canopy fluxes. Using the leaf uptake rates measured in the laboratory, these modeling studies suggest that loss of NOx to deposition in a California oak woodland competes with the pathways of HNO3 and RONO2 formation, with deposition making up 3 %–22 % of the total NOx loss. Additionally, foliar uptake of NOx at these rates could account for ∼15 %–30 % canopy reduction of soil NOx emissions.

Photosynthetic Capacity, Stomatal Behavior and Chloroplast Ultrastructure in Leaves of the Endangered Plant Carpinus putoensis W.C.Cheng during Gaseous NO2 Exposure and after Recovery

Foliar uptake of gaseous NO2 mainly occurs through the stomata and disrupts normal plant growth, but no detailed reports about the physiological responses of plants exposed to NO2 are available. In this study, to study leaf physicochemical responses, stomatal characteristics and chloroplast structure, we observed the leaves of Carpinus putoensis W.C.Cheng after exposure to NO2 (6 μL/L) for five time periods (0, 1, 6, 24, and 72 h) and after 30 days of recovery following NO2 exposure. Our results showed that short-duration exposure to a high concentration of NO2 had significant negative impacts (p &lt; 0.05) on the chlorophyll content, photosynthesis and chloroplast-related physicochemical processes of C. putoensis leaves; with the exception of one hour of NO2 exposure, which was helpful for plant physiological responses. Moreover, NO2 exposure significantly increased the thickness of the palisade/spongy tissue and caused swelling of the thylakoids within the chloroplasts; this thylakoid swelling could be reversed by removing the pollutant from the air flow. Restoration of unpolluted air alleviated the toxic effects of NO2, as indicated by an increased chlorophyll content, net photosynthesis, and PSII maximum quantum yield. These results could support the development of a treatment for roadside trees that are exposed to NO2 as a major road pollutant.

Joining empirical and modelling approaches to estimate dry deposition of nitrogen in Mediterranean forests

In Mediterranean areas, dry deposition is a major component of the total atmospheric N input to natural habitats, particularly to forest ecosystems. An innovative approach, combining the empirical inferential method (EIM) for surface deposition of NO3− and NH4+ with stomatal uptake of NH3, HNO3 and NO2 derived from the DO3SE (Deposition of Ozone and Stomatal Exchange) model, was used to estimate total dry deposition of inorganic N air pollutants in four holm oak forests under Mediterranean conditions in Spain. The estimated total deposition varied among the sites and matched the geographical patterns previously found in model estimates: higher deposition was determined at the northern site (28.9 kg N ha−1 year−1) and at the northeastern sites (17.8 and 12.5 kg N ha−1 year−1) than at the central-Spain site (9.4 kg N ha−1 year−1). On average, the estimated dry deposition of atmospheric N represented 77% ± 2% of the total deposition of N, of which surface deposition of gaseous and particulate atmospheric N averaged 10.0 ± 2.9 kg N ha−1 year−1 for the four sites (58% of the total deposition), and stomatal deposition of N gases averaged 3.3 ± 0.8 kg N ha−1 year−1 (19% of the total deposition). Deposition of atmospheric inorganic N was dominated by the surface deposition of oxidized N in all the forests (means of 54% and 42% of the dry and total deposition, respectively). The relative contribution of NO2 to dry deposition averaged from 19% in the peri-urban forests to 11% in the most natural site. During the monitoring period, the empirical critical loads provisionally proposed for ecosystem protection (10–20 kg N ha−1 year−1) was exceeded in three of the four studied forests.

The sap flow-based assessment of atmospheric trace gas uptake by three forest types in subtropical China on different timescales.

Assessing the uptake of trace gases by forests contributes to understanding the mechanisms of gas exchange between vegetation and the atmosphere and to evaluating the potential risk of these pollutant gases to forests. In this study, the multi-timescale characteristics of the stomatal uptake of NO, NO2, SO2 and O3 by Schima superba, Eucalyptus citriodora and Acacia auriculiformis were investigated by continuous sap flow measurements for a 3-year period. The peak canopy stomatal conductance (GC) for these three species appeared between 9:00 and 12:00, which was jointly regulated by the vapour pressure deficit (VPD) and photosynthetically active radiation (PAR). Additionally, annual and seasonal variations in the stomatal uptake of trace gases for these three tree species suggested that there was a combination effect between canopy stomatal conductance and ambient concentration on the uptake of trace gases. Furthermore, the result demonstrated that the trace gas absorption capacities among these three forest types followed the order of S. superba > E. citriodora > A. auriculiformis. The findings of this study have theoretical significance and application value in assessing air purification and the risk of harm to forests in Southern China.

Nitrous oxide variability at sub-kilometre resolution in the Atlantic sector of the Southern Ocean.

The Southern Ocean is an important region for global nitrous oxide (N2O) cycling. The contribution of different source and sink mechanisms is, however, not very well constrained due to a scarcity of seawater data from the area. Here we present high-resolution surface N2O measurements from the Atlantic sector of the Southern Ocean, taking advantage of a relatively new underway setup allowing for collection of data during transit across mesoscale features such as frontal systems and eddies. Covering a range of different environments and biogeochemical settings, N2O saturations and sea-to-air fluxes were highly variable: Saturations ranged from 96.5% at the sea ice edge in the Weddell Sea to 126.1% across the Polar Frontal Zone during transit to South Georgia. Negative sea-to-air fluxes (N2O uptake) of up to −1.3 µmol m−2 d−1 were observed in the Subantarctic Zone and highest positive fluxes (N2O emission) of 14.5 µmol m−2 d−1 in Stromness Bay, coastal South Georgia. Although N2O saturations were high in areas of high productivity, no correlation between saturations and chlorophyll a (as a proxy for productivity) was observed. Nevertheless, there is a clear effect of islands and shallow bathymetry on N2O production as inferred from supersaturations.

Stable isotopes of nitrate reveal different nitrogen processing mechanisms in streams across a land use gradient during wet and dry periods

Abstract. Understanding the relationship between land use and the dynamics of nitrate (NO3-) is the key to constrain sources of NO3- export in order to aid effective management of waterways. In this study, isotopic compositions of NO3- (δ15N–NO3- and δ18O–NO3-) were used to elucidate the effects of land use (agriculture in particular) and rainfall on the major sources and sinks of NO3- within the Western Port catchment, Victoria, Australia. This study is one of the very few studies carried out in temperate regions with highly stochastic rainfall patterns, enabling a more comprehensive understanding of the applications of NO3- isotopes in catchment ecosystems with different climatic conditions. Longitudinal samples were collected from five streams with different agriculture land use intensities on five occasions – three during dry periods and two during wet periods. At the catchment scale, we observed significant positive relationships between NO3- concentrations (p &lt; 0.05), δ15N–NO3- (p &lt; 0.01) and percentage agriculture (particularly during the wet period), reflecting the dominance of anthropogenic nitrogen inputs within the catchment. Different rainfall conditions appeared to be major controls on the predominance of the sources and transformation processes of NO3- in our study sites. Artificial fertiliser was the dominant source of NO3- during the wet periods. In addition to artificial fertiliser, nitrified organic matter in sediment was also an apparent source of NO3- to the surface water during the dry periods. Denitrification was prevalent during the wet periods, while uptake of NO3- by plants or algae was only observed during the dry periods in two streams. The outcome of this study suggests that effective reduction of NO3- load to the streams can only be achieved by prioritising management strategies based on different rainfall conditions.

Heterogeneous reaction of Cl2 and NO2 on γ-Al2O3: A potential formation pathway of secondary aerosols

The importance of the oxidizing capacity of reactive chlorine species, and the heterogeneous reactions of atmospheric pollution gases on the surface of particles has been well established in field observation, modeling simulation and laboratory exploration. However, less is known about the reactions of reactive chlorine on mineral particles. We studied the effect of Cl2 on the heterogeneous reaction of NO2 with γ-Al2O3 by using ion chromatography and positron annihilation lifetime spectroscopy. The presence of Cl2 can promote the uptake of NO2 on γ-Al2O3 at humid conditions. The probable explanations are that Cl2 rapidly reacts with NO2 on the γ-Al2O3 surface in the presence of adsorbed water, and nitrites, as the intermediate products during the heterogeneous reaction of NO2 on mineral dust, are immediately oxidized by adsorbed Cl2. In the positron annihilation lifetime spectroscopy experiment, a porous γ-Al2O3 was demonstrated by the relatively high fourth lifetime intensity. The increase in the number of anions (onto γ-Al2O3) when the reaction time was prolonged was a direct consequence of the decrease in the o-Ps intensity and the o-Ps lifetime, which illustrated that the heterogeneous reactions might occur on the porous surface of γ-Al2O3. Our results suggest that the oxidative effect of Cl2 on the heterogeneous conversion of NO2 to nitrogen-containing particles might have a significant contribution to the fine particle growth and to the unknown sources of nitrate observed in secondary inorganic aerosols.

Impact of heterogeneous uptake of nitrogen dioxide on the conversion of acetaldehyde on gamma-alumina in the absence and presence of simulated solar irradiation

Heterogeneous reactions of various atmospheric gaseous pollutants on particle surfaces are important pathways for the formation of secondary aerosols. However, these heterogeneous reactions are inevitable affected by each other in the real atmosphere. In this study, the impacts of the heterogeneous uptake of NO2 on the conversion of acetaldehyde on the particle surfaces in the absence and presence of simulated solar irradiation were investigated by using diffuse reflectance infrared spectroscopy (DRIFTS) at 298 K. It is found that in the absence of simulated solar irradiation the hydration reaction and subsequent polyoligomeric reaction as well as oligomeric reaction of CH3CHO are promoted by the pre-adsorption of NO2 for a short reaction time, but these reactions are significantly hindered, accompanied with the slightly enhanced formation of crotonaldehyde and adsorbed acetate by the pre-adsorption of NO2 for a longer time. In the presence of simulated solar irradiation, the occurrence of the aldol condensation and the oxidation of CH3CHO are promoted by the combined impacts of illumination, hydrogen bond (H-bond) catalysis, the enhanced surface acidity and the formed nitrite and nitrate, especially, the photolysis of the formed nitrite and nitrate, whereas the hydration reaction and subsequent polyoligomeric reaction as well as oligomeric reaction of CH3CHO molecules are suppressed. Meanwhile, the hydrogen bond catalysis for aldol condensation is significantly enhanced by light irradiation, showing a combined result of hydrogen bond catalysis and illumination. The heterogeneous reaction mechanism is proposed, and atmospheric implications based on these results are discussed in this study.

The relationship between the characteristics of Biochar produced at different temperatures and its impact on the uptake of NO3 - -N

The relationship between the characteristics of Biochar produced at different temperatures and its impact on the uptake of NO3 - -N